Ajax的基础使用

爱被打了一巴掌 2024-03-30 17:34 20阅读 0赞

## Ajax的基础使用 ##

**简介**：Ajax即Asynchronous Javascript And XML（异步JavaScript和XML）在 2005年被Jesse James Garrett提出的新术语，用来描述一种使用现有技术集合的‘新’方法，包括: HTML 或 XHTML, CSS, JavaScript, DOM, XML, XSLT, 以及最重要的XMLHttpRequest。 使用Ajax技术网页应用能够快速地将增量更新呈现在用户界面上，而不需要重载（刷新）整个页面，这使得程序能够更快地回应用户的操作。

在以前没有ajax的时候，前后端的交互需要使用到，JSP，然后了JSP还是要由后端程序员来写，极大的提高了后端程序员的工作量，降低的开发效率。  
![在这里插入图片描述][70c38ed0280e44b4927a2521e9b5df7f.png]  
有了ajax这种异步请求工具之后，后端程序员就不在需要使用到JSP了，前端的html页面可以通过ajax的异步请求与后端直接联系，这样前后端的分工就更加明确了。  
![在这里插入图片描述][dbbeaf314131418a91b74debcf5f9e80.png]

我们通过一个例子来讲解ajax的使用吧。

### 项目创建 ###

**第一步**：  
![在这里插入图片描述][d2f6ec6b053d4cdeaea878e97e1cf59a.png]  
![在这里插入图片描述][c7c519e0ce95428db0ab8765ebe3169a.png]

**第二步**：  
添加配置文件各种依赖

**pom.xml**

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
      <modelVersion>4.0.0</modelVersion>
      <groupId>org.example</groupId>
      <artifactId>AjaxStudy</artifactId>
      <packaging>war</packaging>
      <version>1.0-SNAPSHOT</version>
      <name>AjaxStudy Maven Webapp</name>
      <url>http://maven.apache.org</url>
    
      <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
      </properties>
    
      <dependencies>
        <dependency>
          <groupId>javax.servlet</groupId>
          <artifactId>javax.servlet-api</artifactId>
          <version>3.1.0</version>
          <scope>provided</scope>
        </dependency>
    
        <dependency>
          <groupId>com.alibaba</groupId>
          <artifactId>fastjson</artifactId>
          <version>1.2.62</version>
        </dependency>
    
      </dependencies>
    
      <build>
        <plugins>
          <plugin>
            <groupId>org.apache.tomcat.maven</groupId>
            <artifactId>tomcat7-maven-plugin</artifactId>
            <version>2.2</version>
          </plugin>
        </plugins>
      </build>
    </project>

**第三步**：  
**AjaxServlet**

package com.jakelihua.servlet;
    
    import javax.servlet.*;
    import javax.servlet.http.*;
    import javax.servlet.annotation.*;
    import java.io.IOException;
    
    @WebServlet("/ajaxServlet")
    public class AjaxServlet extends HttpServlet {
        
        @Override
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
            //1. 响应数据
            response.getWriter().write("hello ajax~");
        }
    
        @Override
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
            this.doGet(request, response);
        }
    }

**第四步**：  
进入w3c官网查看教程  
https://www.w3school.com.cn/js/js\_ajax\_intro.asp  
![在这里插入图片描述][00c37f7e69bf47f2b132a2a5c8dab6fd.png]

1.  创建核心对象  
    ![在这里插入图片描述][81de6a4d0aa2495e83c1c7700518a2ea.png]

var xhttp;
    if (window.XMLHttpRequest) {
        
        xhttp = new XMLHttpRequest();
        } else {
        
        // code for IE6, IE5
         xhttp = new ActiveXObject("Microsoft.XMLHTTP");
    }

1.  发送请求  
    ![在这里插入图片描述][bb39e1ffe1d3489db8755e4b04c8752a.png]  
    ![在这里插入图片描述][e7f80810759f4881adb0b2cdb77f72e5.png]

xhttp.open("GET", "http://localhost:8080/AjaxStudy/ajaxServlet");
    xhttp.send();

1.  获取响应

![在这里插入图片描述][b16e8ce41b4442c69064a2f0549e06e9.png]

xhttp.onreadystatechange = function() {
        
            if (this.readyState == 4 && this.status == 200) {
        
                alert(this.responseText); // 我们这里显示一下这个后端反馈的文本
            }
        };

**完整代码**：

<!DOCTYPE html>
    <html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>Title</title>
    </head>
    <body>
    
    <script>
        // 1. 创建核心对象
        var xhttp;
        if (window.XMLHttpRequest) {
          
            xhttp = new XMLHttpRequest();
        } else {
          
            // code for IE6, IE5
            xhttp = new ActiveXObject("Microsoft.XMLHTTP");
        }
        // 2. 发送请求
        xhttp.open("GET", "http://localhost:8080/AjaxStudy/ajaxServlet");
        xhttp.send();
    
