Android之网络请求5————OkHttp源码2:发送请求

- 日理万妓 2022-05-13 02:03 366阅读 0赞

# Android之网络请求5————OkHttp源码2:发送请求 #

### 一.目录 ###

### 文章目录 ###

*  Android之网络请求5————OkHttp源码2:发送请求
 *   *   *  一.目录
         *  二.目的
         *  三.OkHttpClient()类
         *  四.Call类(RealCall)
         *  五.Dispatcher类
         *  六.同步请求的执行流程
         *   *  1.示例
             *  2.流程分析
         *  七.异步请求的执行流程
         *   *  1.示例
             *  2.流程分析
         *  八.总结
         *  九.参考资料
         *  十.文章索引

### 二.目的 ###

这一篇博客主要是分析，OkHttp使用时提供的Call,OkHttpChile类，以及OkHttp发送请求时，Dispatch调度器调度过程。同时简单分析同步，异步请求的执行流程。

如图是一个简单的同步请求的OkHttp的示例。

new Thread(new Runnable() {
        
                @Override
                public void run() {
        
                    try {
        
    
                        OkHttpClient client = new OkHttpClient();
                        Request request = new Request.Builder().url("http://www.baidu.com")
                                .build();
    
                        try {
        
                            Response response = client.newCall(request).execute();
                            if (response.isSuccessful()) {
        
                                System.out.println("成功");
                            }
                        } catch (IOException e) {
        
                            e.printStackTrace();
                        }
                    } catch (Exception e) {
        
                        e.printStackTrace();
                    }
                }
            }).start();

### 三.OkHttpClient()类 ###

在使用OkHttp是，会先生成一个OkHttpClient类,OkHttpClient类有两种方法，一种是new(就是上面的示例)，另一种是使用建造者()（Builder）模式 – new OkHttpClient.Builder()…Build()。

两种区别在于，第一种会进行默认属性设置，第二种可以对单独的属性进行设置。

下面为第一种的源码：

public OkHttpClient() {
        
        this(new Builder());
      }
    
      OkHttpClient(Builder builder) {
        
        this.dispatcher = builder.dispatcher; //调度器详见下文
        this.proxy = builder.proxy;//代理
        this.protocols = builder.protocols; //默认支持的Http协议版本
        this.connectionSpecs = builder.connectionSpecs;//OKHttp连接（Connection）配置
        this.interceptors = Util.immutableList(builder.interceptors);
        this.networkInterceptors = Util.immutableList(builder.networkInterceptors);
        this.eventListenerFactory = builder.eventListenerFactory; //一个Call的状态监听器
        this.proxySelector = builder.proxySelector;//使用默认的代理选择器
        this.cookieJar = builder.cookieJar; //默认是没有Cookie的；
        this.cache = builder.cache;//缓存
        this.internalCache = builder.internalCache;
        this.socketFactory = builder.socketFactory;//使用默认的Socket工厂产生Socket；
    
        boolean isTLS = false;
        for (ConnectionSpec spec : connectionSpecs) {
        
          isTLS = isTLS || spec.isTls();
        }
    
        if (builder.sslSocketFactory != null || !isTLS) {
        
          this.sslSocketFactory = builder.sslSocketFactory;
          this.certificateChainCleaner = builder.certificateChainCleaner;
        } else {
        
          X509TrustManager trustManager = systemDefaultTrustManager();
          this.sslSocketFactory = systemDefaultSslSocketFactory(trustManager);
          this.certificateChainCleaner = CertificateChainCleaner.get(trustManager);
        }
    
        this.hostnameVerifier = builder.hostnameVerifier;//安全相关的设置
        this.certificatePinner = builder.certificatePinner.withCertificateChainCleaner(
            certificateChainCleaner);
        this.proxyAuthenticator = builder.proxyAuthenticator;
        this.authenticator = builder.authenticator;
        this.connectionPool = builder.connectionPool;//连接池
        this.dns = builder.dns;//域名解析系统 domain name -> ip address；
        this.followSslRedirects = builder.followSslRedirects;
        this.followRedirects = builder.followRedirects;
        this.retryOnConnectionFailure = builder.retryOnConnectionFailure;
        this.connectTimeout = builder.connectTimeout;
        this.readTimeout = builder.readTimeout;
        this.writeTimeout = builder.writeTimeout;
        this.pingInterval = builder.pingInterval;// :这个就和WebSocket有关了。为了保持长连接，我们必须间隔一段时间发送一个ping指令进行保活；
    
        if (interceptors.contains(null)) {
        
          throw new IllegalStateException("Null interceptor: " + interceptors);
        }
        if (networkInterceptors.contains(null)) {
        
          throw new IllegalStateException("Null network interceptor: " + networkInterceptors);
        }
      }

