struts2 폼 중복 제출을 방지하는 세 가지 방법

 <form id="login_form" method="post" action="userAction!login">
			       <s:token></s:token>
			                   <input type="text" name="username"  placeholder=" " />
				           <input type="password" name="password"  placeholder=" " />
				   <div id="btn">
				      <a id="loginbutton" href="javascript:void(0)" onclick="login_submit()"> </a>
				      <a href="javascript:void(0)" onclick="login_reset()"> </a>
				  </div>
				  </form>

<action name="userAction"   class="com.yingjun.sharing.action.UserAction" >
		    <interceptor-ref name="myStack" />
            <interceptor-ref name="token" />
            <result name="invalid.token">/WEB-INF/jsp/login.jsp</result>
			<result  name="input">/WEB-INF/jsp/register.jsp</result>
			<result name="regsuccess">/WEB-INF/jsp/login.jsp</result>
		</action>