源码系列--OkHttp

Posted 2021-02-21 anni-qianqian

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

用法如下：（get请求）

package okhttp3.guide;

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

public class GetExample {
  OkHttpClient client = new OkHttpClient();

  String run(String url) throws IOException {
    Request request = new Request.Builder()
        .url(url)
        .build();

    try (Response response = client.newCall(request).execute()) {
      return response.body().string();
    }
  }

  public static void main(String[] args) throws IOException {
    GetExample example = new GetExample();
    String response = example.run("https://raw.github.com/square/okhttp/master/README.md");
    System.out.println(response);
  }
}

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

4.x以上的版本都大部分更新为kotlin了，可以更改分支下载3.x的版本来看

一。先来看第一步构造函数

OkHttpClient client = new OkHttpClient();

源码：

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

Builder()中就是初始化了一堆变量，没啥东西

二。来看get请求

new Request.Builder()

源码：找内部类Builder的构造函数

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

源码：接着找Headers的内部类Builder，暂时构造了一个变量，还没有做什么

三。下面是执行.url方法，当然是Request内部类Builder的url方法，url暂定为String

源码：

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));
}

前面是加前缀，后面去到HttpUrl里去

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

HttpUrl的内部类Builder的构造函数

public Builder() {
  encodedPathSegments.add(""); // The default path is ‘/‘ which needs a trailing space.
}

encodedPathSegments是一个ArrayList

HttpUrl的内部类Builder的parse方法就是一连串的参数解析，大家可以看源码

最后一个build()方法

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

这个HttpUrl的带参构造函数中也是一堆变量的初始化

回到Request内部类Builder的url方法

public Builder url(HttpUrl url) {
  if (url == null) throw new NullPointerException("url == null");
  this.url = url;
  return this;
}

接着是Request内部类Builder的build方法

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

Request的带参构造函数

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);
}

四。接下来很重要了，是执行请求

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

OkHttpClient中的newCall方法

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

进到RealCall中的newRealCall方法

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;
}

构造函数不用管，进去Transmitter中的构造函数

public Transmitter(OkHttpClient client, Call call) {
  this.client = client;
  this.connectionPool = Internal.instance.realConnectionPool(client.connectionPool());
  this.call = call;
  this.eventListener = client.eventListenerFactory().create(call);
  this.timeout.timeout(client.callTimeoutMillis(), MILLISECONDS);
}

其中这个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RealCall的execute方法了，注意RealCall里有个内部类AsyncCall也有execute方法，注意不要搞混了

@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);
  }
}

client.dispatcher().executed(this)执行的是

synchronized void executed(RealCall call) {
    runningSyncCalls.add(call);
  }

runningSyncCalls就是我们上面提到的Deque双端队列

下面就是最最核心的getResponseWithInterceptorChain方法

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);
    }
  }
}

RetryAndFollowUpInterceptor重试和跳转拦截器

BridgeInterceptor桥接拦截器，即加请求头和去响应头

CacheInterceptor缓存拦截器

ConnectInterceptor连接拦截器

CallServerInterceptor调用服务拦截器

List添加好全部Interceptor之后，执行chain.proceed(originalRequest)来到RealInterceptorChain中的proceed方法

public Response proceed(Request request, Transmitter transmitter, @Nullable Exchange exchange)
    throws IOException {
  if (index >= interceptors.size()) throw new AssertionError();

  calls++;

  // If we already have a stream, confirm that the incoming request will use it.
  if (this.exchange != null && !this.exchange.connection().supportsUrl(request.url())) {
    throw new IllegalStateException("network interceptor " + interceptors.get(index - 1)
        + " must retain the same host and port");
  }

  // If we already have a stream, confirm that this is the only call to chain.proceed().
  if (this.exchange != null && calls > 1) {
    throw new IllegalStateException("network interceptor " + interceptors.get(index - 1)
        + " must call proceed() exactly once");
  }

  // Call the next interceptor in the chain.
  RealInterceptorChain next = new RealInterceptorChain(interceptors, transmitter, exchange,
      index + 1, request, call, connectTimeout, readTimeout, writeTimeout);
  Interceptor interceptor = interceptors.get(index);
  Response response = interceptor.intercept(next);

  // Confirm that the next interceptor made its required call to chain.proceed().
  if (exchange != null && index + 1 < interceptors.size() && next.calls != 1) {
    throw new IllegalStateException("network interceptor " + interceptor
        + " must call proceed() exactly once");
  }

  // Confirm that the intercepted response isn‘t null.
  if (response == null) {
    throw new NullPointerException("interceptor " + interceptor + " returned null");
  }

  if (response.body() == null) {
    throw new IllegalStateException(
        "interceptor " + interceptor + " returned a response with no body");
  }

  return response;
}

Interceptor interceptor = interceptors.get(index);
Response response = interceptor.intercept(next);

一开始传入的index为0，就是从第一个拦截器开始执行每个拦截器的intercept方法，index逐次+1

每个拦截器里都调用chain.proceed，这样所有的拦截器就形成链条。这里每个拦截器的作用就不讲了

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