        // 3. 获取响应
        xhttp.onreadystatechange = function() {
          
            if (this.readyState == 4 && this.status == 200) {
          
                alert(this.responseText); 
            }
        };
    
    </script>
    </body>
    </html>

**运行结果**：  
![在这里插入图片描述][82a3ea8ce7cb4cf5835051a0d1c4ce14.png]  
![在这里插入图片描述][806351611ac241b8b6757cc849864895.png]

### 案例 ###

这个案例的目的就是完成我们常见的像百度啊，那种点击搜索栏就会出现提示词那种异步请求，网页没有刷新，但是确实响应了，然后紧跟时代，这个案例我使用SpringBoot来做，最开始用的还是传统的MVC，但是说实话，太麻烦了，一大堆配置，调试都要半天。  
![在这里插入图片描述][f4cc80bd2fa64fc2aa66b8c2e0571c25.png]

#### 数据库建表语句 ####

/*
     Navicat MySQL Data Transfer
    
     Source Server         : 本机
     Source Server Type    : MySQL
     Source Server Version : 80024
     Source Host           : localhost:3306
     Source Schema         : projectdatabase
    
     Target Server Type    : MySQL
     Target Server Version : 80024
     File Encoding         : 65001
    
     Date: 11/01/2023 20:27:49
    */
    
    SET NAMES utf8mb4;
    SET FOREIGN_KEY_CHECKS = 0;
    
    -- ----------------------------
    -- Table structure for user
    -- ----------------------------
    DROP TABLE IF EXISTS `user`;
    CREATE TABLE `user`  (
      `id` int NOT NULL AUTO_INCREMENT,
      `username` varchar(20) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
      `password` varchar(200) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
      PRIMARY KEY (`id`) USING BTREE
    ) ENGINE = InnoDB AUTO_INCREMENT = 3 CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = DYNAMIC;
    
    -- ----------------------------
    -- Records of user
    -- ----------------------------
    INSERT INTO `user` VALUES (1, 'LIHUA', '123456');
    INSERT INTO `user` VALUES (2, 'zhangsan', '123');
    INSERT INTO `user` VALUES (3, 'LISI', '456489');
    INSERT INTO `user` VALUES (4, 'heheheh', '123456');
    INSERT INTO `user` VALUES (5, 'ahuang', '123');
    INSERT INTO `user` VALUES (6, 'dsdad', '154654');
    
    SET FOREIGN_KEY_CHECKS = 1;

![在这里插入图片描述][091fa91e6bfc42b6abe5bd6f01509aec.png]

#### **项目结构** ####

一定注意一点，就是这个后端的java类，一定要写在Springbootlogincheck包下面，不然会导致网址访问不到404错误。  
![在这里插入图片描述][09e351747ccd40cdb7aa1b8430decd07.png]

##### **User类** #####

package com.example.springbootlogincheck.Bean;
    
    import lombok.AllArgsConstructor;
    import lombok.Data;
    import lombok.NoArgsConstructor;
    
    @Data
    @AllArgsConstructor
    @NoArgsConstructor
    public class User {
        
        private Integer id;
        private String username;
        private String password;
    }

##### IndexController类 #####

package com.example.springbootlogincheck.Controller;
    
    import org.springframework.stereotype.Controller;
    import org.springframework.web.bind.annotation.RequestMapping;
    
    
    @Controller
    public class IndexController {
        
        @RequestMapping("/")
        public String index(){
        
            return"admin/register.html";
        }
    
    }

##### UserController #####

package com.example.springbootlogincheck.Controller;
    
    import com.example.springbootlogincheck.Bean.User;
    import com.example.springbootlogincheck.Dao.UserDao;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.stereotype.Controller;
    import org.springframework.web.bind.annotation.GetMapping;
    import org.springframework.web.bind.annotation.ResponseBody;
    
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import java.io.IOException;
    import java.util.List;
    
    @Controller
    public class UserController {
        
        @Autowired
        UserDao userDao;
    
    
        @ResponseBody
        @GetMapping("/selectUser")
        public String SelectUser(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
            String username = request.getParameter("username");
            boolean flag = false;
            List<User> list = userDao.selectList(null);
            for (User user : list){
        
                if (user.getUsername().equals(username)){
        
                    flag = true;
                }
            }
            if (flag) {
          // 如果查到了就返回true字符串 反之就是false字符串
                return "true";
            }
            return "false";
        }
    }

