從源代碼了解volley架構

用過volley都知道，隻要建立一個RequestQueue，然後每次添加一個Request就行了，就可以在Request中的listenner的response方法得到傳回的資料，但是平時使用的httpclient和httpurlconnection的時候都知道，要發起一個請求，要在新線程，并且線上程阻塞，RequestQueue為啥隻要add進去，就能發送請求呢，今天就來簡要分析下volley架構。

首先猜想估計是建立後，通過線程無限循環取一個隊列，反複申請，是以才能add一下就能繼續的。

是以直接看這個函數Volley.newRequestQueue(context);進入發現return newRequestQueue(context,null),是以，直接看newRequestQueue(context,httpstack)，先上代碼

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));
        }
    }

    Network network = new BasicNetwork(stack);

    RequestQueue queue = new RequestQueue(new DiskBasedCache(cacheDir), network);
    queue.start();

    return queue;
}      

首先前面的是cachedir之類的，看到file，猜想就是本地緩存了，先不管，這裡有個HttpStack，直接進去，發現就一個接口， public HttpResponse performRequest(Request<?> request, Map<String, String> additionalHeaders)

        throws IOException, AuthFailureError;

我們第一次預設傳入的是null，是以，直接看if(stack==null)，這裡判斷sdk版本是否大于9，想想也知道，因為httpclient到23已經被google徹底放棄了，請求麻煩，可能效率也不高吧，但是低版本中有的要httpclient，是以，這裡做了一個判斷。我們平時用的基本都大于9，直接檢視HurlStack代碼，因為都是繼承HttpStack的，是以就隻看performRequest函數就行了，先上代碼

@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;
}      

首先是擷取url（這裡建立request裡已經穿進去了），然後是擷取request.getHeader()，是以，這裡像stringrequest要重寫getHeader()才能傳入header。當然還有後面的additionalHeaders，看名字就知道是其他的header，待會兒看到調用這個函數傳入啥。對url的處理就不說了，這裡看到了最熟悉的HttpURLConnection，這裡通過openConnection建立，直接進去檢視。

private HttpURLConnection openConnection(URL url, Request<?> request) throws IOException {
    HttpURLConnection connection = createConnection(url);

    int timeoutMs = request.getTimeoutMs();
    connection.setConnectTimeout(timeoutMs);
    connection.setReadTimeout(timeoutMs);
    connection.setUseCaches(false);
    connection.setDoInput(true);

    // use caller-provided custom SslSocketFactory, if any, for HTTPS
    if ("https".equals(url.getProtocol()) && mSslSocketFactory != null) {
        ((HttpsURLConnection)connection).setSSLSocketFactory(mSslSocketFactory);
    }

    return connection;
}      

基本就是基本的設定，然後，從request擷取一個逾時時間，順便進去看下

public final int getTimeoutMs() {
    return mRetryPolicy.getCurrentTimeout();
}      

是通過mRetryPolicy的，搜尋下這個變量

public Request<?> setRetryPolicy(RetryPolicy retryPolicy) {
    mRetryPolicy = retryPolicy;
    return this;
}      

