Android DiskLruCache 源码解析 硬盘缓存的绝佳方案

来源:互联网 发布:fifa online 3软件 编辑:程序博客网 时间:2024/05/18 02:39


一、概述

依旧是整理东西,所以近期的博客涉及的东西可能会比较老一点,会分析一些经典的框架,我觉得可能也是每个优秀的开发者必须掌握的东西;那么对于Disk Cache,DiskLruCache可以算佼佼者了,所以我们就来分析下其源码实现。

对于该库的使用,推荐老郭的blog Android DiskLruCache完全解析,硬盘缓存的最佳方案

如果你不是很了解用法,那么注意下面的几点描述,不然直接看源码分析可能雨里雾里的。

  • 首先,这个框架会涉及到一个文件,叫做journal,这个文件中会存储每次读取操作的记录;
  • 对于获取一个DiskLruCache,是这样的:

    <code class="language-java hljs  has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">DiskLruCache.open(directory, appVersion,                     valueCount, maxSize) ;</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li></ul>
  • 关于存一般是这么使用的:

    <code class="language-java hljs  has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">String key = generateKey(url);  DiskLruCache.Editor editor = mDiskLruCache.edit(key); OuputStream os = editor.newOutputStream(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>); </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

    因为每个实体都是个文件,所以你可以认为这个os指向一个文件的FileOutputStream,然后把你想存的东西写入就行了,写完以后记得调用:editor.commit()

  • 关于取一般是这样的:

    <code class="language-java hljs  has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> DiskLruCache.Snapshot snapShot = mDiskLruCache.get(key);  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (snapShot != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) {      InputStream is = snapShot.getInputStream(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>);  }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

    还是那句,因为每个实体都是文件,所以你返回的is是个FileInputStream,你可以利用is读取出里面的内容,然后do what you want .

好了,关于Cache最主要就是存取了,了解这几点,就可以往下去看源码分析了。

还记得第一点说的journal文件么,首先就是它了。


二、journal文件

journal文件你打开以后呢,是这个格式;

<code class="language-xml hljs  has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">libcore.io.DiskLruCache111DIRTY c3bac86f2e7a291a1a200b853835b664CLEAN c3bac86f2e7a291a1a200b853835b664 4698READ c3bac86f2e7a291a1a200b853835b664DIRTY c59f9eec4b616dc6682c7fa8bd1e061fCLEAN c59f9eec4b616dc6682c7fa8bd1e061f 4698READ c59f9eec4b616dc6682c7fa8bd1e061fDIRTY be8bdac81c12a08e15988555d85dfd2bCLEAN be8bdac81c12a08e15988555d85dfd2b 99READ be8bdac81c12a08e15988555d85dfd2bDIRTY 536788f4dbdffeecfbb8f350a941eea3REMOVE 536788f4dbdffeecfbb8f350a941eea3 </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li></ul>

首先看前五行:

  • 第一行固定字符串libcore.io.DiskLruCache
  • 第二行DiskLruCache的版本号,源码中为常量1
  • 第三行为你的app的版本号,当然这个是你自己传入指定的
  • 第四行指每个key对应几个文件,一般为1
  • 第五行,空行

ok,以上5行可以称为该文件的文件头,DiskLruCache初始化的时候,如果该文件存在需要校验该文件头。

接下来的行,可以认为是操作记录。

  • DIRTY 表示一个entry正在被写入(其实就是把文件的OutputStream交给你了)。那么写入分两种情况,如果成功会紧接着写入一行CLEAN的记录;如果失败,会增加一行REMOVE记录。
  • REMOVE除了上述的情况呢,当你自己手动调用remove(key)方法的时候也会写入一条REMOVE记录。
  • READ就是说明有一次读取的记录。
  • 每个CLEAN的后面还记录了文件的长度,注意可能会一个key对应多个文件,那么就会有多个数字(参照文件头第四行)。

