Java模拟post提交表单数据

 package test;

 import java.io.BufferedReader;
 import java.io.DataOutputStream;
 import java.io.IOException;
 import java.io.InputStreamReader;
 import java.net.HttpURLConnection;
 import java.net.URL;
 import java.net.URLEncoder;  

 public class HttpInvoker {  

     public static final String GET_URL = " http://localhost:8080/welcome1 ";  

     public static final String POST_URL = " http://www.court.gov.cn/zgcpwsw/List/ListContent ";  

     public static void readContentFromGet() throws IOException {
         // 拼凑get请求的URL字串，使用URLEncoder.encode对特殊和不可见字符进行编码
         String getURL = GET_URL + " ?username= "
                 + URLEncoder.encode(" fat man ", " utf-8 ");
         URL getUrl = new URL(getURL);
         // 根据拼凑的URL，打开连接，URL.openConnection函数会根据 URL的类型，
         // 返回不同的URLConnection子类的对象，这里URL是一个http，因此实际返回的是HttpURLConnection
         HttpURLConnection connection = (HttpURLConnection) getUrl
                 .openConnection();
         // 进行连接，但是实际上get request要在下一句的 connection.getInputStream()函数中才会真正发到
         // 服务器
         connection.connect();
         // 取得输入流，并使用Reader读取
         BufferedReader reader = new BufferedReader(new InputStreamReader(
                 connection.getInputStream()));
         System.out.println(" ============================= ");
         System.out.println(" Contents of get request ");
         System.out.println(" ============================= ");
         String lines;
         while ((lines = reader.readLine()) != null) {
             System.out.println(lines);
         }
         reader.close();
         // 断开连接
         connection.disconnect();
         System.out.println(" ============================= ");
         System.out.println(" Contents of get request ends ");
         System.out.println(" ============================= ");
     }  

     public static void readContentFromPost() throws IOException {
         // Post请求的url，与get不同的是不需要带参数
         URL postUrl = new URL(POST_URL);
         // 打开连接
         HttpURLConnection connection = (HttpURLConnection) postUrl
                 .openConnection();
         // Output to the connection. Default is
         // false, set to true because post
         // method must write something to the
         // connection
         // 设置是否向connection输出，因为这个是post请求，参数要放在
         // http正文内，因此需要设为true
         connection.setDoOutput(true);
         // Read from the connection. Default is true.
         connection.setDoInput(true);
         // Set the post method. Default is GET
         connection.setRequestMethod("POST");
         // Post cannot use caches
         // Post 请求不能使用缓存
         connection.setUseCaches(false);
         // This method takes effects to  every instances of this class.
         // URLConnection.setFollowRedirects是static 函数，作用于所有的URLConnection对象。
         // connection.setFollowRedirects(true);  

         // This methods only takes effacts to this  instance.
         // URLConnection.setInstanceFollowRedirects 是成员函数，仅作用于当前函数
         connection.setInstanceFollowRedirects(true);
         // Set the content type to urlencoded,
         // because we will write some URL-encoded content to the  connection. Settings above must be set before connect!
         // 配置本次连接的Content-type，配置为application/x- www-form-urlencoded的
         // 意思是正文是urlencoded编码过的form参数，下面我们可以看到我们对正文内容使用URLEncoder.encode
         // 进行编码  

