安卓开发笔记——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

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

package com.lcw.rabbit.image.utils;import android.app.Application;/** * Application类，提供全局上下文对象 * @author Rabbit_Lee * */public class MyApplication extends Application {    public static String TAG;    public static MyApplication myApplication;    public static MyApplication newInstance() {        return myApplication;    }    @Override    public void onCreate() {        super.onCreate();        TAG = this.getClass().getSimpleName();        myApplication = this;    }}

2、Volley请求队列处理类，用来管理Rquest请求对象操作

package com.lcw.rabbit.image;import com.android.volley.Request;import com.android.volley.RequestQueue;import com.android.volley.toolbox.Volley;import com.lcw.rabbit.image.utils.MyApplication;/** * 请求队列处理类 * 获取RequestQueue对象 */public class VolleyRequestQueueManager {    // 获取请求队列类    public static RequestQueue mRequestQueue = Volley.newRequestQueue(MyApplication.newInstance());    //添加任务进任务队列    public static void addRequest(Request<?> request, Object tag) {        if (tag != null) {            request.setTag(tag);        }        mRequestQueue.add(request);    }    //取消任务    public static void cancelRequest(Object tag){        mRequestQueue.cancelAll(tag);    }}

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

package com.lcw.rabbit.image.utils;import java.math.BigInteger;import java.security.MessageDigest;import java.security.NoSuchAlgorithmException;public class MD5Utils {    /**     * 使用md5的算法进行加密     */    public static String md5(String plainText) {        byte[] secretBytes = null;        try {            secretBytes = MessageDigest.getInstance("md5").digest(                    plainText.getBytes());        } catch (NoSuchAlgorithmException e) {            throw new RuntimeException("没有md5这个算法！");        }        String md5code = new BigInteger(1, secretBytes).toString(16);// 16进制数字        // 如果生成数字未满32位，需要前面补0        for (int i = 0; i < 32 - md5code.length(); i++) {            md5code = "0" + md5code;        }        return md5code;    }}MD5转换类

