使用Ajax从前端向后端发起请求的方法示例
作者:肖恩想要年薪百万
在前端使用AJAX向后端发送请求获取数据是一项基本技能,下面这篇文章主要介绍了使用Ajax从前端向后端发起请求的相关资料,文中通过代码介绍的非常详细,需要的朋友可以参考下
一、重点思想
重点思想看过来哇!!!
- 我个人认为做前后端分离的项目,无非就是前后端数据的相互传递,那么以这个思想为基础,学习收参和传参的方式就显得格外重要;
- 另外,我们是以JSON字符串的形式传递数据的,还需要学习JSON字符串的转换与解析!
1、从前端向后端传递数据:
1.将前端数据封装成一个对象:
2.将对象转化为JSON字符串:
3.后端获取对象或属性:
4.解析为Java对象:
2、从后端向前端传递数据
- 将Java对象转化为JSON字符串:
String s = JSON.toJSONString(student); - 实例化一个PrintWrite对象,调用write方法向前端传递:
PrintWriter writer = res.getWriter(); - 前端接收到后端的数据:
let data = xmlHttpRequest.responseText; - 将JSON字符串解析为JS对象:
et parse = JSON.parse(data);(拿到的是一个数组或者一个对象)
二、使用Ajax发起请求的方式
这一部分可看可不看,我主要是自己梳理一下代码
1、使用GET方式向前端请求数据
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>Title</title> <script> function ajax1(){ //以下是AJAX请求流程 let xmlHttpRequest = new XMLHttpRequest();//1.创建XMLHttpRequest对象 xmlHttpRequest.open("get","/javawebstudy2025_war_exploded/ajax1",true)//2.初始化请求,添加请求参数 xmlHttpRequest.onreadystatechange=function(){//3.设置状态监听回调 if (xmlHttpRequest.readyState==4 && xmlHttpRequest.status==200){ let data = xmlHttpRequest.responseText; console.log(data); document.querySelector("#res").innerHTML=data; } } xmlHttpRequest.send();//4.发送请求 } </script> </head> <body> <h1>Ajax测试开始啦!</h1> <div id="res" style="width: 300px;height: 200px;background: aliceblue;border:2px solid lightblue"> 仅更换内容,不刷新页面 </div> <button onclick="ajax1()">更换</button> <h2>版权信息</h2> </body> </html>
小羊碎碎念:
- xmlHttpRequest.open(“get”,“/javawebstudy2025_war_exploded/ajax1”,true),该方法的三个参数分别是:请求方法类型,url,异步请求。(异步请求不写默认为true)
- 异步请求:
@WebServlet("/ajax1") public class TestAjax1 extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { this.doPost(req, resp); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { req.setCharacterEncoding("utf-8"); resp.setContentType("text/html;charset=utf-8"); PrintWriter writer = resp.getWriter(); writer.write("我是来自后端的数据!");//后端向前端传递的数据 } }
小羊碎碎念:
- WebServlet 注解:用于注册 Servlet ,将 Servlet 类与 Web 容器(如 Tomcat)建立关联,让容器能够识别、加载并正确调用 Servlet 处理 HTTP 请求。
- 创建 Servlet 类的常见方式:
继承HttpServlet类(重写doGet、doPost方法或者直接实现service方法也可以);
继承GenerricServlet类(重写service方法);
实现Servlet接口(实现所有抽象方法)。- 实现一个接口必须实现他的抽象方法,否则定义该类为抽象类。
2、使用Get请求从前端向后端传递数据
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>Title</title> <script> function ajax2(){ let xmlHttpRequest = new XMLHttpRequest(); //获取DOM对象,再获取它的值 let user = document.querySelector(".user").value; let pwd = document.querySelector(".pwd").value; xmlHttpRequest.open('get','/javawebstudy2025_war_exploded/ajax2?name='+user+'&password='+pwd); // 异步请求不写默认是true xmlHttpRequest.onreadystatechange=function(){ if (xmlHttpRequest.readyState==4 && xmlHttpRequest.status==200){ let data = xmlHttpRequest.responseText; document.querySelector(".res").innerHTML=data; } } xmlHttpRequest.send(); } </script> </head> <body> <div class="res" style="width: 200px;height: 100px; border:lightskyblue 2px solid"> 用户名和密码是什么? </div> 用户名:<input type="text" class="user"> 密码:<input type="text" class="pwd"> <button onclick="ajax2()">提交</button> </body> </html>
@WebServlet("/ajax2") public class TestAjax2 extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { this.doPost(req, resp); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { req.setCharacterEncoding("utf-8"); resp.setContentType("text/html;charset=utf-8"); PrintWriter writer = resp.getWriter(); String name = req.getParameter("name"); String password = req.getParameter("password"); writer.write("用户名是"+name+",密码是"+password+"!"); } }
三、主要思想代码示例
首先,要明确是从前端向后端传数据还是从后端向前端传数据。
第二,数据在前后端之间以JSON字符串的形式进行传递。那就涉及到JSON字符串的转换与解析
1、获取DOM对象、定义全局变量、初始化
