okhttp之RealCall.execute()流程介绍

103style

发布于 2022-12-19 13:39:56

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文章被收录于专栏：Android开发经验分享Android开发经验分享

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base on 3.12.0

前言

前面我们对 OkHttpClient 和 Request 做了相关的介绍。

此时我们已经构建了 http客户端 和 http请求，接下来就好通过 http客户端 来执行http请求。即先通过OkHttpClient.newCall(Request)构建RealCall，然后通过 RealCall.execute() 来执行请求。

OkHttpClient.newCall(Request)

通过下面的源码我们知道 OkHttpClient 的 newCall 方法即通过 RealCall.newRealCall()构建了一个RealCall实例，将 OkHttpClient 和 Request 赋值给实例的成员变量. 以及初始化了拦截器 RetryAndFollowUpInterceptor.

//OkHttpClient
public Call newCall(Request request) {
    return RealCall.newRealCall(this, request, false );
}
//RealCall
private RealCall(OkHttpClient client, Request originalRequest, boolean forWebSocket) {
    this.client = client;
    this.originalRequest = originalRequest;
    this.forWebSocket = forWebSocket;
    this.retryAndFollowUpInterceptor = new RetryAndFollowUpInterceptor(client, forWebSocket);
    this.timeout = new AsyncTimeout() {
        @Override protected void timedOut() {
            cancel();
        }
    };
    this.timeout.timeout(client.callTimeoutMillis(), MILLISECONDS);
}
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;
}

RealCall.execute()

public Response execute() throws IOException {
    ...
    try {
        client.dispatcher().executed(this);
        Response result = getResponseWithInterceptorChain();
        ...
    } catch (IOException e) {
        ...
    } finally {
        client.dispatcher().finished(this);
    }
}

通过上面的代码我们知道是通过getResponseWithInterceptorChain();获取到请求的结果。

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);
}

getResponseWithInterceptorChain中依次添加了以下的拦截器，后面会具体介绍：

client.interceptors()：我们通过OkhttpClient添加的自定义拦截器
retryAndFollowUpInterceptor：重试及重定向拦截器
BridgeInterceptor：桥接拦截器
CacheInterceptor：缓存拦截器
ConnectInterceptor：连接拦截器
client.networkInterceptors()：网络请求的拦截器
CallServerInterceptor：读写拦截器

然后将 request请求 和 interceptors这个拦截器集合构建了一个 RealInterceptorChain. 然后通过RealInterceptorChain.proceed(originalRequest);返回请求结果。

RealInterceptorChain.proceed(request)

public Response proceed(...) throws IOException {
    if (index >= interceptors.size()) throw new AssertionError();
    calls++;
    ...
    RealInterceptorChain next = new RealInterceptorChain(interceptors, streamAllocation, httpCodec,
            connection, index + 1, request, call, eventListener, connectTimeout, readTimeout,
            writeTimeout);
    Interceptor interceptor = interceptors.get(index);
    Response response = interceptor.intercept(next);
    ...
    return response;
}

我们可以看到这里通过interceptor.intercept(next);获取的请求结果。我们先以RetryAndFollowUpInterceptor来介绍下。

public Response intercept(Chain chain) throws IOException {
    RealInterceptorChain realChain = (RealInterceptorChain) chain;
    ...
    response = realChain.proceed(request, streamAllocation, null, null);
    ...
}

看到上面代码中的realChain.proceed(...);方法，是不是又回到了上面的RealInterceptorChain.proceed(request).

所以由此可知RealInterceptorChain.proceed(request)会 “依次” 去调用拦截器列表每个interceptors中的interceptor.intercept(next)，如下图：