/* * Copyright (C) 2011 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * *      http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */package com.lcw.rabbit.image.utils;import java.io.BufferedInputStream;import java.io.BufferedWriter;import java.io.Closeable;import java.io.EOFException;import java.io.File;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.FileWriter;import java.io.FilterOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.InputStreamReader;import java.io.OutputStream;import java.io.OutputStreamWriter;import java.io.Reader;import java.io.StringWriter;import java.io.Writer;import java.lang.reflect.Array;import java.nio.charset.Charset;import java.util.ArrayList;import java.util.Arrays;import java.util.Iterator;import java.util.LinkedHashMap;import java.util.Map;import java.util.concurrent.Callable;import java.util.concurrent.ExecutorService;import java.util.concurrent.LinkedBlockingQueue;import java.util.concurrent.ThreadPoolExecutor;import java.util.concurrent.TimeUnit;/** ****************************************************************************** * Taken from the JB source code, can be found in: * libcore/luni/src/main/java/libcore/io/DiskLruCache.java * or direct link: * https://android.googlesource.com/platform/libcore/+/android-4.1.1_r1/luni/src/main/java/libcore/io/DiskLruCache.java ****************************************************************************** * * A cache that uses a bounded amount of space on a filesystem. Each cache * entry has a string key and a fixed number of values. Values are byte * sequences, accessible as streams or files. Each value must be between {@code * 0} and {@code Integer.MAX_VALUE} bytes in length. * * <p>The cache stores its data in a directory on the filesystem. This * directory must be exclusive to the cache; the cache may delete or overwrite * files from its directory. It is an error for multiple processes to use the * same cache directory at the same time. * * <p>This cache limits the number of bytes that it will store on the * filesystem. When the number of stored bytes exceeds the limit, the cache will * remove entries in the background until the limit is satisfied. The limit is * not strict: the cache may temporarily exceed it while waiting for files to be * deleted. The limit does not include filesystem overhead or the cache * journal so space-sensitive applications should set a conservative limit. * * <p>Clients call {@link #edit} to create or update the values of an entry. An * entry may have only one editor at one time; if a value is not available to be * edited then {@link #edit} will return null. * <ul> *     <li>When an entry is being <strong>created</strong> it is necessary to *         supply a full set of values; the empty value should be used as a *         placeholder if necessary. *     <li>When an entry is being <strong>edited</strong>, it is not necessary *         to supply data for every value; values default to their previous *         value. * </ul> * Every {@link #edit} call must be matched by a call to {@link Editor#commit} * or {@link Editor#abort}. Committing is atomic: a read observes the full set * of values as they were before or after the commit, but never a mix of values. * * <p>Clients call {@link #get} to read a snapshot of an entry. The read will * observe the value at the time that {@link #get} was called. Updates and * removals after the call do not impact ongoing reads. * * <p>This class is tolerant of some I/O errors. If files are missing from the * filesystem, the corresponding entries will be dropped from the cache. If * an error occurs while writing a cache value, the edit will fail silently. * Callers should handle other problems by catching {@code IOException} and * responding appropriately. */public final class DiskLruCache implements Closeable {    static final String JOURNAL_FILE = "journal";    static final String JOURNAL_FILE_TMP = "journal.tmp";    static final String MAGIC = "libcore.io.DiskLruCache";    static final String VERSION_1 = "1";    static final long ANY_SEQUENCE_NUMBER = -1;    private static final String CLEAN = "CLEAN";    private static final String DIRTY = "DIRTY";    private static final String REMOVE = "REMOVE";    private static final String READ = "READ";    private static final Charset UTF_8 = Charset.forName("UTF-8");    private static final int IO_BUFFER_SIZE = 8 * 1024;    /*     * This cache uses a journal file named "journal". A typical journal file     * looks like this:     *     libcore.io.DiskLruCache     *     1     *     100     *     2     *     *     CLEAN 3400330d1dfc7f3f7f4b8d4d803dfcf6 832 21054     *     DIRTY 335c4c6028171cfddfbaae1a9c313c52     *     CLEAN 335c4c6028171cfddfbaae1a9c313c52 3934 2342     *     REMOVE 335c4c6028171cfddfbaae1a9c313c52     *     DIRTY 1ab96a171faeeee38496d8b330771a7a     *     CLEAN 1ab96a171faeeee38496d8b330771a7a 1600 234     *     READ 335c4c6028171cfddfbaae1a9c313c52     *     READ 3400330d1dfc7f3f7f4b8d4d803dfcf6     *     * The first five lines of the journal form its header. They are the     * constant string "libcore.io.DiskLruCache", the disk cache's version,     * the application's version, the value count, and a blank line.     *     * Each of the subsequent lines in the file is a record of the state of a     * cache entry. Each line contains space-separated values: a state, a key,     * and optional state-specific values.     *   o DIRTY lines track that an entry is actively being created or updated.     *     Every successful DIRTY action should be followed by a CLEAN or REMOVE     *     action. DIRTY lines without a matching CLEAN or REMOVE indicate that     *     temporary files may need to be deleted.     *   o CLEAN lines track a cache entry that has been successfully published     *     and may be read. A publish line is followed by the lengths of each of     *     its values.     *   o READ lines track accesses for LRU.     *   o REMOVE lines track entries that have been deleted.     *     * The journal file is appended to as cache operations occur. The journal may     * occasionally be compacted by dropping redundant lines. A temporary file named     * "journal.tmp" will be used during compaction; that file should be deleted if     * it exists when the cache is opened.     */    private final File directory;    private final File journalFile;    private final File journalFileTmp;    private final int appVersion;    private final long maxSize;    private final int valueCount;    private long size = 0;    private Writer journalWriter;    private final LinkedHashMap<String, Entry> lruEntries            = new LinkedHashMap<String, Entry>(0, 0.75f, true);    private int redundantOpCount;    /**     * To differentiate between old and current snapshots, each entry is given     * a sequence number each time an edit is committed. A snapshot is stale if     * its sequence number is not equal to its entry's sequence number.     */    private long nextSequenceNumber = 0;    /* From java.util.Arrays */    @SuppressWarnings("unchecked")    private static <T> T[] copyOfRange(T[] original, int start, int end) {        final int originalLength = original.length; // For exception priority compatibility.        if (start > end) {            throw new IllegalArgumentException();        }        if (start < 0 || start > originalLength) {            throw new ArrayIndexOutOfBoundsException();        }        final int resultLength = end - start;        final int copyLength = Math.min(resultLength, originalLength - start);        final T[] result = (T[]) Array                .newInstance(original.getClass().getComponentType(), resultLength);        System.arraycopy(original, start, result, 0, copyLength);        return result;    }    /**     * Returns the remainder of 'reader' as a string, closing it when done.     */    public static String readFully(Reader reader) throws IOException {        try {            StringWriter writer = new StringWriter();            char[] buffer = new char[1024];            int count;            while ((count = reader.read(buffer)) != -1) {                writer.write(buffer, 0, count);            }            return writer.toString();        } finally {            reader.close();        }    }    /**     * Returns the ASCII characters up to but not including the next "\r\n", or     * "\n".     *     * @throws java.io.EOFException if the stream is exhausted before the next newline     *     character.     */    public static String readAsciiLine(InputStream in) throws IOException {        // TODO: support UTF-8 here instead        StringBuilder result = new StringBuilder(80);        while (true) {            int c = in.read();            if (c == -1) {                throw new EOFException();            } else if (c == '\n') {                break;            }            result.append((char) c);        }        int length = result.length();        if (length > 0 && result.charAt(length - 1) == '\r') {            result.setLength(length - 1);        }        return result.toString();    }    /**     * Closes 'closeable', ignoring any checked exceptions. Does nothing if 'closeable' is null.     */    public static void closeQuietly(Closeable closeable) {        if (closeable != null) {            try {                closeable.close();            } catch (RuntimeException rethrown) {                throw rethrown;            } catch (Exception ignored) {            }        }    }    /**     * Recursively delete everything in {@code dir}.     */    // TODO: this should specify paths as Strings rather than as Files    public static void deleteContents(File dir) throws IOException {        File[] files = dir.listFiles();        if (files == null) {            throw new IllegalArgumentException("not a directory: " + dir);        }        for (File file : files) {            if (file.isDirectory()) {                deleteContents(file);            }            if (!file.delete()) {                throw new IOException("failed to delete file: " + file);            }        }    }    /** This cache uses a single background thread to evict entries. */    private final ExecutorService executorService = new ThreadPoolExecutor(0, 1,            60L, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());    private final Callable<Void> cleanupCallable = new Callable<Void>() {        @Override public Void call() throws Exception {            synchronized (DiskLruCache.this) {                if (journalWriter == null) {                    return null; // closed                }                trimToSize();                if (journalRebuildRequired()) {                    rebuildJournal();                    redundantOpCount = 0;                }            }            return null;        }    };    private DiskLruCache(File directory, int appVersion, int valueCount, long maxSize) {        this.directory = directory;        this.appVersion = appVersion;        this.journalFile = new File(directory, JOURNAL_FILE);        this.journalFileTmp = new File(directory, JOURNAL_FILE_TMP);        this.valueCount = valueCount;        this.maxSize = maxSize;    }    /**     * Opens the cache in {@code directory}, creating a cache if none exists     * there.     *     * @param directory a writable directory     * @param appVersion     * @param valueCount the number of values per cache entry. Must be positive.     * @param maxSize the maximum number of bytes this cache should use to store     * @throws java.io.IOException if reading or writing the cache directory fails     */    public static DiskLruCache open(File directory, int appVersion, int valueCount, long maxSize)            throws IOException {        if (maxSize <= 0) {            throw new IllegalArgumentException("maxSize <= 0");        }        if (valueCount <= 0) {            throw new IllegalArgumentException("valueCount <= 0");        }        // prefer to pick up where we left off        DiskLruCache cache = new DiskLruCache(directory, appVersion, valueCount, maxSize);        if (cache.journalFile.exists()) {            try {                cache.readJournal();                cache.processJournal();                cache.journalWriter = new BufferedWriter(new FileWriter(cache.journalFile, true),                        IO_BUFFER_SIZE);                return cache;            } catch (IOException journalIsCorrupt) {//                System.logW("DiskLruCache " + directory + " is corrupt: "//                        + journalIsCorrupt.getMessage() + ", removing");                cache.delete();            }        }        // create a new empty cache        directory.mkdirs();        cache = new DiskLruCache(directory, appVersion, valueCount, maxSize);        cache.rebuildJournal();        return cache;    }    private void readJournal() throws IOException {        