是以我們平時建立一個Request的時候，後面通過調用這個函數，傳入一個RetryPolicy來設定逾時時間。

建立完HttpsURLConnection後，下面的周遊，添加剛才的header，再下面就是判斷如果是https協定啥的，就設定一下。

再往下就是setConnectionParametersForRequest，看到名字也知道是設定參數，還是進去看下源代碼

static void setConnectionParametersForRequest(HttpURLConnection connection,
        Request<?> request) throws IOException, AuthFailureError {
    switch (request.getMethod()) {
        case Method.DEPRECATED_GET_OR_POST:
            // This is the deprecated way that needs to be handled for backwards compatibility.
            // If the request's post body is null, then the assumption is that the request is
            // GET.  Otherwise, it is assumed that the request is a POST.
            byte[] postBody = request.getPostBody();
            if (postBody != null) {
                // Prepare output. There is no need to set Content-Length explicitly,
                // since this is handled by HttpURLConnection using the size of the prepared
                // output stream.
                connection.setDoOutput(true);
                connection.setRequestMethod("POST");
                connection.addRequestProperty(HEADER_CONTENT_TYPE,
                        request.getPostBodyContentType());
                DataOutputStream out = new DataOutputStream(connection.getOutputStream());
                out.write(postBody);
                out.close();
            }
            break;
        case Method.GET:
            // Not necessary to set the request method because connection defaults to GET but
            // being explicit here.
            connection.setRequestMethod("GET");
            break;
        case Method.DELETE:
            connection.setRequestMethod("DELETE");
            break;
        case Method.POST:
            connection.setRequestMethod("POST");
            addBodyIfExists(connection, request);
            break;
        case Method.PUT:
            connection.setRequestMethod("PUT");
            addBodyIfExists(connection, request);
            break;
        case Method.HEAD:
            connection.setRequestMethod("HEAD");
            break;
        case Method.OPTIONS:
            connection.setRequestMethod("OPTIONS");
            break;
        case Method.TRACE:
            connection.setRequestMethod("TRACE");
            break;
        case Method.PATCH:
            connection.setRequestMethod("PATCH");
            addBodyIfExists(connection, request);
            break;
        default:
            throw new IllegalStateException("Unknown method type.");
    }
}      

代碼有點長，我們就隻看平時最常用的post，其他方法類似。第一步是設定請求方式為post，第二步就調用了addBodyIfExists，再進去看下源代碼。

private static void addBodyIfExists(HttpURLConnection connection, Request<?> request)
        throws IOException, AuthFailureError {
    byte[] body = request.getBody();
    if (body != null) {
        connection.setDoOutput(true);
        connection.addRequestProperty(HEADER_CONTENT_TYPE, request.getBodyContentType());
        DataOutputStream out = new DataOutputStream(connection.getOutputStream());
        out.write(body);
        out.close();
    }
}      

大概就是從request的getbody擷取，然後，寫入到請求體。再去看getBody()函數

public byte[] getBody() throws AuthFailureError {
    Map<String, String> params = getParams();
    if (params != null && params.size() > 0) {
        return encodeParameters(params, getParamsEncoding());
    }
    return null;
}      

這裡就很簡單了，可以看到是通過調用getParams()擷取參數，然後，編成byte[]，是以我們StringRequest要重寫getParams傳入參數。

至此就建立完了，剩下的就是HttpsURLConnection的使用了，就不多說了，最後傳回一個HttpResponse。

是以，這裡就是我們最常用的方法了，是以隻要接下來就看到哪裡用到了這個方法。

那就繼續剛才的再往下看吧，發現Network network = new BasicNetwork(stack);被傳入了一個叫Network的對象裡。Network這個接口就public NetworkResponse performRequest(Request<?> request) throws VolleyError;這個函數，是以，直接檢視BasicNetwork裡的這個函數。先看構造函數

private static int DEFAULT_POOL_SIZE = 4096;      

public BasicNetwork(HttpStack httpStack) {
    // If a pool isn't passed in, then build a small default pool that will give us a lot of
    // benefit and not use too much memory.
    this(httpStack, new ByteArrayPool(DEFAULT_POOL_SIZE));
}

/**
 * @param httpStack HTTP stack to be used
 * @param pool a buffer pool that improves GC performance in copy operations
 */
public BasicNetwork(HttpStack httpStack, ByteArrayPool pool) {
    mHttpStack = httpStack;
    mPool = pool;
}      

基本就給mHttpStack和mPool指派，接下來看performRequest函數

@Override
public NetworkResponse performRequest(Request<?> request) throws VolleyError {
    long requestStart = SystemClock.elapsedRealtime();
    while (true) {
        HttpResponse httpResponse = null;
        byte[] responseContents = null;
        Map<String, String> responseHeaders = Collections.emptyMap();
        try {
            // Gather headers.
            Map<String, String> headers = new HashMap<String, String>();
            addCacheHeaders(headers, request.getCacheEntry());
            httpResponse = mHttpStack.performRequest(request, headers);
            StatusLine statusLine = httpResponse.getStatusLine();
            int statusCode = statusLine.getStatusCode();

            responseHeaders = convertHeaders(httpResponse.getAllHeaders());
            // Handle cache validation.
            if (statusCode == HttpStatus.SC_NOT_MODIFIED) {

