Filter 过滤器

过滤器CharacterEncodingFilter

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

public class CharacterEncodingFilter implements Filter {
    //初始化
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("初始化！");
    }

    @Override
    /*
        1.设置字符编码
        2，要设置chain链   经过Filter后要转发出去
     */
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException {
        request.setCharacterEncoding("utf-8");
        response.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=utf-8");
        System.out.println("执行前");
        filterChain.doFilter(request,response);//让我们的请求继续走，如歌不写，程序到此截至
        System.out.println("执行后");
    }

    @Override
    public void destroy() {
        System.out.println("销毁");
    }
}

//XML设置

 <servlet>
        <servlet-name>ShowServlet</servlet-name>
        <servlet-class>com.zxy.servlet.ShowServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>ShowServlet</servlet-name>
        <url-pattern>/servlet/show</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>ShowServlet</servlet-name>
        <url-pattern>/ggg/show</url-pattern>
    </servlet-mapping>

<!--只要经过/servlet的任何请求，就会经过这个过滤器     -->
<!-- <url-pattern>/*</url-pattern>  -->
    <filter>
        <filter-name>CharacterEncodingFilter</filter-name>
        <filter-class>com.zxy.filter.CharacterEncodingFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>CharacterEncodingFilter</filter-name>
        <url-pattern>/servlet/*</url-pattern>
    </filter-mapping>
    <filter-mapping>
    <filter-name>CharacterEncodingFilter</filter-name>
    <url-pattern>/ggg/*</url-pattern>
    </filter-mapping>

注意：

1.设置Servlet时 例如只有一级查询时 如   /show   这是过滤器为   /servlet/*   时 无法过滤   要设置为   /*  作为小项目没事  当为当项目时过造成过多的负担

2.可以每一个servlet设置为二级 例如/servlet/show  或者/ggg/show     filte设置为/servlet/*  和/ggg/*   一一对应；