web访问问题

我的web只有第一次访问时才正常，刷新之后就会跳转到global-results里面的页面，即使返回到上一步之后再进入也也是一样进入错误页面，只有重启服务器后，第一次访问才正常，之后再刷新就又不正常了，这是怎么回事，控制台也不报错，每次重启服务器只能访问一次， --------------------编程问答-------------------- 是不是tomcat出问题了 --------------------编程问答-------------------- 是不是tomcat出问题了 --------------------编程问答-------------------- 但运行别的WEB程序是正常的 --------------------编程问答-------------------- 把出错页面提示贴出来看看 --------------------编程问答-------------------- package hb.tm.Action;

import hb.tm.Model.User;
import hb.tm.Service.UserService;

import com.opensymphony.xwork2.ActionSupport;

public class UserAction extends ActionSupport{

private User user;
private UserService userService = new UserService();

public User getUser() {
return user;
}

public void setUser(User user) {
this.user = user;
}

public UserService getUserService() {
return userService;
}

public void setUserService(UserService userService) {
this.userService = userService;
}

public String login() throws Exception {
userService.getCheck(user);
return SUCCESS;
}

}

package hb.tm.Model;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;

@Entity
public class User {
private String username;
private int id;
private String password;
private String role;

@Id
@GeneratedValue
public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getUsername() {
return username;
}

public void setUsername(String username) {
this.username = username;
}

public String getPassword() {
return password;
}

public void setPassword(String password) {
this.password = password;
}

public String getRole() {
return role;
}

public void setRole(String role) {
this.role = role;
}

}

public void getCheck(User user) {
Session session2 = sf.getCurrentSession();
session2.beginTransaction();
Query q = session2.createQuery("select * from " +user.getRole());
List<String> list = q.list();
//System.out.println(u2.getRole());
for(String str:list)  {
System.out.println(str);
}
session2.getTransaction().commit();
sf.close();
}

<struts>
    <constant name="struts.enable.DynamicMethodInvocation" value="false" />
    <constant name="struts.devMode" value="false" />
    <constant name="struts.custom.i18n.resources" value="application"></constant>

    <package name="default" namespace="/" extends="struts-default">

        <default-action-ref name="index" />

        <global-results>
            <result name="error">/error.jsp</result>
        </global-results>

        <global-exception-mappings>
            <exception-mapping exception="java.lang.Exception" result="error"/>
        </global-exception-mappings>
        <action name="user_login" class="hb.tm.Action.UserAction" method="login">
            <result name="success">
             ${user.role}.jsp
            </result>
        </action>
    </package>
</struts>

这段程序的作用就是通过登陆界面中的角色选择跳到相应的界面，但每次都只有第一次成功，之后就全跳到error.jsp这个页面，每次都要重启服务器，这是怎么回事

补充：Java ,  Web 开发