                Entry entry = request.getCacheEntry();
                if (entry == null) {
                    return new NetworkResponse(HttpStatus.SC_NOT_MODIFIED, null,
                            responseHeaders, true,
                            SystemClock.elapsedRealtime() - requestStart);
                }

                // A HTTP 304 response does not have all header fields. We
                // have to use the header fields from the cache entry plus
                // the new ones from the response.
                // http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.3.5
                entry.responseHeaders.putAll(responseHeaders);
                return new NetworkResponse(HttpStatus.SC_NOT_MODIFIED, entry.data,
                        entry.responseHeaders, true,
                        SystemClock.elapsedRealtime() - requestStart);
            }

            // Some responses such as 204s do not have content.  We must check.
            if (httpResponse.getEntity() != null) {
              responseContents = entityToBytes(httpResponse.getEntity());
            } else {
              // Add 0 byte response as a way of honestly representing a
              // no-content request.
              responseContents = new byte[0];
            }

            // if the request is slow, log it.
            long requestLifetime = SystemClock.elapsedRealtime() - requestStart;
            logSlowRequests(requestLifetime, request, responseContents, statusLine);

            if (statusCode < 200 || statusCode > 299) {
                throw new IOException();
            }
            return new NetworkResponse(statusCode, responseContents, responseHeaders, false,
                    SystemClock.elapsedRealtime() - requestStart);
        } catch (SocketTimeoutException e) {
            attemptRetryOnException("socket", request, new TimeoutError());
        } catch (ConnectTimeoutException e) {
            attemptRetryOnException("connection", request, new TimeoutError());
        } catch (MalformedURLException e) {
            throw new RuntimeException("Bad URL " + request.getUrl(), e);
        } catch (IOException e) {
            int statusCode = 0;
            NetworkResponse networkResponse = null;
            if (httpResponse != null) {
                statusCode = httpResponse.getStatusLine().getStatusCode();
            } else {
                throw new NoConnectionError(e);
            }
            VolleyLog.e("Unexpected response code %d for %s", statusCode, request.getUrl());
            if (responseContents != null) {
                networkResponse = new NetworkResponse(statusCode, responseContents,
                        responseHeaders, false, SystemClock.elapsedRealtime() - requestStart);
                if (statusCode == HttpStatus.SC_UNAUTHORIZED ||
                        statusCode == HttpStatus.SC_FORBIDDEN) {
                    attemptRetryOnException("auth",
                            request, new AuthFailureError(networkResponse));
                } else {
                    // TODO: Only throw ServerError for 5xx status codes.
                    throw new ServerError(networkResponse);
                }
            } else {
                throw new NetworkError(networkResponse);
            }
        }
    }
}      

Map<String, String> headers = new HashMap<String, String>();

                addCacheHeaders(headers, request.getCacheEntry());

                httpResponse = mHttpStack.performRequest(request, headers);

看到這裡執行了剛才的代碼，而且看到headers是建立的，通過addCacheHeaders，應該是加入了一些緩存資訊之類的，并不在我們的關心系列中。代碼有點多，就挑重點講了

if (httpResponse.getEntity() != null) {
  responseContents = entityToBytes(httpResponse.getEntity());
} else {
  // Add 0 byte response as a way of honestly representing a
  // no-content request.
  responseContents = new byte[0];
}      

這裡擷取到實體，放到responseContents裡，最後傳回一個NetworkResponse

return new NetworkResponse(statusCode, responseContents, responseHeaders, false,
        SystemClock.elapsedRealtime() - requestStart);      

這裡大概有的資訊是傳回的狀态碼，實體，頭部資訊，和請求的總時間（現在的鍵入請求時候的）這個應該是坐逾時用的。

是以，接下來換成要看哪裡調用了performRequest函數了。

再往下看，發現傳入了RequestQueue，并調用了start函數。

RequestQueue queue = new RequestQueue(new DiskBasedCache(cacheDir), network);
queue.start();      