let tabObj = document.getElementById("tab") let sname = document.getElementById("sname"); let ssex = document.getElementById("ssex"); let sage = document.getElementById("sage"); let user = document.getElementById("user"); let pwd = document.getElementById("pwd"); let jsonData; let indexc; let id; window.onload = function () { ajaxGetData(); } function ajaxGetData() { let xmlHttpRequest = new XMLHttpRequest(); xmlHttpRequest.open("get", "/javawebstudy2025_war_exploded/Do?method=selectDo", true); xmlHttpRequest.onreadystatechange = function () { if (xmlHttpRequest.readyState == 4 && xmlHttpRequest.status == 200) { let data = xmlHttpRequest.responseText; jsonData = JSON.parse(data); let maxIndex = jsonData[jsonData.length - 1].id + 1; initData("tab"); } } xmlHttpRequest.send(); }
2、从前端向后端传数据
(1)校验管理员
/** * 6、校验管理员、 * 关于传参选择普通键值对还是JSON字符串: * 简单数据用普通键值对,直观简洁,在 URL拼接或传统表单提交时很方便,后端解析也容易。 * 而像实体类这种包含多个属性、结构较复杂的数据,JSON 字符串能更好呈现其完整结构,方便前后端处理和交互 * 这里测试过了,两种方法都是可以的 */ function isAdmin() { let xmlHttpRequest = new XMLHttpRequest(); let newData={ "admin":user.value, "password":pwd.value } let s = encodeURIComponent(JSON.stringify(newData)); xmlHttpRequest.open("get", "/javawebstudy2025_war_exploded/Do?method=isAdminDo&Data="+s, true); /*let admin=user.value let password=pwd.value xmlHttpRequest.open("get", "/javawebstudy2025_war_exploded/Do?method=isAdminDo&admin="+admin+"&password="+password, true);*/ xmlHttpRequest.onreadystatechange = function () { if (xmlHttpRequest.readyState == 4 && xmlHttpRequest.status == 200) { let data = xmlHttpRequest.responseText; let parse = JSON.parse(data); if(parse.msg=="success"){ //前端中==就可以比较两个字符串,而Java中需要用equals比较两个对象是否相等,==比较两个对象是否是同一个对象 window.location.href="showList copy 2.html" rel="external nofollow" }else{ alert("用户名或密码错误,请重试") } } } xmlHttpRequest.send(); }
/** * 逻辑2:登录 * * @param servletRequest * @param servletResponse * @throws ServletException * @throws IOException */ public void isAdminDo(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException { String data = servletRequest.getParameter("Data"); JSONObject jsonObject = JSONObject.parseObject(data); String admin = jsonObject.getString("admin"); String password = jsonObject.getString("password"); /* String admin = servletRequest.getParameter("admin"); String password = servletRequest.getParameter("password");*/ StudentImplService studentImplService = new StudentImplService(); Boolean login = studentImplService.isAdminService(admin, password); // System.out.println("login = " + login); PrintWriter writer = servletResponse.getWriter(); if(login!=null){ // HttpServletResponse servletResponse1 = (HttpServletResponse) servletResponse; // servletResponse1.sendRedirect("showList copy 2.html"); // Result result = new Result(1,"success",null); writer.write(JSON.toJSONString(Result.success())); }else{ //return Result.error("登陆失败"); writer.write(JSON.toJSONString(Result.error("登录失败"))); // writer.write(333); } }
(2)添加
/** * 2、添加数据 * @returns */ function addData() { var maxIndex = jsonData[jsonData.length - 1].id + 1 if (sname.value == "" || ssex.value == "" || sage.value == "") { alert("数据不完整") return false; } let newData = { "id": maxIndex, "sname": sname.value, "ssex": ssex.value, "sage": sage.value, } let jsonStr = encodeURIComponent(JSON.stringify(newData)); // let jsonStr = JSON.stringify(newData); // alert(jsonStr) let xmlHttpRequest = new XMLHttpRequest(); xmlHttpRequest.open("get", "/javawebstudy2025_war_exploded/Do?method=addDo&jsondata=" + jsonStr, true); xmlHttpRequest.onreadystatechange = function () { if (xmlHttpRequest.readyState == 4 && xmlHttpRequest.status == 200) { let data = xmlHttpRequest.responseText; ajaxGetData(); } } xmlHttpRequest.send(); }
