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