目录
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 {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//响应数据
response.getWriter().write("hello ajax");
}
@Override
protected 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, IE5
xhttp = 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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* Determine if an object is a Buffer
*
* @author Feross Aboukhadijeh <https://feross.org>
* @license MIT
*/
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//# sourceMappingURL=axios.min.map
https://download.csdn.net/download/weixin_59798969/863975054.22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 {
@Override
protected 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~");
}
@Override
protected 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. get
axios.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
-
给用户名输入框绑定光标失去焦点事件
onblur -
发送 ajax请求，携带username参数
-
处理响应：是否显示提示信息
-
-
后端完成的逻辑
-
接收用户名
-
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
-
返回标记
-
5.1DAO层
<!--mybatis的UserMapper.xml-->
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//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mybatis
package 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();
@Override
protected 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);
}
@Override
protected 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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