可以看到，new 之后，OkHttpClient自动添加了很多的属性。

### 四.Call类(RealCall) ###

在我们定义了请求对象后，我们需要生成一个Call对象，该对象代表一个准备被执行的请求，Call是可以被取消的，Call对象代表了一个request/response 对（Stream）.还有就是一个Call只能被执行一次.  
从newCall进入源码

@Override public Call newCall(Request request) {
        
        return RealCall.newRealCall(this, request, false /* for web socket */);
      }

继续进入newReakCall中

final class RealCall implements Call {
        
      final OkHttpClient client;
      final RetryAndFollowUpInterceptor retryAndFollowUpInterceptor;
    
      /**
       * There is a cycle between the {@link Call} and {@link EventListener} that makes this awkward.
       * This will be set after we create the call instance then create the event listener instance.
       */
      private EventListener eventListener;
    
      /** The application's original request unadulterated by redirects or auth headers. */
      final Request originalRequest;
      final boolean forWebSocket;
    
      // Guarded by this.
      private boolean executed;
    
      private RealCall(OkHttpClient client, Request originalRequest, boolean forWebSocket) {
        
        this.client = client;
        this.originalRequest = originalRequest;
        this.forWebSocket = forWebSocket;
        this.retryAndFollowUpInterceptor = new RetryAndFollowUpInterceptor(client, forWebSocket);
      }
    
      static RealCall newRealCall(OkHttpClient client, Request originalRequest, boolean forWebSocket) {
        
        // Safely publish the Call instance to the EventListener.
        RealCall call = new RealCall(client, originalRequest, forWebSocket);
        call.eventListener = client.eventListenerFactory().create(call);
        return call;
      }
      。。。。。。
    }

可以看出在OkHttp中实际生产的是一个Call的实现类RealCall。

### 五.Dispatcher类 ###

Dispatcher类负责异步任务的请求策略。

首先看它的部分定义

public final class Dispatcher {
        
      private int maxRequests = 64;
      //每个主机的最大请求数,如果超过这个数，那么新的请求就会被放入到readyAsyncCalls队列中
      private int maxRequestsPerHost = 5;
      //是Dispatcher中请求数量为0时的回调，这儿的请求包含同步请求和异步请求，该参数默认为null。 
      private @Nullable Runnable idleCallback;
    
      /** Executes calls. Created lazily. */
      //任务队列线程池
      private @Nullable ExecutorService executorService;
    
      /** Ready async calls in the order they'll be run. */
      //待执行异步任务队列
      private final Deque<AsyncCall> readyAsyncCalls = new ArrayDeque<>();
    
      /** Running asynchronous calls. Includes canceled calls that haven't finished yet. */
      //运行中的异步任务队列
      private final Deque<AsyncCall> runningAsyncCalls = new ArrayDeque<>();
    
      /** Running synchronous calls. Includes canceled calls that haven't finished yet. */
      //运行中同步任务队列
      private final Deque<RealCall> runningSyncCalls = new ArrayDeque<>();
    
      public Dispatcher(ExecutorService executorService) {
        
        this.executorService = executorService;
      }
    
      public Dispatcher() {
        
      }
    }

查看下面的executorService()方法

public synchronized ExecutorService executorService() {
        
        if (executorService == null) {
        
          executorService = new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60, TimeUnit.SECONDS,
              new SynchronousQueue<Runnable>(), Util.threadFactory("OkHttp Dispatcher", false));
        }
        return executorService;
      }

继续查看ThreadPoolExecutor类

public ThreadPoolExecutor(int corePoolSize,
                                  int maximumPoolSize,
                                  long keepAliveTime,
                                  TimeUnit unit,
                                  BlockingQueue<Runnable> workQueue,
                                  ThreadFactory threadFactory) {
        
            this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
                 threadFactory, defaultHandler);
        }

