drp-1、Filter的使用

1、当客户请求一个页面时，都事先要经过Filter处理。处理后，转到相应的页面
2、实现Filter需要，需要实现javax.servlet.Filter接口，还要在web.xml文件中进行配置，如：

<filter>
        <filter-name>CharsetEncodingFilter</filter-name>
        <filter-class>net.nyist.drp.util.filter.CharsetEncodingFilter</filter-class>
<!-- 可以配置相应的参数，也可以不用配置 -->
        <init-param>
            <param-name>encording</param-name>
            <param-value>GBK</param-value>
        </init-param>
    </filter>
    <filter-mapping>
        <filter-name>CharsetEncodingFilter</filter-name>
        <url-pattern>*.jsp</url-pattern>
    </filter-mapping>
    
    <filter-mapping>
        <filter-name>CharsetEncodingFilter</filter-name>
        <url-pattern>/sysmgr/*</url-pattern>
    </filter-mapping>

3、实现javax.serlvet.Filter接口

package net.nyist.drp.util.filter;

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;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class CharsetEncodingFilter implements Filter {

    private String encording;
    
    public void destroy() {
        System.out.println("filter-------destory");
    }

    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        HttpServletRequest servletRequest = (HttpServletRequest)request;
        HttpServletResponse servletResponse = (HttpServletResponse)response;
        servletRequest.setCharacterEncoding("GB18030");
        //System.out.println("doFilter--------------begin");
        chain.doFilter(servletRequest,servletResponse);
        //System.out.println("doFilter--------------end");        
    }

    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("filter------begin");
        this.encording = filterConfig.getInitParameter("encording");
        System.out.println("-----------------------------" + this.encording);
    }

}