注册解决方法

$("#username").blur(function(){        var username = $("#username").val();                if(username == ""){            $("#c_username").html("<img src='images/NO.png'> ");        }else{            $.post("checkUsernameAction.action",                {"username":username},                function(data){                        if(data == "Y"){                            $("#c_username").html("<span><img src='images/OK.png'></span>");                            username_flag = true;                        }else if(data == "N"){                            $("#c_username").html("<span><img src='images/NO.png'></span>");                        }                });        }    });
------解决方案--------------------
public boolean checkUsers(String username) {
 Session session=sessionFactory.getCurrentSession();
 List<User> users=null;
 Query query= session.createQuery("from User where username="+username); 
 users=query.list;
 if(null!=users && users.size>0){
 return true;
 }else{
 return false;
 }
}