ext getCount()=0 得不到返回json数据

public String findAll() {
System.out.println("----------------findAll()-----------");
listmap=(List)biz.findAll();
System.out.println("listmap()---->"+listmap.size());
return null;
}

<?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="emp_struts" namespace="/" extends="json-default">
<action name="findAll" class="EmpAction" method="findAll">
<result type="json">
<param name="includeProperties">listmap</param>
</result>
</action>
</package>
</struts>


var _jsonReader = new Ext.data.JsonReader( {
root : 'listmap',
id : 'eid'
}, new Ext.data.Record.create( [ {
name : 'eid'
}, {
name : 'ename'
}, {
name : 'passwd'
} ]));
var ds = new Ext.data.Store( {
proxy : new Ext.data.HttpProxy( {
method : 'POST',
url : 'findAll.action'
}),
reader : _jsonReader

});
ds.load({
callback:function(){
alert(ds.getCount());
}
});