一个简单的volley网络请求

volley网络请求

类图

1> volley 一个简单的网络请求流程

    ##Creates a default instance of the worker pool and calls {@link RequestQueue#start()} on it.    mQueue = Volley.newRequestQueue(getApplicationContext());    //创建请求体，并且接收回调 成功,失败/         private JsonObjectRequest jsonRespondRequest = new JsonObjectRequest(Method.POST, url, request, new Listener<JSONObject>() {        @Override        public void onResponse(JSONObject response) {            Log.e(TAG, response.toString());        }        }, new ErrorListener() {        @Override        public void onErrorResponse(VolleyError error) {            Log.e(TAG, error.toString());        }        });    //request请求添加到请求队列     mQueue.add(jsonRespondRequest);     //执行请求    mQueue.start();

2> 可以看到主要的流程都在RequestQueue队列中封装处理

2.1 看请求队列是如何初始化的

     Volley.newRequestQueue(getApplicationContext())       /**         * Default on-disk cache directory.         */        private static final String DEFAULT_CACHE_DIR = "volley";        /**         * Creates a default instance of the worker pool and calls {@link RequestQueue#start()} on it.         *         * @param context A {@link Context} to use for creating the cache dir.         * @param stack   An {@link HttpStack} to use for the network, or null for default.         * @return A started {@link RequestQueue} instance.         */        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 {            // Prior to Gingerbread, HttpUrlConnection was unreliable.            // See: http://android-developers.blogspot.com/2011/09/androids-http-clients.html            stack = new HttpClientStack(AndroidHttpClient.newInstance(userAgent));            }        }        //泛型向上转型        Network network = new BasicNetwork(stack);        RequestQueue queue = new RequestQueue(new DiskBasedCache(cacheDir), network);        queue.start();        return queue;        }

3>这个类主要做的事情

 a.建立缓冲文件存储的文件路径。通过 PackageInfo 获取包名和版本号拼装PackageInfo参数 b.根据版本号选择使用的请求协议当apileavel>=9 也就是android2.2 使用HttpURLConnection 反之用 AndroidHttpClient 实现HttpClient接口。和default httpclient对应 c.通过构造函数 初始化缓冲池 ByteArrayPool，避免重复分配堆内存，而进行的优化的 d.通过构造函数 初始化DiskBasedCache 参数，默认缓存path和缓存的最大容量，

      /**         * Creates the worker pool. Processing will not begin until {@link #start()} is called.         *         * @param cache          A Cache to use for persisting responses to disk         * @param network        A Network interface for performing HTTP requests         * @param threadPoolSize Number of network dispatcher threads to create         */        public RequestQueue(Cache cache, Network network, int threadPoolSize) {        this(cache, network, threadPoolSize,            new ExecutorDelivery(new Handler(Looper.getMainLooper())));        }

 并且建立请求response 回调默认处理线程为主线程，同时建立工作线程，初始化  NetworkDispatcher mDispatchers = new NetworkDispatcher[threadPoolSize];的默认大小等， 一些初始化工作。

       /**         * Starts the dispatchers in this queue.         */        public void start() {        stop();         // Make sure any currently running dispatchers are stopped.        // Create the cache dispatcher and start it.        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();        }        }

  e.最后开始线程队列的分发，循环

4> 以上是简单请求队列初始化的。 (不能只，关注设置模式，其他还有好多)

  几种队列 mWaitingRequests 、mCurrentRequests、mCacheQueue、mNetworkQueue四中队列个代表什么意思？

  private final Map<String, Queue<Request<?>>> mWaitingRequests =            new HashMap<String, Queue<Request<?>>>();        /**         * The set of all requests currently being processed by this RequestQueue. A Request         * will be in this set if it is waiting in any queue or currently being processed by         * any dispatcher.         */        private final Set<Request<?>> mCurrentRequests = new HashSet<Request<?>>();        /**         * The cache triage queue.         */        private final PriorityBlockingQueue<Request<?>> mCacheQueue =            new PriorityBlockingQueue<Request<?>>();        /**         * The queue of requests that are actually going out to the network.         */        private final PriorityBlockingQueue<Request<?>> mNetworkQueue =            new PriorityBlockingQueue<Request<?>>();

5>接下来分析sart（）方法！

  /**         * Starts the dispatchers in this queue.         */        public void start() {        stop();  // Make sure any currently running dispatchers are stopped.        // Create the cache dispatcher and start it.        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();        }        }

5.1 执行逻辑

a.停止所有的 dispatchers 分发。 初始化CacheDispatcher，并传递 mCacheQueue, mNetworkQueue, mCache, mDelivery 引用。因为  cacheDiapather 为线程衍生出来。只要分析 run（）方法b.ok这里就将volley读取缓存的逻辑贴出来进行分析

