做个图片的防盗链

目的是，网站本身的图片不防盗链，用户上传的图片不许外链

用户上传的图片都在userfile目录和其子目录下面

1. 配置filter

	<filter>   
	    <filter-name>jpgServlet</filter-name>   
	    <filter-class>   
	        com.djwl.core.filter.JpgFilter
	    </filter-class> 
	</filter>
	<filter-mapping>   
	    <filter-name>jpgServlet</filter-name>   
	    <url-pattern>/userfile/*</url-pattern>   
	</filter-mapping>

2. Filter

package com.djwl.core.filter;

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;

/**
 * Description: <br>
 * 2010-4-13
 * @author huxiao [e-mail]
 */
public class JpgFilter implements Filter {

	@Override
	public void doFilter(ServletRequest servletrequest, ServletResponse servletresponse, FilterChain filterchain) throws IOException, ServletException {
		HttpServletRequest request = (HttpServletRequest)servletrequest;
		HttpServletResponse response = (HttpServletResponse)servletresponse;

		//获取请求来源
		String linkFrom = request.getHeader("referer");
		
		/**
		 * 如果不是从本网站链接，则返回本网站的logo，否则正常走
		 * 注意：这里的linkFrom为null的话也正常走。原因是，用户如果直接输入图片地址的话，linkFrom为null
		 */
		if(linkFrom != null && !linkFrom.contains(request.getServerName())){
			System.out.println("盗链来自： "+linkFrom);
			request.getRequestDispatcher("/images/logo_red.jpg").forward(request, response);
		}else {
			filterchain.doFilter(request, response);
		}
	}

	@Override
	public void destroy() {
		// TODO Auto-generated method stub
		
	}

	@Override
	public void init(FilterConfig filterconfig) throws ServletException {
		// TODO Auto-generated method stub
		
	}

}

3. 测试

图片所在的是localhost1:1111，现在我用localhost1和localhost2去请求，ok的话，前者能显示，后者显示logo

body部分：这里我放了两个图片，前面一个是/images目录下的，不做防盗链，后面的做防盗链

<img src="http://localhost1:1111/images/bq_bgGreen.jpg">
<img src="http://localhost1:1111/userfile/20100405/7ef5d05bacd840e8beb8147653ad2906_81_81.jpg" />

OK，这就达到咱们的目的了