安卓开发——关于图片的三级缓存策略（内存LruCache+磁盘DiskLruCache+网络Volley）

在开发安卓应用中避免不了要使用到网络图片，获取网络图片很简单，但是需要付出一定的代价——流量。对于少数的图片而言问题不大，但如果手机应用中包含大量的图片，这势必会耗费用户的一定流量，如果我们不加以处理，每次打开应用都去网络获取图片，那么用户可就不乐意了，这里的处理就是指今天要讲的缓存策略（缓存层分为三层：内存层，磁盘层，网络层）。

　　关于缓存层的工作，当我们第一次打开应用获取图片时，先到网络去下载图片，然后依次存入内存缓存，磁盘缓存，当我们再一次需要用到刚才下载的这张图片时，就不需要再重复的到网络上去下载，直接可以从内存缓存和磁盘缓存中找，由于内存缓存速度较快，我们优先到内存缓存中寻找该图片，如果找到则运用，如果没有找到（内存缓存大小有限），那么我们再到磁盘缓存中去找。只要我们合理的去协调这三层缓存运用，便可以提升应用性能和用户体验。

 

1、内存层：（手机内存）

内存缓存相对于磁盘缓存而言，速度要来的快很多，但缺点容量较小且会被系统回收，这里的实现我用到了LruCache。

LruCache这个类是Android3.1版本中提供的，如果你是在更早的Android版本中开发，则需要导入android-support-v4的jar包。

 

磁盘层：（SD卡）

相比内存缓存而言速度要来得慢很多，但容量很大，这里的实现我用到了DiskLruCache类。

DiskLruCache是非Google官方编写，但获得官方认证的硬盘缓存类，该类没有限定在Android内，所以理论上java应用也可以使用DiskLreCache来缓存。

这是DiskLruCache类的下载地址：http://pan.baidu.com/s/1hq0D53m 

 

网络层：（移动网络，无线网络）

这个就没什么解释的了，就是我们上网用的流量。这里的网络访问实现我用到了开源框架Volley。

开源框架Volley是2013年Google I/O大会发布的，Volley是Android平台上的网络通信库，能使网络通信更快，更简单，更健壮。它的设计目标就是非常适合去进行数据量不大，但通信频繁的网络操作，而对于大数据量的网络操作，比如说下载文件等，Volley的表现就会非常糟糕。

这是Volley的下载地址：http://pan.baidu.com/s/1hq1t2yo

 

先来看下效果图：

正常网络下：                                    　　　　断开网络，飞行模式下：

  　　　　 　　

Log日志打印：

 

来看下代码实现：

 

1、由于应用中很多地方需要用到上下文对象，这里我自定义了一个全局的Application，用来提供上下文对象

 1 package com.lcw.rabbit.image.utils; 2  3 import android.app.Application; 4 /** 5  * Application类，提供全局上下文对象 6  * @author Rabbit_Lee 7  * 8  */ 9 public class MyApplication extends Application {10 11     public static String TAG;12     public static MyApplication myApplication;13 14     public static MyApplication newInstance() {15         return myApplication;16     }17 18     @Override19     public void onCreate() {20         super.onCreate();21         TAG = this.getClass().getSimpleName();22         myApplication = this;23 24     }25 }

 

2、Volley请求队列处理类，用来管理Rquest请求对象操作

 1 package com.lcw.rabbit.image; 2  3 import com.android.volley.Request; 4 import com.android.volley.RequestQueue; 5 import com.android.volley.toolbox.Volley; 6 import com.lcw.rabbit.image.utils.MyApplication; 7  8 /** 9  * 请求队列处理类10  * 获取RequestQueue对象11  */12 public class VolleyRequestQueueManager {13     // 获取请求队列类14     public static RequestQueue mRequestQueue = Volley.newRequestQueue(MyApplication.newInstance());15 16     //添加任务进任务队列17     public static void addRequest(Request<?> request, Object tag) {18         if (tag != null) {19             request.setTag(tag);20         }21         mRequestQueue.add(request);22     }23     24     //取消任务25     public static void cancelRequest(Object tag){26         mRequestQueue.cancelAll(tag);27     }28     29     30 31 }

 

3、这里附上2个工具类（生成MD5序列帮助类，DiskLruCache磁盘缓存类）

 1 package com.lcw.rabbit.image.utils; 2  3 import java.math.BigInteger; 4 import java.security.MessageDigest; 5 import java.security.NoSuchAlgorithmException; 6  7 public class MD5Utils { 8     /** 9      * 使用md5的算法进行加密10      */11     public static String md5(String plainText) {12         byte[] secretBytes = null;13         try {14             secretBytes = MessageDigest.getInstance("md5").digest(15                     plainText.getBytes());16         } catch (NoSuchAlgorithmException e) {17             throw new RuntimeException("没有md5这个算法！");18         }19         String md5code = new BigInteger(1, secretBytes).toString(16);// 16进制数字20         // 如果生成数字未满32位，需要前面补021         for (int i = 0; i < 32 - md5code.length(); i++) {22             md5code = "0" + md5code;23         }24         return md5code;25     }26 27 }

 

