jar包：

json-lib-2.2.3-jdk15.jar

struts2-json-plugin-2.3.4.1.jar（此包版本必须和Struts2版本对应，否则会抛错）

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js文件：

query-1.7.js和json2.js。

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页面导入js文件路径：

<script language="javascript" src="scripts/javascript/jquery-1.7.js"></script>
<script language="javascript" src="scripts/javascript/json2.js"></script>

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js函数：

function checkUserName(){
var url='checkUserName';
var params={
studentName:'1'
};
$.post(
url,
params,
function callback(json){
var responseData = eval(json);
var result = responseData.ckUserName;
if(result=="pass"){
$("h2").text("pass");
}else{
$("h2").text("npass");
}
},
'json'
);
}

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配置Struts2.xml：

<action name="checkUserName" class="com.shenzhen.management.action.HelloWorldAjaxAction" method = "checkUserName">
<result type="json">
<param name="#root">ckUserName</param>
</result>
</action>

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Action方法（通过Spring注入Service接口抛异常，所以另外写了一个HelloWorldAjaxAction.java文件）：

public String checkUserName()
{
String retStr = "fail";

//通过Spring注入Service接口抛异常，未找到原因，现通过ApplicationContext获取bean，知道如何解决的大神请留言，谢谢！
ServletContext servletContext = ServletActionContext.getServletContext();
ApplicationContext applicationContext = WebApplicationContextUtils.getRequiredWebApplicationContext(servletContext);
StudentService studentService = (StudentService)applicationContext.getBean("studentService");
try{
ckUserName = "pass";
retStr = "success";
}catch(Exception e){
ckUserName = "npass";
}
return retStr;
}