/** * 逻辑4:添加 * * @param servletRequest * @param servletResponse * @throws ServletException * @throws IOException */ public void addDo(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException { HttpServletRequest req1 = (HttpServletRequest) servletRequest; HttpSession session = req1.getSession(false); PrintWriter writer = servletResponse.getWriter(); String newStu = servletRequest.getParameter("jsondata"); JSONObject jsonObject = JSONObject.parseObject(newStu); /*这里收参方式有问题,在前面已经通过getParameter获取到了jsondata,后面在取键时应该.属性名 String sname = servletRequest.getParameter("sname"); String ssex = servletRequest.getParameter("ssex"); String sage = servletRequest.getParameter("sage");*/ String sname = jsonObject.getString("sname"); String ssex = jsonObject.getString("ssex"); String sage = jsonObject.getString("sage"); Student student = new Student(null, sname, ssex, sage); int add = studentImplService.insertService(student); if (add > 0) { // servletRequest.getRequestDispatcher("Do?method=selectDo").forward(servletRequest, servletResponse); HttpServletResponse servletResponse1 = (HttpServletResponse) servletResponse; // servletResponse1.sendRedirect("Do?method=selectDo"); } else { System.out.println("添加失败!"); } }
(3)实现更新
* 5、更新数据:将表格里的新数据又赋给json对象各属性的值 * 这个不用闭包 */ function updateData1() { let xmlHttpRequest = new XMLHttpRequest(); let newData = { "id": id,//这里我就使用的是全局变量,以后每次先点击更新按钮,id就会被重新赋值为当前学号 "sname": sname.value, "ssex": ssex.value, "sage": sage.value, } let s = encodeURIComponent(JSON.stringify(newData)); xmlHttpRequest.open("get", "/javawebstudy2025_war_exploded/Do?method=updateDo&newStu=" + s, true); xmlHttpRequest.onreadystatechange = function () { if (xmlHttpRequest.readyState == 4 && xmlHttpRequest.status == 200) { ajaxGetData(); } } xmlHttpRequest.send(); }
/** * 逻辑6:真正实现更新 * @param req * @param res * @throws ServletException * @throws IOException */ public void updateDo(ServletRequest req, ServletResponse res) throws ServletException, IOException { String newStu = req.getParameter("newStu"); JSONObject jsonObject = JSONObject.parseObject(newStu); Integer id = jsonObject.getInteger("id"); String sname = jsonObject.getString("sname"); String ssex = jsonObject.getString("ssex"); String sage = jsonObject.getString("sage"); Student student = new Student(id, sname, ssex, sage); int update = studentImplService.updateService(student); if (update < 0) { System.out.println("更新失败!"); } } }
3、从后端向前端传数据
(1)查询数据
/** * 1、渲染json数据,并且动态生成表格 */ function initData(tab) { // 清理原来的DOM结构(不清理表头) tabObj.innerHTML = ""; for (let index = 0; index < jsonData.length; index++) { var trObj = document.createElement("tr") if (index % 2 == 0) { trObj.style.backgroundColor = "lightblue"//偶数行是蓝色 } for (let pos = 0; pos < Object.keys(jsonData[0]).length + 2; pos++) { var tdObj = document.createElement("td") trObj.appendChild(tdObj) } let tdObjChildren = trObj.children; let m = 0; Object.keys(jsonData[index]).forEach(key => { tdObjChildren[m++].innerHTML = jsonData[index][key]; } ) let btnObj = document.createElement("button") btnObj.innerHTML = "删除"; btnObj.onclick = delDate(index); // tdObjChildren[4].appendChild(btnObj) tdObjChildren[Object.keys(jsonData[0]).length].appendChild(btnObj) let btnObj1 = document.createElement("button") btnObj1.innerHTML = "更新"; btnObj1.onclick = updateData(jsonData[index].id) tdObjChildren[Object.keys(jsonData[0]).length + 1].appendChild(btnObj1) tabObj.appendChild(trObj) } }
/** * 逻辑1:渲染数据 * * @param req * @param resp * @throws ServletException * @throws IOException */ public void selectDo(ServletRequest req, ServletResponse resp) throws ServletException, IOException { HttpServletRequest req1 = (HttpServletRequest) req; HttpSession session = req1.getSession(false); HttpServletResponse resp1 = (HttpServletResponse) resp; List<Student> allData = studentImplService.getAllService(); String s = JSON.toJSONString(allData); PrintWriter writer = resp.getWriter(); writer.write(s); // req1.setAttribute("data", allData); // req1.getRequestDispatcher("ShowList1.jsp").forward(req1, resp1); }