从这里看出,只有CLEAN且没有REMOVE的记录,才是真正可用的Cache Entry记录。

分析完journal文件,首先看看DiskLruCache的创建的代码。


三、DiskLruCache#open

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> DiskLruCache <span class="hljs-title" style="box-sizing: border-box;">open</span>(File directory, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> appVersion, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> valueCount, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span> maxSize)      <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> IOException {    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// If a bkp file exists, use it instead.</span>    File backupFile = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> File(directory, JOURNAL_FILE_BACKUP);    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (backupFile.exists()) {      File journalFile = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> File(directory, JOURNAL_FILE);      <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// If journal file also exists just delete backup file.</span>      <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (journalFile.exists()) {        backupFile.delete();      } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {        renameTo(backupFile, journalFile, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>);      }    }    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Prefer to pick up where we left off.</span>    DiskLruCache cache = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> DiskLruCache(directory, appVersion, valueCount, maxSize);    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (cache.journalFile.exists()) {      <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {        cache.readJournal();        cache.processJournal();        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> cache;      } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (IOException journalIsCorrupt) {        System.out            .println(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"DiskLruCache "</span>                + directory                + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">" is corrupt: "</span>                + journalIsCorrupt.getMessage()                + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">", removing"</span>);        cache.delete();      }    }    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Create a new empty cache.</span>    directory.mkdirs();    cache = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> DiskLruCache(directory, appVersion, valueCount, maxSize);    cache.rebuildJournal();    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> cache;  }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li></ul>

首先检查存不存在journal.bkp(journal的备份文件)

如果存在:然后检查journal文件是否存在,如果正主在,bkp文件就可以删除了。 
如果不存在,将bkp文件重命名为journal文件。

接下里判断journal文件是否存在:

  • 如果不存在

    创建directory;重新构造disklrucache;调用rebuildJournal建立journal文件

    <code class="language-java hljs  has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/*** Creates a new journal that omits redundant information. This replaces the* current journal if it exists.*/</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">synchronized</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">rebuildJournal</span>() <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> IOException {<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (journalWriter != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) {  journalWriter.close();}Writer writer = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> BufferedWriter(    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> OutputStreamWriter(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> FileOutputStream(journalFileTmp), Util.US_ASCII));<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {  writer.write(MAGIC);  writer.write(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"\n"</span>);  writer.write(VERSION_1);  writer.write(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"\n"</span>);  writer.write(Integer.toString(appVersion));  writer.write(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"\n"</span>);  writer.write(Integer.toString(valueCount));  writer.write(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"\n"</span>);  writer.write(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"\n"</span>);  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (Entry entry : lruEntries.values()) {    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (entry.currentEditor != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) {      writer.write(DIRTY + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">' '</span> + entry.key + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'\n'</span>);    } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {      writer.write(CLEAN + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">' '</span> + entry.key + entry.getLengths() + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'\n'</span>);    }  }} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">finally</span> {  writer.close();}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (journalFile.exists()) {  renameTo(journalFile, journalFileBackup, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>);}renameTo(journalFileTmp, journalFile, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>);journalFileBackup.delete();journalWriter = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> BufferedWriter(    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> OutputStreamWriter(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> FileOutputStream(journalFile, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>), Util.US_ASCII));}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li></ul>

    可以看到首先构建一个journal.tmp文件,然后写入文件头(5行),然后遍历lruEntries(lruEntries = 
    new LinkedHashMap<String, Entry>(0, 0.75f, true);
    ),当然我们这里没有任何数据。接下来将tmp文件重命名为journal文件。

  • 如果存在

    如果已经存在,那么调用readJournal

    <code class="language-java hljs  has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">readJournal</span>() <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> IOException {StrictLineReader reader = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> StrictLineReader(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> FileInputStream(journalFile), Util.US_ASCII);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {  String magic = reader.readLine();  String version = reader.readLine();  String appVersionString = reader.readLine();  String valueCountString = reader.readLine();  String blank = reader.readLine();  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!MAGIC.equals(magic)      || !VERSION_1.equals(version)      || !Integer.toString(appVersion).equals(appVersionString)      || !Integer.toString(valueCount).equals(valueCountString)      || !<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">""</span>.equals(blank)) {    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throw</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> IOException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"unexpected journal header: ["</span> + magic + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">", "</span> + version + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">", "</span>        + valueCountString + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">", "</span> + blank + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"]"</span>);  }  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> lineCount = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">while</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>) {    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {      readJournalLine(reader.readLine());      lineCount++;    } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (EOFException endOfJournal) {      <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;    }  }  redundantOpCount = lineCount - lruEntries.size();  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// If we ended on a truncated line, rebuild the journal before appending to it.</span>  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (reader.hasUnterminatedLine()) {    rebuildJournal();  } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {    journalWriter = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> BufferedWriter(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> OutputStreamWriter(        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> FileOutputStream(journalFile, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>), Util.US_ASCII));  }} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">finally</span> {  Util.closeQuietly(reader);}}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li></ul>

