如JOptionPane.showMessageDialog(null,"请输入密码！！" );弹出的不是模态的啊

把这个null改成一个对话框试试~

super(他的父容器,true);

改成一个对话框？怎么改啊？什么对话框啊？我是菜鸟啊
import javax.faces.context.FacesContext;
import javax.servlet.http.HttpSession;
import javax.swing.JOptionPane;
/**
 * @author Administrator
 *
 */
public class UserBean {
    private java.lang.String userName;
    private java.lang.String password;
    public UserBean() {
    }
public java.lang.String getUserName() {
        return userName;
    }
 public void setUserName(java.lang.String userName) {
        this.userName = userName;
    }
 public java.lang.String getPassword() {
        return password;
    }
public void setPassword(java.lang.String password) {
        this.password = password;
    }
 public String loginUser() {
    if("myeclipse".equals(getUserName()) && "myeclipse".equals(getPassword()))
            {return "success"; }
        else if("".equals(getUserName())||getUserName() == null)
            {
            JOptionPane.showMessageDialog( null,"用户名不能为空");     这里怎么定父窗口啊？？？
          return "re";}
        else if(!"".equals(getUserName()) && "".equals(getPassword()))
                {JOptionPane.showMessageDialog(null,"请输入密码！！");
            return"re";}
           return "failure";}
    public String exitUser(){
        int returnValue;
        returnValue = JOptionPane.showConfirmDialog(null, "确实要退出吗？", "退出程序", JOptionPane.YES_NO_OPTION);
        if (returnValue == JOptionPane.YES_OPTION)
        {FacesContext fc = FacesContext.getCurrentInstance();
        HttpSession session = (HttpSession) fc.getExternalContext().getSession(false);
        session.invalidate();
        return "exit";}
        else return "";
    }
    public String reLogin(){
        return "re";
    }
    private String message;
    public String getMessage() {
    return message;
    }
    public void setMessage(String message) {
    this.message = message;
    }
    }

我是jsf做个登陆界面  想让用户名为空时点登陆弹出模态的提示窗口  

不会啊。。。。父容器怎么弄

奇怪，你这是用JSF做界面，为什么用SWING？你这样运行，界面是显示在Server端吧？

用JQuery啦~轻轻松松~

我是个菜鸟 没学过 百度怎么弹出窗口就看到它了 然后就用他了