Okhttp3使用 + 源码完全解析

在使用过okhttp3之后,必然的一步当是对源码的研究 这样可以对其优劣和功能封装有一个全面详尽的了解 ok 下面粘贴okhttp3的核心代码(url暂时随意定义)

 OkHttpClient okHttpClient = new OkHttpClient();
        Request request = new Request.Builder()
                .url("www.baidu.com")
                .build();
        Call call = okHttpClient.newCall(request);
        call.enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {

            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {

            }
        });

下面进入正题,来对源码进行分析

1.okhttp实例 和Request实例和配置

相当于初始化实例 比较简单 首先来看okhttp初始化实例

1.1 //OkHttpClient okHttpClient = new OkHttpClient();

public OkHttpClient() {
    this(new Builder());
  }


    public Builder() {
      dispatcher = new Dispatcher();
      protocols = DEFAULT_PROTOCOLS;
      connectionSpecs = DEFAULT_CONNECTION_SPECS;
      eventListenerFactory = EventListener.factory(EventListener.NONE);
      proxySelector = ProxySelector.getDefault();
      cookieJar = CookieJar.NO_COOKIES;
      socketFactory = SocketFactory.getDefault();
      hostnameVerifier = OkHostnameVerifier.INSTANCE;
      certificatePinner = CertificatePinner.DEFAULT;
      proxyAuthenticator = Authenticator.NONE;
      authenticator = Authenticator.NONE;
      connectionPool = new ConnectionPool();
      dns = Dns.SYSTEM;
      followSslRedirects = true;
      followRedirects = true;
      retryOnConnectionFailure = true;
      connectTimeout = 10_000;
      readTimeout = 10_000;
      writeTimeout = 10_000;
      pingInterval = 0;
    }

其实就是初始化对象 和属性的相关配置过程

1.2Requst的初始化

 Request request = new Request.Builder()
                .url("www.baidu.com")
                .build();

下面来看其源码:

 public Builder() {
      this.method = "GET";
      this.headers = new Headers.Builder();
    }

  public Builder url(String url) {
      if (url == null) throw new NullPointerException("url == null");

      // Silently replace web socket URLs with HTTP URLs.
      if (url.regionMatches(true, 0, "ws:", 0, 3)) {
        url = "http:" + url.substring(3);
      } else if (url.regionMatches(true, 0, "wss:", 0, 4)) {
        url = "https:" + url.substring(4);
      }

      HttpUrl parsed = HttpUrl.parse(url);
      if (parsed == null) throw new IllegalArgumentException("unexpected url: " + url);
      return url(parsed);
    }


public Request build() {
      if (url == null) throw new IllegalStateException("url == null");
      return new Request(this);
    }

到这里准备工作就完成了

下面来从请求开始详细看源码(以上比较简单 没有什么可以讲的)

2.请求处理

//Call call = okHttpClient.newCall(request);

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




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;
  }

okhttp3创建请求的主体call对象 其实返回的是一个realCall的实例化对象,并完成一系列的相关初始化配置; 下面来看请求

//call.enqueue

 @Override public void enqueue(Callback responseCallback) {
    synchronized (this) {
      if (executed) throw new IllegalStateException("Already Executed");
      executed = true;
    }
    captureCallStackTrace();
    eventListener.callStart(this);
    client.dispatcher().enqueue(new AsyncCall(responseCallback));
  }

由以上代码 可以看出来 okhttp的请求是由dispatcher来完成的;而dispatcher又是什么呢 ?
其实是一个网络的任务调度器;
那么下面来看下调度器的实现.

3.dispatcher任务调度

  //最大请求数
  private int maxRequests = 64;
  //最大主机请求数
  private int maxRequestsPerHost = 5;
  private @Nullable Runnable idleCallback;
  //消费者线程池
  private @Nullable ExecutorService executorService;
  //将要运行的异步请求队列
  private final Deque<AsyncCall> readyAsyncCalls = new ArrayDeque<>();
  //正在运行的异步请求队列
  private final Deque<AsyncCall> runningAsyncCalls = new ArrayDeque<>();
  //正在运行的同步请求队列
  private final Deque<RealCall> runningSyncCalls = new ArrayDeque<>();

  public Dispatcher(ExecutorService executorService) {
    this.executorService = executorService;
  }

  public Dispatcher() {
  }

Dispatcher主要用于控制并发 并且维护了一部分变量
在请求之前dispatcher会自己创建线程池
当然也可以有程序员自己来创建线程池

ok~初步了解调度器之后来看异步请求的源码

  synchronized void enqueue(AsyncCall call) {
    if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {
      runningAsyncCalls.add(call);
      executorService().execute(call);
    } else {
      readyAsyncCalls.add(call);
    }
  }

