struts2做计算器报错，希望高手指出解决方法?报错

我这个代码出现报错，我已经找了很多方法去解决，但是还是没能查出空指针异常的错误在哪里，希望各位高手帮帮忙

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee   http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
	<filter>
		<filter-name>struts2</filter-name>
		<filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class>
	</filter>
	
    <filter-mapping>
        <filter-name>struts2</filter-name>
        <url-pattern>/*</url-pattern>
        <dispatcher>REQUEST</dispatcher>
    </filter-mapping>
</web-app>

以上这个是struts.XML代码，我放在src目录下的

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE struts PUBLIC
    "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
    "http://struts.apache.org/dtds/struts-2.0.dtd">

<struts>
	<package name="struts2" namespace="" extends="struts-default">
		<action name="cal" class="cn.itcast.calculator.myCalculator"
			method="execute">
			<result name="success" type="dispatcher">
				/calculator.jsp
			</result>
		</action>
	</package>
</struts>

以上是我写的calculate.XML文件

这是我写的jsp文件
<%@ page language="java" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <body>
  	<form action="/myday33/cal" method="post">
  		<table border="2" align="center">
  			<caption><h2>计算器[struts2版本]</h2></caption>
  			<tr>
  				<th>操作数1</th>
  				<td><input type="text" name="num1" maxlength="4"/></td>
  			</tr>
  			<tr>
  				<th>操作符</th>
  				<td align="center"><input type="radio" name="+"  value="+" checked="checked">加
  				                    <input type="radio" name="-" value="-">减
  									<input type="radio" name="*" value="*">乘
  									<input type="radio" name="/" value="/">除
  				</td>
  			</tr>
  			<tr>
  				<th>操作数2</th>
  				<td><input type="text" name="num2" maxlength="4"/></td>
  			</tr>
  			<tr>
  				<td colspan="2" align="center">
  					<input type="submit" value="计算" style="font-size:22px"/>
  				</td>
  			</tr>
  		</table>
  		<hr/>
  		结果：${requestScope.sum}
  	</form>
  </body>
</html>

其起名是calculate.JSP

还有就是我的java文件

package cn.itcast.calculator;

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

public class myCalculator extends ActionSupport{

	
	public myCalculator() {
		super();
		//这是一个检验
		System.out.println("lala");//成功 的
	}
	//数字的封装
	private String num1;
	private String num2;
	private String name;//这个是操作符
	
	public String getNum1() {
		return num1;
	}
	public String getNum2() {
		return num2;
	}
	public String getName() {
		return name;
	}
	public void setNum1(String num1) {
		this.num1 = num1;
	}
	public void setNum2(String num2) {
		this.num2 = num2;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String execute() throws Exception {

		//转化好要改变的数字
		Integer number1 = Integer.parseInt(num1);
		Integer number2 = Integer.parseInt(num2);

		int sum = 0;
		//判断符号，做计算
		if(name.equals("+")){
			sum = number1 + number2;
		}else if(name.equals("-")){
			sum = number1 - number2;
		}else if(name.equals("*")){
			sum = number1 * number2;
		}else if(name.equals("/")){
			sum = number1 / number2;
		}
		
		ActionContext.getContext().put("sum", sum);
		
		return "success";
	}
}

以上就是我写的代码，但是当我运行tomcat，浏览器出现以下错误。希望高手告诉我怎么回事了，更重要的是我应该如何解决问题。

struts2做计算器报错，希望高手指出解决方法?报错

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