🥼JavaWeb~(伍)架构,filter,listener,demo.

笔记代码
MVC 架构
中间层工具

笔记代码

MVC 架构

Model 模型 view 视图 Controller 控制三方分离的架构

之前的架构:
- Servlet 直接进行 CRUD 操作,程序比较臃肿,不利于维护
于是,为了解决这种不便利性,再加一层! (没有什么是加一层解决不了的)
各部分的职责:
- Model
  - 业务处理：业务逻辑（Service）
  - 数据持久层：CRUD （Dao - 数据持久化对象）
- View
  - 展示数据
  - 提供链接发起 Servlet 请求（a，form，img…）
- Controller （Servlet）
  - 接收用户的请求：（req：请求参数、Session 信息….）
  - 交给业务层处理对应的代码
  - 控制视图的跳转 (转发/重定向)
一条流程:
View 层点击登录 --> 接收用户的登录请求 --> 处理用户的请求（获取用户登录的参数，username，password）–> 交给业务层处理登录业务（判断用户名密码是否正确：操作事务）–> Dao 层查询用户名和密码是否正确 --> 数据库
顺利查询到数据之后就是反过来再进行数据传递

中间层工具

常见的有过滤器 filter,监听器 listener,拦截器 Interceptor
请教一下关于过滤器，拦截器，监听器具体应用上的区别？
下面介绍 filter(重点) 和 listener

Filter 过滤器

介绍

比如处理中文乱码,敏感词汇,登录验证…

例子: 比如 Shiro 安全框架技术就是用 Filter 来实现的

导入依赖

老四样:

<!-- servlet依赖 -->
<dependency>
  <groupId>javax.servlet</groupId>
  <artifactId>javax.servlet-api</artifactId>
  <version>4.0.1</version>
  <scope>provided</scope>
</dependency>
<!-- JSP依赖 -->
<dependency>
  <groupId>javax.servlet.jsp</groupId>
  <artifactId>javax.servlet.jsp-api</artifactId>
  <version>2.3.3</version>
  <scope>provided</scope>
</dependency>
<!-- JSTL表达式依赖 -->
<dependency>
  <groupId>javax.servlet</groupId>
  <artifactId>jstl</artifactId>
  <version>1.2</version>
</dependency>
<!-- Standard标签库 -->
<dependency>
  <groupId>taglibs</groupId>
  <artifactId>standard</artifactId>
  <version>1.1.2</version>
</dependency>

之后好像还会用到 SQL 驱动依赖,到时候在说.

filter 例子

src/main/java/filter/CharacterEncodingFilter.java

package filter;

import javax.servlet.*;
import java.io.IOException;

public class CharacterEncodingFilter implements Filter {
  //初始化并等待过滤对象出现
  @Override
  public void init(FilterConfig filterConfig) throws ServletException {
    System.out.println("CharacterEncodingFilter初始化");
  }

  /*
    1. 过滤中的所有代码，在过滤特定请求的时候都会执行
    2. 必须要让过滤器继续执行 (因为filter可能不止一个,需要传递)
      chain.doFilter(request,response);
  */
  @Override
  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    request.setCharacterEncoding("utf-8");
    response.setCharacterEncoding("utf-8");
    response.setContentType("text/html");

    System.out.println("CharacterEncodingFilter执行前....");
    chain.doFilter(request, response); //让我们的请求继续走，如果不写，程序到这里就被拦截停止！
    System.out.println("CharacterEncodingFilter执行后....");
  }

  //销毁：web服务器关闭的时候，过滤器会销毁
  @Override
  public void destroy() {
    System.out.println("CharacterEncodingFilter销毁");
  }
}

src/main/java/servlet/Show.java

package servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class Show 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 {
    // 通过filter实现处理乱码
    resp.getWriter().write("你好!");
  }
}

web.xml 配置 servlet 和 filter

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">
  <servlet>
    <servlet-name>show</servlet-name>
    <servlet-class>servlet.Show</servlet-class>
  </servlet>
  <filter>
    <filter-name>characterEncodingFilter</filter-name>
    <filter-class>filter.CharacterEncodingFilter</filter-class>
  </filter>

  <!--还是乱码的页面-->
  <servlet-mapping>
    <servlet-name>show</servlet-name>
    <url-pattern>/show</url-pattern>
  </servlet-mapping>
  <!--通过过滤器解决了乱码的页面-->
  <servlet-mapping>
    <servlet-name>show</servlet-name>
    <url-pattern>/servlet/show</url-pattern>
  </servlet-mapping>
  <!--filter的地址映射-->
  <filter-mapping>
    <filter-name>characterEncodingFilter</filter-name>
    <url-pattern>/servlet/*</url-pattern>
  </filter-mapping>
</web-app>

监听器

对应不同业务需求,存在 N 中不同的监听器接口可供实现.
监听器经常在 GUI 编程中使用.