*  corePoolSize :核心线程数，默认情况下核心线程会一直存活
 *  maximumPoolSize: 线程池所能容纳的最大线程数。超过这个数的线程将被阻塞。
 *  keepAliveTime: 非核心线程的闲置超时时间，超过这个时间就会被回收。
 *  unit: keepAliveTime的单位。
 *  workQueue: 线程池中的任务队列。
 *  threadFactory: 线程工厂，提供创建新线程的功能

corePoolSize设置为0表示一旦有闲置的线程就可以回收。容纳最大线程数设置的非常大，但是由于受到maxRequests的影响，并不会创建特别多的线程。60秒的闲置时间。

### 六.同步请求的执行流程 ###

#### 1.示例 ####

#### 2.流程分析 ####

可以看出，在同步请求里，调用了 client.newCall(request).execute()的方法，在上文说过newCall返回的是一个RealCall对象，所以execute的实现在RealCall中

//RealCall类中
      @Override public Response execute() throws IOException {
        
        //设置execute标志为true，即同一个Call只允许执行一次，执行多次就会抛出异常
        synchronized (this) {
        
          if (executed) throw new IllegalStateException("Already Executed");
          executed = true;
        }
        
        //重定向拦截器相关
        captureCallStackTrace();
        eventListener.callStart(this);
        
        try {
        
          //调用dispatcher()获取Dispatcher对象，调用executed方法
          client.dispatcher().executed(this);
          
          //getResponseWithInterceptorChain拦截器链,详见下一篇文章
          Response result = getResponseWithInterceptorChain();
          
          if (result == null) throw new IOException("Canceled");
    	      return result;
        } catch (IOException e) {
        
          eventListener.callFailed(this, e);
          throw e;
        } finally {
        
           //调用Dispatcher的finished方法
          client.dispatcher().finished(this);
        }
      }

进入 captureCallStackTrace()；

private void captureCallStackTrace() {
        
        Object callStackTrace = Platform.get().getStackTraceForCloseable("response.body().close()");
        //retryAndFollowUpInterceptor重定向拦截器，详见下一篇文章。
        retryAndFollowUpInterceptor.setCallStackTrace(callStackTrace);
      }

进入dispatcher的executed方法中

//Dispatcher类中
      /** Used by {@code Call#execute} to signal it is in-flight. */
      synchronized void executed(RealCall call) {
        
        //将同步请求加入到runningSyncCalls队列中。
        runningSyncCalls.add(call);
      }

继续查看dispatcher的finished方法：

//Dispatcher类中
      void finished(RealCall call) {
        
        finished(runningSyncCalls, call, false);
      }
    
    private <T> void finished(Deque<T> calls, T call, boolean promoteCalls) {
        
        int runningCallsCount;
        Runnable idleCallback;
        synchronized (this) {
        
           //移出请求，如果不能移除，则抛出异常
          if (!calls.remove(call)) throw new AssertionError("Call wasn't in-flight!");
    
          //传入参数为flase，不执行这个语句
          if (promoteCalls) promoteCalls();
    	
          //unningCallsCount统计目前还在运行的请求
          runningCallsCount = runningCallsCount();
    
          //请求数为0时的回调
          idleCallback = this.idleCallback;
        }
    
        //如果请求数为0，且idleCallback不为NULL，回调idleCallback的run方法。
        if (runningCallsCount == 0 && idleCallback != null) {
        
          idleCallback.run();
        }
      }

查看runningCallsCount();方法

public synchronized int runningCallsCount() {
        
        return runningAsyncCalls.size() + runningSyncCalls.size();
      }

### 七.异步请求的执行流程 ###

相对于同步请求的，异步请求较为复杂些

#### 1.示例 ####

private void getDataAsync() {
        
            OkHttpClient client = new OkHttpClient();
            Request request = new Request.Builder()
                    .url("http://www.baidu.com")
                    .build();
            client.newCall(request).enqueue(new Callback() {
        
                @Override
                public void onFailure(Call call, IOException e) {
        
                }
                @Override
                public void onResponse(Call call, Response response) throws IOException {
        
                    if(response.isSuccessful()){
        //回调的方法执行在子线程。
                        Log.d("OkHttp","获取数据成功了");
                        Log.d("OkHttp","response.code()=="+response.code());
                        Log.d("OkHttp","response.body().string()=="+response.body().string());
                    }
                }
            });
        }

#### 2.流程分析 ####

和同步请求类似，clieentnewCall(request).enqueue的方法，所以enqueue的实现在RealCall中,查看具体源码

@Override public void enqueue(Callback responseCallback) {
        
       //设置exexuted参数为true，表示不可以执行两次。
        synchronized (this) {
        
          if (executed) throw new IllegalStateException("Already Executed");
          executed = true;
        }
    
