在项目开发过程中,博主曾写过大量的访问网络重复代码,特别是ListView adapter很难避免getView()方法不被重复调用,如果ImageView不利用缓存机制,那么网络的负荷就会更大!曾将访问网络代码和缓存封装起来使用,但是中间仍存在不少瑕疵!今年的Google I/O 2013上,Volley发布了!Volley是Android平台上的网络通信库,能使网络通信更快,更简单,更健壮
Volley特别适合数据量不大但是通信频繁的场景,现在android提供的源码已经包含Volley,以后在项目中,可以根据需求引入Volley jar文件!
(1).Volley.java
Volley.newRequestQueue()方法在一个app最好执行一次,可以使用单例设计模式或者在application完成初始化,具体原因请查看代码分析
/** * @author zimo2013 * @see http://blog.csdn.net/zimo2013 */ public static RequestQueue newRequestQueue(Context context, HttpStack stack) { File cacheDir = new File(context.getCacheDir(), DEFAULT_CACHE_DIR); String userAgent = "volley/0"; try { String packageName = context.getPackageName(); PackageInfo info = context.getPackageManager().getPackageInfo(packageName, 0); userAgent = packageName + "/" + info.versionCode; } catch (NameNotFoundException e) { } if (stack == null) { if (Build.VERSION.SDK_INT >= 9) { stack = new HurlStack(); } else { stack = new HttpClientStack(AndroidHttpClient.newInstance(userAgent)); } } Network network = new BasicNetwork(stack); //cacheDir 缓存路径 /data/data/<pkg name>/cache/<name> RequestQueue queue = new RequestQueue(new DiskBasedCache(cacheDir), network); queue.start(); /* * 实例化一个RequestQueue,其中start()主要完成相关工作线程的开启, * 比如开启缓存线程CacheDispatcher先完成缓存文件的扫描, 还包括开启多个NetworkDispatcher访问网络线程, * 该多个网络线程将从 同一个 网络阻塞队列中读取消息 * * 此处可见,start()已经开启,所有我们不用手动的去调用该方法,在start()方法中如果存在工作线程应该首先终止,并重新实例化工作线程并开启 * 在访问网络很频繁,而又重复调用start(),势必会导致性能的消耗;但是如果在访问网络很少时,调用stop()方法,停止多个线程,然后调用start(),反而又可以提高性能,具体可折中选择 */ return queue; }(2).RequestQueue.java
/** * RequestQueue类存在2个非常重要的PriorityBlockingQueue类型的成员字段mCacheQueue mNetworkQueue ,该PriorityBlockingQueue为java1.5并发库提供的新类 * 其中有几个重要的方法,比如take()为从队列中取得对象,如果队列不存在对象,将会被阻塞,直到队列中存在有对象,类似于Looper.loop() * * 实例化一个request对象,调用RequestQueue.add(request),该request如果不允许被缓存,将会被添加至mNetworkQueue队列中,待多个NetworkDispatcher线程take()取出对象 * 如果该request可以被缓存,该request将会被添加至mCacheQueue队列中,待mCacheDispatcher线程从mCacheQueue.take()取出对象, * 如果该request在mCache中不存在匹配的缓存时,该request将会被移交添加至mNetworkQueue队列中,待网络访问完成后,将关键头信息添加至mCache缓存中去! * * @author zimo2013 * @see http://blog.csdn.net/zimo2013 */ public void start() { stop(); mCacheDispatcher = new CacheDispatcher(mCacheQueue, mNetworkQueue, mCache, mDelivery); mCacheDispatcher.start(); // Create network dispatchers (and corresponding threads) up to the pool size. for (int i = 0; i < mDispatchers.length; i++) { NetworkDispatcher networkDispatcher = new NetworkDispatcher(mNetworkQueue, mNetwork, mCache, mDelivery); mDispatchers[i] = networkDispatcher; networkDispatcher.start(); } }(3).CacheDispatcher.java
/** * @author zimo2013 * @see http://blog.csdn.net/zimo2013 */ @Override public void run() { Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND); //缓存初始化,会遍历整个缓存文件夹 mCache.initialize(); { //执行代码 /*if (!mRootDirectory.exists()) { if (!mRootDirectory.mkdirs()) { VolleyLog.e("Unable to create cache dir %s", mRootDirectory.getAbsolutePath()); } return; } File[] files = mRootDirectory.listFiles(); if (files == null) { return; } for (File file : files) { FileInputStream fis = null; try { fis = new FileInputStream(file); CacheHeader entry = CacheHeader.readHeader(fis); entry.size = file.length(); putEntry(entry.key, entry); } catch (IOException e) { if (file != null) { file.delete(); } } finally { try { if (fis != null) { fis.close(); } } catch (IOException ignored) { } } }*/ } while (true) { try { //该方法可能会被阻塞 final Request request = mCacheQueue.take(); Cache.Entry entry = mCache.get(request.getCacheKey()); if (entry == null) { //缓存不存在,则将该request添加至网络队列中 mNetworkQueue.put(request); continue; } //是否已经过期 if (entry.isExpired()) { request.setCacheEntry(entry); mNetworkQueue.put(request); continue; } Response<?> response = request.parseNetworkResponse( new NetworkResponse(entry.data, entry.responseHeaders)); //存在缓存,执行相关操作 } catch (InterruptedException e) { } } }(4).NetworkDispatcher.java
/** * @author zimo2013 * @see http://blog.csdn.net/zimo2013 */ @Override public void run() { Request request; while (true) { try { //可能会被 request = mQueue.take(); } catch (InterruptedException e) { // We may have been interrupted because it was time to quit. if (mQuit) { return; } continue; } try { //访问网络,得到数据 NetworkResponse networkResponse = mNetwork.performRequest(request); if (networkResponse.notModified && request.hasHadResponseDelivered()) { request.finish("not-modified"); continue; } // Parse the response here on the worker thread. Response<?> response = request.parseNetworkResponse(networkResponse); // 写入缓存 if (request.shouldCache() && response.cacheEntry != null) { mCache.put(request.getCacheKey(), response.cacheEntry); request.addMarker("network-cache-written"); } // Post the response back. request.markDelivered(); mDelivery.postResponse(request, response); } catch (VolleyError volleyError) { parseAndDeliverNetworkError(request, volleyError); } catch (Exception e) { VolleyLog.e(e, "Unhandled exception %s", e.toString()); mDelivery.postError(request, new VolleyError(e)); } } }(5).StringRequest.java
其中在parseNetworkResponse()中,完成将byte[]到String的转化,可能会出现字符乱码,HttpHeaderParser.parseCharset(response.headers)方法在尚未指定是返回为ISO-8859-1,可以修改为utf-8
public class StringRequest extends Request<String> { private final Listener<String> mListener; /** * Creates a new request with the given method. * * @param method the request {@link Method} to use * @param url URL to fetch the string at * @param listener Listener to receive the String response * @param errorListener Error listener, or null to ignore errors */ public StringRequest(int method, String url, Listener<String> listener, ErrorListener errorListener) { super(method, url, errorListener); mListener = listener; } public StringRequest(String url, Listener<String> listener, ErrorListener errorListener) { this(Method.GET, url, listener, errorListener); } @Override protected void deliverResponse(String response) { mListener.onResponse(response); } @Override protected Response<String> parseNetworkResponse(NetworkResponse response) { String parsed; try { //将data字节数据转化为String对象 parsed = new String(response.data, HttpHeaderParser.parseCharset(response.headers)); } catch (UnsupportedEncodingException e) { parsed = new String(response.data); } //返回Response对象,其中该对象包含访问相关数据 return Response.success(parsed, HttpHeaderParser.parseCacheHeaders(response)); } }(6).ImageLoader.java
