from表单如果未指定action，submit提交时候会执行当前url

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
    <% out.println("@:"+request.getParameter("test")+"<br>"); %>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<form>
<input name="test"/>
<input type="submit" value="提交">
</form>
</body>
</html>
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原文地址：https://www.cnblogs.com/Nbge/p/5972598.html