HttpURLConnection connection = (HttpURLConnection) url.openConnection(); 

connection.setConnectTimeout(3000);

connection.set...;　　　　　　//设置请求体

connection.connect;

OutputStream outputStream = connection.getOutputStream(); 

outputStream.write(mydata,0,mydata.length);

connection.getInputStream()

import java.io.IOException; 
import java.io.InputStream; 
import java.io.OutputStream; 
import java.io.UnsupportedEncodingException; 
import java.net.HttpURLConnection; 
import java.net.MalformedURLException; 
import java.net.URL; 
import java.net.URLEncoder; 
import java.util.HashMap; 
import java.util.Map; 
   
public class HttpUtils { 
   
    private static String PATH = "http://172.24.87.47:8088/myhttp/servlet/LoginAction"; 
    private static URL url; 
    public HttpUtils() {} 
   
    static{ 
        try { 
            url = new URL(PATH); 
        } catch (MalformedURLException e) { 
            e.printStackTrace(); 
        } 
    } 
　　

public static void main(String[] arsg){ 
        Map<String, String> params = new HashMap<String, String>(); 
        params.put("username", "lili"); 
        params.put("password", "123"); 
        String result = sendPostMessage(params,"utf-8"); 
        System.out.println("result->"+result); 
    }

/**
     * @param params 填写的url的参数
     * @param encode 字节编码
     * @return
     */ 
    public static String sendPostMessage(Map<String, String> params,String encode){ 
        StringBuffer buffer = new StringBuffer(); 
        try {//把请求的主体写入正文！！ 
             if(params != null&&!params.isEmpty()){ 
                //迭代器 
　　　　　　　　　 //Map.Entry 是Map中的一个接口，他的用途是表示一个映射项（里面有Key和Value）
　　　　　　　　　　　for(Map.Entry<String, String> entry : params.entrySet()){ 
                  buffer.append(entry.getKey()).append("="). 
                  append(URLEncoder.encode(entry.getValue(),encode)). 
                  append("&"); 
              } 
            } 
//            System.out.println(buffer.toString()); 
              //删除最后一个字符&，多了一个;主体设置完毕 
              buffer.deleteCharAt(buffer.length()-1); 
              byte[] mydata = buffer.toString().getBytes();  
              HttpURLConnection connection = (HttpURLConnection) url.openConnection(); 
              connection.setConnectTimeout(3000); 
              connection.setDoInput(true);//表示从服务器获取数据 
              connection.setDoOutput(true);//表示向服务器写数据 
           
             connection.setRequestMethod("POST"); 
              //是否使用缓存 
              connection.setUseCaches(false); 
              //表示设置请求体的类型是文本类型 
              connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded"); 
                 
              connection.setRequestProperty("Content-Length", String.valueOf(mydata.length)); 
              connection.connect();   //连接，不写也可以。。？？有待了解 
              
              //获得输出流，向服务器输出数据 
              OutputStream outputStream = connection.getOutputStream(); 
                   outputStream.write(mydata,0,mydata.length); 
                   //获得服务器响应的结果和状态码 
              int responseCode = connection.getResponseCode();  
              if(responseCode == HttpURLConnection.HTTP_OK){ 
                 return changeInputeStream(connection.getInputStream(),encode); 
                     
              } 
        } catch (UnsupportedEncodingException e) { 
            // TODO Auto-generated catch block 
            e.printStackTrace(); 
        } catch (IOException e) { 
            // TODO Auto-generated catch block 
            e.printStackTrace(); 
        } 
           
        return ""; 
    } 
   /**
    * 将一个输入流转换成字符串
    * @param inputStream
    * @param encode
    * @return
    */ 
    private static String changeInputeStream(InputStream inputStream,String encode) { 
        //通常叫做内存流，写在内存中的 
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream(); 
        byte[] data = new byte[1024]; 
        int len = 0; 
        String result = ""; 
        if(inputStream != null){ 
            try { 
                while((len = inputStream.read(data))!=-1){ 
                    data.toString(); 
                       
                    outputStream.write(data, 0, len); 
                } 
                //result是在服务器端设置的doPost函数中的 
                result = new String(outputStream.toByteArray(),encode); 
                outputStream.flush(); 
            } catch (IOException e) { 
                // TODO Auto-generated catch block 
                e.printStackTrace(); 
            } 
        } 
        return result; 
    } 
   
}