网络请求 乱码

public class test {
    public static void main(String[] args){
      String str="哈哈";
      try {
           byte[] b1 = str.getBytes("GB2312");
           byte[] b2 = str.getBytes("UTF-8");
           for (int i = 0; i < b1.length; i++) {
                System.out.print(b1[i]);
          }
           System.out.println();
           for (int i = 0; i < b2.length; i++) {
                System.out.print(b2[i]);
           }
          System.out.println();
           System.out.println(new String(b1));
           System.out.println(new String(b1, "UTF-8"));
           System.out.println(new String(b2, "UTF-8"));
      } catch (UnsupportedEncodingException e) {
       // TODO Auto-generated catch block
       e.printStackTrace();
      }    
     }
}
 
运行一下例子，你会发现，结果是：
-71-2-71-2
-27-109-120-27-109-120
哈哈
????
哈哈

  　　　　if (conn.getResponseCode()==200){

                InputStreamReader isr=new InputStreamReader(conn.getInputStream(),"utf-8");
                StringBuffer sb=new StringBuffer();
                char buf[]=new char[1024];
                int len=0;

                while ((len = isr.read(buf)) != -1)
                {
                    sb.append(new String(buf, 0, len));
                }
                isr.close();
            }