okHttp3总结

本文主要是介绍okHttp3总结，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

1 okhttp3总体流程

下图摘抄自网络
在这里插入图片描述

图1.1 okHttp3总体流程图

2 Request、Response、Call基本概念

Request
request主要是对url，请求方法，请求参数，请求头等参数进行初始化，是通过Builder模式进行初始化
Response
请求返回给用户的一些参数，如协议，响应码，信息，返回数据等。
Call
Call是一个接口，它的实现类是RealCall。RealCall是final类型，是不可被继承的。RealCall主要作用是发送请求、建立拦截器和异步回调。请求方式有同步请求execute和异步请求enqueue。

2.1 OkHttp3总体流程解析

初始化OkHttpClient对象，可以直接new一个对象，也可以通过Builder方法来build一个对象
初始化一个Request对象，Request类主要是对url、请求参数、请求头以及请求方法进行初始化
通过okHttpClient.newCall来初始化一个Call对象，newCall方法有个Request参数，该参数是上一步初始化的Request对象
然后通过初始化的call对象调用异步请求方法enqueue()或者同步请求方法execute()，如果call调用的是异步请求方法enqueue()，则会调用Dispatcher类的enqueue(AsyncCall)方法，最终会执行AsyncCall的execute()方法。
同步方法enquene()和异步方法execute()最终都会调用getResponseWithInspectorChain()方法，该方法会初始化几个拦截器，利用拦截器分层实现缓存、透明压缩、网络 IO 等功能。
最后通过Response返回请求的结果信息。

2.2 流程源码

初始化OkHttpClient对象，可以直接new一个对象，也可以通过Builder方法来build一个对象

  private OkHttpClient(Builder builder) {this.dispatcher = builder.dispatcher;this.proxy = builder.proxy;this.protocols = builder.protocols;this.connectionSpecs = builder.connectionSpecs;this.interceptors = Util.immutableList(builder.interceptors);this.networkInterceptors = Util.immutableList(builder.networkInterceptors);this.proxySelector = builder.proxySelector;this.cookieJar = builder.cookieJar;this.cache = builder.cache;this.internalCache = builder.internalCache;this.socketFactory = builder.socketFactory;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;this.certificatePinner = builder.certificatePinner.withCertificateChainCleaner(certificateChainCleaner);this.proxyAuthenticator = builder.proxyAuthenticator;this.authenticator = builder.authenticator;this.connectionPool = builder.connectionPool;this.dns = builder.dns;this.followSslRedirects = builder.followSslRedirects;this.followRedirects = builder.followRedirects;this.retryOnConnectionFailure = builder.retryOnConnectionFailure;this.connectTimeout = builder.connectTimeout;this.readTimeout = builder.readTimeout;this.writeTimeout = builder.writeTimeout;}

    public OkHttpClient build() {return new OkHttpClient(this);}

初始化一个Request对象，Request类主要是对url、请求参数、请求头以及请求方法进行初始化

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

通过okHttpClient.newCall来初始化一个Call对象，newCall方法有个Request参数，该参数是上一步初始化的Request对象。执行newCall时会初始化一个RealCall对象，该对象实现了call接口。

  @Override public Call newCall(Request request) {return new RealCall(this, request);}

然后通过初始化的call对象调用异步请求方法enqueue()或者同步请求方法execute()。
（1）如果call调用的是异步请求方法enqueue()，则会调用Dispatcher类的enqueue(AsyncCall)方法，最终会执行AsyncCall的execute()方法。

//RealCall的enqueue方法void enqueue(Callback responseCallback, boolean forWebSocket) {synchronized (this) {if (executed) throw new IllegalStateException("Already Executed");executed = true;}client.dispatcher().enqueue(new AsyncCall(responseCallback, forWebSocket));}//Dispatcher方法的enqueue方法synchronized void enqueue(AsyncCall call) {if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {runningAsyncCalls.add(call);//executorService()返回的是ExecutorService对象，该对象用的是线程池ThreadPoolExecutor进行初始化executorService().execute(call);} else {readyAsyncCalls.add(call);}}//AsyncCall的execute方法@Override protected void execute() {boolean signalledCallback = false;try {Response response = getResponseWithInterceptorChain(forWebSocket);if (canceled) {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 {responseCallback.onFailure(RealCall.this, e);}} finally {client.dispatcher().finished(this);}}}

（2）使用call调用同步方法execute

@Override protected void execute() {boolean signalledCallback = false;try {Response response = getResponseWithInterceptorChain(forWebSocket);if (canceled) {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 {responseCallback.onFailure(RealCall.this, e);}} finally {client.dispatcher().finished(this);}}

由上可得，不管同步还是异步，最终都会调用getResponseWithInterceptorChain(forWebSocket);方法。该方法会初始化几个拦截器，利用拦截器分层实现缓存、透明压缩、网络 IO 等功能。

private 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 (!retryAndFollowUpInterceptor.isForWebSocket()) {interceptors.addAll(client.networkInterceptors());}interceptors.add(new CallServerInterceptor(retryAndFollowUpInterceptor.isForWebSocket()));Interceptor.Chain chain = new RealInterceptorChain(interceptors, null, null, null, 0, originalRequest);return chain.proceed(originalRequest);
}

在配置 OkHttpClient 时设置的 interceptors；
负责失败重试以及重定向的 RetryAndFollowUpInterceptor；
负责把用户构造的请求转换为发送到服务器的请求、把服务器返回的响应转
为用户友好的响应的 BridgeInterceptor；
负责读取缓存直接返回、更新缓存的 CacheInterceptor；
负责和服务器建立连接的 ConnectInterceptor；
配置 OkHttpClient 时设置的 networkInterceptors；
负责向服务器发送请求数据、从服务器读取响应数据的CallServerInterceptor。

最后通过Response返回请求的结果信息。

  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);}