<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>a</title>
</head>
<body>
    <h1>这是a</h1>
    <h3>a的路径为http://localhost:8080/bServlet/a.html</h3>
    <a href="demo4">相对路径到demo4</a><br>
    <a href="./demo4">相对路径到demo4</a><br>
    <a href="/bServlet/demo4">绝对路径到demo4</a>
</body>
</html>

b.html的代码为

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>b</title>
</head>
<body>
    <h1>这是b</h1>
    <h3>b的路径为http://localhost:8080/bServlet/html/b.html</h3>
    <a href="../demo4">相对路径到demo4</a><br>
</body>
</html>

资源/demo4的代码为

package com.lingaolu.servlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
import java.io.IOException;

/**
 * @author 林高禄
 * @create 2020-07-07-16:46
 */
@WebServlet(value="/demo4")
public class ServletDemo4 extends HttpServlet {


    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("doGet.....demo4.");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("doPost......demo4");
    }
}

启动访问

从上面可以知道

/demo4的全路径为http://localhost:8080/bServlet/demo4

a.html的全路径为http://localhost:8080/bServlet/a.html

b.html的全路径为http://localhost:8080/bServlet/html/a.html

所以，对本次例子来说：

a.html相对路径访问/demo4的时候，可以是./demo4也可以是demo4，因为demo4也会被转为./demo4

a.html绝对路径访问/demo4的时候，是/bServlet/demo4

b.html相对路径访问/demo4的时候，因为b.html和/demo4不在同一层路径目录，而b.html的上一层html和/demo4才在同一层目录，所以b.html相对路径访问/demo4是../demo4,(../表示返回上一层)