朝花夕拾之Volley源码分析

292 阅读9分钟

RequestQueue

这个是Volley的起点和请求队列,Volley在初始化的时候线通过newRequestQueue方法创建请求队列

	requestQueue = Volley.newRequestQueue(this);

创建的时候到底做了什么?

   /**
     * 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())));
    }

		/**
     * 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
     * @param delivery A ResponseDelivery interface for posting responses and errors
     */
    public RequestQueue(Cache cache, Network network, int threadPoolSize,
            ResponseDelivery delivery) {
        mCache = cache;
        mNetwork = network;
        mDispatchers = new NetworkDispatcher[threadPoolSize];
        mDelivery = delivery;
    }
	public static RequestQueue newRequestQueue(Context context) {
        return newRequestQueue(context, null);
    }


  public static RequestQueue newRequestQueue(Context context, HttpStack stack) {
        //创建缓存的文件夹
        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) {
        }
				//如果网络请求客户端不存在,创建网络请求的客户端
        if (stack == null) {
            if (Build.VERSION.SDK_INT >= 9) {
              	//如果2.2以上版本,使用HurlStack(HttpUrlConnnection)
                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));
            }
        }
				 //创建网络请求器
        Network network = new BasicNetwork(stack);
				
    		//创建网络请求队列
        RequestQueue queue = new RequestQueue(new DiskBasedCache(cacheDir), network);
    		//开启队列中的调度器
        queue.start();

        return queue;
    }

BasicNetwork(后续详细说明)

 //处理网络请求,并返回response
    @Override
    public NetworkResponse performRequest(Request<?> request) throws VolleyError {
        long requestStart = SystemClock.elapsedRealtime();
        while (true) {
            .......
            }
        }
    }

queue.start();

 /**
     * Starts the dispatchers in this queue.
     */
    public void start() {
        stop();  // Make sure any currently running dispatchers are stopped.
        // 创建缓存调度器并开始调度,其实本质是一个带有死循环的线程
        mCacheDispatcher = new CacheDispatcher(mCacheQueue, mNetworkQueue, mCache, mDelivery);
        mCacheDispatcher.start();

        //根据线程池大小创建网络调度器 
        //mDeliver Respionse传递器
        for (int i = 0; i < mDispatchers.length; i++) {
            NetworkDispatcher networkDispatcher = new NetworkDispatcher(mNetworkQueue, mNetwork,
                    mCache, mDelivery);
            mDispatchers[i] = networkDispatcher;
            networkDispatcher.start();
        }
    }

RequestQueue.add()

 /**
     * Adds a Request to the dispatch queue.
     * @param request The request to service
     * @return The passed-in request
     */
    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()) {
            //不需要缓存直接添加到网络请求队列中,不需要的地方可以控制缓存
            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);
                //如果有等待的请求则覆盖之前的网络请求把这个网络请求也加进去
                //当请求执行完成之后会从等待队列中遍历加入到缓存队列中
                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);
                //加入到缓存队列中由缓存调度器处理
                mCacheQueue.add(request);
            }
            return request;
        }
    }

小结一波

  • CacheDispatcher
  • NetWorkDispatcher
  • BasicNetWork
  • ResponseDelivery

CacheDispatcher

/**
 * Provides a thread for performing cache triage on a queue of requests.
 *
 * Requests added to the specified cache queue are resolved from cache.
 * Any deliverable response is posted back to the caller via a
 * {@link ResponseDelivery}.  Cache misses and responses that require
 * refresh are enqueued on the specified network queue for processing
 * by a {@link NetworkDispatcher}.
 //继承自线程
 */
public class CacheDispatcher extends Thread {

    private static final boolean DEBUG = VolleyLog.DEBUG;

    /** The queue of requests coming in for triage. */
    private final BlockingQueue<Request<?>> mCacheQueue;

    /** The queue of requests going out to the network. */
    private final BlockingQueue<Request<?>> mNetworkQueue;

    /** The cache to read from. */
    private final Cache mCache;

    /** For posting responses. */
    private final ResponseDelivery mDelivery;

    /** Used for telling us to die. */
    private volatile boolean mQuit = false;

