Filter_细节

1.web.xml配置方式

 <filter>
        <filter-name>filterDemo01</filter-name>
        <filter-class>com.bai.Filter.FilterDemo01</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>filterDemo01</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

运行结果

2.过滤器执行流程

执行过滤器
执行放行后的资源
回来执行过滤器放行代码下边的代码

3.过滤器生命周期方法

init:在服务器启动后会创建Filter对象然后调用init方法只执行一次用于加载资源
doFilter:每一次请求被拦截资源时会执行执行多次
destroy:在服务器关闭后 filter对象被销毁如果服务器是正常关闭则会执行destroy方法只执行一次用于释放资源

java代码

package com.bai.filter;

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

@WebFilter("/*")
public class FilterDemo02 implements Filter {
    /**
     * 在服务器启动后 会创建Filter对象 然后调用init方法
     * @param filterConfig
     * @throws ServletException
     */
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("init....");
    }

    /**
     * 每一次请求被拦截资源时 会执行 执行多次
     * @param servletRequest
     * @param servletResponse
     * @param filterChain
     * @throws IOException
     * @throws ServletException
     */
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("doFilter....");
        //放行
        filterChain.doFilter(servletRequest, servletResponse);

    }

    /**
     * 在服务器关闭后 filter对象被销毁 如果服务器是正常关闭 则会执行destroy方法
     */
    public void destroy() {
        System.out.println("destroy....");
    }
}

运行结果

4.过滤器配置详解

拦截路径配置
- 具体资源路径：/index.jsp:只有访问index.jsp资源过滤器才会被执行
- 拦截目录：/user/*:访问/user下的所有资源时过滤器都会被执行
- 后缀名拦截：*.jsp:访问所有后缀名为jsp资源时过滤器都会被执行
- 拦截所有资源：/*:访问所有资源时过滤器都会被执行

具体资源路径代码

@WebFilter("/index.jsp")

运行结果

拦截目录代码

FilterDemo03类

package com.bai.filter;

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

@WebFilter("/user/*")//1./index.jsp:只有访问index.jsp资源 过滤器才会被执行
public class FilterDemo03 implements Filter {
    public void init(FilterConfig filterConfig) throws ServletException {
    }

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

    }

    public void destroy() {

    }
}

ServletDemo01类

package com.bai.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("/user/ServletDemo01")
public class ServletDemo01 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("执行了ServletDemo01类");
    }

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

ServletDemo02类

package com.bai.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("/user/ServletDemo02")
public class ServletDemo02 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("执行了ServletDemo02类");
    }

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

运行结果

后缀名拦截运行结果

拦截方式配置：资源被访问的方式
- 注解配置
  - 设置dispatcherTypes属性
    1. REQUEST:默认值。浏览器直接请求资源
    2. FORWARD:转发访问资源
    3. INCLUDE:包含访问资源
    4. ERROR:错误跳转资源
    5. ASYNC:异步访问资源

java代码

FilterDemo04类

package com.bai.filter;

import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import java.io.IOException;
//浏览器直接请求index.jsp资源时 该浏览器会被执行
//@WebFilter(value = "/index.jsp",dispatcherTypes = DispatcherType.REQUEST)
//只有转发访问index.jsp时 该过滤器才会被执行
@WebFilter(value = "/index.jsp",dispatcherTypes = DispatcherType.FORWARD)
public class FilterDemo04 implements Filter {
    public void init(FilterConfig filterConfig) throws ServletException {
    }

    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("FilterDemo04....");
        //放行
        filterChain.doFilter(servletRequest, servletResponse);

    }

    public void destroy() {

    }
}

ServletDemo02类

package com.bai.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("/user/ServletDemo02")
public class ServletDemo02 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("执行了ServletDemo02类");
        //转发到hello.jsp
        req.getRequestDispatcher("/hello.jsp").forward(req,resp);
    }

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

运行结果

5.过滤器链（配置多个过滤器）

执行顺序:如果有两个过滤器：过滤器1和过滤器2
1. 过滤器1
2. 过滤器2
3. 资源执行
4. 过滤器2
5. 过滤器1

代码

package com.bai.filter;

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

@WebFilter("/*")
public class FilterDemo05 implements Filter {
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        //对request对象请求消息增强
        System.out.println("FilterDemo05执行了....");
        //放行
        filterChain.doFilter(servletRequest, servletResponse);
        //对response对象的响应消息增强
        System.out.println("FilterDemo05回来了....");
    }

    public void destroy() {

    }
}

package com.bai.filter;

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

@WebFilter("/*")
public class FilterDemo06 implements Filter {
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        //对request对象请求消息增强
        System.out.println("FilterDemo06执行了....");
        //放行
        filterChain.doFilter(servletRequest, servletResponse);
        //对response对象的响应消息增强
        System.out.println("FilterDemo06回来了....");
    }

    public void destroy() {

    }
}