    首先校验文件头,接下来调用readJournalLine按行读取内容。我们来看看readJournalLine中的操作。

    <code class="language-java hljs  has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">readJournalLine</span>(String line) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> IOException {<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> firstSpace = line.indexOf(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">' '</span>);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (firstSpace == -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>) {  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throw</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> IOException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"unexpected journal line: "</span> + line);}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> keyBegin = firstSpace + <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> secondSpace = line.indexOf(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">' '</span>, keyBegin);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> String key;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (secondSpace == -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>) {  key = line.substring(keyBegin);  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (firstSpace == REMOVE.length() && line.startsWith(REMOVE)) {    lruEntries.remove(key);    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span>;  }} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {  key = line.substring(keyBegin, secondSpace);}Entry entry = lruEntries.get(key);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (entry == <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) {  entry = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Entry(key);  lruEntries.put(key, entry);}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (secondSpace != -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> && firstSpace == CLEAN.length() && line.startsWith(CLEAN)) {  String[] parts = line.substring(secondSpace + <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>).split(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">" "</span>);  entry.readable = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>;  entry.currentEditor = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;  entry.setLengths(parts);} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (secondSpace == -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> && firstSpace == DIRTY.length() && line.startsWith(DIRTY)) {  entry.currentEditor = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Editor(entry);} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (secondSpace == -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> && firstSpace == READ.length() && line.startsWith(READ)) {  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// This work was already done by calling lruEntries.get().</span>} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throw</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> IOException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"unexpected journal line: "</span> + line);}}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li></ul>

    大家可以回忆下:每个记录至少有一个空格,有的包含两个空格。首先,拿到key,如果是REMOVE的记录呢,会调用lruEntries.remove(key);

    如果不是REMOVE记录,继续往下,如果该key没有加入到lruEntries,则创建并且加入。

    接下来,如果是CLEAN开头的合法记录,初始化entry,设置readable=true,currentEditor为null,初始化长度等。

    如果是DIRTY,设置currentEditor对象。

    如果是READ,那么直接不管。

    ok,经过上面这个过程,大家回忆下我们的记录格式,一般DIRTY不会单独出现,会和REMOVE、CLEAN成对出现(正常操作);也就是说,经过上面这个流程,基本上加入到lruEntries里面的只有CLEAN且没有被REMOVE的key。

    好了,回到readJournal方法,在我们按行读取的时候,会记录一下lineCount,然后最后给redundantOpCount赋值,这个变量记录的应该是没用的记录条数(文件的行数-真正可以的key的行数)。

    最后,如果读取过程中发现journal文件有问题,则重建journal文件。没有问题的话,初始化下journalWriter,关闭reader。

    readJournal完成了,会继续调用processJournal()这个方法内部:

    <code class="language-java hljs  has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">processJournal</span>() <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> IOException {deleteIfExists(journalFileTmp);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (Iterator<Entry> i = lruEntries.values().iterator(); i.hasNext(); ) {  Entry entry = i.next();  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (entry.currentEditor == <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) {    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> t = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; t < valueCount; t++) {      size += entry.lengths[t];    }  } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {    entry.currentEditor = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> t = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; t < valueCount; t++) {      deleteIfExists(entry.getCleanFile(t));      deleteIfExists(entry.getDirtyFile(t));    }    i.remove();  }}}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li></ul>

    统计所有可用的cache占据的容量,赋值给size;对于所有非法DIRTY状态(就是DIRTY单独出现的)的entry,如果存在文件则删除,并且从lruEntries中移除。此时,剩的就真的只有CLEAN状态的key记录了。

ok,到此就初始化完毕了,太长了,根本记不住,我带大家总结下上面代码。

根据我们传入的dir,去找journal文件,如果找不到,则创建个,只写入文件头(5行)。 
如果找到,则遍历该文件,将里面所有的CLEAN记录的key,存到lruEntries中。

这么长的代码,其实就两句话的意思。经过open以后,journal文件肯定存在了;lruEntries里面肯定有值了;size存储了当前所有的实体占据的容量;。


四、存入缓存

还记得,我们前面说过是怎么存的么?

