一、概述
Android开发中，网络请求是很重要的一部分，而缓存网络请求来的图片或者响应结果字符串或者结果流，既可以省流量，同时也可以帮助我们解决无网或弱网情况下加载情况，当然也可以提升程序性能效率。纵所周知，缓存管理中肯定需要用到内存缓存，这里我们采用LruCache来管理内存的缓存。
LruCahce虽然速度快，但是只是内存级别的缓存，为了实现持久化的缓存，我们还需要文件级别的缓存，也就是说我们要把缓存保存到文件，而文件则是保存到手机存储或者SD卡存储中，即实现Disk级别的缓存，这里我们借助DiskLruCache这个辅助工具类来实现。顾名思义，这个工具类的作用就是使用Lru算法来存储信息到Disk上。
二、实例效果图
下面是个简单的实例演示效果图
三、缓存管理框架的实现解
1、内存缓存类的实现
该类主要实现内存级别的缓存管理类MemoryCache，使用LruCache来实现，因为无论是内存缓存还是Disk缓存，都需要读写操作，所以我们先抽象出一个缓存接口类：Cache接口：
public interface Cache { String get(final String key); void put(final String key, final String value); boolean remove(final String key);
}然后，我们的内存缓存类MemoryCache需要实现Cache这个接口:
/**
* 内存缓存类
* Created by caizhiming on 2015/12/4.
*/public class MemoryCache implements Cache { private LruCache<String, String> mMemoryLruCache; private EvictedListener mEvictedListener; public MemoryCache() {
init();
} public MemoryCache(EvictedListener listener) {
init(); this.mEvictedListener = listener;
} public void setEvictedListener(EvictedListener listener) { this.mEvictedListener = listener;
} public boolean hasEvictedListener() { return mEvictedListener != null;
} private void init() { // 计算可使用的最大内存
final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024); // 取可用内存空间的1/4作为缓存
final int cacheSize = maxMemory / 4;
mMemoryLruCache = new LruCache<String, String>(cacheSize) { @Override
protected int sizeOf(String key, String value) { return value.getBytes().length;
} @Override
protected void entryRemoved(boolean evicted, String key, String oldValue, String newValue) { if (evicted) { if (mEvictedListener != null) {
mEvictedListener.handleEvictEntry(key, oldValue);
}
}
}
};
} @Override
public String get(String key) { return mMemoryLruCache.get(key);
} @Override
public void put(String key, String value) {
mMemoryLruCache.put(key, value);
} @Override
public boolean remove(String key) { return Boolean.parseBoolean(mMemoryLruCache.remove(key));
} /**
* called when mMemoryLruCache evict entrys,
* <p/>
* using by CacheManager.Strategy.MEMORY_FIRST
*/
public interface EvictedListener { void handleEvictEntry(String evictKey, String evictValue);
}2、文件级别的Disk缓存类实现
接下来我们需要写一个用于Disk缓存管理的类：DiskCache类，该类我们也实现Cache接口，该类的主要功能也是提供Disk缓存的读取和写入操作管理。
/**
* Disk磁盘缓存类
* Created by caizhiming on 2015/12/4.
*/public class DiskCache implements Cache{ private DiskLruCache mDiskLruCache = null; public DiskCache(Context context){
init(context);
} /**
* 初始化 DiskLruCache
*/
public void init(Context context){ try {
File cacheDir = getDiskCacheDir(context, "http_cache"); if (!cacheDir.exists()) {
cacheDir.mkdirs();
}
Log.v("czm", "cache file=" + cacheDir.getAbsolutePath());
mDiskLruCache = DiskLruCache.open(cacheDir, getAppVersion(context), 1, 10 * 1024 * 1024);
} catch (IOException e) {
e.printStackTrace();
}
}
@Override public String get(String key) {
String result = null; try {
DiskLruCache.Snapshot snapShot = mDiskLruCache.get(hashKeyForDisk(key)); if (snapShot != null) {
result = snapShot.getString(0); return result;
}
} catch (IOException e) {
e.printStackTrace(); return null;
} return result;
}
@Override public void put(String key, String value) {
DiskLruCache.Editor editor = null; try {
editor = mDiskLruCache.edit(hashKeyForDisk(key)); if (editor != null) {
editor.set(0, value);
editor.commit();
}
mDiskLruCache.flush();
} catch (IOException e) {
e.printStackTrace();
}
}
@Override public boolean remove(String key) { try { return mDiskLruCache.remove(hashKeyForDisk(key));
} catch (IOException e) {
e.printStackTrace();
} return false;
} public Bitmap getImageCache(String key){
Bitmap bitmap = null; try {
DiskLruCache.Snapshot snapShot = mDiskLruCache.get(hashKeyForDisk(key)); if (snapShot != null) {
InputStream is = snapShot.getInputStream(0);
bitmap = BitmapFactory.decodeStream(is); return bitmap;
}
} catch (IOException e) {
e.printStackTrace();
} return bitmap;
} public void putImageCache(final String key){ new Thread(new Runnable() {
@Override public void run() { try {
DiskLruCache.Editor editor = mDiskLruCache.edit(hashKeyForDisk(key)); if (editor != null) {
OutputStream outputStream = editor.newOutputStream(0); if (downloadUrlToStream(key, outputStream)) {
editor.commit();
} else {
editor.abort();
}
}
mDiskLruCache.flush();