        //同上文
        captureCallStackTrace();
        eventListener.callStart(this);
        调用dispatcher()的enqueuef方法，不过在里面传入一次新的参数，AsyncCall类
        client.dispatcher().enqueue(new AsyncCall(responseCallback));
      }

进入 AsyncCall类

final class AsyncCall extends NamedRunnable {
        
        private final Callback responseCallback;
    
        AsyncCall(Callback responseCallback) {
        
          super("OkHttp %s", redactedUrl());
          this.responseCallback = responseCallback;
        }
    
        String host() {
        
          return originalRequest.url().host();
        }
    
        Request request() {
        
          return originalRequest;
        }
    
        RealCall get() {
        
          return RealCall.this;
        }
    
        @Override protected void execute() {
        
          boolean signalledCallback = false;
          try {
        
    	//执行耗时的IO操作
    	//获取拦截器链，详见下篇文章
            Response response = getResponseWithInterceptorChain();
            if (retryAndFollowUpInterceptor.isCanceled()) {
        
              signalledCallback = true;
                  
    	  //回调，注意这里回调是在线程池中，而不是向当前的主线程回调
              responseCallback.onFailure(RealCall.this, new IOException("Canceled"));
            } else {
        
              signalledCallback = true;
              //回调，同上
              responseCallback.onResponse(RealCall.this, response);
            }
          } catch (IOException e) {
        
            if (signalledCallback) {
        
              // Do not signal the callback twice!
              Platform.get().log(INFO, "Callback failure for " + toLoggableString(), e);
            } else {
        
              eventListener.callFailed(RealCall.this, e);
              //回调，同上
              responseCallback.onFailure(RealCall.this, e);
            }
          } finally {
        
            
            client.dispatcher().finished(this);
          }
        }
      }

继续查看AsyncCall的父类NamedRunnable

//实现了Runnable接口
    public abstract class NamedRunnable implements Runnable {
        
      protected final String name;
    
      public NamedRunnable(String format, Object... args) {
        
        this.name = Util.format(format, args);
      }
    
      @Override public final void run() {
        
        String oldName = Thread.currentThread().getName();
        Thread.currentThread().setName(name);
        try {
        
        //执行抽象方法，也就是 AsyncCall中的execute
          execute();
        } finally {
        
          Thread.currentThread().setName(oldName);
        }
      }
    
      protected abstract void execute();
    }

重新回到RealCall的enqueue，进入到Dispatcher().enqueue中

//Dispatcher()类
      synchronized void enqueue(AsyncCall call) {
        
       //如果正在运行的异步请求的数量小于maxRequests并且与该请求相同的主机数量小于maxRequestsPerHost
        if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {
        
        //放入runningAsyncCalls队列中
          runningAsyncCalls.add(call);
    
         //这里调用了executorService()（源码见第五节中）
          executorService().execute(call);
        } else {
        
        //否则，放入readyAsyncCalls队列
          readyAsyncCalls.add(call);
        }
      }

当线程池执行AsyncCall任务时，它的execute方法会被调用

继续查看Dispatcher的finished方法，

//Dispatcher
      /** Used by {@code AsyncCall#run} to signal completion. */
      void finished(AsyncCall call) {
        
        finished(runningAsyncCalls, call, true);
      }

和同步请求类似，不同的是第三个参数为true

//Dispatcher
    
      private <T> void finished(Deque<T> calls, T call, boolean promoteCalls) {
        
        int runningCallsCount;
        Runnable idleCallback;
        synchronized (this) {
        
          //从队列中删除
          if (!calls.remove(call)) throw new AssertionError("Call wasn't in-flight!");
          
          //异步请求调用 promoteCalls()方法
          if (promoteCalls) promoteCalls();
          runningCallsCount = runningCallsCount();
          idleCallback = this.idleCallback;
        }
    
        if (runningCallsCount == 0 && idleCallback != null) {
        
          idleCallback.run();
        }
      }

查看promoteCalls()源码

private void promoteCalls() {
        
      
        //运行中的异步任务队列大于等于最大的请求数
        if (runningAsyncCalls.size() >= maxRequests) return; // Already running max capacity.
        //待执行异步任务队列为空
        if (readyAsyncCalls.isEmpty()) return; // No ready calls to promote.
    