InputStream in = new BufferedInputStream(new FileInputStream(journalFile), IO_BUFFER_SIZE);        try {            String magic = readAsciiLine(in);            String version = readAsciiLine(in);            String appVersionString = readAsciiLine(in);            String valueCountString = readAsciiLine(in);            String blank = readAsciiLine(in);            if (!MAGIC.equals(magic)                    || !VERSION_1.equals(version)                    || !Integer.toString(appVersion).equals(appVersionString)                    || !Integer.toString(valueCount).equals(valueCountString)                    || !"".equals(blank)) {                throw new IOException("unexpected journal header: ["                        + magic + ", " + version + ", " + valueCountString + ", " + blank + "]");            }            while (true) {                try {                    readJournalLine(readAsciiLine(in));                } catch (EOFException endOfJournal) {                    break;                }            }        } finally {            closeQuietly(in);        }    }    private void readJournalLine(String line) throws IOException {        String[] parts = line.split(" ");        if (parts.length < 2) {            throw new IOException("unexpected journal line: " + line);        }        String key = parts[1];        if (parts[0].equals(REMOVE) && parts.length == 2) {            lruEntries.remove(key);            return;        }        Entry entry = lruEntries.get(key);        if (entry == null) {            entry = new Entry(key);            lruEntries.put(key, entry);        }        if (parts[0].equals(CLEAN) && parts.length == 2 + valueCount) {            entry.readable = true;            entry.currentEditor = null;            entry.setLengths(copyOfRange(parts, 2, parts.length));        } else if (parts[0].equals(DIRTY) && parts.length == 2) {            entry.currentEditor = new Editor(entry);        } else if (parts[0].equals(READ) && parts.length == 2) {            // this work was already done by calling lruEntries.get()        } else {            throw new IOException("unexpected journal line: " + line);        }    }    /**     * Computes the initial size and collects garbage as a part of opening the     * cache. Dirty entries are assumed to be inconsistent and will be deleted.     */    private void processJournal() throws IOException {        deleteIfExists(journalFileTmp);        for (Iterator<Entry> i = lruEntries.values().iterator(); i.hasNext(); ) {            Entry entry = i.next();            if (entry.currentEditor == null) {                for (int t = 0; t < valueCount; t++) {                    size += entry.lengths[t];                }            } else {                entry.currentEditor = null;                for (int t = 0; t < valueCount; t++) {                    deleteIfExists(entry.getCleanFile(t));                    deleteIfExists(entry.getDirtyFile(t));                }                i.remove();            }        }    }    /**     * Creates a new journal that omits redundant information. This replaces the     * current journal if it exists.     */    private synchronized void rebuildJournal() throws IOException {        if (journalWriter != null) {            journalWriter.close();        }        Writer writer = new BufferedWriter(new FileWriter(journalFileTmp), IO_BUFFER_SIZE);        writer.write(MAGIC);        writer.write("\n");        writer.write(VERSION_1);        writer.write("\n");        writer.write(Integer.toString(appVersion));        writer.write("\n");        writer.write(Integer.toString(valueCount));        writer.write("\n");        writer.write("\n");        for (Entry entry : lruEntries.values()) {            if (entry.currentEditor != null) {                writer.write(DIRTY + ' ' + entry.key + '\n');            } else {                writer.write(CLEAN + ' ' + entry.key + entry.getLengths() + '\n');            }        }        writer.close();        journalFileTmp.renameTo(journalFile);        journalWriter = new BufferedWriter(new FileWriter(journalFile, true), IO_BUFFER_SIZE);    }    private static void deleteIfExists(File file) throws IOException {//        try {//            Libcore.os.remove(file.getPath());//        } catch (ErrnoException errnoException) {//            if (errnoException.errno != OsConstants.ENOENT) {//                throw errnoException.rethrowAsIOException();//            }//        }        if (file.exists() && !file.delete()) {            throw new IOException();        }    }    /**     * Returns a snapshot of the entry named {@code key}, or null if it doesn't     * exist is not currently readable. If a value is returned, it is moved to     * the head of the LRU queue.     */    public synchronized Snapshot get(String key) throws IOException {        checkNotClosed();        validateKey(key);        Entry entry = lruEntries.get(key);        if (entry == null) {            return null;        }        if (!entry.readable) {            return null;        }        /*         * Open all streams eagerly to guarantee that we see a single published         * snapshot. If we opened streams lazily then the streams could come         * from different edits.         */        InputStream[] ins = new InputStream[valueCount];        try {            for (int i = 0; i < valueCount; i++) {                ins[i] = new FileInputStream(entry.getCleanFile(i));            }        } catch (FileNotFoundException e) {            // a file must have been deleted manually!            return null;        }        redundantOpCount++;        journalWriter.append(READ + ' ' + key + '\n');        if (journalRebuildRequired()) {            executorService.submit(cleanupCallable);        }        return new Snapshot(key, entry.sequenceNumber, ins);    }    /**     * Returns an editor for the entry named {@code key}, or null if another     * edit is in progress.     */    public Editor edit(String key) throws IOException {        return edit(key, ANY_SEQUENCE_NUMBER);    }    private synchronized Editor edit(String key, long expectedSequenceNumber) throws IOException {        checkNotClosed();        validateKey(key);        Entry entry = lruEntries.get(key);        if (expectedSequenceNumber != ANY_SEQUENCE_NUMBER                && (entry == null || entry.sequenceNumber != expectedSequenceNumber)) {            return null; // snapshot is stale        }        if (entry == null) {            entry = new Entry(key);            lruEntries.put(key, entry);        } else if (entry.currentEditor != null) {            return null; // another edit is in progress        }        Editor editor = new Editor(entry);        entry.currentEditor = editor;        // flush the journal before creating files to prevent file leaks        journalWriter.write(DIRTY + ' ' + key + '\n');        journalWriter.flush();        return editor;    }    /**     * Returns the directory where this cache stores its data.     */    public File getDirectory() {        return directory;    }    /**     * Returns the maximum number of bytes that this cache should use to store     * its data.     */    public long maxSize() {        return maxSize;    }    /**     * Returns the number of bytes currently being used to store the values in     * this cache. This may be greater than the max size if a background     * deletion is pending.     */    public synchronized long size() {        return size;    }    private synchronized void completeEdit(Editor editor, boolean success) throws IOException {        Entry entry = editor.entry;        if (entry.currentEditor != editor) {            throw new IllegalStateException();        }        // if this edit is creating the entry for the first time, every index must have a value        if (success && !entry.readable) {            for (int i = 0; i < valueCount; i++) {                if (!entry.getDirtyFile(i).exists()) {                    editor.abort();                    throw new IllegalStateException("edit didn't create file " + i);                }            }        }        for (int i = 0; i < valueCount; i++) {            File dirty = entry.getDirtyFile(i);            if (success) {                if (dirty.exists()) {                    File clean = entry.getCleanFile(i);                    dirty.renameTo(clean);                    long oldLength = entry.lengths[i];                    long newLength = clean.length();                    entry.lengths[i] = newLength;                    size = size - oldLength + newLength;                }            } else {                deleteIfExists(dirty);            }        }        redundantOpCount++;        entry.currentEditor = null;        if (entry.readable | success) {            entry.readable = true;            journalWriter.write(CLEAN + ' ' + entry.key + entry.getLengths() + '\n');            if (success) {                entry.sequenceNumber = nextSequenceNumber++;            }        } else {            lruEntries.remove(entry.key);            journalWriter.write(REMOVE + ' ' + entry.key + '\n');        }        if (size > maxSize || journalRebuildRequired()) {            executorService.submit(cleanupCallable);        }    }    /**     * We only rebuild the journal when it will halve the size of the journal     * and eliminate at least 2000 ops.     */    private boolean journalRebuildRequired() {        final int REDUNDANT_OP_COMPACT_THRESHOLD = 2000;        return redundantOpCount >= REDUNDANT_OP_COMPACT_THRESHOLD                && redundantOpCount >= lruEntries.size();    }    /**     * Drops the entry for {@code key} if it exists and can be removed. Entries     * actively being edited cannot be removed.     *     * @return true if an entry was removed.     */    public synchronized boolean remove(String key) throws IOException {        checkNotClosed();        validateKey(key);        Entry entry = lruEntries.get(key);        if (entry == null || entry.currentEditor != null) {            return false;        }        for (int i = 0; i < valueCount; i++) {            File file = entry.getCleanFile(i);            if (!file.delete()) {                throw new IOException("failed to delete " + file);            }            size -= entry.lengths[i];            entry.lengths[i] = 0;        }        redundantOpCount++;        journalWriter.append(REMOVE + ' ' + key + '\n');        lruEntries.remove(key);        if (journalRebuildRequired()) {            executorService.submit(cleanupCallable);        }        return true;    }    /**     * Returns true if this cache has been closed.     */    public boolean isClosed() {        return journalWriter == null;    }    private void checkNotClosed() {        if (journalWriter == null) {            throw new IllegalStateException("cache is closed");        }    }    /**     * Force buffered operations to the filesystem.     */    public synchronized void flush() throws IOException {        checkNotClosed();        trimToSize();        journalWriter.flush();    }    /**     * Closes this cache. Stored values will remain on the filesystem.     */    public synchronized void close() throws IOException {        if (journalWriter == null) {            return; // already closed        }        for (Entry entry : new ArrayList<Entry>(lruEntries.values())) {            if (entry.currentEditor != null) {                entry.currentEditor.abort();            }        }        trimToSize();        journalWriter.close();        journalWriter = null;    }    private void trimToSize() throws IOException {        while (size > maxSize) {//            Map.Entry<String, Entry> toEvict = lruEntries.eldest();            final Map.Entry<String, Entry> toEvict = lruEntries.entrySet().iterator().next();            remove(toEvict.getKey());        }    }    /**     * Closes the cache and deletes all of its stored values. This will delete     * all files in the cache directory including files that weren't created by     * the cache.     */    public void delete() throws IOException {        close();        deleteContents(directory);    }    private void validateKey(String key) {        if (key.contains(" ") || key.contains("\n") || key.contains("\r")) {            throw new IllegalArgumentException(                    "keys must not contain spaces or newlines: \"" + key + "\"");        }    }    private static String inputStreamToString(InputStream in) throws IOException {        return readFully(new InputStreamReader(in, UTF_8));    }    /**     * A snapshot of the values for an entry.     */    public final class Snapshot implements Closeable {        private final String key;        private final long sequenceNumber;        private final InputStream[] ins;        private Snapshot(String key, long sequenceNumber, InputStream[] ins) {            this.key = key;            this.sequenceNumber = sequenceNumber;            this.ins = ins;        }        /**         * Returns an editor for this snapshot's entry, or null if either the         * entry has changed since this snapshot was created or if another edit         * is in progress.         */        public Editor edit() throws IOException {            return DiskLruCache.this.edit(key, sequenceNumber);        }        /**         * Returns the unbuffered stream with the value for {@code index}.         */        public InputStream getInputStream(int index) {            return ins[index];        }        /**         * Returns the string value for {@code index}.         */        public String getString(int index) throws IOException {            return inputStreamToString(getInputStream(index));        }        @Override public void close() {            for (InputStream in : ins) {                closeQuietly(in);            }        }    }    /**     * Edits the values for an entry.     */    public final class Editor {        private final Entry entry;        private boolean hasErrors;        private Editor(Entry entry) {            this.entry = entry;        }        /**         * Returns an unbuffered input stream to read the last committed value,         * or null if no value has been committed.         */        public InputStream newInputStream(int index) throws IOException {            synchronized (DiskLruCache.this) {                if (entry.currentEditor != this) {                    throw new IllegalStateException();                }                if (!entry.readable) {                    return null;                }                return new FileInputStream(entry.getCleanFile(index));            }        }        /**         * Returns the last committed value as a string, or null if no value         * has been committed.         */        public String getString(int index) throws IOException {            InputStream in = newInputStream(index);            return in != null ? inputStreamToString(in) : null;        }        /**         * 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.         */        public OutputStream newOutputStream(int index) throws IOException {            synchronized (DiskLruCache.this) {                if (entry.currentEditor != this) {                    throw new IllegalStateException();                }                return new FaultHidingOutputStream(new FileOutputStream(entry.getDirtyFile(index)));            }        }        /**         * Sets the value at {@code index} to {@code value}.         */        public void set(int index, String value) throws IOException {            Writer writer = null;            try {                writer = new OutputStreamWriter(newOutputStream(index), UTF_8);                writer.write(value);            } finally {                closeQuietly(writer);            }        }        /**         * Commits this edit so it is visible to readers.  This releases the         * edit lock so another edit may be started on the same key.         */        public void commit() throws IOException {            if (hasErrors) {                completeEdit(this, false);                remove(entry.key); // the previous entry is stale            } else {                completeEdit(this, true);            }        }        /**         * Aborts this edit. This releases the edit lock so another edit may be         * started on the same key.         */        public void abort() throws IOException {            completeEdit(this, false);        }        private class FaultHidingOutputStream extends FilterOutputStream {            private FaultHidingOutputStream(OutputStream out) {                super(out);            }            @Override public void write(int oneByte) {                try {                    out.write(oneByte);                } catch (IOException e) {                    hasErrors = true;                }            }            @Override public void write(byte[] buffer, int offset, int length) {                try {                    out.write(buffer, offset, length);                } catch (IOException e) {                    hasErrors = true;                }            }            @Override public void close() {                try {                    out.close();                } catch (IOException e) {                    hasErrors = true;                }            }            @Override public void flush() {                try {                    out.flush();                } catch (IOException e) {                    hasErrors = true;                }            }        }    }    private final class Entry {        private final String key;        /** Lengths of this entry's files. */        private final long[] lengths;        /** True if this entry has ever been published */        private boolean readable;        /** The ongoing edit or null if this entry is not being edited. */        private Editor currentEditor;        /** The sequence number of the most recently committed edit to this entry. */        private long sequenceNumber;        private Entry(String key) {            this.key = key;            this.lengths = new long[valueCount];        }        public String getLengths() throws IOException {            StringBuilder result = new StringBuilder();            for (long size : lengths) {                result.append(' ').append(size);            }            return result.toString();        }        /**         * Set lengths using decimal numbers like "10123".         */        private void setLengths(String[] strings) throws IOException {            if (strings.length != valueCount) {                throw invalidLengths(strings);            }            try {                for (int i = 0; i < strings.length; i++) {                    lengths[i] = Long.parseLong(strings[i]);                }            } catch (NumberFormatException e) {                throw invalidLengths(strings);            }        }        private IOException invalidLengths(String[] strings) throws IOException {            throw new IOException("unexpected journal line: " + Arrays.toString(strings));        }        public File getCleanFile(int i) {            return new File(directory, key + "." + i);        }        public File getDirtyFile(int i) {            return new File(directory, key + "." + i + ".tmp");        }    }}DiskLruCache磁盘缓存类

