/*
* 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.mzeat.image;
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;
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.mzeat.util.BuildConfig;
/**
*
* A simple disk LRU bitmap cache to illustrate how a disk cache would be used
* for bitmap caching.
* 一个简单的内存LRU位图缓存来举例如何为位图缓冲使用内存缓存
* 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 = "cache_";
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 = 64; // 64 item default
private long maxCacheByteSize = 1024 * 1024 * 5; // 5MB default
private CompressFormat mCompressFormat = CompressFormat.JPEG;
private int mCompressQuality = 70;
private final Map<String, String> mLinkedHashMap = Collections
.synchronizedMap(new LinkedHashMap<String, String>(
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() {
@Override
public boolean accept(File dir, String filename) {
return filename.startsWith(CACHE_FILENAME_PREFIX);
}
};
/**
* Used to fetch an instance of DiskLruCache.
* 用来取得DiskLruCache的一个实例
* @param context
* @param cacheDir
* @param maxByteSize
* @return
*/
public static DiskLruCache openCache(Context context, File cacheDir,
long maxByteSize) {
if (!cacheDir.exists()) {
cacheDir.mkdir();
}
if (cacheDir.isDirectory() && cacheDir.canWrite()
&& Utils.getUsableSpace(cacheDir) > maxByteSize) {
return new DiskLruCache(cacheDir, maxByteSize);
}
return null;
}
/**
* 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.
* 不要直接调用构造方法，在建立DiskLruCache实例之前要运行几个额外的检查。
* @param cacheDir
* @param maxByteSize
*/
private DiskLruCache(File cacheDir, long maxByteSize) {
mCacheDir = cacheDir;
maxCacheByteSize = maxByteSize;
}
/**
* Add a bitmap to the disk cache.
*
* @param key
* A unique identifier for the bitmap.
* @param data
* 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();
}
/**
* 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<String, String> 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.
*
* @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.
*
* @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 HashMap
if (mLinkedHashMap.containsKey(key)) {
return true;
}
// Now check if there's an actual file that exists based on the key
final String existingFile = createFilePath(mCacheDir, key);
if (new File(existingFile).exists()) {
// File found, add it to the HashMap for future use
put(key, existingFile);
return true;
}
return false;
}
/**
* 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.
*
* @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);
}
/**
* 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).
* 取得一个有用的缓存目录
* @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 dir
// 检查是否有安装好的多媒体和插入的存储卡，如果有，尝试使用外部的缓存目录，否则使用内部的缓存目录。
final String cachePath = Environment.getExternalStorageState() == Environment.MEDIA_MOUNTED
|| !Utils.isExternalStorageRemovable() ? Utils
.getExternalCacheDir(context).getPath() : context.getCacheDir()
.getPath();
return new File(cachePath + File.separator + uniqueName);
}
/**
* Creates a constant cache file path given a target cache directory and an
* image key.
* 用当前的缓存目录和图片KEY创建一个常量的缓存文件路径。
* @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 example
return 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.
* 用当前的缓存目录和图片KEY创建一个常量的缓存文件路径。
* @param key
* @return
*/
public String createFilePath(String key) {
return createFilePath(mCacheDir, key);
}
/**
* 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;
}
/**
* Writes a bitmap to a file. Call
* {@link DiskLruCache#setCompressParams(CompressFormat, int)} first to set
* the target bitmap compression and format.
*
* @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);
return bitmap.compress(mCompressFormat, mCompressQuality, out);
} finally {
if (out != null) {
out.close();
}
}
}
}