ページ転送のいくつかの状況について

/*
 * @(#)ImageFilter.java	1.00	2010/03/17
 * CopyRight(C) stephen830 2010-2011, All rights reserved.
 */
package com.stephen.filter;

import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * @author stephen
 *
 *     .
 *             .
 */
public class ImageFilter implements Filter {
	
	/**
	 *     .
	 */
	protected FilterConfig filterConfig = null;

	/**
	 *    .
	 * @see javax.servlet.Filter#init(javax.servlet.FilterConfig)
	 */
	public void init(FilterConfig filterConfig) throws ServletException {
		this.filterConfig = filterConfig;
	}

	/**
	 *     .
	 * @see javax.servlet.Filter#doFilter(javax.servlet.ServletRequest, javax.servlet.ServletResponse, javax.servlet.FilterChain)
	 */
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
		if(request instanceof HttpServletRequest){
			HttpServletRequest httpRequest = (HttpServletRequest)request;
			String imagePath = httpRequest.getRequestURL().toString().toLowerCase();
			
			//  1
			//     url，          request  
			//   url      url
			RequestDispatcher rd = httpRequest.getRequestDispatcher("new_url");
			rd.forward(request,response);
			
			//  2
			//  ，     request  
			//   url       url
			HttpServletResponse httpResponse = (HttpServletResponse)response;
			httpResponse.sendRedirect("new_url");
			
			//  3
			//     Servlet(   Servlet)，          request  
			//   url      url
			RequestDispatcher rd2 = this.filterConfig.getServletContext().getNamedDispatcher("OtherServlet");
			rd.forward(request,response);
		}
		chain.doFilter(request,response);
	}

	/**
	 *   .
	 * @see javax.servlet.Filter#destroy()
	 */
	public void destroy() {
		this.filterConfig = null;
	}

}

	<filter>
		<filter-name>ImageFilter</filter-name>
		<filter-class>com.stephen.filter.ImageFilter</filter-class>
	</filter>
	

	
	<filter-mapping>
		<filter-name>ImageFilter</filter-name>
		<url-pattern>/*</url-pattern>
	</filter-mapping>