(2)获取一条数据
/** * 4、更新数据:将json数据放在表格里 */ function updateData(index) { let index1 = index//闭包函数写法 return function () { indexc = index1;//全局的indexc记录了要修改的数据的下标 let xmlHttpRequest = new XMLHttpRequest(); xmlHttpRequest.open("get", "/javawebstudy2025_war_exploded/Do?method=getOneDo&id=" + indexc, true); xmlHttpRequest.onreadystatechange = function () { if (xmlHttpRequest.readyState == 4 && xmlHttpRequest.status == 200) { let data = xmlHttpRequest.responseText; /* if(data.code==200 && data.msg=="success") { }*/ let parse = JSON.parse(data); id = parse.id;//我将这里的id设置为全局变量,为了在真正实现更新时给“id”值 // console.log(id); sname.value = parse.name//注意,这里返回了一条从数据库里面查出来的数据,你通过.属性名时这里的属性名是表中字段名 ssex.value = parse.sex sage.value = parse.age // console.log(parse); ajaxGetData(); } } xmlHttpRequest.send(); } }
/** * 逻辑5:获取一条数据:服务器端渲染 * @param req * @param res * @throws ServletException * @throws IOException */ public void getOneDo(ServletRequest req, ServletResponse res) throws ServletException, IOException { Integer id = Integer.valueOf(req.getParameter("id")); Student student = studentImplService.getOneService(id); String s = JSON.toJSONString(student); PrintWriter writer = res.getWriter(); writer.write(s); }
(3)删除一条数据
/** * 3、删除数据 * @param {*} index * @returns */ //也可以在调用处传参jsonData[index].id,然后让他等于index1,在地址里面传参index1即可 function delDate(index) { let index1 = index; return function () { if (confirm("确认删除吗?")) { let xmlHttpRequest = new XMLHttpRequest(); xmlHttpRequest.open("get", "/javawebstudy2025_war_exploded/Do?method=delDo&id=" + jsonData[index1].id, true); xmlHttpRequest.onreadystatechange = function () { if (xmlHttpRequest.readyState == 4 && xmlHttpRequest.status == 200) { // let data = xmlHttpRequest.responseText; ajaxGetData(); } } xmlHttpRequest.send(); } } }
/** * 逻辑3;删除 * * @param req * @param res * @throws ServletException * @throws IOException */ public void delDo(ServletRequest req, ServletResponse res) throws ServletException, IOException { // 获取删除的那条记录的主键ID String id = req.getParameter("id"); System.out.println("id = " + id); // 数据访问层 Integer idd = Integer.valueOf(id); int i = studentImplService.delService(idd); System.out.println("i = " + i); if (i > 0) { // req.getRequestDispatcher("/Do?method=selectDo").forward(req, res); HttpServletResponse servletResponse1 = (HttpServletResponse) res; // servletResponse1.sendRedirect("Do?method=selectDo"); } else { System.out.println("删除失败!"); } }
4、数据访问层展示
我的这个项目实现了数据的增删查改与校验管理员(通过vscode中我那个纯前端的项目改造的),分别写了两个实体类:学生类和管理员类,我也为他们分别写了数据访层。我记得当时没有写管理员类,然后通过mybatis操作数据库失败了,所以定义管理员类是必要的。
package dao; import moudle.Student; import org.apache.ibatis.annotations.*; import java.util.List; public interface StudentDao { // 渲染数据 @Select("select * from Student") List<Student> getAllDao(); // 删除 @Delete("delete from student where id=#{id}") int delDao(Integer id); // 添加 @Insert("insert into student values (null,#{name},#{sex},#{age})") int insertDao(Student student); // 拿到一条数据 @Select("select * from student where id=#{id}") Student getOneDao(Integer id); // 更新 @Update("update student set name=#{name},sex=#{sex},age=#{age} where id=#{id}") int updateDao(Student student); // 分页查询 @Select("select * from student limit #{start},#{pageSize}") List<Student> fenYeDao(@Param("start") Integer start,@Param("pageSize") Integer pageSize); }
package dao; import org.apache.ibatis.annotations.Param; import org.apache.ibatis.annotations.Select; public interface ManagerDao { @Select("select * from manager where admin=#{admin} and password=#{password}") Boolean isAdminDao(@Param("admin") String admin,@Param("password") String password); }
5、分页查询前端代码备份
这是一个jsp文件
