jsp中如何实现按下回车键自动提交表单？

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ include file="../../common/include_tag.jsp"%>
<%@ include file="../../common/page_var.jsp"%>
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title><%=pageTitle%>-用户登录</title>
<%@ include file="../../common/page_head.jsp"%>
<link rel="stylesheet" type="text/css"
    href="<s:url value='/css/common_green.css'/>" />
<script type="text/javascript" src="<s:url value='/js/jquery.min.js'/>"></script>
<script type="text/javascript" src="<s:url value='/js/common.js'/>"></script>
<style type="text/css">
.logo{
    padding-top: 20px;
    padding-left: 20px;
    padding-right: 20px;
    padding-bottom: 20px;
    font-size: 28px;
}
.top{
    padding-bottom: 100px;
}
.login{
    line-height: 32px;
}
.content {
    width: 350px;
    margin: 15px auto auto;
    padding: 50px 50px;
    border: 2px solid #ccc;
    border-radius: 10px;
    box-shadow: 0 0 30px #ccc;
}
.bottom{
    padding-top: 100px;
}
.button{
    margin-top: 10px;
    margin-left: 105px;
}
.update {
    margin: 0 auto;
    padding: 0;
    width: 98%;
}

.update td {
    margin: 0;
    height: 30px;
    padding: 5px;
}

.update .name {
    text-align: right;
}

.title_div {
    width: 350px;
}

body {
    background: url("< s : url value = '/images/gray_bg.png'/ >") 0 0
        repeat-y #F6F6F6;
}
</style>
<script type="text/javascript">
    $(function() {
        pilicat.title2div('title2div');
        pilicat.keysubmit('form1', 'submit', true);
    });
</script>
</head>
<body>
    <div class="logo">首都机场空地自动化协同决策系统</div>
    <div class="rounded table">
        <div class="top"></div>
        <div class="content">
        <form id="form1" action="<s:url value='/u/ulogin'/>" method="post">
        <div align="center"><span style="color: red;">${captcha}</span></div>
        <table class="table table-bordered table-striped" style="width: 310px; padding-left: 50px;">
        <tbody>
            <tr class="login">
                <td><span>账 号: </span></td>
                <td><input type="text" id="userName" name="userName"
                    class="input rounded" value="" placeholder="账号" /></td>
            </tr>
            <tr class="login">
                <td><span>密 码: </span></td>
                <td><input type="password" id="passWd" name="passWd"
                    class="input rounded" value="" placeholder="密码" /></td>
            </tr>
            <tr class="login">
                <td><span>验证码: </span></td>
                <td><input type="text" id="captcha" name="captcha" size="5" maxlength="5" class="input rounded" value="" placeholder="验证码" />
                <img id="captcha" style="cursor: pointer; cursor: hand; margin-top: -5px; margin-right: -10px;" align="middle"
                        onclick="this.src='<s:url value='/u/captcha.htm'/>?'+Math.random();"
                        src="<s:url value='/u/captcha.htm'/>">
                </td>
            </tr>
            <tr class="login">
                <td colspan="2">
                    <a id="submit" class="submit" href="javascript:;" onclick="submitForm();">登录</a>
                </td>
            </tr>
        </tbody>
        </table>
        </form>
        </div>
        <div class="bottom"></div>
    </div>
    <%@ include file="../../common/bottom.jsp"%>
</body>
</html>

把form表单放在一个div里面，然后对这个div监听事件$("#id").keydown(function (){});

页面编写js脚本进行监听。。。

js监听enter事件

//监听回车事件
document.onkeydown=function() {

if(event.keyCode==13) {

//这里提交你的表单

$('#ff_login').submit();
}
}

获取焦点监听enter

监听整个body的keypress事件，如果是回车键，激发submit按钮的click事件，当然你的click事件中会有相关的数据验证之类的，如果验证不过，不会提交