Java Web------过滤器Filter

一、Filter简介

过滤器是一个程序，它先于与之相关的Servlet或JSP页面运行在服务器上。过滤器可附加到一个或多个Servlet或JSP页面上，并且可以检查进入这些支援的请求信息（WEB开发人员通过Filter技术，对web服务器管理的所有web资源：例如Jsp, Servlet, 静态图片文件或静态 html 文件等进行拦截，从而实现一些特殊的功能。例如实现URL级别的权限访问控制、过滤敏感词汇、解决中文乱码问题、压缩响应信息等一些高级功能。）。
Servlet API中提供了一个Filter接口，开发web应用时，如果编写的Java类实现了这个接口，则把这个java类称之为过滤器Filter。他和用户及web资源的关系如下：

演示：
Servlet： ServletDemo1

public class ServletDemo1 extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public ServletDemo1() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        System.out.println("调用doGet方法");

    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        System.out.println("调用doPost方法");
    }

}

Filter：FilterDemo01

public class FilterDemo01 implements Filter {

    /**
     * Default constructor. 
     */
    public FilterDemo01() {
        // TODO Auto-generated constructor stub
    }

    /**
     * @see Filter#destroy()
     */
    public void destroy() {
        // TODO Auto-generated method stub
    }

    /**
     * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
     */
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        // TODO Auto-generated method stub
        // place your code here

        // pass the request along the filter chain
        System.out.println("过滤前");
        chain.doFilter(request, response);
        System.out.println("过滤后");
    }

    /**
     * @see Filter#init(FilterConfig)
     */
    public void init(FilterConfig fConfig) throws ServletException {
        // TODO Auto-generated method stub
    }

}

在web. xml中配置过滤器：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
  <display-name>Learning-JavaWeb</display-name>
  <filter>
    <filter-name>FilterDemo01</filter-name>
    <filter-class>servlet.FilterDemo01</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>FilterDemo01</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
  <servlet>
    <servlet-name>servletDemo1</servlet-name>
    <servlet-class>servlet.ServletDemo1</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>servletDemo1</servlet-name>
    <url-pattern>/servletDemo1</url-pattern>
  </servlet-mapping>
</web-app>

在浏览器中输入：http://localhost:8080/Learning-JavaWeb/servletDemo1

二、参考连接

【孤傲苍狼】：http://www.cnblogs.com/xdp-gacl/p/3948353.html