目录

一：过滤器的使用以及实现原理

（1）当前的oa项目还存在什么缺陷？

（2）Filter是什么，有什么用，执行原理是什么？

（3）过滤器怎么写？

（4）过滤器的调用顺序？

（5）Filter的生命周期？

二：责任链设计模式改造oa项目

一：过滤器的使用以及实现原理

（1）当前的oa项目还存在什么缺陷？

（2）Filter是什么，有什么用，执行原理是什么？

（3）过滤器怎么写？

package com.bjpowernode.javaweb.servlet;

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

/**
 * @Author：朗朗乾坤
 * @Package：com.bjpowernode.javaweb.servlet
 * @Project：JavaWeb
 * @name：MyFilter
 * @Date：2022/12/3 15:31
 */
public class MyFilter implements Filter {
    public MyFilter() {
        System.out.println("无参数构造方法执行");
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("init方法执行");
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        System.out.println("Filter1 doFilter方法开始执行");
        
    }

    @Override
    public void destroy() {
        System.out.println("destroy方法执行");
    }
}

<?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">
    <filter>
        <filter-name>myfilter</filter-name>
        <filter-class>com.bjpowernode.javaweb.servlet.MyFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>myfilter</filter-name>
        <url-pattern>/a.do</url-pattern>
    </filter-mapping>
</web-app>

package com.bjpowernode.javaweb.servlet;

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

/**
 * @Author：朗朗乾坤
 * @Package：com.bjpowernode.javaweb.servlet
 * @Project：JavaWeb
 * @name：Aservlet
 * @Date：2022/12/3 15:40
 */
@WebFilter("/a.do")
public class AServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        System.out.println("AServlet中的doGet方法执行了。");
    }
}

BServlet类

package com.bjpowernode.javaweb.servlet;

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

/**
 * @Author：朗朗乾坤
 * @Package：com.bjpowernode.javaweb.servlet
 * @Project：JavaWeb
 * @name：BServlet
 * @Date：2022/12/3 15:41
 */
@WebFilter("/b.do")
public class BServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        System.out.println("BServlet中的doGet方法执行了。");
    }
}

package com.bjpowernode.javaweb.servlet;

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

/**
 * @Author：朗朗乾坤
 * @Package：com.bjpowernode.javaweb.servlet
 * @Project：JavaWeb
 * @name：MyFilter
 * @Date：2022/12/3 15:31
 */
public class MyFilter implements Filter {
    public MyFilter() {
        System.out.println("无参数构造方法执行");
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("init方法执行");
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        // 在请求的时候添加过滤规则。
        System.out.println("Filter1 doFilter方法开始执行");
        // 执行下一个过滤器，如果下一个不是过滤器了，则执行目标程序Servlet
        // 简单理解就是向下走
        chain.doFilter(request,response);
        // 在响应的时候添加过滤规则。
        System.out.println("Filter1 doFilter方法执行结束。");
    }

    @Override
    public void destroy() {
        System.out.println("destroy方法执行");
    }
}

执行结果如下：

 补充：

（4）过滤器的调用顺序？

定义一个MyFilter1过滤器

package com.bjpowernode.javaweb.servlet;

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


public class MyFilter1 implements Filter {
   
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("init方法执行");
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {       
        System.out.println("Filter1 doFilter方法开始执行");
        chain.doFilter(request,response);
        System.out.println("Filter1 doFilter方法执行结束。");
    }

    @Override
    public void destroy() {
        System.out.println("destroy方法执行");
    }
}

定义一个MyFilter2过滤器

package com.bjpowernode.javaweb.servlet;

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

public class MyFilter2 implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        System.out.println("Filter2 doFilter begin");
        chain.doFilter(request, response);
        System.out.println("Filter2 doFilter end");
    }

    @Override
    public void destroy() {
    }
}

选择在xml文件中配置，对应的web.xml文件

<?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">
    <filter>
        <filter-name>myfilter</filter-name>
        <filter-class>com.bjpowernode.javaweb.servlet.MyFilter1</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>myfilter</filter-name>
        <url-pattern>*.do</url-pattern>
    </filter-mapping>

    <filter>
        <filter-name>myfilter2</filter-name>
        <filter-class>com.bjpowernode.javaweb.servlet.MyFilter2</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>myfilter2</filter-name>
        <url-pattern>*.do</url-pattern>
    </filter-mapping>
</web-app>

