request.getHeader所想到的

request.getHeader("")，简单的说就是获取请求的头部信息，根据http协议，它能获取到用户访问链接的信息。

/**
 * Returns the value of the specified request header
 * as a <code>String</code>. If the request did not include a header
 * of the specified name, this method returns <code>null</code>.
 * If there are multiple headers with the same name, this method
 * returns the first head in the request.
 * The header name is case insensitive. You can use
 * this method with any request header.
 * @param name  a <code>String</code> specifying the
 *                header name
 * @return        a <code>String</code> containing the
 *                value of the requested
 *                header, or <code>null</code>
 *                if the request does not
 *                have a header of that name
 */
public String getHeader(String name); 

比如我访问http://www.cnblogs.com/winner-0715/category/828769.html

可以抓取http请求头

GET /winner-0715/category/828769.html HTTP/1.1
Host: www.cnblogs.com
Connection: keep-alive
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.87 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Referer: http://www.cnblogs.com/winner-0715/p/6215102.html
Accept-Encoding: gzip, deflate, sdch
Accept-Language: zh-CN,zh;q=0.8

request.getHeader("Referer");

得到的就是

http://www.cnblogs.com/winner-0715/p/6215102.html

-----

request.getHeader("Host");

得到的就是

http://www.cnblogs.com/