小黑子—JavaWeb：第六章 - Filter、Listener、AJAX与JSON

1. Filter

• 概念: Filter表示过滤器，是JavaWeb三大组件(Servlet、Filter、Listener)之一。
• 过滤器可以把对资源的请求拦截下来，从而实现一些特殊的功能。
• 过滤器一般完成一些通用的操作，比如：权限控制、统一编码处理、敏感字符处理等等
  

1.1 Filter快速入门

1. 定义类，实现Filter接口，并重写其所有方法

public class FilterDemo implements Filter {public void init(FilterConfig filterConfig)public void doFilter(ServletRequest request)public void destroy(){}
}

2. 配置Filter拦截资源的路径：再类上定义@WebFilter注解

@WebFilter("/*")public class FilterDemo implements Filter {}

3. 在doFilter方法中输出一句话，并放行

 public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {System.out.println("Filter....");//放行filterChain.doFilter(servletRequest,servletResponse);}

例子：

package com.itheima.web.filter;import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import java.io.IOException;@WebFilter("/*")
public class FilterDemo implements Filter{@Overridepublic void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {System.out.println("FilterDemo...");//放行chain.doFilter(request,response);}@Overridepublic void init(FilterConfig filterConfig) throws ServletException {}@Overridepublic void destroy() {}
}

放行之后访问才成功：

1.2 Filter执行流程

1. 放行后访问对应资源，资源访问完成后，还会回到Filter中吗?
   • 会
2. 如果回到Filter中，是重头执行还是执行放行后的逻辑呢?
   • 放行后逻辑
     

1.3 Filter拦截路径配置

Filter 可以根据需求，配置不同的拦截资源路径

 @WebFilter("/*")public class FilterDemo

• 拦截具体的资源：/index.jsp:只有访问index.jsp时才会被拦截。
• 目录拦截：/user/*:访问/user下的所有资源，都会被拦截
• 后缀名拦截： *.jsp:访问后缀名为jsp的资源，都会被拦截
• 拦截所有：/*:访问所有资源，都会被拦截

1.4 Filter过滤器链

一个Web应用，可以配置多个过滤器，这多个过滤器被称为过滤器链

注解配置的Filter，优先级按照过滤器类名(字符串)的自然排序

1.5 案例登录验证

在brand-demo下：LoginFilter

@WebFilter("/*")
public class LoginFilter implements Filter {@Overridepublic void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws ServletException, IOException {HttpServletRequest req = (HttpServletRequest) request;//判断访问资源路径是否和登录注册相关String[] urls = {"/login.jsp","/imgs","/css/","loginServlet","register.jsp","registerServlet","checkCodeServlet"};//获取当前访问的资源路径String url = req.getRequestURL().toString();//循环判断for (String u : urls) {if(url.contains(u)){//找到了就放行chain.doFilter(request,response);// break不能写return;}}//1.判断session中 userHttpSession session = req.getSession();Object user = session.getAttribute("user");//2.判断 user 是否为nullif(user!=null){//登录过了//放行chain.doFilter(request, response);}else{//没有登录，存储提示信息，跳转到登录页面req.setAttribute("login_msg","您尚未登录");req.getRequestDispatcher("/login.jsp").forward(request,response);}}public void init(FilterConfig config) throws ServletException {}public void destroy() {}}

2. Listener

• 概念: Listener表示监听器，是JavaWeb三大组件(Servlet、Filter、Listener)之一。
• 监听器可以监听就是在application,session,request三个对象创建、销毁或者往其中添加修改删除属性时自动执行代码的功能组件
• Listener分类: JavaWeb中提供了8个监听器

监听器分类	监听器名称	Value
ServletContext监听	ServletContextListener	用于对ServletContext对象进行监听(创建、销毁)
	ServletContextAttributeListener	对ServletContext对象中属性的监听(增删改属性)
Session监听	HttpsessionListener	对Session对象的整体状态的监听（创建、销毁)
	HttpSessionAttributeListener	对Session对象中的属性监听(增删改属性)
	HttpSessionBindingListener	监听对象于Session的绑定和解除
	HttpSessionActivationListener	对Session数据的钝化和活化的监听
Request监听	ServletRequestListener	对Request对象进行监听(创建、销毁)
	ServletRequestAttributeListener	对Request对象中属性的监听（增删改属性)

2.1 ServletContextListener使用

Listener的基本使用都是类似的，掌握一个便可通类

1. 定义类，实现ServletContextListener接口

public class ContextLoaderListener implements ServletContextListener {/*** ServletContext对象被创建:整个web应用发布成功* @param sce*/public void contextInitialized(ServletcintextEvent sce){}/** ServletContext对象被销毁:整个web应用卸载* @param sce*/public void contextDestroyed(ServletContextEvent sce){}}

