[已解决]操作名称竟然区分大小写

我想向服务器发出ajax请求以获取JSON。我正在使用以这种方式配置的struts2软件包

<package name="it.polito.ai.e3" namespace=""
    extends="struts-default,json-default">
    <action name="getDay" class="it.polito.ai.e3.GetDayAction" >
        <result name="success" type="json" />
        <result name="error" type="json" />
    </action>
</package>

GetDayAction类为

package it.polito.ai.e3;

import java.util.Date;

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

@SuppressWarnings("serial")
public class GetDayAction extends ActionSupport
{
private String startDate;

public String execute()
{
    try
    {
        System.out.println("Ciao");
        System.out.println(startDate);
    }
    catch (Exception e)
    {
        e.printStackTrace();
        return Action.ERROR;
    }

    return Action.SUCCESS;
}

public String getStartDate()
{
    return startDate;
}

public void setStartDate(String startDate)
{
    this.startDate = startDate;
}

}

jQuery post块是

$(function() {
    $.post('getday.action', document.getElementById('startDate').innerHTML,
        function(data) {

        });  
});

在获取jQuery块的情况下

$(function() {
    $.getJSON('getday.action', document.getElementById('startDate').innerHTML,
        function(data) {

        });  
});

document.getElementById('startDate').innerHTML 获取以字符串格式设置的日期。

当它通过ajax执行get或post时，Tomcat给我500个内部服务器错误，并且此堆栈跟踪

java.lang.NullPointerException
org.apache.struts2.impl.StrutsActionProxy.getErrorMessage(StrutsActionProxy.java:69)
com.opensymphony.xwork2.DefaultActionProxy.prepare(DefaultActionProxy.java:185)
org.apache.struts2.impl.StrutsActionProxy.prepare(StrutsActionProxy.java:63)
org.apache.struts2.impl.StrutsActionProxyFactory.createActionProxy(StrutsActionProxyFactory.java:39)
com.opensymphony.xwork2.DefaultActionProxyFactory.createActionProxy(DefaultActionProxyFactory.java:58)
org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:500)
org.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:434)

Tomcat7控制台不显示任何内容，System.out.println（）或其他消息均不显示。

我不知道我在做什么错。谢谢