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

package com.lcw.rabbit.image.utils;import java.io.File;import java.io.IOException;import java.io.OutputStream;import android.content.Context;import android.content.pm.PackageInfo;import android.content.pm.PackageManager.NameNotFoundException;import android.graphics.Bitmap;import android.graphics.Bitmap.CompressFormat;import android.graphics.BitmapFactory;import android.os.Environment;import android.support.v4.util.LruCache;import android.util.Log;import com.android.volley.toolbox.ImageLoader.ImageCache;import com.lcw.rabbit.image.utils.DiskLruCache.Snapshot;/** * 图片缓存帮助类 *  * 包含内存缓存LruCache和磁盘缓存DiskLruCache *  * @author Rabbit_Lee *  */public class ImageCacheUtil implements ImageCache {    private String TAG=ImageCacheUtil.this.getClass().getSimpleName();    //缓存类    private static LruCache<String, Bitmap> mLruCache;    private static DiskLruCache mDiskLruCache;    //磁盘缓存大小    private static final int DISKMAXSIZE = 10 * 1024 * 1024;    public ImageCacheUtil() {        // 获取应用可占内存的1/8作为缓存        int maxSize = (int) (Runtime.getRuntime().maxMemory() / 8);        // 实例化LruCaceh对象        mLruCache = new LruCache<String, Bitmap>(maxSize) {            @Override            protected int sizeOf(String key, Bitmap bitmap) {                return bitmap.getRowBytes() * bitmap.getHeight();            }        };        try {            // 获取DiskLruCahce对象            mDiskLruCache = DiskLruCache.open(getDiskCacheDir(MyApplication.newInstance(), "Rabbit"), getAppVersion(MyApplication.newInstance()), 1, DISKMAXSIZE);        } catch (IOException e) {            e.printStackTrace();        }    }    /**     * 从缓存（内存缓存，磁盘缓存）中获取Bitmap     */    @Override    public Bitmap getBitmap(String url) {        if (mLruCache.get(url) != null) {            // 从LruCache缓存中取            Log.i(TAG,"从LruCahce获取");            return mLruCache.get(url);        } else {            String key = MD5Utils.md5(url);            try {                if (mDiskLruCache.get(key) != null) {                    // 从DiskLruCahce取                    Snapshot snapshot = mDiskLruCache.get(key);                    Bitmap bitmap = null;                    if (snapshot != null) {                        bitmap = BitmapFactory.decodeStream(snapshot.getInputStream(0));                        // 存入LruCache缓存                        mLruCache.put(url, bitmap);                        Log.i(TAG,"从DiskLruCahce获取");                    }                    return bitmap;                }            } catch (IOException e) {                e.printStackTrace();            }        }        return null;    }    /**     * 存入缓存（内存缓存，磁盘缓存）     */    @Override    public void putBitmap(String url, Bitmap bitmap) {        // 存入LruCache缓存        mLruCache.put(url, bitmap);        // 判断是否存在DiskLruCache缓存，若没有存入        String key = MD5Utils.md5(url);        try {            if (mDiskLruCache.get(key) == null) {                DiskLruCache.Editor editor = mDiskLruCache.edit(key);                if (editor != null) {                    OutputStream outputStream = editor.newOutputStream(0);                    if (bitmap.compress(CompressFormat.JPEG, 100, outputStream)) {                        editor.commit();                    } else {                        editor.abort();                    }                }                mDiskLruCache.flush();            }        } catch (IOException e) {            e.printStackTrace();        }    }    /**     * 该方法会判断当前sd卡是否存在，然后选择缓存地址     *      * @param context     * @param uniqueName     * @return     */    public static File getDiskCacheDir(Context context, String uniqueName) {        String cachePath;        if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState()) || !Environment.isExternalStorageRemovable()) {            cachePath = context.getExternalCacheDir().getPath();        } else {            cachePath = context.getCacheDir().getPath();        }        return new File(cachePath + File.separator + uniqueName);    }    /**     * 获取应用版本号     *      * @param context     * @return     */    public int getAppVersion(Context context) {        try {            PackageInfo info = context.getPackageManager().getPackageInfo(context.getPackageName(), 0);            return info.versionCode;        } catch (NameNotFoundException e) {            e.printStackTrace();        }        return 1;    }}