2. 在类上添加@WebListener注解

例子演示：

package com.itheima.web.listener;import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;@WebListener
public class ContexLoaderListener implements ServletContextListener {@Overridepublic void contextInitialized(ServletContextEvent servletContextEvent) {//加载资源System.out.println(" ContexLoaderListener ...");}@Overridepublic void contextDestroyed(ServletContextEvent servletContextEvent) {//释放资源}
}

3. AJAX

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

AJAX作用:

1. 与服务器进行数据交换:通过AJAX可以给服务器发送请求，并获取服务器响应的数据

   • 使用了AJAX和服务器进行通信，就可以使用HTML+AJAX来替换JSP页面了
     

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…

同步和异步的概念：

3.1 AJAX 快速入门

1. 编写AjaxServlet，并使用response输出字符串

2. 创建XMLHttpRequest 对象:用于和服务器交换数据

var xmlhttp;
if (window.XMLHttpRequest) {
//code for IE7+, Firefox, Chrome, Opera, Safari
xmlhttp = new XMLHttpRequest();
}else {
//code for lE6,IE5
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
}

3. 向服务器发送请求

xmlhttp.open("GET","url");
xmlhttp.send();//发送请求

4. 获取服务器响应数据

xmlhttp.onreadystatechange = function () {if (xmlhttp.readyState == 4 && xmlhttp.status == 200){alert(xmlhttp.responseText)}
};

例子：
AjaxServlet：

@WebServlet("/ajaxServlet")
public class AjaxServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//1.响应数据response.getWriter().write("hello ajax");}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doGet(request, response);}
}

01-ajax-demo1.html：

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><title>Title</title>
</head>
<body><script>//1.创建核心对象var xmlhttp;if (window.XMLHttpRequest) {
//code for IE7+, Firefox, Chrome, Opera, Safarixmlhttp = new XMLHttpRequest();}else {
//code for lE6,IE5xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");}//2.发送请求xmlhttp.open("GET","http://localhost:8080/ajax-demo/ajaxServlet");//写全路径的原因是前端和后端是不在一个服务器部署的，要访问就全路径xmlhttp.send();//发送请求//3.获取响应xmlhttp.onreadystatechange = function () {if (xmlhttp.readyState == 4 && xmlhttp.status == 200){alert(this.responseText);}};
</script></body>
</html>

3.2 案例 验证用户名是否存在

套用案例的静态页面：
SelectUserServlet：

package com.itheima.web.servlet;import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;@WebServlet("/selectUserServlet")
public class SelectUserServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//1. 接收用户名String username = request.getParameter("username");//2.调用service查询User对象boolean flag = true;//3.响应标记response.getWriter().write(""+flag);}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doGet(request, response);}
}

注册页面：

<!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><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 xmlhttp;if (window.XMLHttpRequest) {
//code for IE7+, Firefox, Chrome, Opera, Safarixmlhttp = new XMLHttpRequest();}else {
//code for lE6,IE5xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");}//2.1 发送请求xmlhttp.open("GET","http://localhost:8080/ajax-demo/selectUserServlet?username="+username);//写全路径的原因是前端和后端是不在一个服务器部署的，要访问就全路径xmlhttp.send();//发送请求//2.3获取响应xmlhttp.onreadystatechange = function () {if (xmlhttp.readyState == 4 && xmlhttp.status == 200){// alert(this.responseText);if(this.responseText == "true"){//用户名存在，显示提示信息document.getElementById("username_err").style.display = '';}else {//用户不存在 清除提示信息document.getElementById("username_err").style.display = 'none';}}};}
</script>
</body>
</html>

3.3 Axios 异步框架

Axios对原生的AJAX进行封装，简化书写
Axios官网

3.3.1 Axios 快速入门

1. 引入axios 的js文件

<script src="jslaxios-0.18.0.js"</script>

2. 使用axios 发送请求，并获取响应结果

axios({method:"get",url:"http://localhost:8080/ajax_demo/axiosServlet?username=zhangsan"}).then(function (resp){alert(resp.data);});

axios({method:"post",url:"http://localhost:8080/ajax_demo/axiosServlet",data:"username=zhangsan"}).then(function (resp){alert(resp.data);});

例子：
axios-0.18.0.js 文件

/* axios v0.18.0 | (c) 2018 by Matt Zabriskie */
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//# sourceMappingURL=axios.min.map

AxiosServlet：

package com.itheima.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);}
}

1、get请求部分：

<!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({method:"get",url:"http://localhost:8080/ajax-demo/axiosServlet?username=zhangsan"}).then(function (resp){alert(resp.data);})</script>
</body>
</html>