  1 /*  2  * Copyright (C) 2011 The Android Open Source Project  3  *  4  * Licensed under the Apache License, Version 2.0 (the "License");  5  * you may not use this file except in compliance with the License.  6  * You may obtain a copy of the License at  7  *  8  *      http://www.apache.org/licenses/LICENSE-2.0  9  * 10  * Unless required by applicable law or agreed to in writing, software 11  * distributed under the License is distributed on an "AS IS" BASIS, 12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13  * See the License for the specific language governing permissions and 14  * limitations under the License. 15  */ 16  17 package com.lcw.rabbit.image.utils; 18  19 import java.io.BufferedInputStream; 20 import java.io.BufferedWriter; 21 import java.io.Closeable; 22 import java.io.EOFException; 23 import java.io.File; 24 import java.io.FileInputStream; 25 import java.io.FileNotFoundException; 26 import java.io.FileOutputStream; 27 import java.io.FileWriter; 28 import java.io.FilterOutputStream; 29 import java.io.IOException; 30 import java.io.InputStream; 31 import java.io.InputStreamReader; 32 import java.io.OutputStream; 33 import java.io.OutputStreamWriter; 34 import java.io.Reader; 35 import java.io.StringWriter; 36 import java.io.Writer; 37 import java.lang.reflect.Array; 38 import java.nio.charset.Charset; 39 import java.util.ArrayList; 40 import java.util.Arrays; 41 import java.util.Iterator; 42 import java.util.LinkedHashMap; 43 import java.util.Map; 44 import java.util.concurrent.Callable; 45 import java.util.concurrent.ExecutorService; 46 import java.util.concurrent.LinkedBlockingQueue; 47 import java.util.concurrent.ThreadPoolExecutor; 48 import java.util.concurrent.TimeUnit; 49  50 /** 51  ****************************************************************************** 52  * Taken from the JB source code, can be found in: 53  * libcore/luni/src/main/java/libcore/io/DiskLruCache.java 54  * or direct link: 55  * https://android.googlesource.com/platform/libcore/+/android-4.1.1_r1/luni/src/main/java/libcore/io/DiskLruCache.java 56  ****************************************************************************** 57  * 58  * A cache that uses a bounded amount of space on a filesystem. Each cache 59  * entry has a string key and a fixed number of values. Values are byte 60  * sequences, accessible as streams or files. Each value must be between {@code 61  * 0} and {@code Integer.MAX_VALUE} bytes in length. 62  * 63  * <p>The cache stores its data in a directory on the filesystem. This 64  * directory must be exclusive to the cache; the cache may delete or overwrite 65  * files from its directory. It is an error for multiple processes to use the 66  * same cache directory at the same time. 67  * 68  * <p>This cache limits the number of bytes that it will store on the 69  * filesystem. When the number of stored bytes exceeds the limit, the cache will 70  * remove entries in the background until the limit is satisfied. The limit is 71  * not strict: the cache may temporarily exceed it while waiting for files to be 72  * deleted. The limit does not include filesystem overhead or the cache 73  * journal so space-sensitive applications should set a conservative limit. 74  * 75  * <p>Clients call {@link #edit} to create or update the values of an entry. An 76  * entry may have only one editor at one time; if a value is not available to be 77  * edited then {@link #edit} will return null. 78  * <ul> 79  *     <li>When an entry is being <strong>created</strong> it is necessary to 80  *         supply a full set of values; the empty value should be used as a 81  *         placeholder if necessary. 82  *     <li>When an entry is being <strong>edited</strong>, it is not necessary 83  *         to supply data for every value; values default to their previous 84  *         value. 85  * </ul> 86  * Every {@link #edit} call must be matched by a call to {@link Editor#commit} 87  * or {@link Editor#abort}. Committing is atomic: a read observes the full set 88  * of values as they were before or after the commit, but never a mix of values. 89  * 90  * <p>Clients call {@link #get} to read a snapshot of an entry. The read will 91  * observe the value at the time that {@link #get} was called. Updates and 92  * removals after the call do not impact ongoing reads. 93  * 94  * <p>This class is tolerant of some I/O errors. If files are missing from the 95  * filesystem, the corresponding entries will be dropped from the cache. If 96  * an error occurs while writing a cache value, the edit will fail silently. 97  * Callers should handle other problems by catching {@code IOException} and 98  * responding appropriately. 99  */100 public final class DiskLruCache implements Closeable {101     static final String JOURNAL_FILE = "journal";102     static final String JOURNAL_FILE_TMP = "journal.tmp";103     static final String MAGIC = "libcore.io.DiskLruCache";104     static final String VERSION_1 = "1";105     static final long ANY_SEQUENCE_NUMBER = -1;106     private static final String CLEAN = "CLEAN";107     private static final String DIRTY = "DIRTY";108     private static final String REMOVE = "REMOVE";109     private static final String READ = "READ";110 111     private static final Charset UTF_8 = Charset.forName("UTF-8");112     private static final int IO_BUFFER_SIZE = 8 * 1024;113 114     /*115      * This cache uses a journal file named "journal". A typical journal file116      * looks like this:117      *     libcore.io.DiskLruCache118      *     1119      *     100120      *     2121      *122      *     CLEAN 3400330d1dfc7f3f7f4b8d4d803dfcf6 832 21054123      *     DIRTY 335c4c6028171cfddfbaae1a9c313c52124      *     CLEAN 335c4c6028171cfddfbaae1a9c313c52 3934 2342125      *     REMOVE 335c4c6028171cfddfbaae1a9c313c52126      *     DIRTY 1ab96a171faeeee38496d8b330771a7a127      *     CLEAN 1ab96a171faeeee38496d8b330771a7a 1600 234128      *     READ 335c4c6028171cfddfbaae1a9c313c52129      *     READ 3400330d1dfc7f3f7f4b8d4d803dfcf6130      *131      * The first five lines of the journal form its header. They are the132      * constant string "libcore.io.DiskLruCache", the disk cache's version,133      * the application's version, the value count, and a blank line.134      *135      * Each of the subsequent lines in the file is a record of the state of a136      * cache entry. Each line contains space-separated values: a state, a key,137      * and optional state-specific values.138      *   o DIRTY lines track that an entry is actively being created or updated.139      *     Every successful DIRTY action should be followed by a CLEAN or REMOVE140      *     action. DIRTY lines without a matching CLEAN or REMOVE indicate that141      *     temporary files may need to be deleted.142      *   o CLEAN lines track a cache entry that has been successfully published143      *     and may be read. A publish line is followed by the lengths of each of144      *     its values.145      *   o READ lines track accesses for LRU.146      *   o REMOVE lines track entries that have been deleted.147      *148      * The journal file is appended to as cache operations occur. The journal may149      * occasionally be compacted by dropping redundant lines. A temporary file named150      * "journal.tmp" will be used during