##### UserDao #####

package com.example.springbootlogincheck.Dao;
    
    import com.baomidou.mybatisplus.core.mapper.BaseMapper;
    import com.example.springbootlogincheck.Bean.User;
    import org.apache.ibatis.annotations.Mapper;
    
    @Mapper
    public interface UserDao extends BaseMapper<User> {
        
    }

#### **前端网页** ####

##### **register.css** #####

* {
        
        margin: 0;
        padding: 0;
        list-style-type: none;
    }
    .reg-content{
        
        padding: 30px;
        margin: 3px;
    }
    a, img {
        
        border: 0;
    }
    
    body {
        
        background-image: url("../imgs/reg_bg_min.jpg") ;
        text-align: center;
    }
    
    table {
        
        border-collapse: collapse;
        border-spacing: 0;
    }
    
    td, th {
        
        padding: 0;
        height: 90px;
    
    }
    .inputs{
        
        vertical-align: top;
    }
    
    .clear {
        
        clear: both;
    }
    
    .clear:before, .clear:after {
        
        content: "";
        display: table;
    }
    
    .clear:after {
        
        clear: both;
    }
    
    .form-div {
        
        background-color: rgba(255, 255, 255, 0.27);
        border-radius: 10px;
        border: 1px solid #aaa;
        width: 424px;
        margin-top: 150px;
        margin-left:1050px;
        padding: 30px 0 20px 0px;
        font-size: 16px;
        box-shadow: inset 0px 0px 10px rgba(255, 255, 255, 0.5), 0px 0px 15px rgba(75, 75, 75, 0.3);
        text-align: left;
    }
    
    .form-div input[type="text"], .form-div input[type="password"], .form-div input[type="email"] {
        
        width: 268px;
        margin: 10px;
        line-height: 20px;
        font-size: 16px;
    }
    
    .form-div input[type="checkbox"] {
        
        margin: 20px 0 20px 10px;
    }
    
    .form-div input[type="button"], .form-div input[type="submit"] {
        
        margin: 10px 20px 0 0;
    }
    
    .form-div table {
        
        margin: 0 auto;
        text-align: right;
        color: rgba(64, 64, 64, 1.00);
    }
    
    .form-div table img {
        
        vertical-align: middle;
        margin: 0 0 5px 0;
    }
    
    .footer {
        
        color: rgba(64, 64, 64, 1.00);
        font-size: 12px;
        margin-top: 30px;
    }
    
    .form-div .buttons {
        
        float: right;
    }
    
    input[type="text"], input[type="password"], input[type="email"] {
        
        border-radius: 8px;
        box-shadow: inset 0 2px 5px #eee;
        padding: 10px;
        border: 1px solid #D4D4D4;
        color: #333333;
        margin-top: 5px;
    }
    
    input[type="text"]:focus, input[type="password"]:focus, input[type="email"]:focus {
        
        border: 1px solid #50afeb;
        outline: none;
    }
    
    input[type="button"], input[type="submit"] {
        
        padding: 7px 15px;
        background-color: #3c6db0;
        text-align: center;
        border-radius: 5px;
        overflow: hidden;
        min-width: 80px;
        border: none;
        color: #FFF;
        box-shadow: 1px 1px 1px rgba(75, 75, 75, 0.3);
    }
    
    input[type="button"]:hover, input[type="submit"]:hover {
        
        background-color: #5a88c8;
    }
    
    input[type="button"]:active, input[type="submit"]:active {
        
        background-color: #5a88c8;
    }
    .err_msg{
        
        color: red;
        padding-right: 170px;
    }
    #password_err,#tel_err{
        
        padding-right: 195px;
    }
    
    #reg_btn{
        
        margin-right:50px; width: 285px; height: 45px; margin-top:20px;
    }
    
    #checkCode{
        
        width: 100px;
    }
    
    #changeImg{
        
        color: aqua;
    }

##### img #####

**a.jpg**  
![在这里插入图片描述][f2afd31d3ede45f6b6ebdd8a062e5938.png]

**reg\_bg\_min.jpg**  
![在这里插入图片描述][6a16a42543a847cab589db75bbff1bb0.png]

##### register.html #####

**js部分**  
在这个js部分里面，一个点需要注意一下，就是这个`responseText`这个属性，这个属性接受的值首先是String类型，然后了，这个值就是访问的链接下对应的方法的返回值的对应的String类型格式。

**完整代码**：

<!DOCTYPE html>
    <html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>欢迎注册</title>
        <link href="css/register.css" rel="stylesheet">
    </head>
    <body>
    
    <div class="form-div">
        <div class="reg-content">
            <h1>欢迎注册</h1>
            <span>已有帐号？</span> <a href="login.html">登录</a>
        </div>
        <form id="reg-form" action="#" method="get">
    
