<filter>
        <filter-name>FilterDemo3</filter-name>
        <filter-class>cn.web.servlet.filter.FilterDemo3</filter-class>
        <init-param>
           <param-name>encoding</param-name>
           <param-value>UTF-8</param-value>
        </init-param>
    </filter>
    <filter-mapping>
        <filter-name>FilterDemo3</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

java代码

import java.io.IOException;
import java.util.Enumeration;

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 {
    private FilterConfig filterConfig;

    public FilterDemo3()
    {

    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

        this.filterConfig = filterConfig;
    }

    //WEB容器
    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {

        //从web.xml中全部获取参数
        Enumeration<String> enums  = filterConfig.getInitParameterNames();
        while(enums.hasMoreElements())
        {
            String key = enums.nextElement();
            String value = filterConfig.getInitParameter(key);
            System.out.println(key+":"+value);
        }
        String encoding = filterConfig.getInitParameter("encoding");
        response.setContentType("text/html;charset="+encoding);
        chain.doFilter(request,response);
    }

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

}

结果：
摧毁 方法: destroy()
四月 18, 2018 9:38:57 下午 org.apache.catalina.core.StandardContext reload
信息: Reloading Context with name [/day04] has started
四月 18, 2018 9:38:57 下午 org.apache.catalina.core.StandardContext reload
信息: Reloading Context with name [/day04] is completed
encoding:UTF-8

使用FilterConfig读取配置文件的信息 ---学习笔记

原文：http://blog.51cto.com/357712148/2105106