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">String key = generateKey(url);  DiskLruCache.Editor editor = mDiskLruCache.edit(key); OuputStream os = editor.newOutputStream(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//...after op</span>editor.commit();</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

那么首先就是editor方法;

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**   * Returns an editor for the entry named {@code key}, or null if another   * edit is in progress.   */</span>  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> Editor <span class="hljs-title" style="box-sizing: border-box;">edit</span>(String key) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> IOException {    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> edit(key, ANY_SEQUENCE_NUMBER);  }  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">synchronized</span> Editor <span class="hljs-title" style="box-sizing: border-box;">edit</span>(String key, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span> expectedSequenceNumber) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> IOException {      checkNotClosed();    validateKey(key);    Entry entry = lruEntries.get(key);    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (expectedSequenceNumber != ANY_SEQUENCE_NUMBER && (entry == <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>        || entry.sequenceNumber != expectedSequenceNumber)) {      <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Snapshot is stale.</span>    }    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (entry == <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) {      entry = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Entry(key);      lruEntries.put(key, entry);    } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (entry.currentEditor != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) {      <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Another edit is in progress.</span>    }    Editor editor = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Editor(entry);    entry.currentEditor = editor;    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Flush the journal before creating files to prevent file leaks.</span>    journalWriter.write(DIRTY + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">' '</span> + key + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'\n'</span>);    journalWriter.flush();    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> editor;  }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li></ul>

首先验证key,可以必须是字母、数字、下划线、横线(-)组成,且长度在1-120之间。

然后通过key获取实体,因为我们是存,只要不是正在编辑这个实体,理论上都能返回一个合法的editor对象。

所以接下来判断,如果不存在,则创建一个Entry加入到lruEntries中(如果存在,直接使用),然后为entry.currentEditor进行赋值为new Editor(entry);,最后在journal文件中写入一条DIRTY记录,代表这个文件正在被操作。

注意,如果entry.currentEditor != null不为null的时候,意味着该实体正在被编辑,会retrun null ;

拿到editor对象以后,就是去调用newOutputStream去获得一个文件输入流了。

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**     * Returns a new unbuffered output stream to write the value at     * {@code index}. If the underlying output stream encounters errors     * when writing to the filesystem, this edit will be aborted when     * {@link #commit} is called. The returned output stream does not throw     * IOExceptions.     */</span>    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> OutputStream <span class="hljs-title" style="box-sizing: border-box;">newOutputStream</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> index) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> IOException {      <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (index < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> || index >= valueCount) {        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throw</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> IllegalArgumentException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Expected index "</span> + index + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">" to "</span>                + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"be greater than 0 and less than the maximum value count "</span>                + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"of "</span> + valueCount);      }      <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">synchronized</span> (DiskLruCache.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>) {        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (entry.currentEditor != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>) {          <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throw</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> IllegalStateException();        }        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!entry.readable) {          written[index] = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>;        }        File dirtyFile = entry.getDirtyFile(index);        FileOutputStream outputStream;        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {          outputStream = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> FileOutputStream(dirtyFile);        } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (FileNotFoundException e) {          <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Attempt to recreate the cache directory.</span>          directory.mkdirs();          <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {            outputStream = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> FileOutputStream(dirtyFile);          } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (FileNotFoundException e2) {            <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// We are unable to recover. Silently eat the writes.</span>            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> NULL_OUTPUT_STREAM;          }        }        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> FaultHidingOutputStream(outputStream);      }    }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li></ul>

首先校验index是否在valueCount范围内,一般我们使用都是一个key对应一个文件所以传入的基本都是0。接下来就是通过entry.getDirtyFile(index);拿到一个dirty File对象,为什么叫dirty file呢,其实就是个中转文件,文件格式为key.index.tmp。 
将这个文件的FileOutputStream通过FaultHidingOutputStream封装下传给我们。

最后,别忘了我们通过os写入数据以后,需要调用commit方法。

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">commit</span>() <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> IOException {      <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (hasErrors) {        completeEdit(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>);        remove(entry.key); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// The previous entry is stale.</span>      } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {        completeEdit(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>);      }      committed = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>;    }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul>

首先通过hasErrors判断,是否有错误发生,如果有调用completeEdit(this, false)且调用remove(entry.key);。如果没有就调用completeEdit(this, true);

那么这里这个hasErrors哪来的呢?还记得上面newOutputStream的时候,返回了一个os,这个os是FileOutputStream,但是经过了FaultHidingOutputStream封装么,这个类实际上就是重写了FilterOutputStream的write相关方法,将所有的IOException给屏蔽了,如果发生IOException就将hasErrors赋值为true.

