Hello World

OkHttp源码分析

需要了解以下三点

1.OkHttp请求流程
2.网络请求缓存处理
3.连接池

OkHttp请求get的步骤

OkHttpClient client=new OkHtppClient();
Request request=new Request.Builder()
				.url(url)
				.build();
Response responde=client.newCall(request).execute();

新建OkHttpClient客户端

OkHttpClient client = new OkHttpClient();

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

OkHttpClient(Builder builder) {
    ....
}

::可以看到，OkHttpClient使用了建造者模式，builder里面的可配置参数如下::

public static final class Builder {
    Dispatcher dispatcher;// 分发器
    @Nullable Proxy proxy;
    List<Protocol> protocols;
    List<ConnectionSpec> connectionSpecs;// 传输层版本和连接协议
    final List<Interceptor> interceptors = new ArrayList<>();// 拦截器
    final List<Interceptor> networkInterceptors = new ArrayList<>();
    EventListener.Factory eventListenerFactory;
    ProxySelector proxySelector;
    CookieJar cookieJar;
    @Nullable Cache cache;
    @Nullable InternalCache internalCache;// 内部缓存
    SocketFactory socketFactory;
    @Nullable SSLSocketFactory sslSocketFactory;// 安全套接层socket 工厂，用于HTTPS
    @Nullable CertificateChainCleaner certificateChainCleaner;// 验证确认响应证书 适用 HTTPS 请求连接的主机名。
    HostnameVerifier hostnameVerifier;// 验证确认响应证书 适用 HTTPS 请求连接的主机名。  
    CertificatePinner certificatePinner;// 证书锁定，使用CertificatePinner来约束哪些认证机构被信任。
    Authenticator proxyAuthenticator;// 代理身份验证
    Authenticator authenticator;// 身份验证
    ConnectionPool connectionPool;// 连接池
    Dns dns;
    boolean followSslRedirects; // 安全套接层重定向
    boolean followRedirects;// 本地重定向
    boolean retryOnConnectionFailure;// 重试连接失败
    int callTimeout;
    int connectTimeout;
    int readTimeout;
    int writeTimeout;
    int pingInterval;

    // 这里是默认配置的构建参数
    public Builder() {
        dispatcher = new Dispatcher();
        protocols = DEFAULT_PROTOCOLS;
        connectionSpecs = DEFAULT_CONNECTION_SPECS;
        ...
    }

    // 这里传入自己配置的构建参数
    Builder(OkHttpClient okHttpClient) {
        this.dispatcher = okHttpClient.dispatcher;
        this.proxy = okHttpClient.proxy;
        this.protocols = okHttpClient.protocols;
        this.connectionSpecs = okHttpClient.connectionSpecs;
        this.interceptors.addAll(okHttpClient.interceptors);
        this.networkInterceptors.addAll(okHttpClient.networkInterceptors);
        ...
    }
## 2.同步请求流程
Response response = client.newCall(request).execute();

/**
* Prepares the {@code request} to be executed at   some point in the future.
*/
@Override public Call newCall(Request request) {
    return RealCall.newRealCall(this, request, false /* for web socket */);
}

// RealCall为真正的请求执行者
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;
}

@Override public Response execute() throws IOException {
    synchronized (this) {
        // 每个Call只能执行一次
        if (executed) throw new IllegalStateException("Already Executed");
        executed = true;
    }
    captureCallStackTrace();
    timeout.enter();
    eventListener.callStart(this);
    try {
        // 通知dispatcher已经进入执行状态
        client.dispatcher().executed(this);
        // 通过一系列的拦截器请求处理和响应处理得到最终的返回结果
        Response result = getResponseWithInterceptorChain();
        if (result == null) throw new IOException("Canceled");
        return result;
    } catch (IOException e) {
        e = timeoutExit(e);
        eventListener.callFailed(this, e);
        throw e;
    } finally {
        // 通知 dispatcher 自己已经执行完毕
        client.dispatcher().finished(this);
    }
}

Response getResponseWithInterceptorChain() throws IOException {
    // Build a full stack of interceptors.
    List<Interceptor> interceptors = new ArrayList<>();
    // 在配置 OkHttpClient 时设置的 interceptors；
    interceptors.addAll(client.interceptors());
    // 负责失败重试以及重定向
    interceptors.add(retryAndFollowUpInterceptor);
    // 请求时，对必要的Header进行一些添加，接受响应时，移除必要的Header
    interceptors.add(new BridgeInterceptor(client.cookieJar()));
    // 负责读取缓存直接返回、更新缓存
    interceptors.add(new CacheInterceptor(client.internalCache()));
    // 负责和服务器建立连接
    interceptors.add(new ConnectInterceptor(client));
    if (!forWebSocket) {
        // 配置 OkHttpClient 时设置的 networkInterceptors
        interceptors.addAll(client.networkInterceptors());
    }
    // 负责向服务器发送请求数据、从服务器读取响应数据
    interceptors.add(new CallServerInterceptor(forWebSocket));

    Interceptor.Chain chain = new RealInterceptorChain(interceptors, null, null, null, 0,
        originalRequest, this, eventListener, client.connectTimeoutMillis(),
        client.readTimeoutMillis(), client.writeTimeoutMillis());

    // 使用责任链模式开启链式调用
    return chain.proceed(originalRequest);
}

// StreamAllocation 对象，它相当于一个管理类，维护了服务器连接、并发流
// 和请求之间的关系，该类还会初始化一个 Socket 连接对象，获取输入/输出流对象。
public Response proceed(Request request, StreamAllocation streamAllocation, HttpCodec httpCodec,
  RealConnection connection) throws IOException {
    ...

    // Call the next interceptor in the chain.
    // 实例化下一个拦截器对应的RealIterceptorChain对象
    RealInterceptorChain next = new RealInterceptorChain(interceptors, streamAllocation, httpCodec,
        connection, index + 1, request, call, eventListener, connectTimeout, readTimeout,
        writeTimeout);
    // 得到当前的拦截器
    Interceptor interceptor = interceptors.get(index);
    // 调用当前拦截器的intercept()方法，并将下一个拦截器的RealIterceptorChain对象传递下去,最后得到响应
    Response response = interceptor.intercept(next);

    ...

    return response;
}