我們先看構造函數，第一個參數，用到緩存再去看好了，看名字就知道是本地緩存。第二個參數就是我們關心的network對象了。

/** Number of network request dispatcher threads to start. */
private static final int DEFAULT_NETWORK_THREAD_POOL_SIZE = 4;      

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

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

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

基本，本地緩存就放在mCache裡，我們的network放在mNetwork，再接下來看下哪個start函數

/**
 * 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();
    }
}      

前面的還是依舊處理緩存的，就跳過得了。這裡看下NetworkDispatcher這個類

public NetworkDispatcher(BlockingQueue<Request<?>> queue,
        Network network, Cache cache,
        ResponseDelivery delivery) {
    mQueue = queue;
    mNetwork = network;
    mCache = cache;
    mDelivery = delivery;
}      

這裡的mQueue是一個網絡請求隊列，裡面包含了我們的request（待會兒繼續看），我們的network就放在mNetwork了。看到上面的start然後在看到NetworkDispatcher是繼承于Thread的是以，直接看run函數

@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);
        }
    }
}      

這裡有個無限循環，那就是在這裡無限循環，一直取出添加進去的request，進行操作吧。繼續看

request = mQueue.take();      

這裡代碼看下就知道就是從mQueue取出request，異常啥的先跳過。看到這裡

NetworkResponse networkResponse = mNetwork.performRequest(request);      

終于找到這個函數了，是以，看下networkResponse在哪裡用到了。

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

在這裡，通過調用parseNetworkResponse轉換為Response<?>對象，這裡看下stringrequest吧。

@Override
protected Response<String> parseNetworkResponse(NetworkResponse response) {
    String parsed;
    try {
        parsed = new String(response.data, HttpHeaderParser.parseCharset(response.headers));
    } catch (UnsupportedEncodingException e) {
        parsed = new String(response.data);
    }
    return Response.success(parsed, HttpHeaderParser.parseCacheHeaders(response));
}      

很簡單的把data裡的二進制流取出，轉換為相應的對象，注意這裡

HttpHeaderParser.parseCharset(response.headers)      

/**
 * Returns the charset specified in the Content-Type of this header,
 * or the HTTP default (ISO-8859-1) if none can be found.
 */
public static String parseCharset(Map<String, String> headers) {
    return parseCharset(headers, HTTP.DEFAULT_CONTENT_CHARSET);
}      

這裡，調用parseCharset獲得編碼方式，看注釋知道，預設使用ISO-8859-1，這貨是不支援中文的，我們平常使用的是utf-8，是以如果是stringrequest出現亂碼，就重寫這個方法，其他地方copy下，然後，把調用parseCharset這個函數換成“utf-8”即可（其他編碼類似）

最後通過一句postResponse結束

mDelivery.postResponse(request, response);      

處理先到這裡，我們回到剛才的mQueue，這貨是在這裡傳入的

NetworkDispatcher networkDispatcher = new NetworkDispatcher(mNetworkQueue, mNetwork,
        mCache, mDelivery);      

然後看下mNetworkQueue這貨的變動，初始化就不用說了

private final PriorityBlockingQueue<Request<?>> mNetworkQueue =
    new PriorityBlockingQueue<Request<?>>();      

然後就是添加了，這裡我們知道通過add可以添加一個request，想必就是加入到這裡來了

直接看下我們的RequestQueue.add函數

public <T> Request<T> add(Request<T> request) {
    // Tag the request as belonging to this queue and add it to the set of current requests.
    request.setRequestQueue(this);
    synchronized (mCurrentRequests) {
        mCurrentRequests.add(request);
    }

    // Process requests in the order they are added.
    request.setSequence(getSequenceNumber());
    request.addMarker("add-to-queue");

    // If the request is uncacheable, skip the cache queue and go straight to the network.
    if (!request.shouldCache()) {
        mNetworkQueue.add(request);
        return request;
    }