这样的设计还是很nice的,否则直接将OutputStream返回给用户,如果出错没法检测,还需要用户手动去调用一些操作。

接下来看completeEdit方法。

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">synchronized</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">completeEdit</span>(Editor editor, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> success) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> IOException {    Entry entry = editor.entry;    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (entry.currentEditor != editor) {      <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throw</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> IllegalStateException();    }    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// If this edit is creating the entry for the first time, every index must have a value.</span>    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (success && !entry.readable) {      <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < valueCount; i++) {        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!editor.written[i]) {          editor.abort();          <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throw</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> IllegalStateException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Newly created entry didn't create value for index "</span> + i);        }        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!entry.getDirtyFile(i).exists()) {          editor.abort();          <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span>;        }      }    }    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < valueCount; i++) {      File dirty = entry.getDirtyFile(i);      <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (success) {        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (dirty.exists()) {          File clean = entry.getCleanFile(i);          dirty.renameTo(clean);          <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span> oldLength = entry.lengths[i];          <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span> newLength = clean.length();          entry.lengths[i] = newLength;          size = size - oldLength + newLength;        }      } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {        deleteIfExists(dirty);      }    }    redundantOpCount++;    entry.currentEditor = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (entry.readable | success) {      entry.readable = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>;      journalWriter.write(CLEAN + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">' '</span> + entry.key + entry.getLengths() + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'\n'</span>);      <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (success) {        entry.sequenceNumber = nextSequenceNumber++;      }    } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {      lruEntries.remove(entry.key);      journalWriter.write(REMOVE + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">' '</span> + entry.key + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'\n'</span>);    }    journalWriter.flush();    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (size > maxSize || journalRebuildRequired()) {      executorService.submit(cleanupCallable);    }  }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li></ul>

首先判断if (success && !entry.readable)是否成功,且是第一次写入(如果以前这个记录有值,则readable=true),内部的判断,我们都不会走,因为written[i]在newOutputStream的时候被写入true了。而且正常情况下,getDirtyFile是存在的。

接下来,如果成功,将dirtyFile 进行重命名为 cleanFile,文件名为:key.index。然后刷新size的长度。如果失败,则删除dirtyFile.

接下来,如果成功或者readable为true,将readable设置为true,写入一条CLEAN记录。如果第一次提交且失败,那么就会从lruEntries.remove(key),写入一条REMOVE记录。

写入缓存,肯定要控制下size。于是最后,判断是否超过了最大size,或者需要重建journal文件,什么时候需要重建呢?

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> <span class="hljs-title" style="box-sizing: border-box;">journalRebuildRequired</span>() {    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> redundantOpCompactThreshold = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2000</span>;    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> redundantOpCount >= redundantOpCompactThreshold <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//</span>        && redundantOpCount >= lruEntries.size();  }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

如果redundantOpCount达到2000,且超过了lruEntries.size()就重建,这里就可以看到redundantOpCount的作用了。防止journal文件过大。

ok,到此我们的存入缓存就分析完成了。再次总结下,首先调用editor,拿到指定的dirtyFile的OutputStream,你可以尽情的进行写操作,写完以后呢,记得调用commit. 
commit中会检测是你是否发生IOException,如果没有发生,则将dirtyFile->cleanFile,将readable=true,写入CLEAN记录。如果发生错误,则删除dirtyFile,从lruEntries中移除,然后写入一条REMOVE记录。


五、读取缓存

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">DiskLruCache.Snapshot snapShot = mDiskLruCache.get(key);  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (snapShot != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) {    InputStream is = snapShot.getInputStream(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>);  }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

那么首先看get方法:

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">synchronized</span> Snapshot <span class="hljs-title" style="box-sizing: border-box;">get</span>(String key) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> IOException {    checkNotClosed();    validateKey(key);    Entry entry = lruEntries.get(key);    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (entry == <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) {      <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;    }    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!entry.readable) {      <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;    }    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Open all streams eagerly to guarantee that we see a single published</span>    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// snapshot. If we opened streams lazily then the streams could come</span>    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// from different edits.</span>    InputStream[] ins = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> InputStream[valueCount];    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {      <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < valueCount; i++) {        ins[i] = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> FileInputStream(entry.getCleanFile(i));      }    } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (FileNotFoundException e) {      <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// A file must have been deleted manually!</span>      <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < valueCount; i++) {        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (ins[i] != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) {          Util.closeQuietly(ins[i]);        } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {          <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>;        }      }      <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;    }    redundantOpCount++;    journalWriter.append(READ + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">' '</span> + key + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'\n'</span>);    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (journalRebuildRequired()) {      executorService.submit(cleanupCallable);    }    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Snapshot(key, entry.sequenceNumber, ins, entry.lengths);  }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li></ul>

get方法比较简单,如果取到的为null,或者readable=false,则返回null.否则将cleanFile的FileInputStream进行封装返回Snapshot,且写入一条READ语句。 
然后getInputStream就是返回该FileInputStream了。

好了,到此,我们就分析完成了创建DiskLruCache,存入缓存和取出缓存的源码。

除此以外,还有一些别的方法我们需要了解的。


六、其他方法

remove()

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**   * Drops the entry for {@code key} if it exists and can be removed. Entries   * actively being edited cannot be removed.   *   *<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @return</span> true if an entry was removed.   */</span>  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">synchronized</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> <span class="hljs-title" style="box-sizing: border-box;">remove</span>(String key) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> IOException {    checkNotClosed();    validateKey(key);    Entry entry = lruEntries.get(key);    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (entry == <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span> || entry.currentEditor != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) {      <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>;    }    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < valueCount; i++) {      File file = entry.getCleanFile(i);      <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (file.exists() && !file.delete()) {        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throw</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> IOException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"failed to delete "</span> + file);      }      size -= entry.lengths[i];      entry.lengths[i] = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;    }    redundantOpCount++;    journalWriter.append(REMOVE + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">' '</span> + key + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'\n'</span>);    lruEntries.remove(key);    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (journalRebuildRequired()) {      executorService.submit(cleanupCallable);    }    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>;  }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li></ul>

如果实体存在且不在被编辑,就可以直接进行删除,然后写入一条REMOVE记录。

与open对应还有个remove方法,大家在使用完成cache后可以手动关闭。


close()

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/** Closes this cache. Stored values will remain on the filesystem. */</span>  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">synchronized</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">close</span>() <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> IOException {    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (journalWriter == <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) {      <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Already closed.</span>    }    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (Entry entry : <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ArrayList<Entry>(lruEntries.values())) {      <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (entry.currentEditor != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) {        entry.currentEditor.abort();      }    }    trimToSize();    journalWriter.close();    journalWriter = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>;  }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li></ul>

关闭前,会判断所有正在编辑的实体,调用abort方法,最后关闭journalWriter。至于abort方法,其实我们分析过了,就是存储失败的时候的逻辑:

<code class="language-java hljs  has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">abort</span>() <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> IOException {      completeEdit(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>);    }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

到此,我们的整个源码分析就结束了。可以看到DiskLruCache,利用一个journal文件,保证了保证了cache实体的可用性(只有CLEAN的可用),且获取文件的长度的时候可以通过在该文件的记录中读取。利用FaultHidingOutputStream对FileOutPutStream很好的对写入文件过程中是否发生错误进行捕获,而不是让用户手动去调用出错后的处理方法。其内部的很多细节都很值得推敲。

不过也可以看到,存取的操作不是特别的容易使用,需要大家自己去操作文件流,但在存储比较小的数据的时候(不存在内存问题),很多时候还是希望有类似put(key,value),getAsT(key)等方法直接使用。我看了ASimpleCache 提供的API属于比较好用的了。于是萌生想法,对DiskLruCache公开的API进行扩展,对外除了原有的存取方式以外,提供类似ASimpleCache那样比较简单的API用于存储,而内部的核心实现,依然是DiskLruCache原本的。

github地址: base-diskcache,欢迎star,fork。


转载请标明出处: 
http://blog.csdn.net/lmj623565791/article/details/47251585; 
本文出自:【张鸿洋的博客】

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