Ajax怎么驗(yàn)證數(shù)據(jù)庫(kù)里用戶的唯一性

<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>
 </filter-mapping>

<p class="row">
 <h1>Ajax+Jquery驗(yàn)證用戶的唯一性</h1>
 <form action="" method="post">
 <h3>名字：</h3>
 <input type="text" id="name" class="form-control" name="user.name" id="name" placeholder="請(qǐng)輸入你的用戶名">
 <br><br>
 <input type="submit" class="btn btn-success" value="驗(yàn)證用戶的唯一性"/> 
 <span id="namemsg"></span>
 </form>
</p>

//驗(yàn)證用戶的唯一性
public void isexist() throws IOException {
 boolean exist = name.equals("張三") ;
 JSONObject result=new JSONObject();
 if(exist){
 result.put("exist", true);
 }else{
 result.put("exist", false);
 }
 ServletActionContext.getResponse().setContentType("text/html;charset=utf-8");
 PrintWriter out=ServletActionContext.getResponse().getWriter();
 out.println(result.toString());
 out.flush();
 out.close();
 }

<package name="user" namespace="/" extends="struts-default"> 
 <action name="user_*" class="com.ddge.action.UserAction" method="{1}">
 <result name="error">/login.jsp</result>
 </action>
</package>