compaction; that file should be deleted if151      * it exists when the cache is opened.152      */153 154     private final File directory;155     private final File journalFile;156     private final File journalFileTmp;157     private final int appVersion;158     private final long maxSize;159     private final int valueCount;160     private long size = 0;161     private Writer journalWriter;162     private final LinkedHashMap<String, Entry> lruEntries163             = new LinkedHashMap<String, Entry>(0, 0.75f, true);164     private int redundantOpCount;165 166     /**167      * To differentiate between old and current snapshots, each entry is given168      * a sequence number each time an edit is committed. A snapshot is stale if169      * its sequence number is not equal to its entry's sequence number.170      */171     private long nextSequenceNumber = 0;172 173     /* From java.util.Arrays */174     @SuppressWarnings("unchecked")175     private static <T> T[] copyOfRange(T[] original, int start, int end) {176         final int originalLength = original.length; // For exception priority compatibility.177         if (start > end) {178             throw new IllegalArgumentException();179         }180         if (start < 0 || start > originalLength) {181             throw new ArrayIndexOutOfBoundsException();182         }183         final int resultLength = end - start;184         final int copyLength = Math.min(resultLength, originalLength - start);185         final T[] result = (T[]) Array186                 .newInstance(original.getClass().getComponentType(), resultLength);187         System.arraycopy(original, start, result, 0, copyLength);188         return result;189     }190 191     /**192      * Returns the remainder of 'reader' as a string, closing it when done.193      */194     public static String readFully(Reader reader) throws IOException {195         try {196             StringWriter writer = new StringWriter();197             char[] buffer = new char[1024];198             int count;199             while ((count = reader.read(buffer)) != -1) {200                 writer.write(buffer, 0, count);201             }202             return writer.toString();203         } finally {204             reader.close();205         }206     }207 208     /**209      * Returns the ASCII characters up to but not including the next "\r\n", or210      * "\n".211      *212      * @throws java.io.EOFException if the stream is exhausted before the next newline213      *     character.214      */215     public static String readAsciiLine(InputStream in) throws IOException {216         // TODO: support UTF-8 here instead217 218         StringBuilder result = new StringBuilder(80);219         while (true) {220             int c = in.read();221             if (c == -1) {222                 throw new EOFException();223             } else if (c == '\n') {224                 break;225             }226 227             result.append((char) c);228         }229         int length = result.length();230         if (length > 0 && result.charAt(length - 1) == '\r') {231             result.setLength(length - 1);232         }233         return result.toString();234     }235 236     /**237      * Closes 'closeable', ignoring any checked exceptions. Does nothing if 'closeable' is null.238      */239     public static void closeQuietly(Closeable closeable) {240         if (closeable != null) {241             try {242                 closeable.close();243             } catch (RuntimeException rethrown) {244                 throw rethrown;245             } catch (Exception ignored) {246             }247         }248     }249 250     /**251      * Recursively delete everything in {@code dir}.252      */253     // TODO: this should specify paths as Strings rather than as Files254     public static void deleteContents(File dir) throws IOException {255         File[] files = dir.listFiles();256         if (files == null) {257             throw new IllegalArgumentException("not a directory: " + dir);258         }259         for (File file : files) {260             if (file.isDirectory()) {261                 deleteContents(file);262             }263             if (!file.delete()) {264                 throw new IOException("failed to delete file: " + file);265             }266         }267     }268 269     /** This cache uses a single background thread to evict entries. */270     private final ExecutorService executorService = new ThreadPoolExecutor(0, 1,271             60L, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());272     private final Callable<Void> cleanupCallable = new Callable<Void>() {273         @Override public Void call() throws Exception {274             synchronized (DiskLruCache.this) {275                 if (journalWriter == null) {276                     return null; // closed277                 }278                 trimToSize();279                 if (journalRebuildRequired()) {280                     rebuildJournal();281                     redundantOpCount = 0;282                 }283             }284             return null;285         }286     };287 288     private DiskLruCache(File directory, int appVersion, int valueCount, long maxSize) {289         this.directory = directory;290         this.appVersion = appVersion;291         this.journalFile = new File(directory, JOURNAL_FILE);292         this.journalFileTmp = new File(directory, JOURNAL_FILE_TMP);293         this.valueCount = valueCount;294         this.maxSize = maxSize;295     }296 297     /**298      * Opens the cache in {@code directory}, creating a cache if none exists299      * there.300      *301      * @param directory a writable directory302      * @param appVersion303      * @param valueCount the number of values per cache entry. Must be positive.304      * @param maxSize the maximum number of bytes this cache should use to store305      * @throws java.io.IOException if reading or writing the cache directory fails306      */307     public static DiskLruCache open(File directory, int appVersion, int valueCount, long maxSize)308             throws IOException {309         if (maxSize <= 0) {310             throw new IllegalArgumentException("maxSize <= 0");311         }312         if (valueCount <= 0) {313             throw new IllegalArgumentException("valueCount <= 0");314         }315 316         // prefer to pick up where we left off317         DiskLruCache cache = new DiskLruCache(directory, appVersion, valueCount, maxSize);318         if (cache.journalFile.exists()) {319             try {320                 cache.readJournal();321                 cache.processJournal();322                 cache.journalWriter = new BufferedWriter(new FileWriter(cache.journalFile, true),323                         IO_BUFFER_SIZE);324                 return cache;325             } catch (IOException journalIsCorrupt) {326 //                System.logW("DiskLruCache " + directory + " is corrupt: "327 //                        + journalIsCorrupt.getMessage() + ", removing");328                 cache.delete();329             }330         }331 332         // create a new empty cache333         directory.mkdirs();334         cache = new DiskLruCache(directory, appVersion, valueCount, maxSize);335         cache.rebuildJournal();336         return cache;337     }338 339     