    /**
     * Creates a new cache triage dispatcher thread.  You must call {@link #start()}
     * in order to begin processing.
     *
     * @param cacheQueue Queue of incoming requests for triage
     * @param networkQueue Queue to post requests that require network to
     * @param cache Cache interface to use for resolution
     * @param delivery Delivery interface to use for posting responses
     */
    public CacheDispatcher(
            BlockingQueue<Request<?>> cacheQueue, BlockingQueue<Request<?>> networkQueue,
            Cache cache, ResponseDelivery delivery) {
        mCacheQueue = cacheQueue;
        mNetworkQueue = networkQueue;
        mCache = cache;
        mDelivery = delivery;
    }

    /**
     * Forces this dispatcher to quit immediately.  If any requests are still in
     * the queue, they are not guaranteed to be processed.
     */
    public void quit() {
        mQuit = true;
        interrupt();
    }

    @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.
        mCache.initialize();

        while (true) {
            try {
                // Get a request from the cache triage queue, blocking until
                // 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.
                    //如果缓存中没有加入到网络调度器中进行调度
                    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);
                    //过期也要加入到网络调度器中
                    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.
                    //直接返回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 {
                                //加入到网络调度器中
                                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;
            }
        }
    }
}

NetWorkDispatcher

/**
 * Provides a thread for performing network dispatch from a queue of requests.
 *
 * Requests added to the specified queue are processed from the network via a
 * specified {@link Network} interface. Responses are committed to cache, if
 * eligible, using a specified {@link Cache} interface. Valid responses and
 * errors are posted back to the caller via a {@link ResponseDelivery}.
 */
public class NetworkDispatcher extends Thread {
    /** The queue of requests to service. */
    private final BlockingQueue<Request<?>> mQueue;
    /** The network interface for processing requests. */
    private final Network mNetwork;
    /** The cache to write to. */
    private final Cache mCache;
    /** For posting responses and errors. */
    private final ResponseDelivery mDelivery;
    /** Used for telling us to die. */
    private volatile boolean mQuit = false;

    /**
     * Creates a new network dispatcher thread.  You must call {@link #start()}
     * in order to begin processing.
     *
     * @param queue Queue of incoming requests for triage
     * @param network Network interface to use for performing requests
     * @param cache Cache interface to use for writing responses to cache
     * @param delivery Delivery interface to use for posting responses
     */
    public NetworkDispatcher(BlockingQueue<Request<?>> queue,
            Network network, Cache cache,
            ResponseDelivery delivery) {
        mQueue = queue;
        mNetwork = network;
        mCache = cache;
        mDelivery = delivery;
    }

    /**
     * Forces this dispatcher to quit immediately.  If any requests are still in
     * the queue, they are not guaranteed to be processed.
     */
    public void quit() {
        mQuit = true;
        interrupt();
    }

    @TargetApi(Build.VERSION_CODES.ICE_CREAM_SANDWICH)
    private void addTrafficStatsTag(Request<?> request) {
        // Tag the request (if API >= 14)
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.ICE_CREAM_SANDWICH) {
            TrafficStats.setThreadStatsTag(request.getTrafficStatsTag());
        }
    }

    @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.执行网络请求,返回Response
                /*此处的 mNetWork为 BasicNetwork
                Network network = new BasicNetwork(stack);
       			RequestQueue queue = new RequestQueue(new DiskBasedCache(cacheDir), network);
        		queue.start();
        		*/
                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()) {
                    //finish主要是当前请求队列删除一个,从waiting队列中取一个放入到缓存队列
                    /**
                     // Remove from the set of requests currently being processed.
        synchronized (mCurrentRequests) {
            mCurrentRequests.remove(request);
        }
        synchronized (mFinishedListeners) {
          for (RequestFinishedListener<T> listener : mFinishedListeners) {
            listener.onRequestFinished(request);
          }
        }

        if (request.shouldCache()) {
            synchronized (mWaitingRequests) {
                String cacheKey = request.getCacheKey();
                Queue<Request<?>> waitingRequests = mWaitingRequests.remove(cacheKey);
                if (waitingRequests != null) {
                    if (VolleyLog.DEBUG) {
                        VolleyLog.v("Releasing %d waiting requests for cacheKey=%s.",
                                waitingRequests.size(), cacheKey);
                    }
                    // Process all queued up requests. They won't be considered as in flight, but
                    // that's not a problem as the cache has been primed by 'request'.
                    mCacheQueue.addAll(waitingRequests);
                }
            }
        }
                    */
                    request.finish("not-modified");
                    continue;
                }

