public static FileNameGenerator createFileNameGenerator() { 
return new HashCodeFileNameGenerator(); 
}

File getFileDectory() 返回磁盘缓存的根目录
File get(String imageUri) 根据uri从缓存中获取图片
boolean save(String imageUri,InputStream iamgeStream,IoUtils.CopyListener listener) 把图片保存在磁盘缓存上
boolean save(String imageUri,Bitmap bitmap) 保存bitmap对象到磁盘缓存上
boolean remove(imageUri) 根据imageUri删除文件
void close() 关闭磁盘缓存，释放资源
void clear() 清空磁盘缓存

protected final File cacheDir;//缓存文件的保存Directory
protected final File reserveCacheDir;//后备缓存的Diectory，当cacheDir不存在的情况下就是用reserveCahceDir后备缓存
protected final FileNameGenerator fileNameGenerator;//文件名名称生成器

public BaseDiscCache(File cacheDir) {
this(cacheDir, null);
}
public BaseDiscCache(File cacheDir, File reserveCacheDir) {
this(cacheDir, reserveCacheDir, DefaultConfigurationFactory.createFileNameGenerator());
}
public BaseDiscCache(File cacheDir, File reserveCacheDir, FileNameGenerator fileNameGenerator) {
if (cacheDir == null) {
throw new IllegalArgumentException("cacheDir" + ERROR_ARG_NULL);
}
if (fileNameGenerator == null) {
throw new IllegalArgumentException("fileNameGenerator" + ERROR_ARG_NULL);
}
this.cacheDir = cacheDir;
this.reserveCacheDir = reserveCacheDir;
this.fileNameGenerator = fileNameGenerator;
}

protected File getFile(String imageUri) { 
String fileName = fileNameGenerator.generate(imageUri); 
File dir = cacheDir; 
if (!cacheDir.exists() && !cacheDir.mkdirs()) { 
if (reserveCacheDir != null && (reserveCacheDir.exists() || reserveCacheDir.mkdirs())) { 
dir = reserveCacheDir; 
} 
} 
return new File(dir, fileName); 
}

public boolean save(String imageUri, Bitmap bitmap) throws IOException { 
//获取imageUri的File对象，该对象封装了缓存路径和图片保存后的名称 
File imageFile = getFile(imageUri); 
//获取临时保存文件的tmpFile对象 
File tmpFile = new File(imageFile.getAbsolutePath() + TEMP_IMAGE_POSTFIX); 
OutputStream os = new BufferedOutputStream(new FileOutputStream(tmpFile), bufferSize); 
boolean savedSuccessfully = false; 
try { 
//调用compress把bitMap压缩到tempFile中 
savedSuccessfully = bitmap.compress(compressFormat, compressQuality, os); 
} finally { 
IoUtils.closeSilently(os); 
//如果保存成功并且tempFile的文件没有成功移动到imageFile的话，就删除temFile 
if (savedSuccessfully && !tmpFile.renameTo(imageFile)) { 
savedSuccessfully = false; 
} 
if (!savedSuccessfully) { 
tmpFile.delete(); 
} 
} 
//对bitmap进行垃圾回收 
bitmap.recycle(); 
return savedSuccessfully; 
}

private void rememberUsage(String imageUri) { 
File file = getFile(imageUri); 
long currentTime = System.currentTimeMillis(); 
file.setLastModified(currentTime); 
loadingDates.put(file, currentTime); 
}

@Override 
public File get(String imageUri) { 
File file = super.get(imageUri); 
if (file != null && file.exists()) { 
boolean cached; 
Long loadingDate = loadingDates.get(file); 
if (loadingDate == null) { 
cached = false; 
loadingDate = file.lastModified(); 
} else { 
cached = true; 
} 
if (System.currentTimeMillis() - loadingDate > maxFileAge) { 
file.delete(); 
loadingDates.remove(file); 
} else if (!cached) { 
loadingDates.put(file, loadingDate); 
} 
} 
return file; 
}