private void readJournal() throws IOException {340         InputStream in = new BufferedInputStream(new FileInputStream(journalFile), IO_BUFFER_SIZE);341         try {342             String magic = readAsciiLine(in);343             String version = readAsciiLine(in);344             String appVersionString = readAsciiLine(in);345             String valueCountString = readAsciiLine(in);346             String blank = readAsciiLine(in);347             if (!MAGIC.equals(magic)348                     || !VERSION_1.equals(version)349                     || !Integer.toString(appVersion).equals(appVersionString)350                     || !Integer.toString(valueCount).equals(valueCountString)351                     || !"".equals(blank)) {352                 throw new IOException("unexpected journal header: ["353                         + magic + ", " + version + ", " + valueCountString + ", " + blank + "]");354             }355 356             while (true) {357                 try {358                     readJournalLine(readAsciiLine(in));359                 } catch (EOFException endOfJournal) {360                     break;361                 }362             }363         } finally {364             closeQuietly(in);365         }366     }367 368     private void readJournalLine(String line) throws IOException {369         String[] parts = line.split(" ");370         if (parts.length < 2) {371             throw new IOException("unexpected journal line: " + line);372         }373 374         String key = parts[1];375         if (parts[0].equals(REMOVE) && parts.length == 2) {376             lruEntries.remove(key);377             return;378         }379 380         Entry entry = lruEntries.get(key);381         if (entry == null) {382             entry = new Entry(key);383             lruEntries.put(key, entry);384         }385 386         if (parts[0].equals(CLEAN) && parts.length == 2 + valueCount) {387             entry.readable = true;388             entry.currentEditor = null;389             entry.setLengths(copyOfRange(parts, 2, parts.length));390         } else if (parts[0].equals(DIRTY) && parts.length == 2) {391             entry.currentEditor = new Editor(entry);392         } else if (parts[0].equals(READ) && parts.length == 2) {393             // this work was already done by calling lruEntries.get()394         } else {395             throw new IOException("unexpected journal line: " + line);396         }397     }398 399     /**400      * Computes the initial size and collects garbage as a part of opening the401      * cache. Dirty entries are assumed to be inconsistent and will be deleted.402      */403     private void processJournal() throws IOException {404         deleteIfExists(journalFileTmp);405         for (Iterator<Entry> i = lruEntries.values().iterator(); i.hasNext(); ) {406             Entry entry = i.next();407             if (entry.currentEditor == null) {408                 for (int t = 0; t < valueCount; t++) {409                     size += entry.lengths[t];410                 }411             } else {412                 entry.currentEditor = null;413                 for (int t = 0; t < valueCount; t++) {414                     deleteIfExists(entry.getCleanFile(t));415                     deleteIfExists(entry.getDirtyFile(t));416                 }417                 i.remove();418             }419         }420     }421 422     /**423      * Creates a new journal that omits redundant information. This replaces the424      * current journal if it exists.425      */426     private synchronized void rebuildJournal() throws IOException {427         if (journalWriter != null) {428             journalWriter.close();429         }430 431         Writer writer = new BufferedWriter(new FileWriter(journalFileTmp), IO_BUFFER_SIZE);432         writer.write(MAGIC);433         writer.write("\n");434         writer.write(VERSION_1);435         writer.write("\n");436         writer.write(Integer.toString(appVersion));437         writer.write("\n");438         writer.write(Integer.toString(valueCount));439         writer.write("\n");440         writer.write("\n");441 442         for (Entry entry : lruEntries.values()) {443             if (entry.currentEditor != null) {444                 writer.write(DIRTY + ' ' + entry.key + '\n');445             } else {446                 writer.write(CLEAN + ' ' + entry.key + entry.getLengths() + '\n');447             }448         }449 450         writer.close();451         journalFileTmp.renameTo(journalFile);452         journalWriter = new BufferedWriter(new FileWriter(journalFile, true), IO_BUFFER_SIZE);453     }454 455     private static void deleteIfExists(File file) throws IOException {456 //        try {457 //            Libcore.os.remove(file.getPath());458 //        } catch (ErrnoException errnoException) {459 //            if (errnoException.errno != OsConstants.ENOENT) {460 //                throw errnoException.rethrowAsIOException();461 //            }462 //        }463         if (file.exists() && !file.delete()) {464             throw new IOException();465         }466     }467 468     /**469      * Returns a snapshot of the entry named {@code key}, or null if it doesn't470      * exist is not currently readable. If a value is returned, it is moved to471      * the head of the LRU queue.472      */473     public synchronized Snapshot get(String key) throws IOException {474         checkNotClosed();475         validateKey(key);476         Entry entry = lruEntries.get(key);477         if (entry == null) {478             return null;479         }480 481         if (!entry.readable) {482             return null;483         }484 485         /*486          * Open all streams eagerly to guarantee that we see a single published487          * snapshot. If we opened streams lazily then the streams could come488          * from different edits.489          */490         InputStream[] ins = new InputStream[valueCount];491         try {492             for (int i = 0; i < valueCount; i++) {493                 ins[i] = new FileInputStream(entry.getCleanFile(i));494             }495         } catch (FileNotFoundException e) {496             // a file must have been deleted manually!497             return null;498         }499 500         redundantOpCount++;501         journalWriter.append(READ + ' ' + key + '\n');502         if (journalRebuildRequired()) {503             executorService.submit(cleanupCallable);504         }505 506         return new Snapshot(key, entry.sequenceNumber, ins);507     }508 509     /**510      * Returns an editor for the entry named {@code key}, or null if another511      * edit is in progress.512      */513     public Editor edit(String key) throws IOException {514         return edit(key, ANY_SEQUENCE_NUMBER);515     }516 517     private synchronized Editor edit(String key, long expectedSequenceNumber) throws IOException {518         checkNotClosed();519         validateKey(key);520         Entry entry = lruEntries.get(key);521         if (expectedSequenceNumber != ANY_SEQUENCE_NUMBER522                 && (entry == null || entry.sequenceNumber != expectedSequenceNumber)) {523             return null; // snapshot is stale524         }525         if (entry == null) {526             entry = new Entry(key);527             lruEntries.put(key, entry);528         } else if (entry.currentEditor != null) {529             return null; // another edit is in progress530         }531 532         Editor editor = new Editor(entry);533         entry.currentEditor = editor;534 535         // flush the journal before creating files to prevent file leaks536         journalWriter.write(DIRTY + ' ' + key + '\n');537         journalWriter.flush();538         return editor;539     }540 541     /**542      * Returns the directory where this cache stores its data.543      */544     public File getDirectory() {545         return directory;546     }547 548     /**549      * Returns the maximum number of bytes that this cache should use to store550      * its data.551      */552     public long maxSize() {553         return maxSize;554     }555 556     /**557      * Returns the number of bytes currently being used to store the values in558      * this cache. This may be greater than the max size if a background559      * deletion is pending.560      */561     public synchronized long size() {562         return size;563     }564 565     private synchronized void completeEdit(Editor editor, boolean success) throws IOException {566         Entry entry = editor.entry;567         if (entry.currentEditor != editor) {568             throw new IllegalStateException();569         }570 571         // if this edit is creating the entry for the first time, every index must have a value572         if (success && !entry.readable) {573             for (int i = 0; i < valueCount; i++) {574                 if (!entry.getDirtyFile(i).exists()) {575                     editor.abort();576                     throw new IllegalStateException("edit didn't create file " + i);577                 }578             }579         }580 581         for (int i = 0; i < valueCount; i++) {582             File dirty = entry.getDirtyFile(i);583             if (success) {584                 if (dirty.exists()) {585                     File clean = entry.getCleanFile(i);586                     dirty.renameTo(clean);587                     long oldLength = entry.lengths[i];588                     long newLength = clean.length();589                     entry.lengths[i] = newLength;590                     size = size - oldLength + newLength;591                 }592             } else {593                 deleteIfExists(dirty);594             }595         }596 597         redundantOpCount++;598         entry.currentEditor = null;599         if (entry.readable | success) {600             entry.readable = true;601             journalWriter.write(CLEAN + ' ' + entry.key + entry.getLengths() + '\n');602             if (success) {603                 entry.sequenceNumber = nextSequenceNumber++;604             }605         } else {606             lruEntries.remove(entry.key);607             journalWriter.write(REMOVE + ' ' + entry.key + '\n');608         }609 610         if (size > maxSize || journalRebuildRequired()) {611             executorService.submit(cleanupCallable);612         }613     }614 615     /**616      * We only rebuild the journal when it will halve the size of the journal617      * and eliminate at least 2000 ops.618      */619     private boolean journalRebuildRequired() {620         final int REDUNDANT_OP_COMPACT_THRESHOLD = 2000;621         return redundantOpCount >= REDUNDANT_OP_COMPACT_THRESHOLD622                 && redundantOpCount >= lruEntries.size();623     }624 625     /**626      * Drops the entry for {@code key} if it exists and can be removed. Entries627      * actively being edited cannot be removed.628      *629      * @return true if an entry was removed.630      */631     public synchronized boolean remove(String key) throws IOException {632         checkNotClosed();633         validateKey(key);634         Entry entry = lruEntries.get(key);635         if (entry == null || entry.currentEditor != null) {636             return false;637         }638 639         for (int i = 0; i < valueCount; i++) {640             File file = entry.getCleanFile(i);641             if (!file.delete()) {642                 throw new IOException("failed to delete " + file);643             }644             size -= entry.lengths[i];645             entry.lengths[i] = 0;646         }647 648         redundantOpCount++;649         journalWriter.append(REMOVE + ' ' + key + '\n');650         lruEntries.remove(key);651 652         if (journalRebuildRequired()) {653             executorService.submit(cleanupCallable);654         }655 656         return true;657     }658 659     /**660      * Returns true if this cache has been closed.661      */662     public boolean isClosed() {663         return journalWriter == null;664     }665 666     private void checkNotClosed() {667         if (journalWriter == null) {668             throw new IllegalStateException("cache is closed");669         }670     }671 672     /**673      * Force buffered operations to the filesystem.674      */675     public synchronized void flush() throws IOException {676         checkNotClosed();677         trimToSize();678         journalWriter.flush();679     }680 681     /**682      * Closes this cache. Stored values will remain on the filesystem.683      */684     public synchronized void close() throws IOException {685         if (journalWriter == null) {686             return; // already closed687         }688         for (Entry entry : new ArrayList<Entry>(lruEntries.values())) {689             if (entry.currentEditor != null) {690                 entry.currentEditor.abort();691             }692         }693         trimToSize();694         journalWriter.close();695         journalWriter = null;696     }697 698     private void trimToSize() throws IOException {699         while (size > maxSize) {700 //            Map.Entry<String, Entry> toEvict = lruEntries.eldest();701             final Map.Entry<String, Entry> toEvict = lruEntries.entrySet().iterator().next();702             remove(toEvict.getKey());703         }704     }705 706     /**707      * Closes the cache and deletes all of its stored values. This will delete708      * all files in the cache directory including files that weren't created by709      * the cache.710      */711     public void delete() throws IOException {712         close();713         deleteContents(directory);714     }715 716     private void validateKey(String key) {717         if (key.contains(" ") || key.contains("\n") || key.contains("\r")) {718             throw new IllegalArgumentException(719                     "keys must not contain spaces or newlines: \"" + key + "\"");720         }721     }722 723     private static String inputStreamToString(InputStream in) throws IOException {724         return readFully(new InputStreamReader(in, UTF_8));725     }726 727     /**728      * A snapshot of the values for an entry.729      */730     public final class Snapshot implements Closeable {731         private final String key;732         private final long sequenceNumber;733         private final InputStream[] ins;734 735         private Snapshot(String key, long sequenceNumber, InputStream[] ins) {736             this.key = key;737             this.sequenceNumber = sequenceNumber;738             this.ins = ins;739         }740 741         /**742          * Returns an editor for this snapshot's entry, or null if either