javaweb Filter的使用方法以及配置xml文件

<filter>
<filter-name>yyy</filter-name>
<filter-class>cn.yellowimg.filter.BFilter</filter-class>
</filter>
<filter-mapping>
<!-- 配置拦截方式
即访问请求为 什么时候被拦截 配置方式有
REQUEST
FORWARD
INCLUDE
ERROR
以上四种访问请求会触发拦截 需要配置到<dispactcher>中
默认为拦截REQUEST 当配置其他时 会按照配置进行拦截
-->
<filter-name>yyy</filter-name>
<url-pattern>/AServlet</url-pattern>
<dispatcher>FORWARD</dispatcher>
</filter-mapping>

package cn.yellowimg.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;

public class BFilter implements Filter {

@Override
public void destroy() {
// TODO Auto-generated method stub

}

@Override
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
System.out.println("Bfilter#start");

// 代表不拦截 即放行该方法，可以简单理解为调用severlet类里的方法
chain.doFilter(request, response);

System.out.println("Bfilter#end");
}

@Override
public void init(FilterConfig filterConfig) throws ServletException {
// TODO Auto-generated method stub

}
}