websocket问题 ，请大神指教

初学websocket 为什么访问一直不对啊 代码贴出来

<script type="text/javascript">
    function subOpen(){
    var ws;
    var target="ws://localhost:8080/websocket/demo";
     if ('WebSocket' in window) {
            ws = new WebSocket(target);
        } else if ('MozWebSocket' in window) {
            ws = new MozWebSocket(target);
        } else {
            alert('WebSocket is not supported by this browser.');
            return;
        }
}
</script>
-----------------------------------------
@ServerEndpoint("/demo")

public class DemoSocket {
@OnOpen
public void open(Session session){
System.out.println(session.getId()+"--------------");
}
}

打印不出来。。。