    // Insert request into stage if there's already a request with the same cache key in flight.
    synchronized (mWaitingRequests) {
        String cacheKey = request.getCacheKey();
        if (mWaitingRequests.containsKey(cacheKey)) {
            // There is already a request in flight. Queue up.
            Queue<Request<?>> stagedRequests = mWaitingRequests.get(cacheKey);
            if (stagedRequests == null) {
                stagedRequests = new LinkedList<Request<?>>();
            }
            stagedRequests.add(request);
            mWaitingRequests.put(cacheKey, stagedRequests);
            if (VolleyLog.DEBUG) {
                VolleyLog.v("Request for cacheKey=%s is in flight, putting on hold.", cacheKey);
            }
        } else {
            // Insert 'null' queue for this cacheKey, indicating there is now a request in
            // flight.
            mWaitingRequests.put(cacheKey, null);
            mCacheQueue.add(request);
        }
        return request;
    }
}      

這裡先放進mCurrentRequests，這貨就是記錄目前加入進去的request，就為了能夠關閉了，抛開不管了

如果沒有緩存機制的話直接加入到我們的mNetworkQueue的隊列中。

if (!request.shouldCache()) {
    mNetworkQueue.add(request);
    return request;
}      

如果有緩存的話，如果網址是第一次請求，就放到mCacheQueue，否則就記錄下來，至于這貨哪裡執行了，前面會先執行，細節代碼差不多，就不說了

mCacheDispatcher = new CacheDispatcher(mCacheQueue, mNetworkQueue, mCache, mDelivery);
mCacheDispatcher.start();      

然後，剩下的就是剛才的mDelivery.postResponse(request, response);這貨是啥了。

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

/**
 * 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())));
}      

首先mDelivery這貨是建立的ExecutorDelivery對象，參數是一個帶主線程Lopper的handler，我們去看下ExecutorDelivery對象，看下他的postResponse函數，先看構造函數

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);
        }
    };
}      

穿進去一個handler對象，初始化一個Executor對象，execute函數是将Runnable對象通過handler post出去。

@Override
public void postResponse(Request<?> request, Response<?> response) {
    postResponse(request, response, null);
}

@Override
public void postResponse(Request<?> request, Response<?> response, Runnable runnable) {
    request.markDelivered();
    request.addMarker("post-response");
    mResponsePoster.execute(new ResponseDeliveryRunnable(request, response, runnable));
}      

這裡是調用剛才的Executor對象，将一個建立的ResponseDeliveryRunnable對象post出去，然後，我們看ResponseDeliveryRunnable這個對象的構造函數和run函數

構造沒啥好說的

private final Request mRequest;
private final Response mResponse;
private final Runnable mRunnable;

public ResponseDeliveryRunnable(Request request, Response response, Runnable runnable) {
    mRequest = request;
    mResponse = response;
    mRunnable = runnable;
}      

就是指派

然後看下run函數

@Override
 public void run() {
     // If this request has canceled, finish it and don't deliver.
     if (mRequest.isCanceled()) {
         mRequest.finish("canceled-at-delivery");
         return;
     }

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

     // If this is an intermediate response, add a marker, otherwise we're done
     // and the request can be finished.
     if (mResponse.intermediate) {
         mRequest.addMarker("intermediate-response");
     } else {
         mRequest.finish("done");
     }

     // If we have been provided a post-delivery runnable, run it.
     if (mRunnable != null) {
         mRunnable.run();
     }
}      

我們這裡的mRunnable是為空的，是以就是

if (mResponse.isSuccess()) {
    mRequest.deliverResponse(mResponse.result);
} else {
    mRequest.deliverError(mResponse.error);
}      

這裡了，調的是request的deliverResponse或者deliverError函數（分别處理成功和失敗的情形），

@Override
protected void deliverResponse(String response) {
    mListener.onResponse(response);
}      

這裡，就調用我們傳進去的Listenner的onResponse對象了。至于result的話，就是之前的parseNetworkResponse函數了

return Response.success(parsed, HttpHeaderParser.parseCacheHeaders(response));      

/** Returns a successful response containing the parsed result. */
public static <T> Response<T> success(T result, Cache.Entry cacheEntry) {
    return new Response<T>(result, cacheEntry);
}      

private Response(T result, Cache.Entry cacheEntry) {
    this.result = result;
    this.cacheEntry = cacheEntry;
    this.error = null;
}      

就是這裡了