struts 2 com.opensymphony.xwork2.u报错

Question

六月 29, 2016 8:47:55 上午 com.opensymphony.xwork2.util.logging.jdk.JdkLogger error
严重: Exception occurred during processing request: null
java.lang.NullPointerException

提示在这一个代码段里面 if语句错误

package cn.itcast.actionT;

import cn.itcast.domain.User;

import com.opensymphony.xwork2.ActionContext;
import com.opensymphony.xwork2.ActionSupport;
import com.opensymphony.xwork2.ModelDriven;

public class LoginAction extends ActionSupport implements ModelDriven{
private static final long serializableUID = 1L;
private User user;
@Override
public User getModel() {
return user;
}
@Override
public String execute()throws Exception{
//获取ActionContext
ActionContext context = ActionContext.getContext();
if("tom".equals(user.getUsername())&&"123".equals(user.getPassword())){
context.getSession().put("user","user");
return SUCCESS;
}else {
context.getSession().put("msg", "登录失败");
return INPUT;
}
}
}
我把所有代码都复制上来
package cn.itcast.actionT;

import cn.itcast.domain.User;

import com.opensymphony.xwork2.ActionSupport;

public class BookAction extends ActionSupport{
private User user;
public String add(){
System.out.println("book add");
return SUCCESS;
}
public String del(){
System.out.println("book del");
return SUCCESS;
}
public String update(){
System.out.println("book update");
return SUCCESS;
}
public String find(){
System.out.println("book find");
return SUCCESS;
}
}
package cn.itcast.domain;

public class User {
private String username;
private String password;
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;
}
}

struts.xml

package name="default" namespace="/" extends="struts-default">
interceptors>
interceptor name="privilege" class="cn.itcast.interceptor.PrivilegeInterceptor"/>
/interceptors>
action name="login" class="cn.itcast.actionT.LoginAction">
result>/main.jsp /result>
result name="input">/login.jsp /result>
/action>
action name="book_*" class="cn.itcast.actionT.BookAction" method="{1}">
result>/success.jsp /result>
result name="login">/login.jsp /result>
interceptor-ref name="privilege"/>
/action>

/package>
/struts>

main.jsp

a href="/Two/book_del">book_del /a>
a href="/Two/book_add">book_add /a>
a href="/Two/book_find">book_find /a>
a href="/Two/book_update">book_update /a>

login.jsp

form action="/Two/login.action" method="post">
              用户名:input type="text" name="username"/>br>
             密码:input type="password" name="password"/>br>
  input type="submit" value="登录™†"/>
/form>

Answer 1

user对象不存在，页面上的input通过getter和setter方法注入到后端的username和password，在后端获得的是username和password。
如果需要封装对象，有两种方式：
1、模仿struts1的形式，在action里面声明
private User user;
public User getUser(){...}
public void setUser(User user){...}
JSP中:
<input type="text" name="user.username"/>
<input type="text" name="user.password"/>

2、JSP和Action不变，后端得到username和password，new User()对象，把值放进去