Universal-Image-Loader源码阅读（24）-LimitedAgeDiskCache

有时间限制的硬件缓存。

增加了文件存在的最长时间，超过时间了则删除。

但是存储空间的额大小没有限制。

源码/**
* Cache which deletes files which were loaded more than defined time. Cache size is unlimited.
*
* @author Sergey Tarasevich (nostra13[at]gmail[dot]com)
* @since 1.3.1
*/
public class LimitedAgeDiskCache extends BaseDiskCache {

private final long maxFileAge;

private final Map<File, Long> loadingDates = Collections.synchronizedMap(new HashMap<File, Long>());

/**
* @param cacheDir Directory for file caching
* @param maxAge Max file age (in seconds). If file age will exceed this value then it'll be removed on next
* treatment (and therefore be reloaded).
*/
public LimitedAgeDiskCache(File cacheDir, long maxAge) {
this(cacheDir, null, DefaultConfigurationFactory.createFileNameGenerator(), maxAge);
}

/**
* @param cacheDir Directory for file caching
* @param maxAge Max file age (in seconds). If file age will exceed this value then it'll be removed on next
* treatment (and therefore be reloaded).
*/
public LimitedAgeDiskCache(File cacheDir, File reserveCacheDir, long maxAge) {
this(cacheDir, reserveCacheDir, DefaultConfigurationFactory.createFileNameGenerator(), maxAge);
}

/**
* @param cacheDir Directory for file caching
* @param reserveCacheDir null-ok; Reserve directory for file caching. It's used when the primary directory isn't available.
* @param fileNameGenerator Name generator for cached files
* @param maxAge Max file age (in seconds). If file age will exceed this value then it'll be removed on next
* treatment (and therefore be reloaded).
*/
public LimitedAgeDiskCache(File cacheDir, File reserveCacheDir, FileNameGenerator fileNameGenerator, long maxAge) {
super(cacheDir, reserveCacheDir, fileNameGenerator);
this.maxFileAge = maxAge * 1000; // to milliseconds
}

@Override
public File get(String imageUri) {//如果发现文件超时了，则删除
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;
}

@Override
public boolean save(String imageUri, InputStream imageStream, IoUtils.CopyListener listener) throws IOException {
boolean saved = super.save(imageUri, imageStream, listener);
rememberUsage(imageUri);
return saved;
}

@Override
public boolean save(String imageUri, Bitmap bitmap) throws IOException {
boolean saved = super.save(imageUri, bitmap);
rememberUsage(imageUri);
return saved;
}

@Override
public boolean remove(String imageUri) {
loadingDates.remove(getFile(imageUri));
return super.remove(imageUri);
}

@Override
public void clear() {
super.clear();
loadingDates.clear();
}

private void rememberUsage(String imageUri) {//更新文件最新访问时间
File file = getFile(imageUri);
long currentTime = System.currentTimeMillis();
file.setLastModified(currentTime);
loadingDates.put(file, currentTime);
}
}