OKHTTP简单使用总结

概述

OkHttp是一个高效的HTTP客户端，它具有特性：

允许所有同一个主机地址的请求共享同一个socket连接
使用连接池减少请求延时
透明的GZIP压缩减少响应数据的大小
缓存响应内容，避免一些完全重复的请求

请求主要处理类及UML见下图:

先了解下使用姿势，发送同步网络请求：

OkHttpClient client = new OkHttpClient();
Request request = new Request.Builder().url(Constants.TEST_URL).build();
try {
    Response response = client.newCall(request).execute();
    if (response.isSuccessful()) {
        System.out.println(response.body().string());
    } else {
        System.out.println("网络异常");
    }
} catch (IOException e) {
    e.printStackTrace();
}

发送异步网络请求：

OkHttpClient client = new OkHttpClient();
Request request = new Request.Builder().url(Constants.TEST_URL).build();
client.newCall(request).enqueue(new Callback() {
    @Override
    public void onFailure(Call call, IOException e) {
        System.out.println("网络异常");
    }

    @Override
    public void onResponse(Call call, Response response) throws IOException {
        if (response.isSuccessful()) {
            System.out.println(response.body().string());
        } else {
            System.out.println("网络异常");
        }

    }
});

OkHttpClient 构建

OkHttpClient 实例构建使用建造者模式，方便定制自己的网络请求工具

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

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;

    ......

}

Dispatcher网络请求执行策略

主要成员变量：

// 最大支持同时请求数
private int maxRequests = 64;
// 单个域名最大请求数
private int maxRequestsPerHost = 5;

// 请求线程池
private ExecutorService executorService;

// 等待执行的异步请求
private final Deque<AsyncCall> readyAsyncCalls = new ArrayDeque<>();

// 正在执行的异步请求
private final Deque<AsyncCall> runningAsyncCalls = new ArrayDeque<>();

// 正在执行的同步请求
private final Deque<RealCall> runningSyncCalls = new ArrayDeque<>();

例：更改同时支持最大请求数和单个域名同时最大请求数：

Dispatcher dispatcher = new Dispatcher();
dispatcher.setMaxRequests(20);
dispatcher.setMaxRequestsPerHost(3);
httpClient = new OkHttpClient.Builder()
        .dispatcher(dispatcher)
        .build();

Protocol 默认支持的请求协议

Protocol.HTTP_2
Protocol.SPDY_3 
Protocol.HTTP_1_1

ConnectionPool Socket链接池

// 最大缓存socket链接个数，默认5
private final int maxIdleConnections;
// 空闲回收时间，默认 5分钟
private final long keepAliveDurationNs;
// 缓存socket链接
private final Deque<RealConnection> connections = new ArrayDeque<>();
// 用于网络请求异常时自动切换请求ip
final RouteDatabase routeDatabase = new RouteDatabase();