一、当只有addRequestProperty的时候

URL url = new URL("http://localhost:8080/net/listnets.jsp");  
            URLConnection connection = url.openConnection();  
            connection.addRequestProperty("name", "asad");  
            connection.addRequestProperty("name", "komal");  
            connection.addRequestProperty("class", "10th");  
            connection.addRequestProperty("Address", "Delhi 17");  
  
            Map map = connection.getRequestProperties();  
            Set set = map.entrySet();  
  
            Iterator iterator = set.iterator();  
            while (iterator.hasNext()) {  
                System.out.println(iterator.next());  
            }  

输出结果：name=[komal, asad]  
Address=[Delhi 17]  
class=[10th]  
二、当只有setRequestProperty的时候

URL url = new URL("http://localhost:8080/net/listnets.jsp");  
URLConnection connection = url.openConnection();  
connection.setRequestProperty("name", "komal");  
connection.setRequestProperty("name", "asad");  
connection.setRequestProperty("class", "10th");  
connection.setRequestProperty("Address", "Delhi 17");  
  
Map map = connection.getRequestProperties();  
Set set = map.entrySet();  
  
Iterator iterator = set.iterator();  
while (iterator.hasNext()) {  
    System.out.println(iterator.next());  
}  

输出结果：  

name=[asad]  
Address=[Delhi 17]  
class=[10th]  

注意name的设置，会发生覆盖的作用。  
三、当先set后add的时候
 
 

URL url = new URL("http://localhost:8080/net/listnets.jsp");  
        URLConnection connection = url.openConnection();  
        connection.setRequestProperty("name", "asad");  
        connection.addRequestProperty("name", "komal");  
        connection.addRequestProperty("class", "10th");  
        connection.addRequestProperty("Address", "Delhi 17");  
  
        Map map = connection.getRequestProperties();  
        Set set = map.entrySet();  
  
        Iterator iterator = set.iterator();  
        while (iterator.hasNext()) {  
            System.out.println(iterator.next());  
        }  

输出结果  

name=[komal, asad]  
Address=[Delhi 17]  
class=[10th]  

   

   
四、当先add后set的时候

URL url = new URL("http://localhost:8080/net/listnets.jsp");  
        URLConnection connection = url.openConnection();  
        connection.addRequestProperty("name", "komal");  
        connection.setRequestProperty("name", "asad");  
        connection.addRequestProperty("class", "10th");  
        connection.addRequestProperty("Address", "Delhi 17");  
  
        Map map = connection.getRequestProperties();  
        Set set = map.entrySet();  
  
        Iterator iterator = set.iterator();  
        while (iterator.hasNext()) {  
            System.out.println(iterator.next());  
        }  



name=[asad]  
Address=[Delhi 17]  
class=[10th]  

五、结
setRequestProperty方法，如果key存在，则覆盖；不存在，直接添加。

addRequestProperty方法，不管key存在不存在，直接添加。