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）