Android 缓存的工具类

/* * Copyright (C) 2012 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.qianfeng.day31_cache.cache;import java.io.BufferedOutputStream;import java.io.File;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.FilenameFilter;import java.io.IOException;import java.io.OutputStream;import java.io.UnsupportedEncodingException;import java.net.URLEncoder;import java.util.Collections;import java.util.LinkedHashMap;import java.util.Map;import java.util.Map.Entry;import com.qianfeng.day31_cache.BuildConfig;import com.qianfeng.day31_cache.util.Utils;import android.content.Context;import android.graphics.Bitmap;import android.graphics.Bitmap.CompressFormat;import android.graphics.BitmapFactory;import android.os.Environment;import android.util.Log;/** * A simple disk LRU bitmap cache to illustrate how a disk cache would be used * for bitmap caching. A much more robust and efficient disk LRU cache solution * can be found in the ICS source code * (libcore/luni/src/main/java/libcore/io/DiskLruCache.java) and is preferable * to this simple implementation. */public class DiskLruCache {private static final String TAG = "DiskLruCache";private static final String CACHE_FILENAME_PREFIX = "";private static final int MAX_REMOVALS = 4;private static final int INITIAL_CAPACITY = 32;private static final float LOAD_FACTOR = 0.75f;private final File mCacheDir;private int cacheSize = 0;private int cacheByteSize = 0;private final int maxCacheItemSize = 60; // 64 item default// 默认的缓存大小private long maxCacheByteSize = 1024 * 1024 * 5; // 5MB defaultprivate CompressFormat mCompressFormat = CompressFormat.JPEG;private int mCompressQuality = 70;private final Map mLinkedHashMap = Collections.synchronizedMap(new LinkedHashMap(INITIAL_CAPACITY, LOAD_FACTOR, true));/** * A filename filter to use to identify the cache filenames which have * CACHE_FILENAME_PREFIX prepended. */private static final FilenameFilter cacheFileFilter = new FilenameFilter() {@Overridepublic boolean accept(File dir, String filename) {return filename.startsWith(CACHE_FILENAME_PREFIX);}};/** * Used to fetch an instance of DiskLruCache. *  * @param context * @param cacheDir *            :图片要保存的目录 * @param maxByteSize *            :缓存目录可存空间的最小值 * @return */public static DiskLruCache openCache(File cacheDir, long maxByteSize) {// 如果缓存路径不存在,就创建出来if (!cacheDir.exists()) {cacheDir.mkdir();}// Utils.getUsableSpace(cacheDir):判断指定路径上可用的空间大小if (cacheDir.isDirectory() && cacheDir.canWrite()&& Utils.getUsableSpace(cacheDir) > maxByteSize) {return new DiskLruCache(cacheDir, maxByteSize);}return null;}/** * 磁盘缓存DiskLruCache的构造方法 Constructor that should not be called directly, * instead use {@link DiskLruCache#openCache(Context, File, long)} which * runs some extra checks before creating a DiskLruCache instance. *  * @param cacheDir * @param maxByteSize */private DiskLruCache(File cacheDir, long maxByteSize) {mCacheDir = cacheDir;maxCacheByteSize = maxByteSize;}/** * Add a bitmap to the disk cache. 把一个图片存到磁盘缓存中 *  * @param key *            :bitmap对应的唯一标示 A unique identifier for the bitmap. * @param data *            :要存储的图片 The bitmap to store. */public void put(String key, Bitmap data) {synchronized (mLinkedHashMap) {if (mLinkedHashMap.get(key) == null) {try {final String file = createFilePath(mCacheDir, key);if (writeBitmapToFile(data, file)) {put(key, file);flushCache();}} catch (final FileNotFoundException e) {Log.e(TAG, "Error in put: " + e.getMessage());} catch (final IOException e) {Log.e(TAG, "Error in put: " + e.getMessage());}}}}private void put(String key, String file) {mLinkedHashMap.put(key, file);cacheSize = mLinkedHashMap.size();cacheByteSize += new File(file).length();}/** * 清空磁盘中的缓存.如果磁盘缓存中缓存的文件容量超过了指定的缓存总大小,就清除最早的那个bitmap. Flush the cache, * removing oldest entries if the total size is over the specified cache * size. Note that this isn't keeping track of stale files in the cache * directory that aren't in the HashMap. If the images and keys in the disk * cache change often then they probably won't ever be removed. */private void flushCache() {Entry eldestEntry;File eldestFile;long eldestFileSize;int count = 0;while (count < MAX_REMOVALS&& (cacheSize > maxCacheItemSize || cacheByteSize > maxCacheByteSize)) {eldestEntry = mLinkedHashMap.entrySet().iterator().next();eldestFile = new File(eldestEntry.getValue());eldestFileSize = eldestFile.length();mLinkedHashMap.remove(eldestEntry.getKey());eldestFile.delete();cacheSize = mLinkedHashMap.size();cacheByteSize -= eldestFileSize;count++;if (BuildConfig.DEBUG) {Log.d(TAG, "flushCache - Removed cache file, " + eldestFile+ ", " + eldestFileSize);}}}/** * Get an image from the disk cache. 