串级过滤器

最新推荐文章于 2020-10-06 00:01:38 发布

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本文介绍了串级过滤器的工作原理及其在Java Web应用程序中的应用。通过FilterDemo、FilterDemo2和FilterDemo3三个过滤器的示例，展示了如何设置过滤器及它们的执行顺序。当用户访问资源时，这些过滤器将按配置顺序执行，实现对请求和响应的预处理与后处理。

串级过滤器：一个过滤器接着另外一个过滤器。
例子：
1.FilterDemo.java文件：


import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

public class FilterDemo implements Filter {

    public FilterDemo(){
        System.out.println("调用了默认的构造方法");
    }

    //用户每次访问被过滤的资源，都会由服务器调用该方法实现过滤
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        System.out.println("FilterDemo执行过滤前");
        //对请求进行拦截，代码写在这
        chain.doFilter(request, response);//放行
        //对响应进行拦截，代码写在这
        System.out.println("FilterDemo执行过滤后");
    }

    public void destroy() {
        System.out.println("调用了销毁方法");
    }

    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("调用初始化方法");
    }

}

2.FilterDemo2.java文件：

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

public class FilterDemo2 implements Filter {

    public void init(FilterConfig filterConfig) throws ServletException {

    }

    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        System.out.println("FilterDemo2前");
        chain.doFilter(request, response);
        System.out.println("FilterDemo2后");
    }

    public void destroy() {

    }

}

3.FilterDemo3.java文件：

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

public class FilterDemo3 implements Filter {

    public void init(FilterConfig filterConfig) throws ServletException {

    }

    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        System.out.println("FilterDemo3前");
        chain.doFilter(request, response);
        System.out.println("FilterDemo3后");
    }

    public void destroy() {

    }

}

4。web.xml文件：

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0"
    xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
<filter>
    <filter-name>FilterDemo</filter-name>
    <filter-class>FilterDemo</filter-class>
</filter>
<filter-mapping>
    <filter-name>FilterDemo</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>
<filter>
    <filter-name>FilterDemo2</filter-name>
    <filter-class>FilterDemo2</filter-class>
</filter>
<filter-mapping>
    <filter-name>FilterDemo2</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>
<filter>
    <filter-name>FilterDemo3</filter-name>
    <filter-class>FilterDemo3</filter-class>
</filter>
<filter-mapping>
    <filter-name>FilterDemo3</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

  <servlet>
    <servlet-name>FilterDemo2</servlet-name>
    <servlet-class>FilterDemo2</servlet-class>
  </servlet>
  <servlet>
    <servlet-name>FilterDemo3</servlet-name>
    <servlet-class>FilterDemo3</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>FilterDemo2</servlet-name>
    <url-pattern>/servlet/FilterDemo2</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>FilterDemo3</servlet-name>
    <url-pattern>/servlet/FilterDemo3</url-pattern>
  </servlet-mapping>
<welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>

5。运行：http://localhost:8080/Filter_project/index.jsp
6。结果：

调用了默认的构造方法
调用初始化方法
FilterDemo执行过滤前
FilterDemo2前
FilterDemo3前
FilterDemo3后
FilterDemo2后
FilterDemo执行过滤后
调用了销毁方法