<%@ page import="moudle.Student" %> <%@ page import="java.util.List" %> <%@ page import="service.impl.StudentImplService" %> <%-- Created by IntelliJ IDEA. User: 34806 Date: 2025/5/7 Time: 10:15 To change this template use File | Settings | File Templates. --%> <%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head> <title>学生信息列表展示</title> <meta charset="utf-8"> <meta name="viewport" content="width=device-width, initial-scale=1"> <link rel="stylesheet" href="https://cdn.staticfile.net/twitter-bootstrap/4.3.1/css/bootstrap.min.css" rel="external nofollow" > <script src="https://cdn.staticfile.net/jquery/3.2.1/jquery.min.js"></script> <script src="https://cdn.staticfile.net/popper.js/1.15.0/umd/popper.min.js"></script> <script src="https://cdn.staticfile.net/twitter-bootstrap/4.3.1/js/bootstrap.min.js"></script> </head> <body> <% // List<Student> data = (List<Student>) request.getAttribute("data"); /** * 作用域问题:在 JSP 中, * request.getAttribute("data") 获取数据, * request 作用域仅在一次请求 - 响应过程中有效。 * 点击下一页是新请求,之前 request 作用域里的数据不会自动带到新请求中。 * 若没有重新设置 data 到新 request 作用域,就获取不到。 */ StudentImplService studentImplService1 = new StudentImplService(); List<Student> data = studentImplService1.getAllService(); // 1.计算有多少条数据 int totalCount = data.size(); // 2.设置每一页有几条数据 int pageSize = 3; // 3.计算有多少页 int pageCount = (int) (Math.ceil(totalCount * 1.0 / pageSize)); // 4.获取当前页 int curPage = request.getParameter("curPage") == null ? 1 : Integer.valueOf(request.getParameter("curPage")); // 计算偏移值 int offSet = (curPage - 1) * 3; // 5.获取当前页的数据 StudentImplService studentImplService = new StudentImplService(); List<Student> students = studentImplService.fenYeService(offSet, pageSize); %> <%--你依然保持在线!--%> <a href='/javawebstudy2025_war_exploded/logout'>退出</a> <table class="table"> <thead class="thead-dark"> <tr> <th>学号</th> <th>姓名</th> <th>性别</th> <th>年龄</th> <th>操作1</th> <th>操作2</th> </tr> </thead> <tbody> <% for (int i = 0; i < students.size(); i++) { %> <tr> <td> <%=students.get(i).getId()%> </td> <td> <%=students.get(i).getName()%> </td> <td> <%=students.get(i).getSex()%> </td> <td> <%=students.get(i).getAge()%> </td> <td> <a href="/javawebstudy2025_war_exploded/Do?method=delDo&id=<%=students.get(i).getId()%>" rel="external nofollow" onclick="if(confirm('确认删除吗?')) return true;return false;">删除</a> </td> <td> <a href="/javawebstudy2025_war_exploded/Do?method=getOneDo&id=<%=students.get(i).getId()%>" rel="external nofollow" >更新</a> </td> </tr> <% } %> <% if (curPage == 1) { %> <tr> <td>首页</td> <td>上一页</td> <td><a href="ShowList1.jsp?curPage=<%=curPage+1%>" rel="external nofollow" rel="external nofollow" >下一页</a></td> <td><a href="ShowList1.jsp?curPage=<%=pageCount%>" rel="external nofollow" rel="external nofollow" >尾页</a></td> </tr> <% } else if (curPage == pageCount) { %> <tr> <td><a href="ShowList1.jsp?curPage=1" rel="external nofollow" rel="external nofollow" >首页</a></td> <td><a href="ShowList1.jsp?curPage=<%=curPage-1%>" rel="external nofollow" rel="external nofollow" >上一页</a></td> <td>下一页</td> <td>尾页</td> </tr> <% } else { %> <tr> <td><a href="ShowList1.jsp?curPage=1" rel="external nofollow" rel="external nofollow" >首页</a></td> <td><a href="ShowList1.jsp?curPage=<%=curPage-1%>" rel="external nofollow" rel="external nofollow" >上一页</a></td> <td><a href="ShowList1.jsp?curPage=<%=curPage+1%>" rel="external nofollow" rel="external nofollow" >下一页</a></td> <td><a href="ShowList1.jsp?curPage=<%=pageCount%>" rel="external nofollow" rel="external nofollow" >尾页</a></td> </tr> <% } %> </tbody> </table> <button style='padding: 10px 20px;display: block; margin: 0 auto;'> <a href="/javawebstudy2025_war_exploded/add.html" rel="external nofollow" >添加</a> </button> </body> </html>
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