Unexpected Exception caught setting 'username' on 'class com.bj186.crm.web.action.UserAction: Error setting expression 'username' with value ['艾格尼丝', ]

问题场景: 在使用表单向Action传递数据的时候, 遇到了这个问题, 导致了空指针异常.

问题描述:

10:14:56.622 [http-nio-8080-exec-45] ERROR com.opensymphony.xwork2.interceptor.ParametersInterceptor - Developer Notification (set struts.devMode to false to disable this message):

Unexpected Exception caught setting 'password' on 'class com.bj186.crm.web.action.UserAction: Error setting expression 'password' with value ['123456', ]

10:14:56.648 [http-nio-8080-exec-45] ERROR com.opensymphony.xwork2.interceptor.ParametersInterceptor - Developer Notification (set struts.devMode to false to disable this message):

Unexpected Exception caught setting 'submit' on 'class com.bj186.crm.web.action.UserAction: Error setting expression 'submit' with value ['', ]

10:14:56.649 [http-nio-8080-exec-45] ERROR com.opensymphony.xwork2.interceptor.ParametersInterceptor - Developer Notification (set struts.devMode to false to disable this message):

Unexpected Exception caught setting 'username' on 'class com.bj186.crm.web.action.UserAction: Error setting expression 'username' with value ['艾格尼丝', ]

java.lang.NullPointerException

    at com.bj186.crm.web.action.UserAction.login(UserAction.java:70)

    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)

    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

    at java.lang.reflect.Method.invoke(Method.java:498)

    at ognl.OgnlRuntime.invokeMethod(OgnlRuntime.java:902)

    at ognl.OgnlRuntime.callAppropriateMethod(OgnlRuntime.java:1547)

    at ognl.ObjectMethodAccessor.callMethod(ObjectMethodAccessor.java:68)

问题分析: 这个问题非常隐蔽, 是Struts2在接受值的时候, 不能正确的接收. 问题的根本原因在于没有创建接收数据的对象

解决思路: 在Action中把需要接收数据的类的对象new出来

private User user = new User();

并且设置它的getter和setter方法

然后这个问题就解决了!!!

附Struts2的UserAction.java的代码

package com.bj186.crm.web.action;

import com.bj186.crm.entity.User;

import com.bj186.crm.service.UserService;

import com.opensymphony.xwork2.Action;

import com.opensymphony.xwork2.ActionContext;

import com.opensymphony.xwork2.ActionSupport;

import com.opensymphony.xwork2.ModelDriven;

import com.opensymphony.xwork2.util.ValueStack;

import org.apache.struts2.ServletActionContext;

import org.springframework.web.context.WebApplicationContext;

import org.springframework.web.context.support.WebApplicationContextUtils;

import javax.servlet.ServletContext;

import java.util.Arrays;

import java.util.List;

public class UserAction extends ActionSupport implements ModelDriven<User> {

    private User user = new User();

    private UserService userService;

    private ValueStack valueStack;

    //测试添加上User的get和set方法

    public void setUser(User user) {

        //ServletActionContext.getRequest().getParameter("username")

        this.user = user;

    }

    public User getUser() {

        return user;

    }

    public void setUserService(UserService userService) {

        this.userService = userService;

    }

    public UserAction() {

        //1.获取ServletContext

        ServletContext servletContext = ServletActionContext.getServletContext();

        //2.通过整合包中的工具类, 从servletContext的作用域上获取目标--Spring的容器WebApplicationContext

        WebApplicationContext webApplicationContext = WebApplicationContextUtils.getWebApplicationContext(servletContext);

        //3.从Spring的容器中获取对象

        userService = webApplicationContext.getBean("userService", UserService.class);

        System.out.println("userService:"+userService);

        //4.获取值栈

        ActionContext context = ActionContext.getContext();

        valueStack = context.getValueStack();

    }

    public String execute() {

        System.out.println("正在UserAction的execute()方法中!");

        return Action.SUCCESS;

    }

    /**

     * 添加用户

     * @return 字符串状态

     */

    public String register() {

        User user = (User) valueStack.findValue("user");

        userService.register(user);

        return Action.SUCCESS;

    }

    /**

     * 用户登录

     * @return

     */

    public String login() {

        String username = user.getUsername();

        String password = user.getPassword();

        boolean isLogin = userService.verifyLogin(username,password);

        return isLogin? Action.SUCCESS: Action.NONE;

    }

    /**

     * 删除用户

     * @return 字符串状态

     */

    public String deleteUser(Integer uid) {

        userService.deleteUser(uid);

        return Action.SUCCESS;

    }

    /**

     * 修改用户

     * @return 字符串状态

     */

    public String updateUser() {

        User user = (User)valueStack.findValue("user");

        userService.updateUser(user);

        return Action.SUCCESS;

    }

    /**

     * 查询用户

     * @return 字符串状态

     */

    public String getUserById(Integer uid) {

        User user = userService.selectUserById(uid);

        System.out.println("查询出来的用户是: " + user);

        return Action.SUCCESS;

    }

    /**

     * 显示用户页面

     * @return

     */

    public String showAllUsers() {

        System.out.println("显示所有的用户");

        return Action.SUCCESS;

    }

    /**

     * 查询出所有的用户

     * @return

     */

    public String selectAllUsers() {

        List<User> userList = userService.selectAllUsers();

        valueStack.set("userList",userList);

        System.out.println("查到的用户个数为: " + userList.size());

        return Action.SUCCESS;

    }

    @Override

    public User getModel() {

        return user;

    }

}

前端页面的index.jsp代码

<%-- Created by IntelliJ IDEA. --%>

<%@ page contentType="text/html;charset=UTF-8" language="java" %>

<html>

  <head>

    <title>用户管理系统首页</title>

  </head>

  <body>

      <h2 style="color:red;">欢迎光临!</h2>

  <form action="<%=request.getContextPath()%>/user_login.action" method="post">

      <input name="username" type="text"><br/>

      <input name="password" type="password"><br/>

      <button name="submit" type="submit">登录</button>

  </form>

  </body>

</html>

巴特西

Unexpected Exception caught setting 'username' on 'class com.bj186.crm.web.action.UserAction: Error setting expression 'username' with value ['艾格尼丝', ]

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