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。

package com.lcw.rabbit.image;import android.graphics.Bitmap;import android.widget.ImageView;import com.android.volley.VolleyError;import com.android.volley.toolbox.ImageLoader;import com.android.volley.toolbox.ImageLoader.ImageCache;import com.android.volley.toolbox.ImageLoader.ImageContainer;import com.android.volley.toolbox.ImageLoader.ImageListener;import com.lcw.rabbit.image.utils.ImageCacheUtil;/** * 图片缓存管理类 获取ImageLoader对象 *  * @author Rabbit_Lee *  */public class ImageCacheManager {    private static String TAG = ImageCacheManager.class.getSimpleName();    // 获取图片缓存类对象    private static ImageCache mImageCache = new ImageCacheUtil();    // 获取ImageLoader对象    public static ImageLoader mImageLoader = new ImageLoader(VolleyRequestQueueManager.mRequestQueue, mImageCache);    /**     * 获取ImageListener     *      * @param view     * @param defaultImage     * @param errorImage     * @return     */    public static ImageListener getImageListener(final ImageView view, final Bitmap defaultImage, final Bitmap errorImage) {        return new ImageListener() {            @Override            public void onErrorResponse(VolleyError error) {                // 回调失败                if (errorImage != null) {                    view.setImageBitmap(errorImage);                }            }            @Override            public void onResponse(ImageContainer response, boolean isImmediate) {                // 回调成功                if (response.getBitmap() != null) {                    view.setImageBitmap(response.getBitmap());                } else if (defaultImage != null) {                    view.setImageBitmap(defaultImage);                }            }        };    }    /**     * 提供给外部调用方法     *      * @param url     * @param view     * @param defaultImage     * @param errorImage     */    public static void loadImage(String url, ImageView view, Bitmap defaultImage, Bitmap errorImage) {        mImageLoader.get(url, ImageCacheManager.getImageListener(view, defaultImage, errorImage), 0, 0);    }    /**     * 提供给外部调用方法     *      * @param url     * @param view     * @param defaultImage     * @param errorImage     */    public static void loadImage(String url, ImageView view, Bitmap defaultImage, Bitmap errorImage, int maxWidth, int maxHeight) {        mImageLoader.get(url, ImageCacheManager.getImageListener(view, defaultImage, errorImage), maxWidth, maxHeight);    }}

6、MainActivity类

package com.lcw.rabbit.image;import android.app.Activity;import android.content.res.Resources;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.os.Bundle;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.ImageView;public class MainActivity extends Activity {    private Button mButton;    private ImageView mImageView;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        mButton = (Button) findViewById(R.id.button);        mImageView= (ImageView) findViewById(R.id.image);        mButton.setOnClickListener(new OnClickListener() {            @Override            public void onClick(View v) {                String url = "http://img.blog.csdn.net/20130702124537953?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvdDEyeDM0NTY=/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast";                ImageCacheManager.loadImage(url, mImageView, getBitmapFromRes(R.drawable.ic_launcher), getBitmapFromRes(R.drawable.ic_launcher));            }        });    }    public Bitmap getBitmapFromRes(int resId) {        Resources res = this.getResources();        return BitmapFactory.decodeResource(res, resId);    }}

作者：李晨玮
出处：http://www.cnblogs.com/lichenwei/
本文版权归作者和博客园共有,欢迎转载,但未经作者同意必须保留此段声明,且在文章页面明显位置给出原文链接。
正在看本人博客的这位童鞋，我看你气度不凡，谈吐间隐隐有王者之气，日后必有一番作为！旁边有“推荐”二字，你就顺手把它点了吧，相得准，我分文不收；相不准，你也好回来找我！

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