从磁盘缓存中取出key对应的图片 *  * @param key *            The unique identifier for the bitmap * @return The bitmap or null if not found */public Bitmap get(String key) {synchronized (mLinkedHashMap) {final String file = mLinkedHashMap.get(key);if (file != null) {if (BuildConfig.DEBUG) {Log.d(TAG, "Disk cache hit");}return BitmapFactory.decodeFile(file);} else {final String existingFile = createFilePath(mCacheDir, key);if (new File(existingFile).exists()) {put(key, existingFile);if (BuildConfig.DEBUG) {Log.d(TAG, "Disk cache hit (existing file)");}return BitmapFactory.decodeFile(existingFile);}}return null;}}/** * Checks if a specific key exist in the cache. 判断key对应的图片是否存在 *  * @param key *            The unique identifier for the bitmap * @return true if found, false otherwise */public boolean containsKey(String key) {// See if the key is in our HashMapif (mLinkedHashMap.containsKey(key)) {return true;}// Now check if there's an actual file that exists based on the keyfinal String existingFile = createFilePath(mCacheDir, key);if (new File(existingFile).exists()) {// File found, add it to the HashMap for future useput(key, existingFile);return true;}return false;}/** * 清除磁盘缓存中所有的bitmap Removes all disk cache entries from this instance cache * dir */public void clearCache() {DiskLruCache.clearCache(mCacheDir);}/** * Removes all disk cache entries from the application cache directory in * the uniqueName sub-directory. 清除某个key对应的图片 *  * @param context *            The context to use * @param uniqueName *            A unique cache directory name to append to the app cache *            directory */public static void clearCache(Context context, String uniqueName) {File cacheDir = getDiskCacheDir(context, uniqueName);clearCache(cacheDir);}/** * 清除某个文件下面的缓存内容(图片) Removes all disk cache entries from the given * directory. This should not be called directly, call * {@link DiskLruCache#clearCache(Context, String)} or * {@link DiskLruCache#clearCache()} instead. *  * @param cacheDir *            The directory to remove the cache files from */private static void clearCache(File cacheDir) {final File[] files = cacheDir.listFiles(cacheFileFilter);for (int i = 0; i < files.length; i++) {files[i].delete();}}/** * Get a usable cache directory (external if available, internal otherwise). * 得到磁盘缓存路径 *  * @param context *            The context to use * @param uniqueName *            A unique directory name to append to the cache dir * @return The cache dir */public static File getDiskCacheDir(Context context, String uniqueName) {// Check if media is mounted or storage is built-in, if so, try and use// external cache dir// otherwise use internal cache dirfinal String cachePath = Environment.getExternalStorageState() == Environment.MEDIA_MOUNTED|| !Utils.isExternalStorageRemovable() ? Utils.getExternalCacheDir(context).getPath() : context.getCacheDir().getPath();return new File(cachePath + File.separator + uniqueName);}/** * 创建磁盘缓存到的文件 Creates a constant cache file path given a target cache * directory and an image key. 创建一个缓存路径 *  * @param cacheDir * @param key * @return */public static String createFilePath(File cacheDir, String key) {try {// Use URLEncoder to ensure we have a valid filename, a tad hacky// but it will do for// this examplereturn cacheDir.getAbsolutePath() + File.separator+ CACHE_FILENAME_PREFIX+ URLEncoder.encode(key.replace("*", ""), "UTF-8");} catch (final UnsupportedEncodingException e) {Log.e(TAG, "createFilePath - " + e);}return null;}/** * Create a constant cache file path using the current cache directory and * an image key. *  * @param key * @return */public String createFilePath(String key) {return createFilePath(mCacheDir, key);}/** * 设置图片压缩的格式和质量 Sets the target compression format and quality for images * written to the disk cache. *  * @param compressFormat * @param quality */public void setCompressParams(CompressFormat compressFormat, int quality) {mCompressFormat = compressFormat;mCompressQuality = quality;}/** * 把图片存到某个指定的文件下面 Writes a bitmap to a file. Call * {@link DiskLruCache#setCompressParams(CompressFormat, int)} first to set * the target bitmap compression and format. 将图片存到某个路径下,并对图片进行了压缩处理. *  * @param bitmap * @param file * @return */private boolean writeBitmapToFile(Bitmap bitmap, String file)throws IOException, FileNotFoundException {OutputStream out = null;try {out = new BufferedOutputStream(new FileOutputStream(file),Utils.IO_BUFFER_SIZE);// mCompressFormat:图片压缩保存的格式-->jpeg;// mCompressQuality:压缩的质量.return bitmap.compress(mCompressFormat, mCompressQuality, out);} finally {if (out != null) {out.close();}}}}
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