<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>

<div class="row">
 <h1>Ajax+Jquery验证用户的唯一性</h1>
 <form action="" method="post">
  <h3>名字：</h3>
  <input type="text" id="name" class="form-control" name="user.name" id="name" placeholder="请输入你的用户名">
  <br><br>
  <input type="submit" class="btn btn-success" value="验证用户的唯一性"/>&nbsp;&nbsp;&nbsp;&nbsp;
  <span id="namemsg"></span>
 </form>
</div>

//验证用户的唯一性
public void isexist() throws IOException {
  boolean exist = name.equals("张三") ;
  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>