Volley源码浅析

本文主要从两个入口进行分析:

一,Volley.newRequestQueue(context);

newRequestQueue(Context context, HttpStack stack, int maxDiskCacheBytes)方法中:
A,请求队列requestQueue的初始化:

1. 根据当前手机版本创建网络协议

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));            }        }        Network network = new BasicNetwork(stack);

2. 初始化请求队列 requestQueue

RequestQueue queue;        if (maxDiskCacheBytes <= -1)        {            // No maximum size specified            queue = new RequestQueue(new DiskBasedCache(cacheDir), network);        }        else        {            // Disk cache size specified            queue = new RequestQueue(new DiskBasedCache(cacheDir, maxDiskCacheBytes), network);        }

3. RequestQueue构造函数中接收 DiskBasedCache,network, 并进行如下初始化:

• 创建网络分发线程的数组mDispatchers = new NetworkDispatcher[threadPoolSize]默认数组大小为4;
• mDelivery = new ExecutorDelivery(new Handler(Looper.getMainLooper())),用于交付解析后的response , 需要通过在主线程中创建的handler对象

    public RequestQueue(Cache cache, Network network, int threadPoolSize,            ResponseDelivery delivery) {        mCache = cache;        mNetwork = network;        mDispatchers = new NetworkDispatcher[threadPoolSize];        mDelivery = delivery;    }

4. 同时, requestQueue中会初始化两个成员变量: 缓存队列 和 网络队列

/** 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<?>>();

B:执行 queue.start() 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();        }    }

1. 创建并开启mCacheDispatcher 子线程 run()方法中:

a, mCache.initialize();即DiskBasedCache中的方法,将cache目录下的volley目录中的所有文件遍历,读取每个文件的Header,封装到entry对象中,同时存入集合:

 File file = getFileForKey(key);        CountingInputStream cis = null;        try {            cis = new CountingInputStream(new BufferedInputStream(new FileInputStream(file)));            CacheHeader.readHeader(cis); // eat header            byte[] data = streamToBytes(cis, (int) (file.length() - cis.bytesRead));            return entry.toCacheEntry(data);        } catch (IOException e) {            VolleyLog.d("%s: %s", file.getAbsolutePath(), e.toString());            remove(key);            return null;        }  catch (NegativeArraySizeException e) {            VolleyLog.d("%s: %s", file.getAbsolutePath(), e.toString());            remove(key);            return null;        } finally {            if (cis != null) {                try {                    cis.close();                } catch (IOException ioe) {                    return null;                }            }        }

b,开启无限循环: 从mCacheQueue中获取request

while (true) {...request = mCacheQueue.take();...Cache.Entry entry = mCache.get(request.getCacheKey());...}

二,requestQueue.add(request);

主要是将requestt添加到mCacheQueue中:

    mCacheQueue.add(request);

A, mCacheDispatcher
run()方法中的无限循环会从mCacheQueue中获取到添加进去的request, 根据request.getCacheKey()获取到mCache的集合变量中存储的entry对象

while (true) {   ...   request = mCacheQueue.take();   ...   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);    //缓存数据中不存在,就将request添加到网络队列mNetworkQueue中,                    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);    //缓存数据过期,还是将request添加到mNetworkQueue中,                    continue;                }                // We have a cache hit; parse its data for delivery back to the request.                request.addMarker("cache-hit");                Response<?> response = request.parseNetworkResponse(        //将可以使用的缓存数据使用自己实现的方法解析响应结果                        new NetworkResponse(entry.data, entry.responseHeaders));                request.addMarker("cache-hit-parsed");   ...   mDelivery.postResponse(request, response);  //交付给主线程处理解析后的响应结果    ...}

1.request.parseNetworkResponse 解析成功的返回结果:

return Response.success(new JSONObject(jsonString),        HttpHeaderParser.parseCacheHeaders(response))

2.mDelivery.postResponse(request, response); 将解析出的响应结果交付到主线程处理
即执行:mResponsePoster.execute(new ResponseDeliveryRunnable(request, response, runnable));

传入的ResponseDeliveryRunnable的run()方法:

// Deliver a normal response or error, depending.            if (mResponse.isSuccess()) {                mRequest.deliverResponse(mResponse.result);            } else {                mRequest.deliverError(mResponse.error);            }

即触发初始化Request时设置的监听器

B,NetworkDispatcher 的run()方法中的主要去执行真正的网络请求

NetworkResponse networkResponse = mNetwork.performRequest(request); 

执行网络请求的主要有两个实现类:

• HurlStack的performRequest()方法:

URL parsedUrl = new URL(url);        HttpURLConnection connection = openConnection(parsedUrl, request);

• HttpClientStackde performRequest方法:(适配9以下的API)

  主要使用Apache的httpClient进行网络请求:

HttpPost postRequest = new HttpPost(request.getUrl());

1.将网络结果解析:

Response<?> response = request.parseNetworkResponse(networkResponse);

2.解析的结果存入缓存的集合中:

mCache.put(request.getCacheKey(), response.cacheEntry);

3.交付解析的结果:

mDelivery.postResponse(request, response);