Android 框架修炼-自己封装双缓存管理框架库
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
public void setStrategy(XCCacheManager.Strategy strategy) {
this.mStrategy = strategy;
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);
}
});
}
break;
case MEMORY_ONLY:
if (mMemoryCache.hasEvictedListener())
mMemoryCache.setEvictedListener(null);
break;
case DISK_ONLY:
break;
}
}
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:
mMemoryCache.put(key, value);
mDiskCache.put(key,value);
break;
case MEMORY_ONLY:
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
