Android开源框架Volley(Google IO 2013)源代码及内部实现分析
1.Volley概述
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!
2.Volley源码分析(1).Volley.javaVolley.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
- * [url=home.php?mod=space&uid=189949]@See[/url] 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);
- }
- }
3.总结
![]()
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