Android使用缓存机制实现文件下载及异步请求图片加三级缓存

public abstract class AsyncTask<Params, Progress, Result> {
private static final String LOG_TAG = "AsyncTask";
private static final int CORE_POOL_SIZE = 5;
private static final int MAXIMUM_POOL_SIZE = 128;
private static final int KEEP_ALIVE = 1;
private static final ThreadFactory sThreadFactory = new ThreadFactory() {
private final AtomicInteger mCount = new AtomicInteger(1);
public Thread newThread(Runnable r) {
return new Thread(r, "AsyncTask #" + mCount.getAndIncrement());
}
}; 

private static final InternalHandler sHandler = new InternalHandler(); mFuture = new FutureTask<Result>(mWorker) {
@Override
protected void More ...done() {
Message message;
Result result = null;
try {
result = get();
} catch (InterruptedException e) {
android.util.Log.w(LOG_TAG, e);
} catch (ExecutionException e) {
throw new RuntimeException("An error occured while executing doInBackground()",
e.getCause());
} catch (CancellationException e) {
message = sHandler.obtainMessage(MESSAGE_POST_CANCEL,
new AsyncTaskResult<Result>(AsyncTask.this, (Result[]) null));
message.sendToTarget();
return;
} catch (Throwable t) {
throw new RuntimeException("An error occured while executing "
+ "doInBackground()", t);
}
message = sHandler.obtainMessage(MESSAGE_POST_RESULT,
new AsyncTaskResult<Result>(AsyncTask.this, result));
message.sendToTarget();
}
};
private static class InternalHandler extends Handler {
@SuppressWarnings({"unchecked", "RawUseOfParameterizedType"})
@Override
public void More ...handleMessage(Message msg) {
AsyncTaskResult result = (AsyncTaskResult) msg.obj;
switch (msg.what) {
case MESSAGE_POST_RESULT:
// There is only one result
result.mTask.finish(result.mData[0]);
break;
case MESSAGE_POST_PROGRESS:
result.mTask.onProgressUpdate(result.mData);
break;
case MESSAGE_POST_CANCEL:
result.mTask.onCancelled();
break;
}
}
}

import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.widget.ImageView;
/**
* 网络缓存
* 
* @author Ace
* @date 2016-02-18
*/
public class NetCacheUtils {
private LocalCacheUtils mLocalUtils;
private MemoryCacheUtils mMemoryUtils;
public NetCacheUtils(LocalCacheUtils localUtils,
MemoryCacheUtils memoryUtils) {
mLocalUtils = localUtils;
mMemoryUtils = memoryUtils;
}
public void getBitmapFromNet(ImageView imageView, String url) {
BitmapTask task = new BitmapTask();
task.execute(imageView, url);
}
/**
* AsyncTask是线程池+handler的封装 第一个泛型: 传参的参数类型类型(和doInBackground一致) 第二个泛型:
* 更新进度的参数类型(和onProgressUpdate一致) 第三个泛型: 返回结果的参数类型(和onPostExecute一致,
* 和doInBackground返回类型一致)
*/
class BitmapTask extends AsyncTask<Object, Integer, Bitmap> {
private ImageView mImageView;
private String url;
// 主线程运行, 预加载
@Override
protected void onPreExecute() {
super.onPreExecute();
}
// 子线程运行, 异步加载逻辑在此方法中处理
@Override
protected Bitmap doInBackground(Object... params) {
mImageView = (ImageView) params[0];
url = (String) params[1];
mImageView.setTag(url);// 将imageView和url绑定在一起
// publishProgress(values)//通知进度
// 下载图片
return download(url);
}
// 主线程运行, 更新进度
@Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
}
// 主线程运行, 更新主界面
@Override
protected void onPostExecute(Bitmap result) {
if (result != null) {
// 判断当前图片是否就是imageView要的图片, 防止listview重用导致的图片错乱的情况出现
String bindUrl = (String) mImageView.getTag();
if (bindUrl.equals(url)) {
// 给imageView设置图片
mImageView.setImageBitmap(result);
// 将图片保存在本地
mLocalUtils.setBitmapToLocal(result, url);
// 将图片保存在内存
mMemoryUtils.setBitmapToMemory(url, result);
}
}
}
}
/**
* 下载图片
* 
* @param url
*/
public Bitmap download(String url) {
HttpURLConnection conn = null;
try {
conn = (HttpURLConnection) (new URL(url).openConnection());
conn.setConnectTimeout(5000);
conn.setReadTimeout(5000);
conn.setRequestMethod("GET");
conn.connect();
int responseCode = conn.getResponseCode();
if (responseCode == 200) {
InputStream in = conn.getInputStream();
// 将流转化为bitmap对象
Bitmap bitmap = BitmapFactory.decodeStream(in);
return bitmap;
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (conn != null) {
conn.disconnect();
}
}
return null;
}
}

* A cache that holds strong references to a limited number of values. Each time 
* a value is accessed, it is moved to the head of a queue. When a value is 
* added to a full cache, the value at the end of that queue is evicted and may 
* become eligible for garbage collection. 
* Cache保存一个强引用来限制内容数量，每当Item被访问的时候，此Item就会移动到队列的头部。
* 当cache已满的时候加入新的item时，在队列尾部的item会被回收。 
* <p>If your cached values hold resources that need to be explicitly released, 
* override {@link #entryRemoved}. 
* 如果你cache的某个值需要明确释放，重写entryRemoved()