the743          * entry has changed since this snapshot was created or if another edit744          * is in progress.745          */746         public Editor edit() throws IOException {747             return DiskLruCache.this.edit(key, sequenceNumber);748         }749 750         /**751          * Returns the unbuffered stream with the value for {@code index}.752          */753         public InputStream getInputStream(int index) {754             return ins[index];755         }756 757         /**758          * Returns the string value for {@code index}.759          */760         public String getString(int index) throws IOException {761             return inputStreamToString(getInputStream(index));762         }763 764         @Override public void close() {765             for (InputStream in : ins) {766                 closeQuietly(in);767             }768         }769     }770 771     /**772      * Edits the values for an entry.773      */774     public final class Editor {775         private final Entry entry;776         private boolean hasErrors;777 778         private Editor(Entry entry) {779             this.entry = entry;780         }781 782         /**783          * Returns an unbuffered input stream to read the last committed value,784          * or null if no value has been committed.785          */786         public InputStream newInputStream(int index) throws IOException {787             synchronized (DiskLruCache.this) {788                 if (entry.currentEditor != this) {789                     throw new IllegalStateException();790                 }791                 if (!entry.readable) {792                     return null;793                 }794                 return new FileInputStream(entry.getCleanFile(index));795             }796         }797 798         /**799          * Returns the last committed value as a string, or null if no value800          * has been committed.801          */802         public String getString(int index) throws IOException {803             InputStream in = newInputStream(index);804             return in != null ? inputStreamToString(in) : null;805         }806 807         /**808          * Returns a new unbuffered output stream to write the value at809          * {@code index}. If the underlying output stream encounters errors810          * when writing to the filesystem, this edit will be aborted when811          * {@link #commit} is called. The returned output stream does not throw812          * IOExceptions.813          */814         public OutputStream newOutputStream(int index) throws IOException {815             synchronized (DiskLruCache.this) {816                 if (entry.currentEditor != this) {817                     throw new IllegalStateException();818                 }819                 return new FaultHidingOutputStream(new FileOutputStream(entry.getDirtyFile(index)));820             }821         }822 823         /**824          * Sets the value at {@code index} to {@code value}.825          */826         public void set(int index, String value) throws IOException {827             Writer writer = null;828             try {829                 writer = new OutputStreamWriter(newOutputStream(index), UTF_8);830                 writer.write(value);831             } finally {832                 closeQuietly(writer);833             }834         }835 836         /**837          * Commits this edit so it is visible to readers.  This releases the838          * edit lock so another edit may be started on the same key.839          */840         public void commit() throws IOException {841             if (hasErrors) {842                 completeEdit(this, false);843                 remove(entry.key); // the previous entry is stale844             } else {845                 completeEdit(this, true);846             }847         }848 849         /**850          * Aborts this edit. This releases the edit lock so another edit may be851          * started on the same key.852          */853         public void abort() throws IOException {854             completeEdit(this, false);855         }856 857         private class FaultHidingOutputStream extends FilterOutputStream {858             private FaultHidingOutputStream(OutputStream out) {859                 super(out);860             }861 862             @Override public void write(int oneByte) {863                 try {864                     out.write(oneByte);865                 } catch (IOException e) {866                     hasErrors = true;867                 }868             }869 870             @Override public void write(byte[] buffer, int offset, int length) {871                 try {872                     out.write(buffer, offset, length);873                 } catch (IOException e) {874                     hasErrors = true;875                 }876             }877 878             @Override public void close() {879                 try {880                     out.close();881                 } catch (IOException e) {882                     hasErrors = true;883                 }884             }885 886             @Override public void flush() {887                 try {888                     out.flush();889                 } catch (IOException e) {890                     hasErrors = true;891                 }892             }893         }894     }895 896     private final class Entry {897         private final String key;898 899         /** Lengths of this entry's files. */900         private final long[] lengths;901 902         /** True if this entry has ever been published */903         private boolean readable;904 905         /** The ongoing edit or null if this entry is not being edited. */906         private Editor currentEditor;907 908         /** The sequence number of the most recently committed edit to this entry. */909         private long sequenceNumber;910 911         private Entry(String key) {912             this.key = key;913             this.lengths = new long[valueCount];914         }915 916         public String getLengths() throws IOException {917             StringBuilder result = new StringBuilder();918             for (long size : lengths) {919                 result.append(' ').append(size);920             }921             return result.toString();922         }923 924         /**925          * Set lengths using decimal numbers like "10123".926          */927         private void setLengths(String[] strings) throws IOException {928             if (strings.length != valueCount) {929                 throw invalidLengths(strings);930             }931 932             try {933                 for (int i = 0; i < strings.length; i++) {934                     lengths[i] = Long.parseLong(strings[i]);935                 }936             } catch (NumberFormatException e) {937                 throw invalidLengths(strings);938             }939         }940 941         private IOException invalidLengths(String[] strings) throws IOException {942             throw new IOException("unexpected journal line: " + Arrays.toString(strings));943         }944 945         public File getCleanFile(int i) {946             return new File(directory, key + "." + i);947         }948 949         public File getDirtyFile(int i) {950             return new File(directory, key + "." + i + ".tmp");951         }952     }953 }