        //遍历等待队列
        for (Iterator<AsyncCall> i = readyAsyncCalls.iterator(); i.hasNext(); ) {
        
          AsyncCall call = i.next();
    
          //将符合条件的事件，从等待队列中移出，放入运行队列中。 
          if (runningCallsForHost(call) < maxRequestsPerHost) {
        
            i.remove();
            runningAsyncCalls.add(call);
            executorService().execute(call);
          }
    
          if (runningAsyncCalls.size() >= maxRequests) return; // Reached max capacity.
        }
      }

### 八.总结 ###

[图片来自博客:][Link 1]

![这里写图片描述][aHR0cHM6Ly91cGxvYWQtaW1hZ2VzLmppYW5zaHUuaW8vdXBsb2FkX2ltYWdlcy81MDA0MzA0LTI4YWIxYmE5ZDBmYmE4NTMuUE5H]

*  OkHttp采用Dispatcher技术，类似于Nginx，与线程池配合实现了高并发，低阻塞的运行
 *  Okhttp采用Deque作为缓存，按照入队的顺序先进先出
 *  OkHttp最出彩的地方就是在try/finally中调用了finished函数，可以主动控制等待队列的移动，而不是采用锁或者wait/notify，极大减少了编码复杂性

### 九.参考资料 ###

[okhttp源码解析][okhttp]  
[深入理解OkHttp源码（一）——提交请求][OkHttp]  
[OkHttp 3.7源码分析（三）——任务队列][OkHttp 3.7]

### 十.文章索引 ###

[Android之网络请求1————HTTP协议][Android_1_HTTP]  
[Android之网络请求2————OkHttp的基本使用][Android_2_OkHttp]  
[Android之网络请求3————OkHttp的拦截器和封装][Android_3_OkHttp]  
[Android之网络请求4————OkHttp源码1:框架][Android_4_OkHttp_1]  
[Android之网络请求5————OkHttp源码2:发送请求][Android_5_OkHttp_2]  
[Android之网络请求6————OkHttp源码3:拦截器链][Android_6_OkHttp_3]  
[Android之网络请求7————OkHttp源码4:网络操作][Android_7_OkHttp_4]  
[Android之网络请求8————OkHttp源码5:缓存相关][Android_8_OkHttp_5]  
[Android之网络请求9————Retrofit的简单使用][Android_9_Retrofit]  
[Android之网络请求10————Retrofit的进阶使用][Android_10_Retrofit]  
[Android之网络请求11————Retrofit的源码分析][Android_11_Retrofit]

[Link 1]: https://www.jianshu.com/p/d386894e324c?utm_campaign=haruki&utm_content=note&utm_medium=reader_share&utm_source=qq
[aHR0cHM6Ly91cGxvYWQtaW1hZ2VzLmppYW5zaHUuaW8vdXBsb2FkX2ltYWdlcy81MDA0MzA0LTI4YWIxYmE5ZDBmYmE4NTMuUE5H]: /images/20220513/2f2af42285f54c3cba85108e9950fd8c.png
[okhttp]: https://blog.csdn.net/json_it/article/details/78404010
[OkHttp]: https://blog.csdn.net/qq_19431333/article/details/53141013
[OkHttp 3.7]: https://yq.aliyun.com/articles/78103?spm=a2c4e.11153940.blogcont78105.13.182237bePVcLWJ
[Android_1_HTTP]: https://blog.csdn.net/qq_38499859/article/details/82153094
[Android_2_OkHttp]: https://blog.csdn.net/qq_38499859/article/details/82290738
[Android_3_OkHttp]: https://blog.csdn.net/qq_38499859/article/details/82355954
[Android_4_OkHttp_1]: https://blog.csdn.net/qq_38499859/article/details/82469295
[Android_5_OkHttp_2]: https://blog.csdn.net/qq_38499859/article/details/82561675
[Android_6_OkHttp_3]: https://blog.csdn.net/qq_38499859/article/details/82630630
[Android_7_OkHttp_4]: https://blog.csdn.net/qq_38499859/article/details/82745671
[Android_8_OkHttp_5]: https://blog.csdn.net/qq_38499859/article/details/82778955
[Android_9_Retrofit]: https://blog.csdn.net/qq_38499859/article/details/82807496
[Android_10_Retrofit]: https://blog.csdn.net/qq_38499859/article/details/83010604
[Android_11_Retrofit]: https://blog.csdn.net/qq_38499859/article/details/83042782