相对于httpurlconnection ，httpclient更加丰富，也更加强大，其中apache有两个项目都是httpclient，一个是commonts包下的，这个是通用的，更专业的是org.apache.http.包下的，所以我一般用后者；

httpclient可以处理长连接，保存会话，重连接，以及请求过滤器，连接重用等等...

下面是测试代码（全部总结来自官方文档，以及翻译）

须要下载核心包：httpclient-4.3.4.jar ，也可在官网下载：http://hc.apache.org/downloads.cgi

/**
	 * HTTP认证：
	 * 
	 * HTTPclient支持http标准认证，也支持其他认证，如NTLM和SPNEGO。
	 */
	private static void test17(){
		
		//最简单的明文用户名 密码认证。
		UsernamePasswordCredentials creds = new UsernamePasswordCredentials("user", "pwd");
		System.out.println(creds.getUserPrincipal().getName());
		System.out.println(creds.getPassword());
		
		/**
		 * NTCredentials是微软的windows系统使用的一种凭据，包含username、password，还包括一系列其他的属性，
		 * 比如用户所在的域名。在Microsoft Windows的网络环境中，同一个用户可以属于不同的域，所以他也就有不同的凭据。
		 * workstation:本机的计算机名
		 */
		NTCredentials ntcreds = new NTCredentials("user", "pwd", "workstation", "domain");
		System.out.println(ntcreds.getUserPrincipal().getName());//输出   DOMAIN/user
		System.out.println(ntcreds.getPassword());
		
		
	}
	
	/**
	 * 凭证提供者（CredentialsProvider）内含一套特定的凭证，须要哪种凭证时，CredentialsProvider就能获得对应的凭证。
	 * 获取凭证的时候，可以模糊的指定主机名、端口号、realm和认证方案。
	 * CredentialsProvider会筛选出一个最佳匹配方案。
	 */
	private static void test18() {

		CredentialsProvider credsProvider = new BasicCredentialsProvider();
		
		credsProvider.setCredentials(new AuthScope("somehost",AuthScope.ANY_PORT),
									 new UsernamePasswordCredentials("u1", "p1"));
		credsProvider.setCredentials(new AuthScope("somehost", 8080),
									 new UsernamePasswordCredentials("u2", "p2"));
		credsProvider.setCredentials(new AuthScope("otherhost", 8080,AuthScope.ANY_REALM, "ntlm"), 
									 new UsernamePasswordCredentials("u3", "p3"));
		
		System.out.println(credsProvider.getCredentials(new AuthScope(
				"somehost", 80, "realm", "basic")));
		System.out.println(credsProvider.getCredentials(new AuthScope(
				"somehost", 8080, "realm", "basic")));
		System.out.println(credsProvider.getCredentials(new AuthScope(
				"otherhost", 8080, "realm", "basic")));
		System.out.println(credsProvider.getCredentials(new AuthScope(
				"otherhost", 8080, null, "ntlm")));
		
		/**
		 *   输出：
		 *  [principal: u1]
			[principal: u2]
			null
			[principal: u3]
		 */
	}
	
	
	
	private static void test19() throws ClientProtocolException, IOException {
		
//		CloseableHttpClient httpclient = HttpClients.createDefault();
//		HttpClientContext context = HttpClientContext.create();
//		
//		HttpHost targetHost = new HttpHost("webservice.webxml.com.cn", 80, "http");
//
//		//认证提供者
//		CredentialsProvider credsProvider = new BasicCredentialsProvider();
//		credsProvider.setCredentials(new AuthScope(targetHost.getHostName(),targetHost.getPort()),
//									 new UsernamePasswordCredentials("root", "root"));
//		
//		//基础认证缓存
//		AuthCache authCache = new BasicAuthCache();
//		
//		context.setCredentialsProvider(credsProvider);
//		context.setAuthCache(authCache);
//		
//		HttpGet httpget = new HttpGet("/WebServices/MobileCodeWS.asmx/getDatabaseInfo");
//		
//		CloseableHttpResponse response = httpclient.execute(targetHost,httpget, context);
//		
//		AuthState proxyAuthState = context.getProxyAuthState();
//		
//		System.out.println("Proxy auth state: " + proxyAuthState.getState());
//		System.out.println("Proxy auth scheme: "+ proxyAuthState.getAuthScheme());
//		System.out.println("Proxy auth credentials: "+ proxyAuthState.getCredentials());
//		AuthState targetAuthState = context.getTargetAuthState();
//		System.out.println("Target auth state: " + targetAuthState.getState());
//		System.out.println("Target auth scheme: "+ targetAuthState.getAuthScheme());
//		System.out.println("Target auth credentials: "+ targetAuthState.getCredentials());
		/**
		 * 	Proxy auth state: UNCHALLENGED
			Proxy auth scheme: null
			Proxy auth credentials: null
			Target auth state: UNCHALLENGED
			Target auth scheme: null
			Target auth credentials: null
		 */
	}
	