 

4、图片缓存类，包含（LruCache内存缓存，DiskLruCache磁盘缓存）

  1 package com.lcw.rabbit.image.utils;  2   3 import java.io.File;  4 import java.io.IOException;  5 import java.io.OutputStream;  6   7 import android.content.Context;  8 import android.content.pm.PackageInfo;  9 import android.content.pm.PackageManager.NameNotFoundException; 10 import android.graphics.Bitmap; 11 import android.graphics.Bitmap.CompressFormat; 12 import android.graphics.BitmapFactory; 13 import android.os.Environment; 14 import android.support.v4.util.LruCache; 15 import android.util.Log; 16  17 import com.android.volley.toolbox.ImageLoader.ImageCache; 18 import com.lcw.rabbit.image.utils.DiskLruCache.Snapshot; 19  20 /** 21  * 图片缓存帮助类 22  *  23  * 包含内存缓存LruCache和磁盘缓存DiskLruCache 24  *  25  * @author Rabbit_Lee 26  *  27  */ 28 public class ImageCacheUtil implements ImageCache { 29      30     private String TAG=ImageCacheUtil.this.getClass().getSimpleName(); 31  32     //缓存类 33     private static LruCache<String, Bitmap> mLruCache; 34     private static DiskLruCache mDiskLruCache; 35  36     //磁盘缓存大小 37     private static final int DISKMAXSIZE = 10 * 1024 * 1024; 38  39     public ImageCacheUtil() { 40         // 获取应用可占内存的1/8作为缓存 41         int maxSize = (int) (Runtime.getRuntime().maxMemory() / 8); 42         // 实例化LruCaceh对象 43         mLruCache = new LruCache<String, Bitmap>(maxSize) { 44             @Override 45             protected int sizeOf(String key, Bitmap bitmap) { 46                 return bitmap.getRowBytes() * bitmap.getHeight(); 47             } 48         }; 49         try { 50             // 获取DiskLruCahce对象 51             mDiskLruCache = DiskLruCache.open(getDiskCacheDir(MyApplication.newInstance(), "Rabbit"), getAppVersion(MyApplication.newInstance()), 1, DISKMAXSIZE); 52         } catch (IOException e) { 53             e.printStackTrace(); 54         } 55     } 56  57     /** 58      * 从缓存（内存缓存，磁盘缓存）中获取Bitmap 59      */ 60     @Override 61     public Bitmap getBitmap(String url) { 62         if (mLruCache.get(url) != null) { 63             // 从LruCache缓存中取 64             Log.i(TAG,"从LruCahce获取"); 65             return mLruCache.get(url); 66         } else { 67             String key = MD5Utils.md5(url); 68             try { 69                 if (mDiskLruCache.get(key) != null) { 70                     // 从DiskLruCahce取 71                     Snapshot snapshot = mDiskLruCache.get(key); 72                     Bitmap bitmap = null; 73                     if (snapshot != null) { 74                         bitmap = BitmapFactory.decodeStream(snapshot.getInputStream(0)); 75                         // 存入LruCache缓存 76                         mLruCache.put(url, bitmap); 77                         Log.i(TAG,"从DiskLruCahce获取"); 78                     } 79                     return bitmap; 80                 } 81             } catch (IOException e) { 82                 e.printStackTrace(); 83             } 84         } 85         return null; 86     } 87  88     /** 89      * 存入缓存（内存缓存，磁盘缓存） 90      */ 91     @Override 92     public void putBitmap(String url, Bitmap bitmap) { 93         // 存入LruCache缓存 94         mLruCache.put(url, bitmap); 95         // 判断是否存在DiskLruCache缓存，若没有存入 96         String key = MD5Utils.md5(url); 97         try { 98             if (mDiskLruCache.get(key) == null) { 99                 DiskLruCache.Editor editor = mDiskLruCache.edit(key);100                 if (editor != null) {101                     OutputStream outputStream = editor.newOutputStream(0);102                     if (bitmap.compress(CompressFormat.JPEG, 100, outputStream)) {103                         editor.commit();104                     } else {105                         editor.abort();106                     }107                 }108                 mDiskLruCache.flush();109             }110         } catch (IOException e) {111             e.printStackTrace();112         }113 114     }115 116     /**117      * 该方法会判断当前sd卡是否存在，然后选择缓存地址118      * 119      * @param context120      * @param uniqueName121      * @return122      */123     public static File getDiskCacheDir(Context context, String uniqueName) {124         String cachePath;125         if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState()) || !Environment.isExternalStorageRemovable()) {126             cachePath = context.getExternalCacheDir().getPath();127         } else {128             cachePath = context.getCacheDir().getPath();129         }130         return new File(cachePath + File.separator + uniqueName);131     }132 133     /**134      * 获取应用版本号135      * 136      * @param context137      * @return138      */139     public int getAppVersion(Context context) {140         try {141             PackageInfo info = context.getPackageManager().getPackageInfo(context.getPackageName(), 0);142             return info.versionCode;143         } catch (NameNotFoundException e) {144             e.printStackTrace();145         }146         return 1;147     }148 149 }

