给HttpClient添加Socks代理

本文描述http client使用socks代理过程中需要注意的几个方面：1，socks5支持用户密码授权；2，支持https；3，支持让代理服务器解析DNS；

使用代理创建Socket

从原理上来看，不管用什么http客户端（httpclient，okhttp），最终都要转换到java.net.Socket的创建上去，看到代码：
package java.net;
 public Socket(Proxy proxy) {
    ...
 }

这是JDK中对网络请求使用Socks代理的入口方法。（http代理是在http协议层之上的，不在此文讨论范围之内）。
HttpClient要实现socks代理，就需要塞进去一个Proxy对象，也就是定制两个类：org.apache.http.conn.ssl.SSLConnectionSocketFactory 和org.apache.http.conn.socket.PlainConnectionSocketFactory，分别对应https和http。
 代码如下：
    private class SocksSSLConnectionSocketFactory extends SSLConnectionSocketFactory {

public SocksSSLConnectionSocketFactory(SSLContext sslContext, HostnameVerifier hostnameVerifier) {
            super(sslContext, hostnameVerifier);
        }

@Override
        public Socket createSocket(HttpContext context) throws IOException {
            ProxyConfig proxyConfig = (ProxyConfig) context.getAttribute(ProxyConfigKey);
            if (proxyConfig != null) {//需要代理
                return new Socket(proxyConfig.getProxy());
            } else {
                return super.createSocket(context);
            }
        }

@Override
        public Socket connectSocket(int connectTimeout, Socket socket, HttpHost host, InetSocketAddress remoteAddress,
                                    InetSocketAddress localAddress, HttpContext context) throws IOException {
            ProxyConfig proxyConfig = (ProxyConfig) context.getAttribute(ProxyConfigKey);
            if (proxyConfig != null) {//make proxy server to resolve host in http url
                remoteAddress = InetSocketAddress
                        .createUnresolved(host.getHostName(), host.getPort());
            }
            return super.connectSocket(connectTimeout, socket, host, remoteAddress, localAddress, context);
        }
    }

和
    private class SocksSSLConnectionSocketFactory extends SSLConnectionSocketFactory {

public SocksSSLConnectionSocketFactory(SSLContext sslContext, HostnameVerifier hostnameVerifier) {
            super(sslContext, hostnameVerifier);
        }

@Override
        public Socket createSocket(HttpContext context) throws IOException {
            ProxyConfig proxyConfig = (ProxyConfig) context.getAttribute(ProxyConfigKey);
            if (proxyConfig != null) {
                return new Socket(proxyConfig.getProxy());
            } else {
                return super.createSocket(context);
            }
        }

@Override
        public Socket connectSocket(int connectTimeout, Socket socket, HttpHost host, InetSocketAddress remoteAddress,
                                    InetSocketAddress localAddress, HttpContext context) throws IOException {
            ProxyConfig proxyConfig = (ProxyConfig) context.getAttribute(ProxyConfigKey);
            if (proxyConfig != null) {//make proxy server to resolve host in http url
                remoteAddress = InetSocketAddress
                        .createUnresolved(host.getHostName(), host.getPort());
            }
            return super.connectSocket(connectTimeout, socket, host, remoteAddress, localAddress, context);
        }
    }

然后在创建httpclient对象时，给HttpClientConnectionManager设置socketFactoryRegistry
            Registry<ConnectionSocketFactory> socketFactoryRegistry = RegistryBuilder.<ConnectionSocketFactory>create()
                .register(Protocol.HTTP.toString(), new SocksConnectionSocketFactory())
                .register(Protocol.HTTPS.toString(), new SocksSSLConnectionSocketFactory(sslContext, NoopHostnameVerifier.INSTANCE))
                .build();

PoolingHttpClientConnectionManager connectionManager = new PoolingHttpClientConnectionManager(socketFactoryRegistry);
   

让代理服务器解析域名