OkHttp官网地址：https://square.github.io/okhttp/

前面讲到了get请求，下面我们来看看post请求

package okhttp3.guide;

import java.io.IOException;
import okhttp3.MediaType;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.RequestBody;
import okhttp3.Response;

public class PostExample {
  public static final MediaType JSON = MediaType.get("application/json; charset=utf-8");

  OkHttpClient client = new OkHttpClient();

  String post(String url, String json) throws IOException {
    RequestBody body = RequestBody.create(json, JSON);
    Request request = new Request.Builder()
        .url(url)
        .post(body)
        .build();
    try (Response response = client.newCall(request).execute()) {
      return response.body().string();
    }
  }

  String bowlingJson(String player1, String player2) {
    return "{'winCondition':'HIGH_SCORE',"
        + "'name':'Bowling',"
        + "'round':4,"
        + "'lastSaved':1367702411696,"
        + "'dateStarted':1367702378785,"
        + "'players':["
        + "{'name':'" + player1 + "','history':[10,8,6,7,8],'color':-13388315,'total':39},"
        + "{'name':'" + player2 + "','history':[6,10,5,10,10],'color':-48060,'total':41}"
        + "]}";
  }

  public static void main(String[] args) throws IOException {
    PostExample example = new PostExample();
    String json = example.bowlingJson("Jesse", "Jake");
    String response = example.post("http://www.roundsapp.com/post", json);
    System.out.println(response);
  }
}

Github下载源码地址https://github.com/square/okhttp

第一步。构造函数

OkHttpClient client = new OkHttpClient();

源码：

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

Builder()方法里是一堆变量和对象的初始化

第二步。构造请求body

RequestBody body = RequestBody.create(json, JSON);

RequestBody类中有多个重载方法create，我们来看第二个参数为string的方法

public static RequestBody create(@Nullable MediaType contentType, String content) {
  Charset charset = UTF_8;
  if (contentType != null) {
    charset = contentType.charset();
    if (charset == null) {
      charset = UTF_8;
      contentType = MediaType.parse(contentType + "; charset=utf-8");
    }
  }
  byte[] bytes = content.getBytes(charset);
  return create(contentType, bytes);
}

前面就是设置字符类型，然后把String转为字节数组了，最后调用了另外一个create方法

第二个create方法又调用了第三个create方法，好吧，源码的日常操作

public static RequestBody create(final @Nullable MediaType contentType, final byte[] content,
    final int offset, final int byteCount) {
  if (content == null) throw new NullPointerException("content == null");
  Util.checkOffsetAndCount(content.length, offset, byteCount);
  return new RequestBody() {
    @Override public @Nullable MediaType contentType() {
      return contentType;
    }

    @Override public long contentLength() {
      return byteCount;
    }

    @Override public void writeTo(BufferedSink sink) throws IOException {
      sink.write(content, offset, byteCount);
    }
  };
}

最后return一个RequestBody，还重写了三个内部方法。BufferedSink百度了下是Okio里的一个缓存字符串，就是把构造的json字符串存到一个缓存中去，后面再用

第三步。构造请求

Request request = new Request.Builder()
      .url(url)
      .post(body)
      .build();

1）Request的内部类Builder

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

默认是GET请求方式，后面会修正；第二初始化了一个Headers的内部类Builder，没有做什么实质的操作

2）Request的内部类Builder的url方法

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);
  }

  return url(HttpUrl.get(url));
}

进到HttpUrl类中

public static HttpUrl get(String url) {
  return new Builder().parse(null, url).build();
}

这里面Builder()里面有个ArrayList：encodedPathSegments；parse（）方法里面是一系列参数解析；build（）方法如下

public HttpUrl build() {
  if (scheme == null) throw new IllegalStateException("scheme == null");
  if (host == null) throw new IllegalStateException("host == null");
  return new HttpUrl(this);
}

HttpUrl的构造函数里面是一些对象和变量的初始化

3）Request的内部类Builder的post方法

public Builder post(RequestBody body) {
  return method("POST", body);
}

前面的请求方式默认是GET，这里修改为了POST

public Builder method(String method, @Nullable RequestBody body) {
  if (method == null) throw new NullPointerException("method == null");
  if (method.length() == 0) throw new IllegalArgumentException("method.length() == 0");
  if (body != null && !HttpMethod.permitsRequestBody(method)) {
    throw new IllegalArgumentException("method " + method + " must not have a request body.");
  }
  if (body == null && HttpMethod.requiresRequestBody(method)) {
    throw new IllegalArgumentException("method " + method + " must have a request body.");
  }
  this.method = method;
  this.body = body;
  return this;
}

前面4个if全是异常判断，后面是method和body赋值

4）Request的内部类Builder的post方法

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

Requst的构造函数

Request(Builder builder) {
  this.url = builder.url;
  this.method = builder.method;
  this.headers = builder.headers.build();
  this.body = builder.body;
  this.tags = Util.immutableMap(builder.tags);
}

第四步：

Response response = client.newCall(request).execute()