         connection.setRequestProperty("Accept", "*/*");
         connection.setRequestProperty("Accept-Encoding", "gzip, deflate");
         connection.setRequestProperty("Accept-Language", "zh-CN,zh;q=0.8,en;q=0.6");
         connection.setRequestProperty("Connection", "keep-alive");
         connection.setRequestProperty("Content-Length", "153");
         connection.setRequestProperty("Content-Type",  "application/x-www-form-urlencoded; charset=UTF-8");
 //        connection.setRequestProperty("cookie", "Hm_lvt_692544717e4ca5489bff77b2e9b28e7b=1449645321; Hm_lpvt_692544717e4ca5489bff77b2e9b28e7b=1449645391; __jsluid=8c1e0374852916bf96a7f809c2aee3c8; _gscu_482111853=49645323pc25ob94; _gscbrs_482111853=1; ASP.NET_SessionId=m44tcmadhujdeijinvbiecnw; __jsl_clearance=1450332415.032|0|t2eMmMeGhHeoINln2hPaPf4D5HI%3D; _gscu_1241932522=50249161sf1y6f54; _gscs_1241932522=t50334524zs7d8g57|pv:1; _gscbrs_1241932522=1");
         connection.setRequestProperty("cookie", "Hm_lvt_692544717e4ca5489bff77b2e9b28e7b=1449645321; Hm_lpvt_692544717e4ca5489bff77b2e9b28e7b=1449645391; __jsluid=8c1e0374852916bf96a7f809c2aee3c8; _gscu_482111853=49645323pc25ob94; _gscbrs_482111853=1; ASP.NET_SessionId=m44tcmadhujdeijinvbiecnw; __jsl_clearance=1450340955.958|0|YZsm9pGKRX79ASJMb7gwQkJv%2FS8%3D; _gsref_1241932522=http://www.court.gov.cn/zgcpwsw/List/List?sorttype=1&conditions=searchWord+1+AJLX++%E6%A1%88%E4%BB%B6%E7%B1%BB%E5%9E%8B:%E5%88%91%E4%BA%8B%E6%A1%88%E4%BB%B6; _gscu_1241932522=50249161sf1y6f54; _gscs_1241932522=t5034096609obrb54|pv:2; _gscbrs_1241932522=1");
         connection.setRequestProperty("Host","www.court.gov.cn");
         connection.setRequestProperty("Origin","http://www.court.gov.cn");
         connection.setRequestProperty("Referer","http://www.court.gov.cn/zgcpwsw/List/List?sorttype=1&conditions=searchWord+1+AJLX++%E6%A1%88%E4%BB%B6%E7%B1%BB%E5%9E%8B:%E5%88%91%E4%BA%8B%E6%A1%88%E4%BB%B6");
         connection.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/46.0.2490.86 Safari/537.36");
         connection.setRequestProperty("X-Requested-With","XMLHttpRequest");

         // 连接，从postUrl.openConnection()至此的配置必须要在 connect之前完成，
         // 要注意的是connection.getOutputStream会隐含的进行 connect。
         connection.connect();
         DataOutputStream out = new DataOutputStream(connection
                 .getOutputStream());
         // The URL-encoded contend
         // 正文，正文内容其实跟get的URL中'?'后的参数字符串一致
         // 表单参数包括：（1）Param:案件类型:刑事案件（2）Index:1
         //（3）Page:5（4）Order:法院层级（5）Direction:asc
         String content = "Param=%E6%A1%88%E4%BB%B6%E7%B1%BB%E5%9E%8B%3A%E5%88%91%E4%BA%8B%E6%A1%88%E4%BB%B6&Index=4&Page=5&Order=%E6%B3%95%E9%99%A2%E5%B1%82%E7%BA%A7&Direction=asc";
 //        String content = "Param="
 //                + URLEncoder.encode("案件类型:刑事案件 ", "utf-8");
         // DataOutputStream.writeBytes将字符串中的16位的 unicode字符以8位的字符形式写道流里面
         out.writeBytes(content);  

         out.flush();
         out.close(); // flush and close
         BufferedReader reader = new BufferedReader(new InputStreamReader(
                 connection.getInputStream()));
         String line;
         System.out.println(" ============================= ");
         System.out.println(" Contents of post request ");
         System.out.println(" ============================= ");
         while ((line = reader.readLine()) != null) {
             System.out.println(line);
         }
         System.out.println(" ============================= ");
         System.out.println(" Contents of post request ends ");
         System.out.println(" ============================= ");
         reader.close();
         connection.disconnect();
     }  

     /** */
     /**
      * @param args
      */
     public static void main(String[] args) {
         // TODO Auto-generated method stub
         try {
 //            readContentFromGet();
             readContentFromPost();
         } catch (IOException e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }
     }  

 }  

第一次访问出现了521的错误状态码，原因是：

（https://www.zhihu.com/question/31015275）