刚开始自学Struts2,写了一个程序,运行不了,求大佬指导

<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">




登录界面








package com.zhang.action;

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

public class LoginAction extends ActionSupport {

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;
}

@Override
//返回的字符串是视图的入径
public String execute() throws Exception {
    // TODO Auto-generated method stub
    System.out.println("执行Action");
    System.out.println("username");
    if (username.equals("zhang")
            && password.equals("666") )
    {
        ActionContext.getContext().getSession().put("user",getUsername() );
        return "success";
    }
    return "error";
}

}

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE struts PUBLIC
"-//Apache Software Foundation//DTD Struts Configuration 2.3//EN"
"http://struts.apache.org/dtds/struts-2.3.dtd">

<!-- Add packages here -->

<constant name="struts.devMode" value="true" />
<package name="default" namespace="/" extends="struts-default">
    <action name="login" class="com.zhang.action.LoginAction">
        <result name="error">/WEB-INF/error.jsp</result>
        <result name="success">/WEB-INF/welcome.jsp</result>
    </action>
</package>

错误提示:
Struts Problem Report

Struts has detected an unhandled exception:

Messages:

File: com/zhang/action/LoginAction.java
Line number: 31
Stacktraces

java.lang.NullPointerException
com.zhang.action.LoginAction.execute(LoginAction.java:31

我也是萌新,不知道有没有用,一个if最好跟一个else,你这样,他不会每次都执行
return “error” 吗

jsp界面没有看到,所以只能猜测一下。第一个,jsp登录界面的input 框中的name要和loginaction属性一一对应。
第二个不知道是不是一开始访问项目就走loginaction。建议把username.equals("zhang")
&& password.equals("666")换成
"zhang".equals(username)&&"666".equals(password);望对你有帮助