} catch (IOException e) {
e.printStackTrace();
}
}
}).start();
} private boolean downloadUrlToStream(String urlString, OutputStream outputStream) {
HttpURLConnection urlConnection = null;
BufferedOutputStream out = null;
BufferedInputStream in = null; try {
final URL url = new URL(urlString);
urlConnection = (HttpURLConnection) url.openConnection(); in = new BufferedInputStream(urlConnection.getInputStream(), 8 * 1024); out = new BufferedOutputStream(outputStream, 8 * 1024); int b; while ((b = in.read()) != -1) { out.write(b);
} return true;
} catch (final IOException e) {
e.printStackTrace();
} finally { if (urlConnection != null) {
urlConnection.disconnect();
}
CloseUtils.closeCloseable(out);
CloseUtils.closeCloseable(in);
} return false;
} public String hashKeyForDisk(String key) {
String cacheKey; try {
final MessageDigest mDigest = MessageDigest.getInstance("MD5");
mDigest.update(key.getBytes());
cacheKey = bytesToHexString(mDigest.digest());
} catch (NoSuchAlgorithmException e) {
cacheKey = String.valueOf(key.hashCode());
} return cacheKey;
} private String bytesToHexString(byte[] bytes) {
StringBuilder sb = new StringBuilder(); for (int i = 0; i < bytes.length; i++) {
String hex = Integer.toHexString(0xFF & bytes[i]); if (hex.length() == 1) {
sb.append('0');
}
sb.append(hex);
} return sb.toString();
} public 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);
} public int getAppVersion(Context context) { try {
PackageInfo info = context.getPackageManager().getPackageInfo(context.getPackageName(), 0); return info.versionCode;
} catch (PackageManager.NameNotFoundException e) {
e.printStackTrace();
} return 1;
}
}3、搭建封装双缓存管理框架类XCCacheManager
有了上面的内存缓存类MemoryCache和Disk缓存类DiskCache，我们就可以搭建封装真正的缓存管理类XCCacheManager了。
（1） 首先我们采用线程池技术来实现多线程缓存的读写操作
这样可以提高程序的性能，同时能处理任务量比较大的并发读写操作。
private static XCCacheManager mInstance = null;private Strategy mStrategy = Strategy.MEMORY_FIRST;//线程池private ExecutorService mExecutor = null;//内存缓存private MemoryCache mMemoryCache;//Disk缓存private DiskCache mDiskCache;/**
* 初始化 DiskLruCache
*/
private void init(Context context) {
mExecutor = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors());
mDiskCache = new DiskCache(context);
mMemoryCache = new MemoryCache();
}（2）其次XCCacheManager管理类采用单例实现
public static XCCacheManager getInstance(Context context, Strategy strategy) { if (mInstance == null) { synchronized (XCCacheManager.class) { if (mInstance == null) {
mInstance = new XCCacheManager(context.getApplicationContext(), strategy);
}
}
} else {
mInstance.setStrategy(strategy);
} return mInstance;
}（3）缓存策略
这里我们定义了缓存策略，便于适应各种不同业务需求，可以灵活使用不同的策略
enum Strategy {
MEMORY_ONLY(0), MEMORY_FIRST(1), DISK_ONLY(3); int id;
Strategy(int id) { this.id = id;
}
}默认采用内存优先MEMORY_FIRST这种策略
（4）根据对应的策略从缓存中读取内容
/**
* 从缓存中读取value
*/
public String readCache(final String key) {
Future<String> ret = mExecutor.submit(new Callable<String>() {
@Override public String call() throws Exception {
String result = null; switch (mStrategy) { case MEMORY_ONLY:
result = mMemoryCache.get(key); break; case MEMORY_FIRST:
result = mMemoryCache.get(key); if (result == null) {
result = mDiskCache.get(key);
} break; case DISK_ONLY:
result = mDiskCache.get(key); break;
} return result;
}
}); try { return ret.get();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
} return null;
}（5）将内容写入到缓存中
/**
* 将value 写入到缓存中
*/
public void writeCache(final String key, final String value) {
mExecutor.submit(new Runnable() {
@Override public void run() { switch (mStrategy) { case MEMORY_FIRST: if (!mMemoryCache.hasEvictedListener()) {
mMemoryCache.setEvictedListener(new MemoryCache.EvictedListener() {
@Override public void handleEvictEntry(String evictKey, String evictValue) {
mDiskCache.put(evictKey, evictValue);
}
});
}
mMemoryCache.put(key, value); break; case MEMORY_ONLY: if (mMemoryCache.hasEvictedListener())
mMemoryCache.setEvictedListener(null);
mMemoryCache.put(key, value); break; case DISK_ONLY:
mDiskCache.put(key, value); break;
}
}
});
}到此为止，框架的开发到此完成。希望对有需要的人有所帮助。
四、源码下载
源码下载 : http://download.csdn.net/detail/jczmdeveloper/9348031
GitHub地址：https://github.com/jczmdeveloper/XCCacheManager
原文链接：http://www.codeceo.com/article/android-double-cache.html