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>