            <table>
    
                <tr>
                    <td>用户名</td>
                    <td class="inputs">
                        <input name="username" type="text" id="username">
                        <br>
                        <span id="username_err" class="err_msg" style="display: none">用户名已存在</span>
                    </td>
    
                </tr>
    
                <tr>
                    <td>密码</td>
                    <td class="inputs">
                        <input name="password" type="password" id="password">
                        <br>
                        <span id="password_err" class="err_msg" style="display: none">密码格式有误</span>
                    </td>
                </tr>
    
    
                <tr>
                    <td>验证码</td>
                    <td class="inputs">
                        <input name="checkCode" type="text" id="checkCode">
                        <img src="imgs/a.jpg">
                        <a href="#" id="changeImg">看不清？</a>
                    </td>
                </tr>
    
            </table>
    
            <div class="buttons">
                <input value="注 册" type="submit" id="reg_btn">
            </div>
            <br class="clear">
        </form>
    
    </div>
    
    <script>
    
        //1. 给用户名输入框绑定 失去焦点事件
        document.getElementById("username").onblur = function () {
          
            //2. 发送ajax请求
            // 获取用户名的值
            var username = this.value;
    
            //2.1. 创建核心对象
            var xhttp;
            if (window.XMLHttpRequest) {
          
                xhttp = new XMLHttpRequest();
            } else {
          
                // code for IE6, IE5
                xhttp = new ActiveXObject("Microsoft.XMLHTTP");
            }
            //2.2. 发送请求
            xhttp.open("GET", "http://localhost:8080/ajax-demo/selectUserServlet?username="+username);
            xhttp.send();
    
            //2.3. 获取响应
            xhttp.onreadystatechange = function() {
          
                if (this.readyState == 4 && this.status == 200) {
          
                    //alert(this.responseText);
                    //判断
                    if(this.responseText == "true"){
          
                        //用户名存在，显示提示信息
                        document.getElementById("username_err").style.display = '';
                    }else {
          
                        //用户名不存在 ，清楚提示信息
                        document.getElementById("username_err").style.display = 'none';
                    }
                }
            };
    
        }
    </script>
    </body>
    </html>

**效果展示**：  
如果输入的账户在失去焦点之后，发现这个用户没有在数据库中存在就不会发生啥。  
![在这里插入图片描述][4362cc8d83c74454b3a9cf73c233f38b.png]  
如果存在的话就显示这个信息，已经存在了。  
![在这里插入图片描述][cb01eaa85fd64217a557133773a0ea4f.png]

[70c38ed0280e44b4927a2521e9b5df7f.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/5a1182eb0d0a49719a88ba1638dc1e83.png
[dbbeaf314131418a91b74debcf5f9e80.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/92eb940cf5f3401c8f0a49ab649882e2.png
[d2f6ec6b053d4cdeaea878e97e1cf59a.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/252f0dbfd21944dea9671a7cccd0a7f9.png
[c7c519e0ce95428db0ab8765ebe3169a.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/50726fb1870446c79e5b43358aa52cf4.png
[00c37f7e69bf47f2b132a2a5c8dab6fd.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/3d3274ead3834f9ca79da176bef6e978.png
[81de6a4d0aa2495e83c1c7700518a2ea.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/1de3ad656ecb48559616b06d1703138f.png
[bb39e1ffe1d3489db8755e4b04c8752a.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/5a261ddbe0f54427a5110b884975be55.png
[e7f80810759f4881adb0b2cdb77f72e5.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/7eed8b01d7074d3f8c5a46f1c8ad82d3.png
[b16e8ce41b4442c69064a2f0549e06e9.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/e63aecdf371a41a7b34d975c58a093c4.png
[82a3ea8ce7cb4cf5835051a0d1c4ce14.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/2bb642909af448458eeba0172459c877.png
[806351611ac241b8b6757cc849864895.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/b829689dc7fc44228a3b37bac18223a0.png
[f4cc80bd2fa64fc2aa66b8c2e0571c25.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/c0ab94be4262487a970270ecfddb6ff8.png
[091fa91e6bfc42b6abe5bd6f01509aec.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/2ddeb3cc5c464d6b8f590f3255c84212.png
[09e351747ccd40cdb7aa1b8430decd07.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/855c652384cb400a80d6c9fb079cf517.png
[f2afd31d3ede45f6b6ebdd8a062e5938.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/136c527f5fb548c993647970f0457216.png
[6a16a42543a847cab589db75bbff1bb0.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/693af8489648497faf5c90528fef66c5.png
[4362cc8d83c74454b3a9cf73c233f38b.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/99605e9489074d768f629eef49169a21.png
[cb01eaa85fd64217a557133773a0ea4f.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/0214e1357265432eaacf4131346cd065.png