Ajax和Axios 的简介及简单应用案例

1.ajax概念

2.ajax作用

2.1与服务器进行数据交换：

2.2异步交互：

3.ajax快速入门

3.1传送数据

3.2接受并响应数据

4.axios快速入门

4.1axios概念

4.2axios快速入门

4.21创建 axios 的 js 文件

4.22案例

4.3axios起别名方法

5.用户注册案例

5.1DAO层

5.2service层

5.3web层

5.4HTML页面

6.VUE使用ajax的前端代码优化

1.ajax概念

AJAX (Asynchronous JavaScript And XML)：异步的 JavaScript 和 XML。

2.ajax作用

AJAX 作用有以下两方面：

2.1与服务器进行数据交换：

通过AJAX可以给服务器发送请求，服务器将数据直接响应回给浏览器。如下图

我们先来看之前做功能的流程，如下图：

如上图，Servlet 调用完业务逻辑层后将数据存储到域对象中，然后跳转到指定的 jsp 页面，在页面上使用 EL表达式 和 JSTL 标签库进行数据的展示。

而我们学习了AJAX 后，就可以使用AJAX和服务器进行通信，以达到使用 HTML+AJAX来替换JSP页面了。如下图，浏览器发送请求servlet，servlet 调用完业务逻辑层后将数据直接响应回给浏览器页面，页面使用 HTML 来进行数据展示。

2.2异步交互：

可以在“不重新加载整个页面”的情况下，与服务器交换数据并“更新部分网页”的技术，如：搜索联想、用户名是否可用校验，等等…

上图所示的效果我们经常见到，在我们输入一些关键字（例如 奥运）后就会在下面联想出相关的内容，而联想出来的这部分数据肯定是存储在百度的服务器上，而我们并没有看出页面重新刷新，这就是更新局部页面的效果。再如下图：

我们在用户名的输入框输入用户名，当输入框一失去焦点，如果用户名已经被占用就会在下方展示提示的信息；在这整个过程中也没有页面的刷新，只是在局部展示出了提示信息，这就是更新局部页面的效果。

3.ajax快速入门

3.1传送数据

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

3.2接受并响应数据

<!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, IE5xhttp = new ActiveXObject("Microsoft.XMLHTTP");}//2.发送请求// method：请求的类型：GET 还是 POST// url：服务器（文件）位置，url要写全路径// async：true（异步）或 false（同步）xhttp.open("GET", "http://localhost:8080/ajax-demo/AjaxServlet",true);xhttp.send();//3.获取响应xhttp.onreadystatechange = function() {if (this.readyState == 4 && this.status == 200) {alert(this.responseText);}};</script></body>
</html>

4.axios快速入门

4.1axios概念

Axios 对原生的AJAX进行封装，简化书写。

4.2axios快速入门

4.21创建 axios 的 js 文件

axios-0.18.0.js

/* axios v0.18.0 | (c) 2018 by Matt Zabriskie */
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o=n(23);r.prototype.throwIfRequested=function(){if(this.reason)throw this.reason},r.source=function(){var e,t=new r(function(t){e=t});return{token:t,cancel:e}},e.exports=r},function(e,t){"use strict";e.exports=function(e){return function(t){return e.apply(null,t)}}}])});
//# sourceMappingURL=axios.min.map

VUE和AXios使用的JS文件及Element组件库-Javascript文档类资源-CSDN文库https://download.csdn.net/download/weixin_59798969/86397505

4.22案例

package com.web.servlet;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;@WebServlet("/axiosServlet")
public class AxiosServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {System.out.println("get...");//1. 接收请求参数String username = request.getParameter("username");System.out.println(username);//2. 响应数据response.getWriter().write("hello Axios~");}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {System.out.println("post...");this.doGet(request, response);}
}

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><title>Title</title>
</head>
<body><!--引入名为js包下js代码-->
<script src="js/axios-0.18.0.js"></script><script>//1. get/* axios({method:"get",url:"http://localhost:8080/ajax-demo/axiosServlet?username=zhangsan"}).then(function (resp) {alert(resp.data);})*///2. post  在js中{} 表示一个js对象，而这个js对象中有三个属性axios({method:"post",url:"http://localhost:8080/ajax-demo/axiosServlet",data:"username=zhangsan"}).then(function (resp) {alert(resp.data);})
</script>
</body>
</html>

axios() 是用来发送异步请求的，小括号中使用 js 对象传递请求相关的参数：

method 属性：用来设置请求方式的。取值为 get 或者 post。
url 属性：用来书写请求的资源路径。如果是 get 请求，需要将请求参数拼接到路径的后面，格式为： url?参数名=参数值&参数名2=参数值2。
data 属性：作为请求体被发送的数据。也就是说如果是 post 请求的话，数据需要作为 data 属性的值。

then() 需要传递一个匿名函数。我们将 then() 中传递的匿名函数称为回调函数，意思是该匿名函数在发送请求时不会被调用，而是在成功响应后调用的函数。而该回调函数中的 resp 参数是对响应的数据进行封装的对象，通过 resp.data 可以获取到响应的数据。

4.3axios起别名方法

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><title>Title</title>
</head>
<body><script src="js/axios-0.18.0.js"></script>
<script>//1. getaxios.get("http://localhost:8080/ajax-demo/axiosServlet?username=zhangsan").then(function (resp) {alert(resp.data);});//2. post  在js中{} 表示一个js对象，而这个js对象中有三个属性axios.post("http://localhost:8080/ajax-demo/axiosServlet","username=zhangsan").then(function (resp) {alert(resp.data);})
</script>
</body>
</html>

