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

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

[java] view
plaincopy

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

[java] view
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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）

[java] view
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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

[java] view
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/*

* 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 21054832 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）

[java] view
plaincopy

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。

[java] view
plaincopy

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

[java] view
plaincopy

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 = "https://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。