	
	/**
	 * HttpClientContext 设置抢先认证  和  认证提供者：
	 * 
	 * 在HTTP中，基本认证是一种用来允许Web浏览器或其他客户端程序在请求时提供以用户名和口令形式的凭证。
	 * 
	 * 一般http basic认证，首先登录服务器， 然后服务器会返回401码让客户端输入用户名和密码，客户端把用户名密码进行BASE64加密，
	 * 
	 * 最后把加密后的用户名和密码发送给服务器进行验证。 
	 * 
	 * 抢先验证则省略了前几部，直接发送BASE64位密文，进行验证，但存在风险，慎用！
	 */
	private static void test20() throws ClientProtocolException, IOException {
		
		
		HttpClientContext context = HttpClientContext.create();
		CloseableHttpClient httpclient = HttpClients.createDefault();
		//配置主机 ， 端口可随意填写
		HttpHost targetHost = new HttpHost("webservice.webxml.com.cn", 80, "http");
		//认证提供者
		CredentialsProvider credsProvider = new BasicCredentialsProvider();
		
		credsProvider.setCredentials(
				new AuthScope(targetHost.getHostName(),targetHost.getPort()), 
				new UsernamePasswordCredentials("username", "password"));
		
		AuthCache authCache = new BasicAuthCache();
		
		BasicScheme basicAuth = new BasicScheme();
		authCache.put(targetHost, basicAuth);
		
		//提前填充认证信息缓存到上下文中，这样，以这个上下文执行的方法，就会使用抢先认证。可能会出错
		context.setAuthCache(authCache);
		context.setCredentialsProvider(credsProvider);
		
		HttpGet httpget = new HttpGet("/WebServices/MobileCodeWS.asmx/getDatabaseInfo");

		CloseableHttpResponse response = httpclient.execute(targetHost,httpget, context);
		try {
			HttpEntity entity = response.getEntity();
			String result = EntityUtils.toString(entity);
			System.out.println(result);

		} finally {
			response.close();
		}
	}
	
	
	
	/**
	 * NTLM连接认证：
	 * 
	 * windows提供的一套安全、复杂的、有状态的协议。
	 * 
	 * 相比Basic和Digest认证，NTLM认证要明显需要更多的计算开销，性能影响也比较大。
	 * 
	 * 也就是说，NTLM连接一旦建立，用户的身份就会在其整个生命周期和它相关联。
	 */
	private static void test21() throws ClientProtocolException, IOException {
		
		// 确保使用同一个上下文
		HttpClientContext context = HttpClientContext.create();
		CloseableHttpClient httpclient = HttpClients.createDefault();
		
		CredentialsProvider credsProvider = new BasicCredentialsProvider();
		//构建详细nt认证信息：NTCredentials 参数1：用户名  2：密码  3：本机名 3：domain域
		credsProvider.setCredentials(new AuthScope("somehost",AuthScope.ANY_PORT) , 
									 new NTCredentials("username", "password", "myworkstation", "domain"));
		
		context.setCredentialsProvider(credsProvider);
		
		HttpHost target = new HttpHost("somehost", 80, "http");
		
		HttpGet httpget = new HttpGet("/");
		
		CloseableHttpResponse response1 = httpclient.execute(target, httpget, context);
		
		try {
			HttpEntity entity1 = response1.getEntity();
			System.out.println(EntityUtils.toString(entity1,"GB2312"));
		} finally {
			response1.close();
		}
		
		HttpPost httppost = new HttpPost("/");
		httppost.setEntity(new StringEntity("lots and lots of data"));
		CloseableHttpResponse response2 = httpclient.execute(target, httppost, context);
		try {
			HttpEntity entity2 = response2.getEntity();
		} finally {
			response2.close();
		}

	}
	
	
	

JAVA: httpclient 详解——第四章；