JAVA判断一个URL是否有效

try {   
     url = new URL("http://127.0.0.1/sj/user/getUser");   
     in = url.openStream();   
} catch (Exception e1) {   
     System.out.println("连接打不开!");   
     url = null;   
}  

/**  
      * 功能：检测当前URL是否可连接或是否有效,  
      * 描述：最多连接网络 3 次, 如果 3 次都不成功，视为该地址不可用  
      * @param  urlStr 指定URL网络地址  
      * @return URL  
      */  
     public synchronized String isConnect(String urlStr) {   
         int counts = 0;   
         retu = "";   
         if (urlStr == null || urlStr.length() <= 0) {                          
             return null;                    
         }   
         while (counts < StaticConstant.REQUEST_COUNT) {   
             long start = 0;   
             try {   
                 url = new URL(urlStr);   
                 start = System.currentTimeMillis();   
                 con = (HttpURLConnection) url.openConnection();   
                 state = con.getResponseCode();   
                 log.info("请求断开的URL一次需要："+(System.currentTimeMillis()-start)+"毫秒");   
                 if (state == 200) {   
                     retu = "ok";   
                     log.info(urlStr+"--可用");   
                 }   
                 break;   
             }catch (Exception ex) {   
                 counts++;    
                 log.info("请求断开的URL一次需要："+(System.currentTimeMillis()-start)+"毫秒");   
                 log.info("连接第 "+counts+" 次，"+urlStr+"--不可用");   
                 continue;   
             }   
         }   
         return retu;   
     }