在调度器的enqueue中会先判断当前最大请求数和当前最大主机请求数 如果不超过默认的最大值 则吧请求加入到正在运行的请求队列—->runningAsyncCalls; 否则会加入到将要运行的请求队列中进行等待—->readyAsyncCalls

然后 executorService().execute(call);开始运行传入的线程 即传入的AsyncCall;而AsyncCall作为RealCall的内部实现类 会走execute;

ok下面来看AsyncCall–>execute ,在这里 开始进行网络请求:

  @Override protected void execute() {
      boolean signalledCallback = false;
      try {
        Response response = getResponseWithInterceptorChain();
        if (retryAndFollowUpInterceptor.isCanceled()) {
          signalledCallback = true;
          responseCallback.onFailure(RealCall.this, new IOException("Canceled"));
        } else {
          signalledCallback = true;
          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);
          responseCallback.onFailure(RealCall.this, e);
        }
      } finally {
        client.dispatcher().finished(this);
      }
    }
  }

在上面代码中不难看出走了一系列方法 来进行网络请求 为了方便读者理解 先来看finally下的方法 (这个方法必然会走到的):

  void finished(AsyncCall call) {
    finished(runningAsyncCalls, call, true);
  }

//finished
  private <T> void finished(Deque<T> calls, T call, boolean promoteCalls) {
    int runningCallsCount;
    Runnable idleCallback;
    synchronized (this) {
      if (!calls.remove(call)) throw new AssertionError("Call wasn't in-flight!");
      if (promoteCalls) promoteCalls();
      runningCallsCount = runningCallsCount();
      idleCallback = this.idleCallback;
    }

    if (runningCallsCount == 0 && idleCallback != null) {
      idleCallback.run();
    }
  }




//####promoteCalls()
private void promoteCalls() {
    if (runningAsyncCalls.size() >= maxRequests) return; // Already running max capacity.
    if (readyAsyncCalls.isEmpty()) return; // No ready calls to promote.

    for (Iterator<AsyncCall> i = readyAsyncCalls.iterator(); i.hasNext(); ) {
      AsyncCall call = i.next();

      if (runningCallsForHost(call) < maxRequestsPerHost) {
        i.remove();
        runningAsyncCalls.add(call);
        executorService().execute(call);
      }

      if (runningAsyncCalls.size() >= maxRequests) return; // Reached max capacity.
    }
  }

直接提取关键代码: finished—->if (promoteCalls) promoteCalls(); 当请求完之后 promoteCalls为true 则会走promoteCalls() ;从上面代码中可图看出来promoteCalls()中用迭代器遍历readyAsyncCalls 然后加入到runningAsyncCalls

其实就是在请求完成后 来请求缓存池中的线程

那么继续回头看AsyncCall–>execute中的逻辑,在这之前先简单介绍一下拦截器 okhttp中请求有用到拦截器

4.拦截器Interceptors

拦截器主要是用来监听网络的请求和响应 拦截器的添加可以添加,移除或者转换请求头;其实简单来说就是对网络请求和响应的一个包装吧,有兴趣可以自己研究一下 这里简单介绍一下方便接下来的讲解;

继续回到代码:AsyncCall–>execute:

    @Override protected void execute() {
      boolean signalledCallback = false;
      try {
        Response response = getResponseWithInterceptorChain();
        if (retryAndFollowUpInterceptor.isCanceled()) {
          signalledCallback = true;
          responseCallback.onFailure(RealCall.this, new IOException("Canceled"));
        } else {
          signalledCallback = true;
          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);
          responseCallback.onFailure(RealCall.this, e);
        }
      } finally {
        client.dispatcher().finished(this);
      }
    }

上面代码中关键的请求代码是:

Response response = getResponseWithInterceptorChain();

下面我们来看见其源码:

 Response getResponseWithInterceptorChain() throws IOException {
    // Build a full stack of interceptors.
    List<Interceptor> interceptors = new ArrayList<>();
    interceptors.addAll(client.interceptors());
    interceptors.add(retryAndFollowUpInterceptor);
    interceptors.add(new BridgeInterceptor(client.cookieJar()));
    interceptors.add(new CacheInterceptor(client.internalCache()));
    interceptors.add(new ConnectInterceptor(client));
    if (!forWebSocket) {
      interceptors.addAll(client.networkInterceptors());
    }
    interceptors.add(new CallServerInterceptor(forWebSocket));

    Interceptor.Chain chain = new RealInterceptorChain(interceptors, null, null, null, 0,
        originalRequest, this, eventListener, client.connectTimeoutMillis(),
        client.readTimeoutMillis(), client.writeTimeoutMillis());

    return chain.proceed(originalRequest);
  }

在上面代码中:

 Interceptor.Chain chain = new RealInterceptorChain(interceptors, null, null, null, 0,
        originalRequest, this, eventListener, client.connectTimeoutMillis(),
        client.readTimeoutMillis(), client.writeTimeoutMillis());

其实是初始化了拦截器 传参为读取/请求超时等…. 实际请求的代码是:chain.proceed(originalRequest);

@Override public Response proceed(Request request) throws IOException {
      // If there's another interceptor in the chain, call that.
      if (index < client.interceptors().size()) {
        Interceptor.Chain chain = new ApplicationInterceptorChain(index + 1, request, forWebSocket);
        //从拦截器列表取出拦截器
        Interceptor interceptor = client.interceptors().get(index);
        Response interceptedResponse = interceptor.intercept(chain);

        if (interceptedResponse == null) {
          throw new NullPointerException("application interceptor " + interceptor
              + " returned null");
        }

        return interceptedResponse;
      }

      // No more interceptors. Do HTTP.
      return getResponse(request, forWebSocket);
    }

在拦截器拦截过程中,当存在多个拦截器,需要拦截等待,即第一个请求完下一个请求;其中拦截的代码会在上面代码中:

    Interceptor interceptor = client.interceptors().get(index);
        Response interceptedResponse = interceptor.intercept(chain);

而真正请求的代码是//getResponse(request, forWebSocket); 那么接着来看它的源码:

Response getResponse(Request request, boolean forWebSocket) throws IOException {
 //请求成功的核心源码

    engine = new HttpEngine(client, request, false, false, forWebSocket, null, null, null);

    int followUpCount = 0;
    while (true) {
      if (canceled) {
        engine.releaseStreamAllocation();
        throw new IOException("Canceled");
      }

      boolean releaseConnection = true;
      try {
        engine.sendRequest();
        engine.readResponse();
        releaseConnection = false;
      } catch (RequestException e) {
        // The attempt to interpret the request failed. Give up.
        throw e.getCause();
      } catch (RouteException e) {
        ...    
    }


     //请求失败的核心源码
     boolean releaseConnection = true;
      try {
        engine.sendRequest();
        engine.readResponse();
        releaseConnection = false;
      } catch (RequestException e) {
        // The attempt to interpret the request failed. Give up.
        throw e.getCause();
      } catch (RouteException e) {
        // The attempt to connect via a route failed. The request will not have been sent.
        HttpEngine retryEngine = engine.recover(e.getLastConnectException(), null);
        if (retryEngine != null) {
          releaseConnection = false;
          engine = retryEngine;
          continue;
        }
        // Give up; recovery is not possible.
        throw e.getLastConnectException();
      } catch (IOException e) {
        // An attempt to communicate with a server failed. The request may have been sent.
        HttpEngine retryEngine = engine.recover(e, null);
        if (retryEngine != null) {
          releaseConnection = false;
          engine = retryEngine;
          continue;
        }

        // Give up; recovery is not possible.
        throw e;
      } finally {
        // We're throwing an unchecked exception. Release any resources.
        if (releaseConnection) {
          StreamAllocation streamAllocation = engine.close();
          streamAllocation.release();
        }
      }
     .....
      engine = new HttpEngine(client, request, false, false, forWebSocket, streamAllocation, null,
          response);
    }

  }

到这里okhttp3的源码就解析完毕了 感谢支持 希望可以帮到你们~