例子: 设置 session 监听器监听有多少 session 连接

src/main/java/listener/OnlineCountListener.java

package listener;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

//统计网站在线人数 -> 统计session
public class OnlineCountListener implements HttpSessionListener {
  private ServletContext ctx;
  private Integer onlineCount;

  //一旦创建Session就会触发一次这个事件
  public void sessionCreated(HttpSessionEvent se) {
    initParam(se);
    ctx.setAttribute("OnlineCount", ++onlineCount);
  }

  /*
    一旦销毁Session就会触发一次这个事件
    Session销毁：
      1. 手动销毁  getSession().invalidate();
      2. 自动销毁
  */
  public void sessionDestroyed(HttpSessionEvent se) {
    initParam(se);
    ctx.setAttribute("OnlineCount", --onlineCount);
  }

  public void initParam(HttpSessionEvent se) {
    ctx = se.getSession().getServletContext();
    onlineCount = (Integer) ctx.getAttribute("OnlineCount");

    if (onlineCount == null) {
      ctx.setAttribute("OnlineCount", 0);
    }
  }
}

index.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
  <title>在线人数测试</title>
</head>
<body>
<h1>当前有 <span
    style="color: turquoise;"><%=this.getServletConfig().getServletContext().getAttribute("OnlineCount")%></span> 人在线
</h1>
</body>
</html>

注册监听器

<!--注册监听器-->
<listener>
  <listener-class>listener.OnlineCountListener</listener-class>
</listener>

GUI 编程例子

GUI 编程常会用到监听器,这里简单介绍一下 : src/main/java/listener/TestPanel.java

package listener;

import java.awt.*;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

public class TestPanel {
  public static void main(String[] args) {
    Frame frame = new Frame("Hello World!");  //新建一个窗体
    Panel panel = new Panel(null); //面板
    frame.setLayout(null); //设置窗体的布局

    frame.setBounds(300, 300, 500, 500);
    frame.setBackground(new Color(0, 0, 255)); //设置背景颜色

    panel.setBounds(50, 50, 300, 300);
    panel.setBackground(new Color(0, 255, 0)); //设置背景颜色

    frame.add(panel);

    frame.setVisible(true);

    //监听事件，监听关闭事件
    frame.addWindowListener(new WindowAdapter() {
      @Override
      public void windowClosing(WindowEvent e) {
        System.exit(0);
      }
    });
  }
}

登录验证 demo

项目结构,如图:

JSP 页面

主页(登录页面): web/demo/index.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
  <title>主页</title>
</head>
<body>
<h1>登录</h1>
<form action="${pageContext.request.contextPath}/demo/login" method="post">
  <label>
    用户名:
    <input type="text" name="username"/>
  </label>
  <input type="submit" value="登录">
</form>
</body>
</html>

登陆失败: web/demo/failed.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
  <title>登录失败</title>
</head>
<body>
<h1>登录失败进入的页面</h1>

<a href="${pageContext.request.contextPath}/demo/index.jsp">返回主页</a>
</body>
</html>

登录成功: web/demo/sys/success.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
  <title>已登录</title>
</head>
<body>
<h1>登录成功后进入的页面</h1>

<hr>

<a href="${pageContext.request.contextPath}/demo/logout">注销</a>
</body>
</html>

Java 后端

package demo.servlet;

import demo.utils.Constants;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

public class Login extends HttpServlet {
  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
    this.doPost(req, resp);
  }

  @Override
  protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException {
    String username = req.getParameter("username");
    HttpSession session = req.getSession();

    if (username.equals("admin")) {
      session.setAttribute(Constants.USER_SESSION, session.getId());
      resp.sendRedirect("/demo/sys/success.jsp");
    } else {
      resp.sendRedirect("/demo/failed.jsp");
    }
  }
}

注销: src/main/java/demo/servlet/Logout.java

package demo.servlet;

import demo.utils.Constants;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

public class Logout extends HttpServlet {
  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    doPost(req, resp);
  }

  @Override
  protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

    HttpSession session = req.getSession();
    Object attribute = session.getAttribute(Constants.USER_SESSION);

    /*
      频繁操作session连接会影响性能,通过attribute间接验证登录信息
      通过设置或移除 USER_SESSION 属性来验证是否登录
      存在一个Bug: 在注销状态通过浏览器的后退,可以返回登陆成功的页面(且不存在USER_SESSION)
    */
    if (attribute != null) {
      session.removeAttribute(Constants.USER_SESSION);
      resp.sendRedirect("/demo/index.jsp");
    }
  }

提取的常量工具类: src/main/java/demo/utils/Constants.java

package demo.utils;

/**
* 此类内定义一些其他各种地方需要经常调用的常量
*/
public class Constants {
  public final static String USER_SESSION = "USER_SESSION";
}

过滤器类: src/main/java/demo/filter/SysFilter.java

package demo.filter;

import demo.utils.Constants;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class SysFilter implements Filter {
  @Override
  public void init(FilterConfig filterConfig) throws ServletException {

  }

  @Override
  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    HttpServletRequest req = (HttpServletRequest) request;
    HttpServletResponse resp = (HttpServletResponse) response;

    Object attribute = req.getSession().getAttribute(Constants.USER_SESSION);
    if (attribute == null) {
      resp.sendRedirect("/demo/failed.jsp");
    }

    chain.doFilter(request, response);
  }

  @Override
  public void destroy() {

  }
}

Web.xml

<servlet>
  <servlet-name>login</servlet-name>
  <servlet-class>demo.servlet.Login</servlet-class>
</servlet>
<servlet>
  <servlet-name>logout</servlet-name>
  <servlet-class>demo.servlet.Logout</servlet-class>
</servlet>
<filter>
  <filter-name>sysFilter</filter-name>
  <filter-class>demo.filter.SysFilter</filter-class>
</filter>

<servlet-mapping>
  <servlet-name>login</servlet-name>
  <url-pattern>/demo/login</url-pattern>
</servlet-mapping>
<servlet-mapping>
  <servlet-name>logout</servlet-name>
  <url-pattern>/demo/logout</url-pattern>
</servlet-mapping>
<filter-mapping>
  <filter-name>sysFilter</filter-name>
  <url-pattern>/demo/sys/*</url-pattern>
</filter-mapping>