okHttp源码分析(一)

我们在项目中使用Okhttp的时候，就直接一句代码：

OkHttpClient client = new OkHttpClient.Builder() .build();

就创建了一个默认网络请求对象。我们来看OkHttpClient内部源码是怎么实现的
先看描述部分

/**
 * Factory for {@linkplain Call calls}, which can be used to send HTTP requests and read their
 * responses.
 *
 * <h3>OkHttpClients should be shared</h3>
 *
 * <p>OkHttp performs best when you create a single {@code OkHttpClient} instance and reuse it for
 * all of your HTTP calls. This is because each client holds its own connection pool and thread
 * pools. Reusing connections and threads reduces latency and saves memory. Conversely, creating a
 * client for each request wastes resources on idle pools.
 *

它是一个执行调用Call请求的工厂，用来发送Http请求和读取返回的Response
OkHttpClients是应该被共享的。

okHttpClients最好只创建一个单例对象，这样对你的所有Http请求进行复用，这是因为每个client都有自己的连接池和线程池，复用连接池和请求池能减少延迟和节省内存。相反的，对每个请求创建一个client，会浪费空闲池的资源。

我们现在项目中也是这么处理的,创建一个单例的client对象，处理所有的网络请求

private HttpClientUtil() {

        okHttpBuilder = new OkHttpClient.Builder();

        okHttpBuilder.connectTimeout(CONNECT_TIMEOUT, TimeUnit.SECONDS);
        // 添加统一的header
        okHttpBuilder.addInterceptor(new CustomInterceptor());

        retrofit = new Retrofit.Builder()
                .baseUrl(ApiClient.CHANGE_BUSINESS_SERVICE_URL)
                .client(okHttpBuilder.build())
                .addConverterFactory(GsonConverterFactory.create())
                .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                .build();

        apiService = retrofit.create(ApiService.class);
    }

    public static HttpClientUtil getInstance() {
        if (instance == null) {
            instance = new HttpClientUtil();
        }

        return instance;
    }

继续看描述部分：

<h3>Shutdown isn't necessary</h3>
 *
 * <p>The threads and connections that are held will be released automatically if they remain idle.
 * But if you are writing a application that needs to aggressively release unused resources you may
 * do so.
 *
 * <p>Shutdown the dispatcher's executor service with {@link ExecutorService#shutdown shutdown()}.
 * This will also cause future calls to the client to be rejected. <pre>   {@code
 *
 *     client.dispatcher().executorService().shutdown();
 * }</pre>
 *
 * <p>Clear the connection pool with {@link ConnectionPool#evictAll() evictAll()}. Note that the
 * connection pool's daemon thread may not exit immediately. <pre>   {@code
 *
 *     client.connectionPool().evictAll();
 * }</pre>
 *
 * <p>If your client has a cache, call {@link Cache#close close()}. Note that it is an error to
 * create calls against a cache that is closed, and doing so will cause the call to crash.
 * <pre>   {@code
 *
 *     client.cache().close();
 * }</pre>
 *
 * <p>OkHttp also uses daemon threads for HTTP/2 connections. These will exit automatically if they
 * remain idle.

关闭不是必须的。
保持空闲的线程和连接数会自动释放。
但是如果你要是在写一个应用需要积极的释放未使用的资源，你可以这么做。
用ExecutorService.shutdown()关闭线程池资源，这样也会导致

 client.dispatcher().executorService().shutdown();

用ConnectionPool的evictAll()来清除连接池，需要指出的是，连接池的守护线程不会立即退出

 client.connectionPool().evictAll();

如果你的client有缓存，调用Cache.close()来关闭它,请注意，对已经关闭的缓存创建调用，会导致崩溃

 client.cache().close();

我们接下来OkHttp中最重要的Builder类的Builder方法

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;
    }

OkHttp3 只使用 Http/1.1或者 Http/2

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