* <p>By default, the cache size is measured in the number of entries. Override 
* {@link #sizeOf} to size the cache in different units. For example, this cache 
* is limited to 4MiB of bitmaps: 默认cache大小是测量的item的数量，重写sizeof计算不同item的
* 大小。
 {@code 
 * int cacheSize = 4 * 1024 * 1024; // 4MiB 
 * LruCache<String, Bitmap> bitmapCache = new LruCache<String, Bitmap>(cacheSize) { 
 * protected int sizeOf(String key, Bitmap value) { 
 * return value.getByteCount(); 
 * } 
 * }}
-------------------------------------------------------------------
<p>This class is thread-safe. Perform multiple cache operations atomically by 
* synchronizing on the cache: <pre> {@code 
* synchronized (cache) { 
* if (cache.get(key) == null) { 
* cache.put(key, value); 
* } 
* }}</pre> 
* 他是线程安全的,自动地执行多个缓存操作并且加锁
-------------------------
<p>This class does not allow null to be used as a key or value. A return 
* value of null from {@link #get}, {@link #put} or {@link #remove} is 
* unambiguous: the key was not in the cache.
* 不允许key或者value为null
* 当get（），put（），remove（）返回值为null时，key相应的项不在cache中

import android.graphics.Bitmap;
import android.support.v4.util.LruCache;
/**
* 内存缓存工具类
* 
* @author Ace
* @date 2016-02-19
*/
public class MemoryCacheUtils {

// Android 2.3 (API Level
// 9)开始，垃圾回收器会更倾向于回收持有软引用或弱引用的对象，这让软引用和弱引用变得不再可靠,建议用LruCache,它是强引用
private LruCache<String, Bitmap> mCache;
public MemoryCacheUtils() {
int maxMemory = (int) Runtime.getRuntime().maxMemory();// 获取虚拟机分配的最大内存
// 16M
// LRU 最近最少使用, 通过控制内存不要超过最大值(由开发者指定), 来解决内存溢出,就像上面翻译的所说 如果cache满了会清理最近最少使用的缓存对象
mCache = new LruCache<String, Bitmap>(maxMemory / 8) {
@Override
protected int sizeOf(String key, Bitmap value) {
// 计算一个bitmap的大小
int size = value.getRowBytes() * value.getHeight();// 每一行的字节数乘以高度
return size;
}
};
}
public Bitmap getBitmapFromMemory(String url) {
return mCache.get(url);
}
public void setBitmapToMemory(String url, Bitmap bitmap) {
mCache.put(url, bitmap);
}
}

/**
* 本地缓存工具类
* 
* @author Ace
* @date 2016-02-19
*/
public class LocalCacheUtils {
// 图片缓存的文件夹
public static final String DIR_PATH = Environment
.getExternalStorageDirectory().getAbsolutePath()
+ "/ace_bitmap_cache";
public Bitmap getBitmapFromLocal(String url) {
try {
File file = new File(DIR_PATH, MD5Encoder.encode(url));
if (file.exists()) {
Bitmap bitmap = BitmapFactory.decodeStream(new FileInputStream(
file));
return bitmap;
}
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
public void setBitmapToLocal(Bitmap bitmap, String url) {
File dirFile = new File(DIR_PATH);
// 创建文件夹 文件夹不存在或者它不是文件夹 则创建一个文件夹.mkdirs,mkdir的区别在于假如文件夹有好几层路径的话,前者会创建缺失的父目录 后者不会创建这些父目录
if (!dirFile.exists() || !dirFile.isDirectory()) {
dirFile.mkdirs();
}
try {
File file = new File(DIR_PATH, MD5Encoder.encode(url));
// 将图片压缩保存在本地,参1:压缩格式;参2:压缩质量(0-100);参3:输出流
bitmap.compress(CompressFormat.JPEG, 100,
new FileOutputStream(file));
} catch (Exception e) {
e.printStackTrace();
}
}
}

import java.security.MessageDigest;
public class MD5Encoder {
public static String encode(String string) throws Exception {
byte[] hash = MessageDigest.getInstance("MD5").digest(string.getBytes("UTF-8"));
StringBuilder hex = new StringBuilder(hash.length * 2);
for (byte b : hash) {
if ((b & 0xFF) < 0x10) {
hex.append("0");
}
hex.append(Integer.toHexString(b & 0xFF));
}
return hex.toString();
}
}

/**
* 三级缓存工具类
* 
* @author Ace
* @date 2016-02-19
*/
public class MyBitmapUtils {
// 网络缓存工具类
private NetCacheUtils mNetUtils;
// 本地缓存工具类
private LocalCacheUtils mLocalUtils;
// 内存缓存工具类
private MemoryCacheUtils mMemoryUtils;
public MyBitmapUtils() {
mMemoryUtils = new MemoryCacheUtils();
mLocalUtils = new LocalCacheUtils();
mNetUtils = new NetCacheUtils(mLocalUtils, mMemoryUtils);
}
public void display(ImageView imageView, String url) {
// 设置默认加载图片
imageView.setImageResource(R.drawable.news_pic_default);
// 先从内存缓存加载
Bitmap bitmap = mMemoryUtils.getBitmapFromMemory(url);
if (bitmap != null) {
imageView.setImageBitmap(bitmap);
System.out.println("从内存读取图片啦...");
return;
}
// 再从本地缓存加载
bitmap = mLocalUtils.getBitmapFromLocal(url);
if (bitmap != null) {
imageView.setImageBitmap(bitmap);
System.out.println("从本地读取图片啦...");
// 给内存设置图片
mMemoryUtils.setBitmapToMemory(url, bitmap);
return;
}
// 从网络缓存加载
mNetUtils.getBitmapFromNet(imageView, url);
}
}