servlet防盗链

package cn.itcast.web.tag;

import java.io.IOException;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.SkipPageException;
import javax.servlet.jsp.tagext.SimpleTagSupport;

public class RefererTag extends SimpleTagSupport {

private String site;
private String page;
public void setSite(String site) {
this.site = site;
}
public void setPage(String page) {
this.page = page;
}


@Override
public void doTag() throws JspException, IOException {
//看来访问者是从哪个页面来的
PageContext pageContext = (PageContext)this.getJspContext();
HttpServletRequest request = (HttpServletRequest) pageContext.getRequest();
String referer = request.getHeader("referer"); //http://www.sina.com/index.html

//判断
if(referer==null || !referer.startsWith(site)){
HttpServletResponse response = (HttpServletResponse) pageContext.getResponse();
String webroot = request.getContextPath(); //day11_example
if(page.startsWith(webroot)){
response.sendRedirect(page);
}else{
response.sendRedirect(webroot + page);
}
//重定向后，控制保护的页面不要执行
throw new SkipPageException();
}


}



}