2、post部分

 //2.postaxios({method:"post",url:"http://localhost:8080/ajax-demo/axiosServlet",data:"username=zhangsan"}).then(function (resp){alert(resp.data);})

3.3.2 Axios 请求方式别名

为了方便起见， Axios已经为所有支持的请求方法提供了别名

方法名	作用
get(url)	发起GET方式请求
post(url,请求参数)	发起POST方式请求

• 发送get请求

    axios.get("url").then(function (resp){alert(resp.data)})

• 发送post请求

axios.post("url","参数").then(function (resp){alert(resp.data)})

方便例子：

<!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.postaxios.post("http://localhost:8080/ajax-demo/axiosServlet","username=zhangsan").then(function (resp){alert(resp.data)})</script>
</body>
</html>

案例练习：

<!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">用户名太受欢迎了</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>
</body>
<script src="js/axios-0.18.0.js"></script>
<script>document.getElementById("username").onblur = function (){axios.get("http://localhost:8080/ajax-demo/selectServlet?username="+username).then(function (resp){console.log(resp.data)if ("true" == resp.data.toString()){//此时没有查询到数据document.getElementById("username_err").style.display = "";}else {//查询到有该数据document.getElementById("username_err").style.display = "none";}})}
</script>
</html>

4. JSON

• 概念：JavaScript Object Notation。JavaScript 对象表示法
• 由于其语法简单，层次结构鲜明，现多用于作为数据载体，在网络中进行数据传输
  

4.1 JSON基础语法

• 定义：

var 变量名 ={"key1": value1,"key2": value2,...};

示例

	var json ={"name": "zhangsan","age": 23,"addr":["北京","上海","广州"]};

value的数据类型为:

• 数字 (整数或浮点数)

• 字符串 (在双引号中)

• 逻辑值 (true或false)

• 数组 (在方括号中)

• 对象 (在花括号中)

• null

获取数据:

变量名.key

json.name

例子：

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><title>Title</title>
</head>
<body><script>//定义josnvar json = {"name":"zhangsan","age":23,"addr":["北京","上海","西安"]}//获取值alert(josn.name);</script>
</body>
</html>

4.2 JSON数据和Java对象转换

• 请求数据：JSON字符串转为Java对象
• 响应数据：Java对象转为JSON字符串
  

Fastjson是阿里巴巴提供的一个Java语言编写的高性能功能完善的JSON库，是目前Java语言中最快的JSON库，可以实现Java对象和JSON字符串的相互转换。

使用：

1. 导入坐标

<dependency><groupId>com.alibaba</groupId><artifactId>fastjson</artifactId><version>1.2.62</version>
</dependency>

2. Java对象转JSON

String jsonStr = JSON.toJSONString(obj);

3. JSON字符串转Java对象

User user = JSON.parseObject(jsonStr,User.class);

例子：

package com.itheima.json;import com.alibaba.fastjson.JSON;public class FastJsonDemo {public static void main(String[] args) {//1.将java对象转换为json字符串User user = new User();user.setId(1);user.setUsername("zhangsan");user.setPassword("123");String jsonString = JSON.toJSONString(user);System.out.println(jsonString);//{"id":1,"password":"123","username":"zhangsan"}//2.将JSON字符串转为java对象User u = JSON.parseObject("{\"id\":1,\"password\":\"123\",\"username\":\"zhangsan\"}", User.class);System.out.println(u);}
}

4.3 案例 品牌数据列表

4.3.1 查询所有

核心配置文件：

<?xml version="1.0" encoding="UTF-8"?><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/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>org.example</groupId><artifactId>brand-demo</artifactId><version>1.0-SNAPSHOT</version><packaging>war</packaging><properties><maven.compiler.source>17</maven.compiler.source><maven.compiler.target>17</maven.compiler.target></properties><dependencies><!--        servlet--><dependency><groupId>javax.servlet</groupId><artifactId>javax.servlet-api</artifactId><version>3.1.0</version><scope>provided</scope></dependency><!--    fastjson--><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>