   @Override        public void run() {        if (DEBUG) VolleyLog.v("start new dispatcher");        Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);          // Make a blocking call to initialize the cache. 做一个阻塞调用初始化缓存。            mCache.initialize();        while (true) {            try {            // Get a request from the cache triage queue, blocking until  得到一个请求从缓存中分类队列,阻塞直到            // at least one is available.            final Request<?> request = mCacheQueue.take();            request.addMarker("cache-queue-take");            // If the request has been canceled, don't bother dispatching it.            if (request.isCanceled()) {                request.finish("cache-discard-canceled");                continue;            }            // Attempt to retrieve this item from cache.            Cache.Entry entry = mCache.get(request.getCacheKey());            if (entry == null) {                request.addMarker("cache-miss");                // Cache miss; send off to the network dispatcher.                mNetworkQueue.put(request);                continue;            }            // If it is completely expired, just send it to the network.            if (entry.isExpired()) {                request.addMarker("cache-hit-expired");                request.setCacheEntry(entry);                mNetworkQueue.put(request);                continue;            }            // We have a cache hit; parse its data for delivery back to the request.            request.addMarker("cache-hit");            Response<?> response = request.parseNetworkResponse(                new NetworkResponse(entry.data, entry.responseHeaders));            request.addMarker("cache-hit-parsed");            if (!entry.refreshNeeded()) {                // Completely unexpired cache hit. Just deliver the response.                mDelivery.postResponse(request, response);            } else {                // Soft-expired cache hit. We can deliver the cached response,                // but we need to also send the request to the network for                // refreshing.                request.addMarker("cache-hit-refresh-needed");                request.setCacheEntry(entry);                // Mark the response as intermediate.                response.intermediate = true;                // Post the intermediate response back to the user and have                // the delivery then forward the request along to the network.                mDelivery.postResponse(request, response, new Runnable() {                @Override                public void run() {                    try {                    mNetworkQueue.put(request);                    } catch (InterruptedException e) {                    // Not much we can do about this.                    }                }                });            }            } catch (InterruptedException e) {            // We may have been interrupted because it was time to quit.            if (mQuit) {                return;            }            continue;            }        }        }

  ---------------------------------------------------------------------------   // Make a blocking call to initialize the cache. 做一个阻塞调用初始化缓存。        mCache.initialize();     主要进行文件操作，缓存设置，放在下面单独进行分析   while (true) {          ......       }     1.首先从mCacheQueue.take()中弹栈，添加loger ，判断 isCanceled（）      Returns true if this request has been canceled. 请求是否已经取消如果取消就更新finish（），并将该请求从请求队列中      mCurrentRequests.remove(request);，并且从mWaitingRequests 队列中移除。更新 mCacheQueue.addAll(waitingRequests);然后继续弹栈     2.试图从缓存检索，如果未进行缓存，那么将该请求加入  mNetworkQueue.put(request);排队处理，并继续弹栈

    // Attempt to retrieve this item from cache.                Cache.Entry entry = mCache.get(request.getCacheKey());                if (entry == null) {                    request.addMarker("cache-miss");                    // Cache miss; send off to the network dispatcher.                    mNetworkQueue.put(request);                    continue;                }

     3.如果缓存中存有缓存，判断是否过期     // If it is completely expired, just send it to the network.            if (entry.isExpired()) {                request.addMarker("cache-hit-expired");                request.setCacheEntry(entry);                mNetworkQueue.put(request);                continue;            }     4.如果缓存命中并且没有过期，则直接去取缓存，进行返回

    // We have a cache hit; parse its data for delivery back to the request.                request.addMarker("cache-hit");                Response<?> response = request.parseNetworkResponse(                        new NetworkResponse(entry.data, entry.responseHeaders));                request.addMarker("cache-hit-parsed");

      5.另一种缓存命中，不仅返回缓存数据，并且返回将请求放入网络进行分发

 if (!entry.refreshNeeded()) {                    // Completely unexpired cache hit. Just deliver the response.                    mDelivery.postResponse(request, response);                } else {                    // Soft-expired cache hit. We can deliver the cached response,                    // but we need to also send the request to the network for                    // refreshing.                    request.addMarker("cache-hit-refresh-needed");                    request.setCacheEntry(entry);                    // Mark the response as intermediate.                    response.intermediate = true;                    // Post the intermediate response back to the user and have                    // the delivery then forward the request along to the network.                    mDelivery.postResponse(request, response, new Runnable() {                        @Override                        public void run() {                            try {                                mNetworkQueue.put(request);                            } catch (InterruptedException e) {                                // Not much we can do about this.                            }                        }                    });                }

6>接下来就要分析网络分发了，NetWorkDispatcher 。因为HurlStack 和 HttpClientStack 衍生为HttpStack 而 HttpStack 衍生NetWorkDispatcher。