 

5、图片缓存管理类

这里的图片加载运用到了Volley自带的ImageLoader，在它的构造方法中需要一个ImageCache对象，在上面的图片缓存类已实现了该接口。

这里向外部提供了一个loadImage的重载方法，一个传入加载图片的宽高，一个默认加载原图，使得外部不再需要关注任何关于缓存的操作。

 1 package com.lcw.rabbit.image; 2  3 import android.graphics.Bitmap; 4 import android.widget.ImageView; 5  6 import com.android.volley.VolleyError; 7 import com.android.volley.toolbox.ImageLoader; 8 import com.android.volley.toolbox.ImageLoader.ImageCache; 9 import com.android.volley.toolbox.ImageLoader.ImageContainer;10 import com.android.volley.toolbox.ImageLoader.ImageListener;11 import com.lcw.rabbit.image.utils.ImageCacheUtil;12 13 /**14  * 图片缓存管理类 获取ImageLoader对象15  * 16  * @author Rabbit_Lee17  * 18  */19 public class ImageCacheManager {20 21     private static String TAG = ImageCacheManager.class.getSimpleName();22 23     // 获取图片缓存类对象24     private static ImageCache mImageCache = new ImageCacheUtil();25     // 获取ImageLoader对象26     public static ImageLoader mImageLoader = new ImageLoader(VolleyRequestQueueManager.mRequestQueue, mImageCache);27 28     /**29      * 获取ImageListener30      * 31      * @param view32      * @param defaultImage33      * @param errorImage34      * @return35      */36     public static ImageListener getImageListener(final ImageView view, final Bitmap defaultImage, final Bitmap errorImage) {37 38         return new ImageListener() {39 40             @Override41             public void onErrorResponse(VolleyError error) {42                 // 回调失败43                 if (errorImage != null) {44                     view.setImageBitmap(errorImage);45                 }46             }47 48             @Override49             public void onResponse(ImageContainer response, boolean isImmediate) {50                 // 回调成功51                 if (response.getBitmap() != null) {52                     view.setImageBitmap(response.getBitmap());53                 } else if (defaultImage != null) {54                     view.setImageBitmap(defaultImage);55                 }56             }57         };58 59     }60 61     /**62      * 提供给外部调用方法63      * 64      * @param url65      * @param view66      * @param defaultImage67      * @param errorImage68      */69     public static void loadImage(String url, ImageView view, Bitmap defaultImage, Bitmap errorImage) {70         mImageLoader.get(url, ImageCacheManager.getImageListener(view, defaultImage, errorImage), 0, 0);71     }72 73     /**74      * 提供给外部调用方法75      * 76      * @param url77      * @param view78      * @param defaultImage79      * @param errorImage80      */81     public static void loadImage(String url, ImageView view, Bitmap defaultImage, Bitmap errorImage, int maxWidth, int maxHeight) {82         mImageLoader.get(url, ImageCacheManager.getImageListener(view, defaultImage, errorImage), maxWidth, maxHeight);83     }84 }

 

6、MainActivity类

 1 package com.lcw.rabbit.image; 2  3 import android.app.Activity; 4 import android.content.res.Resources; 5 import android.graphics.Bitmap; 6 import android.graphics.BitmapFactory; 7 import android.os.Bundle; 8 import android.view.View; 9 import android.view.View.OnClickListener;10 import android.widget.Button;11 import android.widget.ImageView;12 13 public class MainActivity extends Activity {14 15     private Button mButton;16     private ImageView mImageView;17 18     @Override19     protected void onCreate(Bundle savedInstanceState) {20         super.onCreate(savedInstanceState);21         setContentView(R.layout.activity_main);22         mButton = (Button) findViewById(R.id.button);23         mImageView= (ImageView) findViewById(R.id.image);24         25 26         mButton.setOnClickListener(new OnClickListener() {27 28             @Override29             public void onClick(View v) {30                 String url = "http://img.blog.csdn.net/20130702124537953?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvdDEyeDM0NTY=/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast";31                 ImageCacheManager.loadImage(url, mImageView, getBitmapFromRes(R.drawable.ic_launcher), getBitmapFromRes(R.drawable.ic_launcher));32 33             }34         });35     }36 37     public Bitmap getBitmapFromRes(int resId) {38         Resources res = this.getResources();39         return BitmapFactory.decodeResource(res, resId);40 41     }42 43 }

 

到这里代码就结束了，由于主要是讲关于缓存层的运用，关于Volley，LruCache，DiskCache的介绍使用，这里就不再阐述了，网上资料很多，大家查阅下便是。

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