Android.Volley的解读：初始接触volley

public class Volley {
     ...
     public static RequestQueue newRequestQueue(Context context) {
        return newRequestQueue(context, null);
    }  
}

 1 public static RequestQueue newRequestQueue(Context context, HttpStack stack) {
 2         File cacheDir = new File(context.getCacheDir(), DEFAULT_CACHE_DIR);
 3 
 4         String userAgent = "volley/0";
 5         try {
 6             String packageName = context.getPackageName();
 7             PackageInfo info = context.getPackageManager().getPackageInfo(packageName, 0);
 8             userAgent = packageName + "/" + info.versionCode;
 9         } catch (NameNotFoundException e) {
10         }
11 
12         if (stack == null) {//你开始传null，所以走这里
13             if (Build.VERSION.SDK_INT >= 9) {
14                 stack = new HurlStack();//SDK如果大于等于9，也就是Android 2.3以后，因为引进了HttpUrlConnection 
15             } else {//如果小于9,则是用HttpClient来实现
16                 // Prior to Gingerbread, HttpUrlConnection was unreliable.
17                 // See: http://android-developers.blogspot.com/2011/09/androids-http-clients.html
18                 stack = new HttpClientStack(AndroidHttpClient.newInstance(userAgent));
19             }
20         }
21 
22         Network network = new BasicNetwork(stack);
23 　　　　　　//创建一个Network，参数stack是用来网络通信
24         RequestQueue queue = new RequestQueue(new DiskBasedCache(cacheDir), network);
25         queue.start();
26 
27         return queue;
28     }

public RequestQueue(Cache cache, Network network) {
        this(cache, network, DEFAULT_NETWORK_THREAD_POOL_SIZE);
    }

 ...

public RequestQueue(Cache cache, Network network, int threadPoolSize) {
        this(cache, network, threadPoolSize,
                new ExecutorDelivery(new Handler(Looper.getMainLooper())));
    }

 ...

public RequestQueue(Cache cache, Network network, int threadPoolSize,
            ResponseDelivery delivery) {
        mCache = cache;　　//private final Cache mCache用于缓存
        mNetwork = network;　　//private final Network mNetwork用于连接网络
        mDispatchers = new NetworkDispatcher[threadPoolSize];　　/NetworkDispatcher继承thread，网络派发线程池
        mDelivery = delivery;　　// 传递Response的实现
    }

public ExecutorDelivery(final Handler handler) {
        // Make an Executor that just wraps the handler.
        mResponsePoster = new Executor() {
            @Override
            public void execute(Runnable command) {
                handler.post(command);
            }
        };
    }

/**
     * 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();
        }
    }

    /**
     * Stops the cache and network dispatchers.
     */
    public void stop() {
        if (mCacheDispatcher != null) {
            mCacheDispatcher.quit();
        }
        for (int i = 0; i < mDispatchers.length; i++) {
            if (mDispatchers[i] != null) {
                mDispatchers[i].quit();
            }
        }
    }

    /** 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<?>>();