java 和ajax get请求


html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Titletitle>
    <link rel="stylesheet" href="css/insert.css">
head>
<body>
学号：<input type="text" name="sno"> <br>
<button>查询button>

<div class="box2">
    <ul>
        <li>学号li>
        <li>姓名li>
        <li>年龄li>
        <li>课程li>
        <li>成绩li>
    ul>
div>
<script>
    window.onload=function (){
        var but = document.querySelector("button")
        var snoo = document.querySelector("input")
        var div = document.querySelector(".box2")
        var xmr = new XMLHttpRequest()
        but.addEventListener("click",function () {
            //调用回调函数
            xmr.onreadystatechange = function () {
                if (this.readyState == 4) {
                    if (this.status == 200) {
                        var student = JSON.parse(xmr.responseText);
                        /*for (var i in clsses) {
                            var ul = document.createElement("ul")
                            div.appendChild(ul)
                            var li1 = document.createElement("li")
                            li1.innerHTML = student.sno
                            ul.appendChild(li1)

                            var li2 = document.createElement("li")
                            li2.innerHTML = student.name
                            ul.appendChild(li2)

                            var li3 = document.createElement("li")
                            li3.innerHTML = student.age
                            ul.appendChild(li3)

                            var li4 = document.createElement("li")
                            li4.innerHTML = i.cname
                            ul.appendChild(li4)

                            var li5 = document.createElement("li")
                            li5.innerHTML = i.grade
                            ul.appendChild(li5)
                        }*/

                    } else {
                        alert(this.status);
                    }
                }
            }
            //打开通道
            xmr.open("GET","/Student/selectbysno?sno="+snoo.innerHTML,true);
            //发送请求
            xmr.send();
        })
    }


script>

body>
html>


package serlvet;

import com.alibaba.fastjson2.JSON;
import pojo.Student;
import service.Service;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

@WebServlet("/selectbysno")
public class ServletSelectbysno extends HttpServlet {
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=utf-8");
        request.setCharacterEncoding("utf-8");
        PrintWriter writer = response.getWriter();
        Service service = new Service();
        String sno = request.getParameter("sno");
        Student select = service.select(sno);
        String sss = JSON.toJSONString(select);
        writer.print(sss);
    }
}

get请求传不过去值，这是为啥呀？

您可以通过控制台看一下您具体的请求内容，最好提供下完整的get请求路径。