定义一个AServlet类，路径通过注解的方式

package com.bjpowernode.javaweb.servlet;

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


@WebFilter("/a.do")
public class AServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        System.out.println("AServlet中的doGet方法执行了。");
    }
}

（5）Filter的生命周期？

二：责任链设计模式改造oa项目

package com.bjpowernode.javaweb.servlet;

public class Test {
    public static void main(String[] args) {
        System.out.println("main begin");
        m1();
        System.out.println("main over");
    }

    private static void m1() {
        System.out.println("m1 begin");
        m2();
        System.out.println("m1 over");
    }

    private static void m2() {
        System.out.println("m2 begin");
        m3();
        System.out.println("m2 over");
    }

    private static void m3() {
        System.out.println("目标正在执行中。。。。");
    }
}

①首先配置web.xml文件

    <filter>
        <filter-name>loginfilter</filter-name>
        <filter-class>com.bjpowernode.oa.filter.LoginFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>loginfilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

②编写一个过滤器，作为判断的登录

package com.bjpowernode.oa.filter;

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

/**
 * @Author：朗朗乾坤
 * @Package：com.bjpowernode.oa.filter
 * @Project：JavaWeb
 * @name：LoginFilter
 * @Date：2022/12/3 17:39
 */
public class LoginFilter implements Filter {
    // 也可以只重写其中一个方法
    @Override
    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain)
            throws IOException, ServletException {
        // 注意这里要先进行强转为HttpServlet，后面才能调用对应的方法
        HttpServletRequest request = (HttpServletRequest)req;
        HttpServletResponse response = (HttpServletResponse) resp;
        // 获取请求路径
        String servletPath = request.getServletPath();
        // 获取当前session对象，获取不到就返回null
        HttpSession session = request.getSession(false);
        if("/index.jsp".equals(servletPath) || "/welcome".equals(servletPath) ||
                "/dept/login".equals(servletPath) || "/dept/exit".equals(servletPath)
                || (session != null && session.getAttribute("username") != null)){
            // 经过上面过滤，只有上面的路径才会直接通过；其它的操作都要先跳转到登录页面
            // 继续往下走
            chain.doFilter(request, response);
        }else{
            response.sendRedirect(request.getContextPath() + "/index.jsp");
        }

    }
}

package com.bjpowernode.oa.web.action;

import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import jakarta.servlet.http.HttpSession;

import java.io.IOException;

/**
 * 员工管理的。
 * 员工管理的前提也是需要先登录。
 */
public class EmpServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
        // 乱码问题也可以写入过滤器当中
        // post请求乱码问题
        request.setCharacterEncoding("UTF-8");
        // 响应中文乱码问题
        response.setContentType("text/html;charset=UTF-8");

        HttpSession session = request.getSession(false);
        if(session != null && session.getAttribute("username") != null){
            String servletPath = request.getServletPath();
            //...
        }else{
            response.sendRedirect(request.getContextPath() + "/index.jsp");
        }
    }
}

        HttpSession session = request.getSession(false);
        if (session != null && session.getAttribute("username") != null){ // session对象不一定为null
            // 获取servlet path
            String servletPath = request.getServletPath();
            if ("/dept/list".equals(servletPath)){
                doList(request,response);
            }else if("/dept/detail".equals(servletPath)){
                doDetail(request,response);
            }else if("/dept/delete".equals(servletPath)) {
                doDel(request, response);
            }else if("/dept/add".equals(servletPath)) {
                doAdd(request, response);
            }else if("/dept/modify".equals(servletPath)) {
                doModify(request, response);
            }
        }else{
            // 跳转到登录页面
            response.sendRedirect(request.getContextPath()+"/index.jsp");
        }

修改为：

        String servletPath = request.getServletPath();
        if ("/dept/list".equals(servletPath)){
            doList(request,response);
        }else if("/dept/detail".equals(servletPath)){
            doDetail(request,response);
        }else if("/dept/delete".equals(servletPath)) {
            doDel(request, response);
        }else if("/dept/add".equals(servletPath)) {
            doAdd(request, response);
        }else if("/dept/modify".equals(servletPath)) {
            doModify(request, response);
        }