                // Parse the response here on the worker thread. 解析请求
                Response<?> response = request.parseNetworkResponse(networkResponse);
                request.addMarker("network-parse-complete");

                // Write to cache if applicable.加入到缓存中
                // 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();
                //传递网络请求和相应数据
                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);
            }
        }
    }

    private void parseAndDeliverNetworkError(Request<?> request, VolleyError error) {
        error = request.parseNetworkError(error);
        mDelivery.postError(request, error);
    }
}

BasicNetwork

主要是使用httpstack进行网络请求,然后返回数据

 /**
     * @param httpStack HTTP stack to be used
     */
    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;
    }

    //处理网络请求,并返回response
    @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());
                //主要是这里执行网络请求,交给HttpUrlConnect来实现
                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;
                if (httpResponse != null) {
                    statusCode = httpResponse.getStatusLine().getStatusCode();
                } else {
                    throw new NoConnectionError(e);
                }
                VolleyLog.e("Unexpected response code %d for %s", statusCode, request.getUrl());
                NetworkResponse networkResponse;
                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 if (statusCode >= 400 && statusCode <= 499) {
                        // Don't retry other client errors.
                        throw new ClientError(networkResponse);
                    } else if (statusCode >= 500 && statusCode <= 599) {
                        if (request.shouldRetryServerErrors()) {
                            attemptRetryOnException("server",
                                    request, new ServerError(networkResponse));
                        } else {
                            throw new ServerError(networkResponse);
                        }
                    } else {
                        // 3xx? No reason to retry.
                        throw new ServerError(networkResponse);
                    }
                } else {
                    attemptRetryOnException("network", request, new NetworkError());
                }
            }
        }
    }

ExecutorDelivery

ResponseDelivery的实现类,重点关注postResponse方法和ResponseDeliveryRunnable

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.volley;

import android.os.Handler;

import java.util.concurrent.Executor;

/**
 * Delivers responses and errors.
 */
public class ExecutorDelivery implements ResponseDelivery {
    /** Used for posting responses, typically to the main thread. */
    //把response回调的主线程中,原因如下代码
    /**
      public RequestQueue(Cache cache, Network network, int threadPoolSize) {
        this(cache, network, threadPoolSize,
                new ExecutorDelivery(new Handler(Looper.getMainLooper())));
    }
    */
    private final Executor mResponsePoster;

    /**
     * Creates a new response delivery interface.
     * @param handler {@link Handler} to post responses on
     */
    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);
            }
        };
    }

    /**
     * Creates a new response delivery interface, mockable version
     * for testing.
     * @param executor For running delivery tasks
     */
    public ExecutorDelivery(Executor executor) {
        mResponsePoster = executor;
    }

    @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));
    }

    @Override
    public void postError(Request<?> request, VolleyError error) {
        request.addMarker("post-error");
        Response<?> response = Response.error(error);
        mResponsePoster.execute(new ResponseDeliveryRunnable(request, response, null));
    }

    /**
     * A Runnable used for delivering network responses to a listener on the
     * main thread.
     */
    @SuppressWarnings("rawtypes")
    private class ResponseDeliveryRunnable implements Runnable {
        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;
        }

        @SuppressWarnings("unchecked")
        @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()) {
                //回到Request的方法,也就是创建Reuqest的回调方法listener
                /*
                  @Override
                protected void deliverResponse(String response) {
                    mListener.onResponse(response);
                }
                //listener的来源
                public StringRequest(String url, Listener<String> listener, ErrorListener errorListener) {
        this(Method.GET, url, listener, errorListener);
    			}
                */
                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();
            }
       }
    }
}

总结

从添加请求一路分析又回到了添加请求的回到中,也就是我们常使用Volley的请求方式