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;

/**

 * 自定义的 HttpFilter, 实现自 Filter 接口

 *

 */

public abstract class HttpFilter implements Filter {

    /**

     * 用于保存 FilterConfig 对象.

     */

    private FilterConfig filterConfig;

    /**

     * 不建议子类直接覆盖. 若直接覆盖, 将可能会导致 filterConfig 成员变量初始化失败

     */

    @Override

    public void init(FilterConfig filterConfig) throws ServletException {

        this.filterConfig = filterConfig;

        init();

    }

    /**

     * 供子类继承的初始化方法. 可以通过 getFilterConfig() 获取 FilterConfig 对象.

     */

    protected void init() {}

    /**

     * 直接返回 init(ServletConfig) 的 FilterConfig 对象

     */

    public FilterConfig getFilterConfig() {

        return filterConfig;

    }

    /**

     * 原生的 doFilter 方法, 在方法内部把 ServletRequest 和 ServletResponse

     * 转为了 HttpServletRequest 和 HttpServletResponse, 并调用了

     * doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)

     *

     * 若编写 Filter 的过滤方法不建议直接继承该方法. 而建议继承

     * doFilter(HttpServletRequest request, HttpServletResponse response,

     *        FilterChain filterChain) 方法

     */

    @Override

    public void doFilter(ServletRequest req, ServletResponse resp,

            FilterChain chain) throws IOException, ServletException {

        HttpServletRequest request = (HttpServletRequest) req;

        HttpServletResponse response = (HttpServletResponse) resp;

        doFilter(request, response, chain);

    }

    /**

     * 抽象方法, 为 Http 请求定制. 必须实现的方法.

     * @param request

     * @param response

     * @param filterChain

     * @throws IOException

     * @throws ServletException

     */

    public abstract void doFilter(HttpServletRequest request, HttpServletResponse response,

            FilterChain filterChain) throws IOException, ServletException;

    /**

     * 空的 destroy 方法。

     */

    @Override

    public void destroy() {}

}