5.用户注册案例

功能：用户注册时通过ajax自动检验该用户名是否存在。

分析：

前端完成的逻辑
1. 给用户名输入框绑定光标失去焦点事件 onblur
2. 发送 ajax请求，携带username参数
3. 处理响应：是否显示提示信息
后端完成的逻辑
1. 接收用户名
2. 调用service查询User。此案例是为了演示前后端异步交互，所以此处我们不做业务逻辑处理
3. 返回标记

5.1DAO层

<!--mybatis的UserMapper.xml--><?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.mapper.UserMapper"></mapper>

package com.mapper;import com.pojo.User;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;public interface UserMapper {/*** 根据用户名和密码查询用户对象* @param username* @param password* @return*///可直接这样写，也可以写到UserMapper.XML中@Select("select * from tb_user where username = #{username} and password = #{password}")User select(@Param("username") String username,@Param("password")  String password);/*** 根据用户名查询用户对象* @param username* @return*/@Select("select * from tb_user where username = #{username}")User selectByUsername(String username);/*** 添加用户* @param user*/@Insert("insert into tb_user values(null,#{username},#{password})")void add(User user);
}

5.2service层

//util工具包：实现mybatispackage com.util;import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;import java.io.IOException;
import java.io.InputStream;public class SqlSessionFactoryUtils {private static SqlSessionFactory sqlSessionFactory;static {//静态代码块会随着类的加载而自动执行，且只执行一次try {String resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);} catch (IOException e) {e.printStackTrace();}}public static SqlSessionFactory getSqlSessionFactory(){return sqlSessionFactory;}
}

package com.service;import com.mapper.UserMapper;
import com.pojo.User;
import com.util.SqlSessionFactoryUtils;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;public class UserService {SqlSessionFactory sqlSessionFactory = SqlSessionFactoryUtils.getSqlSessionFactory();public boolean register(User user){SqlSession sqlSession = sqlSessionFactory.openSession();UserMapper mapper = sqlSession.getMapper(UserMapper.class);User user1 = mapper.selectByUsername(user.getUsername());if(user1==null){//调用DAO层UserMapper的方法mapper.add(user);sqlSession.commit();}sqlSession.close();return user1==null;}public boolean selectByName(String username){SqlSession sqlSession = sqlSessionFactory.openSession();UserMapper mapper = sqlSession.getMapper(UserMapper.class);User user1 = mapper.selectByUsername(username);sqlSession.close();//        if(user1!=null){
//            //该用户名不存在，为真
//            return true;
//        }
//        else{
//            //该用户名存在，为假
//            return false;
//        }return user1==null;}
}

5.3web层

package com.web.servlet;import com.pojo.User;
import com.service.UserService;import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;@WebServlet(name = "SelectUserServlet", value = "/SelectUserServlet")
public class SelectUserServlet extends HttpServlet {private UserService userService = new UserService();@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//1.获取用户名String username = request.getParameter("username");//2.调用service查询user对象boolean flag=userService.selectByName(username);//3.响应标记response.getWriter().write(""+flag);}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doGet(request, response);}
}

5.4HTML页面

<!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>//第二种方法添加
<script src="js/axios-0.18.0.js"></script><script>//第一种方法// //1.给用户名输入框绑定一个，失去焦点的事件// 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//     // method：请求的类型：GET 还是 POST//     // url：服务器（文件）位置，url要写全路径//     // async：true（异步）或 false（同步）//     xhttp.open("GET", "http://localhost:8080/ajax-demo/SelectUserServlet?username="+username,true);//     xhttp.send();////     //2.3.获取响应//     xhttp.onreadystatechange = function() {//         if (this.readyState == 4 && this.status == 200) {//             //alert(this.responseText);//             //responseText:获取字符串形式的响应数据//             if(this.responseText=="true"){//                 //若注册用户名存在，显示提示信息//                 document.getElementById("username_err").style.display='';//             }else{//                 //若注册用户名不存在，清除提示信息//                 //默认为none，是隐藏的//                 document.getElementById("username_err").style.display='none';//             }//         }//     };// }//第二种方法document.getElementById("username").onblur=function (){var username=this.value;axios.get("http://localhost:8080/ajax-demo/SelectUserServlet?username="+username).then(function (resp) {//alert(resp.data);if(resp.data){//若注册用户名存在，显示提示信息document.getElementById("username_err").style.display='';}else{//若注册用户名不存在，清除提示信息//默认为none，是隐藏的document.getElementById("username_err").style.display='none';}});}</script>
</body>
</html>

6.VUE使用ajax的前端代码优化

针对前端代码中的发送异步请求的代码，如下：

//进行this的转化
var _this = this;axios({method:"post",url:"http://localhost:8080/brand-case/brand/selectByPageAndCondition?currentPage="+this.currentPage+"&pageSize="+this.pageSize,data:this.brand
}).then(function (resp) {//设置表格数据_this.tableData = resp.data.rows; // {rows:[],totalCount:100}//设置总记录数_this.totalCount = resp.data.totalCount;
})

需要在成功的回调函数（也就是then 函数中的匿名函数）中使用this，都需要在外边使用 _this 记录一下 this 所指向的对象；因为在外边的 this 表示的是 Vue 对象，而回调函数中的 this 表示的不是 vue 对象，是window对象。这里我们可以使用 ECMAScript6 中的新语法（箭头函数）来简化这部分代码，如上面的代码可以简化为:

axios({method:"post",url:"http://localhost:8080/brand-case/brand/selectByPageAndCondition?currentPage="+this.currentPage+"&pageSize="+this.pageSize,data:this.brand
}).then((resp) => {//设置表格数据this.tableData = resp.data.rows; // {rows:[],totalCount:100}//设置总记录数this.totalCount = resp.data.totalCount;
})

箭头函数作用：

替换（简化）匿名函数。then(箭头函数)里面的this是vue不是window。
所有的function (resp){}均可替换为resp =>{}，且不再需要this的转化。

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