brand.html

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><title>Title</title>
</head>
<body>
<a href="addBrand.html"><input type="button" value="新增"></a><br>
<hr>
<table id="brandTable" border="1" cellspacing="0" width="100%"><tr><th>序号</th><th>品牌名称</th><th>企业名称</th><th>排序</th><th>品牌介绍</th><th>状态</th><th>操作</th></tr><tr align="center"><td>1</td><td>三只松鼠</td><td>三只松鼠</td><td>100</td><td>三只松鼠，好吃不上火</td><td>启用</td><td><a href="#">修改</a> <a href="#">删除</a></td></tr><tr align="center"><td>2</td><td>优衣库</td><td>优衣库</td><td>10</td><td>优衣库，服适人生</td><td>禁用</td><td><a href="#">修改</a> <a href="#">删除</a></td></tr><tr align="center"><td>3</td><td>小米</td><td>小米科技有限公司</td><td>1000</td><td>为发烧而生</td><td>启用</td><td><a href="#">修改</a> <a href="#">删除</a></td></tr>
</table><script src="js/axios-0.18.0.js"></script><script>//1. 当页面加载完成后，发送ajax请求window.onload = function () {//2. 发送ajax请求axios({method:"get",url:"http://localhost:8080/brand-demo/selectAllServlet"}).then(function (resp) {//获取数据let brands = resp.data;let tableData = " <tr>\n" +"        <th>序号</th>\n" +"        <th>品牌名称</th>\n" +"        <th>企业名称</th>\n" +"        <th>排序</th>\n" +"        <th>品牌介绍</th>\n" +"        <th>状态</th>\n" +"        <th>操作</th>\n" +"    </tr>";for (let i = 0; i < brands.length ; i++) {let brand = brands[i];tableData += "\n" +"    <tr align=\"center\">\n" +"        <td>"+(i+1)+"</td>\n" +"        <td>"+brand.brandName+"</td>\n" +"        <td>"+brand.companyName+"</td>\n" +"        <td>"+brand.ordered+"</td>\n" +"        <td>"+brand.description+"</td>\n" +"        <td>"+brand.status+"</td>\n" +"\n" +"        <td><a href=\"#\">修改</a> <a href=\"#\">删除</a></td>\n" +"    </tr>";}// 设置表格数据document.getElementById("brandTable").innerHTML = tableData;})}</script></body>
</html>

SelectAllService

package com.itheima.web;import com.alibaba.fastjson.JSON;
import com.itheima.pojo.Brand;
import com.itheima.service.BrandService;import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;
import java.util.List;@WebServlet("/selectAllServlet")
public class SelectAllServlet extends HttpServlet {private BrandService brandService = new BrandService();@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//1. 调用Service查询List<Brand> brands = brandService.selectAll();//2. 将集合转换为JSON数据   序列化String jsonString = JSON.toJSONString(brands);//3. 响应数据response.setContentType("text/json;charset=utf-8");response.getWriter().write(jsonString);}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doGet(request, response);}
}

4.3.2 新增品牌

addBrand.html：

<!DOCTYPE html>
<html lang="en"><head><meta charset="UTF-8"><title>添加品牌</title>
</head>
<body>
<h3>添加品牌</h3>
<form action="" method="post">品牌名称：<input id="brandName" name="brandName"><br>企业名称：<input id="companyName" name="companyName"><br>排序：<input id="ordered" name="ordered"><br>描述信息：<textarea rows="5" cols="20" id="description" name="description"></textarea><br>状态：<input type="radio" name="status" value="0">禁用<input type="radio" name="status" value="1">启用<br><input type="button" id="btn"  value="提交">
</form><script src="js/axios-0.18.0.js"></script><script>//1. 给按钮绑定单击事件document.getElementById("btn").onclick = function () {// 将表单数据转为jsonvar formData = {brandName:"",companyName:"",ordered:"",description:"",status:"",};// 获取表单数据let brandName = document.getElementById("brandName").value;// 设置数据formData.brandName = brandName;// 获取表单数据let companyName = document.getElementById("companyName").value;// 设置数据formData.companyName = companyName;// 获取表单数据let ordered = document.getElementById("ordered").value;// 设置数据formData.ordered = ordered;// 获取表单数据let description = document.getElementById("description").value;// 设置数据formData.description = description;let status = document.getElementsByName("status");for (let i = 0; i < status.length; i++) {if(status[i].checked){//formData.status = status[i].value ;}}console.log(formData);//2. 发送ajax请求axios({method:"post",url:"http://localhost:8080/brand-demo/addServlet",data:formData}).then(function (resp) {// 判断响应数据是否为 successif(resp.data == "success"){location.href = "http://localhost:8080/brand-demo/brand.html";}})}</script>
</body>
</html>

addServlet：

@WebServlet("/addServlet")
public class AddServlet extends HttpServlet {private BrandService brandService = new BrandService();@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//1. 接收数据,request.getParameter 不能接收json的数据/* String brandName = request.getParameter("brandName");System.out.println(brandName);*/// 获取请求体数据BufferedReader br = request.getReader();String params = br.readLine();// 将JSON字符串转为Java对象Brand brand = JSON.parseObject(params, Brand.class);//2. 调用service 添加brandService.add(brand);//3. 响应成功标识response.getWriter().write("success");}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doGet(request, response);}