怎么用ajax访问action中的方法

本来是跳转到新页面显示错误信息,现在需要在点击按钮时,就直接在原来的页面上弹出提示信息.

action中的方法如下:
    public String sendEmail() throws Exception {
        MailBean mailBean = setMailBean();
        try {

            if(!isWriteRight(mailBean,mailInfoFB.getTo())){
                mailInfoFB.setSended(false);
                mailInfoFB.setFrom("收件人错误,请检查您填写的收件人是否有误!");
                deleteAttachment();// 发完信息时删除硬盘中的附件信息
                return "sendMailSuccess";
            }
        }
Struts的信息
 <action name="sendMail" class="userSendMailAction">
            <result name="success">/user/user_send_mail.jsp</result>
            <result name="sendMailSuccess">/user/user_sendMail_success.jsp</result>

            <interceptor-ref name="loginInterceptor" />
        </action>
jsp中的代码
 <input type="button" title="发信" value="发&nbsp;信" onclick="checkTo()"/>
    function checkTo(){
        var to =$.trim($("#i_receive").val());
        var sub = $("#i_subject").val();
        var con = $("#i_content").val();
        var cc =$.trim($("#i_cc").val());
        var bcc =$.trim($("#i_bcc").val());
        if(to == "" || to.length==0){
            alert("请填写联系人！");return ;
        } 
        if(sub == "" || sub.length==0){
            alert("请填写邮件主题！");return ;
        } 
        if(to != "" && to.length>0){
            if(!reg.test(to)){
                    alert("你输入的收件人地址不正确!");return ;
            }
        } 
        if(cc != "" && cc.length>0){
            if(!reg.test(cc)){
                alert("你输入的抄送人地址不正确!");return ;
            }
        } 
        if(bcc != "" && bcc.length>0){
            if(!reg.test(bcc)){
                alert("你输入的密送人地址不正确!");return ;
            }
        } 
            showProgress("正在发送邮件...");//显示保存进度
            $("#sendmail").submit();

    }

增加form
`<form action="<%=basePath %>user/sendMail!sendEmail.action" method="post" id="sendmail">