OkHttpClient的newCall方法

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

进到RealCall类中

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.transmitter = new Transmitter(client, call);
  return call;
}

Transmitter构造函数中有个这个Internal.instance.realConnectionPool(client.connectionPool())可以找到OkHttpClient的static代码块执行后返回了一个RealConnectionPool

private static final Executor executor = new ThreadPoolExecutor(0 /* corePoolSize */,
    Integer.MAX_VALUE /* maximumPoolSize */, 60L /* keepAliveTime */, TimeUnit.SECONDS,
    new SynchronousQueue<>(), Util.threadFactory("OkHttp ConnectionPool", true));

RealConnectionPool一看就知道是0个核心线程，最大值个非核心线程的线程池；这里还出现了一个Deque双端队列，即队列的升级版，两个端口都可以进出元素，更加灵活

最后就是执行请求execute方法，实际执行的是RealCall的execute方法

@Override public Response execute() throws IOException {
  synchronized (this) {
    if (executed) throw new IllegalStateException("Already Executed");
    executed = true;
  }
  transmitter.timeoutEnter();
  transmitter.callStart();
  try {
    client.dispatcher().executed(this);
    return getResponseWithInterceptorChain();
  } finally {
    client.dispatcher().finished(this);
  }
}

下面就是其他博客常说的链式拦截器

Response getResponseWithInterceptorChain() throws IOException {
  // Build a full stack of interceptors.
  List<Interceptor> interceptors = new ArrayList<>();
  interceptors.addAll(client.interceptors());
  interceptors.add(new RetryAndFollowUpInterceptor(client));
  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, transmitter, null, 0,
      originalRequest, this, client.connectTimeoutMillis(),
      client.readTimeoutMillis(), client.writeTimeoutMillis());

  boolean calledNoMoreExchanges = false;
  try {
    Response response = chain.proceed(originalRequest);
    if (transmitter.isCanceled()) {
      closeQuietly(response);
      throw new IOException("Canceled");
    }
    return response;
  } catch (IOException e) {
    calledNoMoreExchanges = true;
    throw transmitter.noMoreExchanges(e);
  } finally {
    if (!calledNoMoreExchanges) {
      transmitter.noMoreExchanges(null);
    }
  }
}

每个拦截器里都调用chain.proceed，这样所有的拦截器就形成链条

五。另外，还有个异步请求

private final OkHttpClient client = new OkHttpClient();

public void run() throws Exception {
  Request request = new Request.Builder()
      .url("http://publicobject.com/helloworld.txt")
      .build();

  client.newCall(request).enqueue(new Callback() {
    @Override public void onFailure(Call call, IOException e) {
      e.printStackTrace();
    }

    @Override public void onResponse(Call call, Response response) throws IOException {
      try (ResponseBody responseBody = response.body()) {
        if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);

        Headers responseHeaders = response.headers();
        for (int i = 0, size = responseHeaders.size(); i < size; i++) {
          System.out.println(responseHeaders.name(i) + ": " + responseHeaders.value(i));
        }

        System.out.println(responseBody.string());
      }
    }
  });
}

RealCall的enqueue方法

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

client.dispatcher().enqueue(new AsyncCall(responseCallback))

进到Dispatcher类的enqueue方法

void enqueue(AsyncCall call) {
  synchronized (this) {
    readyAsyncCalls.add(call);

    // Mutate the AsyncCall so that it shares the AtomicInteger of an existing running call to
    // the same host.
    if (!call.get().forWebSocket) {
      AsyncCall existingCall = findExistingCallWithHost(call.host());
      if (existingCall != null) call.reuseCallsPerHostFrom(existingCall);
    }
  }
  promoteAndExecute();
}

readyAsyncCalls是一个Deque双端队列

@Nullable private AsyncCall findExistingCallWithHost(String host) {
  for (AsyncCall existingCall : runningAsyncCalls) {
    if (existingCall.host().equals(host)) return existingCall;
  }
  for (AsyncCall existingCall : readyAsyncCalls) {
    if (existingCall.host().equals(host)) return existingCall;
  }
  return null;
}

最后的promoteAndExecute方法里有行代码

asyncCall.executeOn(executorService())

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

executorService也是一个核心线程为0个，非核心线程为最大个数的线程池

最后进到RealCall的内部类AsyncCall的executeOn方法

void executeOn(ExecutorService executorService) {
  assert (!Thread.holdsLock(client.dispatcher()));
  boolean success = false;
  try {
    executorService.execute(this);
    success = true;
  } catch (RejectedExecutionException e) {
    InterruptedIOException ioException = new InterruptedIOException("executor rejected");
    ioException.initCause(e);
    transmitter.noMoreExchanges(ioException);
    responseCallback.onFailure(RealCall.this, ioException);
  } finally {
    if (!success) {
      client.dispatcher().finished(this); // This call is no longer running!
    }
  }
}

主要就是executorService.execute方法

可以看出GET请求和POST请求还是差不多的，关键的就是各个拦截器里面的实现了

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