//過濾器：每個servlet都要經過filter的處理
public class FilterTest implements Filter{

    @Override
    public void destroy() {
        System.out.println("destroy!1");
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        System.out.println(
 
"檢查！！");
        chain.doFilter(request, response);
        System.out.println("完成！！");
    }

    @Override
    public void init(FilterConfig arg0) throws ServletException {
        System.out.println("init");
    }
}

<filter>
        <filter-name>filter</filter-name>
        <
 
filter-class>com.study.filter.FilterTest</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>filter</filter-name>
　　　　　　//*號代表所有servlet請求都要過濾
        <url-pattern>/*</url-pattern>
    </filter-mapping>