Filter

Filter的主要用处：

　　在HttpServletRequest到达Servlet之前，拦截客户的请求，可以修改请求的头和数据

　　在HttpServletResponse到达客户端之前，拦截响应，可以修改响应的头和数据

 

Filter的种类

　　用户授权的Filter：Filter负责检查用户的请求，过滤非法的请求

　　日志Filter：详细记录某些用户的请求

　　负责解码的Filter：对非标准的请求进行解码

　　能改变XML内容的XSLT Filter

 

 

@WebFilter(filterName = "/LogFilter",
    urlPatterns = { "/*" })
public class LogFilter implements Filter {

    private FilterConfig config;

    /**
     * Default constructor.
     */
    public LogFilter() {}

    /**
     * @see Filter#destroy()
     */
    public void destroy() {

        this.config = null;
    }

    /**
     */
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException,
        ServletException {

        System.currentTimeMillis();
        System.out.println("beginning...");

        HttpServletRequest httpRequest = (HttpServletRequest) request;
        System.out.println("Servlet path :" + httpRequest.getServletPath());

        // pass the request along the filter chain
        chain.doFilter(request, response);

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

    /**
     * @see Filter#init(FilterConfig)
     */
    public void init(FilterConfig fConfig) throws ServletException {

        this.config = fConfig;
    }

}

 

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