过滤器filter

应用：

  • web服务器有一些垃圾请求那么我们后台就应该报错或者不处理
  • 乱码问题

测试代码：

  1. 过滤器
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package com.saxon.filter;

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

public class filterDemo implements Filter {
    @Override
    public void init (FilterConfig filterConfig) throws ServletException {
        System.out.println ("过滤器初始化完毕");//在一切之前初始化
    }

    @Override
    public void doFilter (ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        servletRequest.setCharacterEncoding ("utf-8");
        servletResponse.setContentType ("text/html;charset=utf-8");
        servletResponse.setCharacterEncoding ("utf-8");
        System.out.println ("start***************************");
        filterChain.doFilter (servletRequest,servletResponse);//必须写
        System.out.println ("end***************************");
    }

    @Override
    public void destroy () {
        System.out.println ("销毁");//在服务器关闭时注销
    }
}

2.测试类

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package com.saxon.filter;

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 Demo extends HttpServlet {
    @Override
    protected void doGet (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter ().write ("只有爱，才会喜欢代码");
    }

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

3.配置文件

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<servlet>
        <servlet-name>s</servlet-name>
        <servlet-class>com.saxon.filter.Demo</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>s</servlet-name>
        <url-pattern>/r/r</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>s</servlet-name>
        <url-pattern>/r</url-pattern>
    </servlet-mapping>
<filter>
    <filter-name>f</filter-name>
    <filter-class>com.saxon.filter.filterDemo</filter-class>
</filter>
    <filter-mapping>
        <filter-name>f</filter-name>
        <url-pattern>/r/*</url-pattern>//文件目录
    </filter-mapping>