场景：运行httpClient的进程所在主机可能并不能上公网，大部分时候，也无法进行DNS解析，这时通常会出现域名无法解析的IO异常，下面介绍怎么避免在客户端解析域名。
上面有一行代码非常关键：
remoteAddress = InetSocketAddress
.createUnresolved(host.getHostName(), host.getPort());
变量host是你发起http请求的目标主机和端口信息，这里创建了一个未解析(Unresolved)的SocketAddress，在socks协议握手阶段，InetSocketAddress信息会原封不动的发送到代理服务器，由代理服务器解析出具体的IP地址。
Socks的协议描述中有个片段：
The SOCKS request is formed as follows:
+----+-----+-------+------+----------+----------+
|VER | CMD | RSV | ATYP | DST.ADDR | DST.PORT |
+----+-----+-------+------+----------+----------+
| 1 | 1 | X'00' | 1 | Variable | 2 |
+----+-----+-------+------+----------+----------+
Where:
o VER protocol version: X'05'
o CMD
o CONNECT X'01'
o BIND X'02'
o UDP ASSOCIATE X'03'
o RSV RESERVED
o ATYP address type of following address
o IP V4 address: X'01'
o DOMAINNAME: X'03'
o IP V6 address: X'04'
代码按上面方法写，协议握手发送的是ATYP=X'03'，即采用域名的地址类型。否则，HttpClient会尝试在客户端解析，然后发送ATYP=X'01'进行协商。当然，大多数时候HttpClient在解析域名的时候就挂了。
https中需要注意的问题
在使用httpclient访问https网站的时候，经常会遇到javax.net.ssl包中的异常，例如：
Caused by: javax.net.ssl.SSLException: Received fatal alert: internal_error
at sun.security.ssl.Alerts.getSSLException(Unknown Source) ~[na:1.7.0_80]
at sun.security.ssl.Alerts.getSSLException(Unknown Source) ~[na:1.7.0_80]
一般需要做几个设置：
创建不校验证书链的SSLContext
SSLContext sslContext = null;
try {
sslContext = new SSLContextBuilder().loadTrustMaterial(null, new TrustStrategy() {
@Override
public boolean isTrusted(X509Certificate[] chain, String authType)
throws CertificateException {
return true;
}
}).build();
} catch (Exception e) {
throw new com.aliyun.oss.ClientException(e.getMessage());
}
...
new SocksSSLConnectionSocketFactory(sslContext, NoopHostnameVerifier.INSTANCE)
创建不校验域名的HostnameVerifier
public class NoopHostnameVerifier implements javax.net.ssl.HostnameVerifier {
public static final NoopHostnameVerifier INSTANCE = new NoopHostnameVerifier();
@Override
public boolean verify(final String s, final SSLSession sslSession) {
return true;
}
}
如何使用用户密码授权？
java SDK中给Socks代理授权有点特殊，不是按socket来的，而是在系统层面做的全局配置。比如，可以通过下面代码设置一个全局的Authenticator：
Authenticator.setDefault(new MyAuthenticator("userName", "Password"));
...
class MyAuthenticator extends java.net.Authenticator {
private String user ;
private String password ;
public MyAuthenticator(String user, String password) {
this.user = user;
this.password = password;
}
protected PasswordAuthentication getPasswordAuthentication() {
return new PasswordAuthentication(user, password.toCharArray());
}
}