/** * @author zimo2013 * @see http://blog.csdn.net/zimo2013 */ public ImageContainer get(String requestUrl, ImageListener imageListener, int maxWidth, int maxHeight) { throwIfNotOnMainThread(); final String cacheKey = getCacheKey(requestUrl, maxWidth, maxHeight); //从mCache得到bitmap对象,因此可以覆写ImageCache,完成图片的三级缓存,即在原有的LruCache添加一个软引用缓存 Bitmap cachedBitmap = mCache.getBitmap(cacheKey); if (cachedBitmap != null) { //得到缓存对象 ImageContainer container = new ImageContainer(cachedBitmap, requestUrl, null, null); imageListener.onResponse(container, true); return container; } ImageContainer imageContainer = new ImageContainer(null, requestUrl, cacheKey, imageListener); // 首先更新该view,其指定了defaultImage imageListener.onResponse(imageContainer, true); // 根据可以去检查该请求是否已经发起过 BatchedImageRequest request = mInFlightRequests.get(cacheKey); if (request != null) { request.addContainer(imageContainer); return imageContainer; } Request<?> newRequest = new ImageRequest(requestUrl, new Listener<Bitmap>() { @Override public void onResponse(Bitmap response) { //如果请求成功 onGetImageSuccess(cacheKey, response); } }, maxWidth, maxHeight, Config.RGB_565, new ErrorListener() { @Override public void onErrorResponse(VolleyError error) { onGetImageError(cacheKey, error); } }); //添加至请求队列中 mRequestQueue.add(newRequest); //同一添加进map集合,以方便检查该request是否正在请求网络,可以节约资源 mInFlightRequests.put(cacheKey, new BatchedImageRequest(newRequest, imageContainer)); return imageContainer; }private void onGetImageSuccess(String cacheKey, Bitmap response) { //缓存对象 mCache.putBitmap(cacheKey, response); // 请求完成,不需要检测 BatchedImageRequest request = mInFlightRequests.remove(cacheKey); if (request != null) { request.mResponseBitmap = response; //处理结果 batchResponse(cacheKey, request); } }private void batchResponse(String cacheKey, BatchedImageRequest request) { mBatchedResponses.put(cacheKey, request); //通过handler,发送一个操作 if (mRunnable == null) { mRunnable = new Runnable() { @Override public void run() { for (BatchedImageRequest bir : mBatchedResponses.values()) { for (ImageContainer container : bir.mContainers) { if (container.mListener == null) { continue; } if (bir.getError() == null) { container.mBitmap = bir.mResponseBitmap; //更新结果 container.mListener.onResponse(container, false); } else { container.mListener.onErrorResponse(bir.getError()); } } } mBatchedResponses.clear(); mRunnable = null; } }; // mHandler对应的looper是MainLooper,因此被MainLooper.loop()得到该message,故该runnable操作在主线程中执行, mHandler.postDelayed(mRunnable, mBatchResponseDelayMs); } }
RequestQueue类存在2个非常重要的PriorityBlockingQueue类型的成员字段mCacheQueue mNetworkQueue ,该PriorityBlockingQueue为java1.5并发库提供的!其中有几个重要的方法,比如take()为从队列中取得对象,如果队列不存在对象,将会被阻塞,直到队列中存在有对象,类似于Looper.loop()。实例化一个request对象,调用RequestQueue.add(request),该request如果不允许被缓存,将会被添加至mNetworkQueue队列中,待多个NetworkDispatcher线程从mNetworkQueue中take()取出对象。如果该request可以被缓存,该request将会被添加至mCacheQueue队列中,待mCacheDispatcher线程从mCacheQueue.take()取出对象,如果该request在mCache中不存在匹配的缓存时,该request将会被移交添加至mNetworkQueue队列中,待网络访问完成后,将关键头信息添加至mCache缓存中去,并通过ResponseDelivery主线程调用request的相关方法!
Volley实例,>>Android_开源框架_Volley实例