首先分析NetWorkDispatcher类

很显然NetworkDispatcher 同样继承Thread类，这里只要分析Run（）方法体

 @Override    public void run() {        Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);        while (true) {            long startTimeMs = SystemClock.elapsedRealtime();            Request<?> request;            try {                // Take a request from the queue.                request = mQueue.take();            } catch (InterruptedException e) {                // We may have been interrupted because it was time to quit.                if (mQuit) {                    return;                }                continue;            }            try {                request.addMarker("network-queue-take");                // If the request was cancelled already, do not perform the                // network request.                if (request.isCanceled()) {                    request.finish("network-discard-cancelled");                    continue;                }                addTrafficStatsTag(request);                // Perform the network request.                NetworkResponse networkResponse = mNetwork.performRequest(request);                request.addMarker("network-http-complete");                // If the server returned 304 AND we delivered a response already,                // we're done -- don't deliver a second identical response.                if (networkResponse.notModified && request.hasHadResponseDelivered()) {                    request.finish("not-modified");                    continue;                }                // Parse the response here on the worker thread.                Response<?> response = request.parseNetworkResponse(networkResponse);                request.addMarker("network-parse-complete");                // Write to cache if applicable.                // TODO: Only update cache metadata instead of entire record for 304s.                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) {                volleyError.setNetworkTimeMs(SystemClock.elapsedRealtime() - startTimeMs);                parseAndDeliverNetworkError(request, volleyError);            } catch (Exception e) {                VolleyLog.e(e, "Unhandled exception %s", e.toString());                VolleyError volleyError = new VolleyError(e);                volleyError.setNetworkTimeMs(SystemClock.elapsedRealtime() - startTimeMs);                mDelivery.postError(request, volleyError);            }        }    }

a.首先设置线程的优先级，同样是一个阻塞式的循环，记录开始时间，然后从队列中取

 long startTimeMs = SystemClock.elapsedRealtime();            Request<?> request;            try {                // Take a request from the queue.                request = mQueue.take();            } catch (InterruptedException e) {                // We may have been interrupted because it was time to quit.                if (mQuit) {                    return;                }                continue;            }

b.同样添加loger日志，判断请求是否已经取消过，如果已经isCanceled（）则进行finished（）   mRequestQueue.finish(this); c.否则添加网络流量监控，调用相应的处理方式（这里用到了泛型 mNetwork，接收两种类型的参数 HurlStack，httpClientStack ）

 addTrafficStatsTag(request);        // Perform the network request.        NetworkResponse networkResponse = mNetwork.performRequest(request);        request.addMarker("network-http-complete");

d.这里只简单介绍HurlStack的处理方式，httpClientStack和HurlStack是相同的

      @Override    public HttpResponse performRequest(Request<?> request, Map<String, String> additionalHeaders)            throws IOException, AuthFailureError {        String url = request.getUrl();        HashMap<String, String> map = new HashMap<String, String>();        map.putAll(request.getHeaders());        map.putAll(additionalHeaders);        if (mUrlRewriter != null) {            String rewritten = mUrlRewriter.rewriteUrl(url);            if (rewritten == null) {                throw new IOException("URL blocked by rewriter: " + url);            }            url = rewritten;        }        URL parsedUrl = new URL(url);        HttpURLConnection connection = openConnection(parsedUrl, request);        for (String headerName : map.keySet()) {            connection.addRequestProperty(headerName, map.get(headerName));        }        setConnectionParametersForRequest(connection, request);        // Initialize HttpResponse with data from the HttpURLConnection.        ProtocolVersion protocolVersion = new ProtocolVersion("HTTP", 1, 1);        int responseCode = connection.getResponseCode();        if (responseCode == -1) {            // -1 is returned by getResponseCode() if the response code could not be retrieved.            // Signal to the caller that something was wrong with the connection.            throw new IOException("Could not retrieve response code from HttpUrlConnection.");        }        StatusLine responseStatus = new BasicStatusLine(protocolVersion,                connection.getResponseCode(), connection.getResponseMessage());        BasicHttpResponse response = new BasicHttpResponse(responseStatus);        response.setEntity(entityFromConnection(connection));        for (Entry<String, List<String>> header : connection.getHeaderFields().entrySet()) {            if (header.getKey() != null) {                Header h = new BasicHeader(header.getKey(), header.getValue().get(0));                response.addHeader(h);            }        }        return response;    }

这里前面和httpURLConnection相同，后面则是将返回结果进行了一个封装。直接返回。

 StatusLine responseStatus = new BasicStatusLine(protocolVersion,                connection.getResponseCode(), connection.getResponseMessage());        BasicHttpResponse response = new BasicHttpResponse(responseStatus);        response.setEntity(entityFromConnection(connection));        for (Entry<String, List<String>> header : connection.getHeaderFields().entrySet()) {            if (header.getKey() != null) {                Header h = new BasicHeader(header.getKey(), header.getValue().get(0));                response.addHeader(h);            }        }        return response;

返回到NetworkDispather中进行解析处理，最后调用返回Ui线程。 这就是一个网络请求的简单流程

  NetworkResponse networkResponse = mNetwork.performRequest(request);                request.addMarker("network-http-complete");                // If the server returned 304 AND we delivered a response already,                // we're done -- don't deliver a second identical response.                if (networkResponse.notModified && request.hasHadResponseDelivered()) {                    request.finish("not-modified");                    continue;                }                // Parse the response here on the worker thread.                Response<?> response = request.parseNetworkResponse(networkResponse);                request.addMarker("network-parse-complete");                // Write to cache if applicable.                // TODO: Only update cache metadata instead of entire record for 304s.                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);

1.接下来会将volley单独拆分出来，分块进行详细分析。