OKhttp源码解析---OkHttpClient创建

OkHttpC客户端是通过new OkHttpClient()创建的，我们看下里面都做了什么

首先是一些static的初始化

private static final List DEFAULT_PROTOCOLS = Util.immutableList(
      Protocol.HTTP_2, Protocol.SPDY_3, Protocol.HTTP_1_1);

  private static final List DEFAULT_CONNECTION_SPECS = Util.immutableList(
      ConnectionSpec.MODERN_TLS, ConnectionSpec.COMPATIBLE_TLS, ConnectionSpec.CLEARTEXT);

  static {
    Internal.instance = new Internal() {
      @Override public void addLenient(Headers.Builder builder, String line) {
        builder.addLenient(line);
      }

      @Override public void addLenient(Headers.Builder builder, String name, String value) {
        builder.addLenient(name, value);
      }

      @Override public void setCache(OkHttpClient.Builder builder, InternalCache internalCache) {
        builder.setInternalCache(internalCache);
      }

      @Override public boolean connectionBecameIdle(
          ConnectionPool pool, RealConnection connection) {
        return pool.connectionBecameIdle(connection);
      }

      @Override public RealConnection get(
          ConnectionPool pool, Address address, StreamAllocation streamAllocation) {
        return pool.get(address, streamAllocation);
      }

      @Override public void put(ConnectionPool pool, RealConnection connection) {
        pool.put(connection);
      }

      @Override public RouteDatabase routeDatabase(ConnectionPool connectionPool) {
        return connectionPool.routeDatabase;
      }

      @Override public StreamAllocation callEngineGetStreamAllocation(Call call) {
        return ((RealCall) call).streamAllocation();
      }

      @Override
      public void apply(ConnectionSpec tlsConfiguration, SSLSocket sslSocket, boolean isFallback) {
        tlsConfiguration.apply(sslSocket, isFallback);
      }

      @Override public HttpUrl getHttpUrlChecked(String url)
          throws MalformedURLException, UnknownHostException {
        return HttpUrl.getChecked(url);
      }

      @Override public void setCallWebSocket(Call call) {
        ((RealCall) call).setForWebSocket();
      }
    };
  }

这里主要是一些http协议和连接配置，然后是初始化了一个Internal.instance的变量，这个变量我们后面会用到。

接下来看下OkHttpClient的构造函数

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

Builder是它的内部类

public Builder() {
      dispatcher = new Dispatcher();
      protocols = DEFAULT_PROTOCOLS;
      connectionSpecs = DEFAULT_CONNECTION_SPECS;
      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;
    }

这里主要是一些变量的初始化。

Dispatcher是用来调度异步请求执行的，我们可以看下它的一些成员变量

  private int maxRequests = 64;
  private int maxRequestsPerHost = 5;
  private Runnable idleCallback;

  /** Executes calls. Created lazily. */
  private ExecutorService executorService;

  /** Ready async calls in the order they'll be run. */
  private final Deque readyAsyncCalls = new ArrayDeque<>();

  /** Running asynchronous calls. Includes canceled calls that haven't finished yet. */
  private final Deque runningAsyncCalls = new ArrayDeque<>();

  /** Running synchronous calls. Includes canceled calls that haven't finished yet. */
  private final Deque runningSyncCalls = new ArrayDeque<>();

maxRequestsPerHost说明当前连接请求地址的连接的最大数量，而maxRequests是总的最大连接数

ProxySelector是连接代理服务器，它可以它根据不同的连接使用不同的代理服务器。系统默认的ProxySelector会检测各种系统属性和URL协议，然后决定怎样连接不同的主机。

SocketFactory用来创建socket，这里也使用的默认的

OkHostnameVerifier、Authenticator和CertificatePinner是认证相关的

然后最重要的是创建了一个ConnectionPool连接池

  public ConnectionPool() {
    this(5, 5, TimeUnit.MINUTES);
  }

  public ConnectionPool(int maxIdleConnections, long keepAliveDuration, TimeUnit timeUnit) {
    this.maxIdleConnections = maxIdleConnections;
    this.keepAliveDurationNs = timeUnit.toNanos(keepAliveDuration);

    // Put a floor on the keep alive duration, otherwise cleanup will spin loop.
    if (keepAliveDuration <= 0) {
      throw new IllegalArgumentException("keepAliveDuration <= 0: " + keepAliveDuration);
    }
  }
 
  
 
  
 
  
 设置最大空闲连接数，保持连接的时间 
  
 
  
回到前面的初始化函数，最后是设置Dns，以及连接超时，读超时，写超时时间
 
  
Builder创建完成之后会用他初始化OkHttpClient
 
  
 
  
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;
  }
 
  
 这样OkHttpClient就创建完成了。