Servlet怎么得到服务器的信息

Servlet如何得到服务器的信息？
Servlet可以使用如下四种方法来得到server的name, port和info
如下代码实现用servlet取得server的信息并输出到客户端浏览器：
import java.io.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class DemoServerSnoop extends GenericServlet{

public void service(ServletRequest req , ServletResponse res)
throws ServletException,IOException{

res.setContentType("text/plain");
PrintWriter out= res.getWriter();
out.println("req.getServerName()" + req.getServerName());
out.println("req.getServerPort()" + req.getServerPort());

out.println("ServletContext().getServerInfo()" +
getServletContext().getServerInfo());

out.println("getServerInfo() name:" +
getServerInfoName(getServletContext().getServerInfo()));

out.println("getServerInfo() version:" +
getServerInfoVersion(getServletContext().getServerInfo()));

out.println("getServerContext().getAttribute(\"attribute\")" +
getServletContext().getAttribute("attribute"));
}
private String getServerInfoName(String serverInfo){

int slash = serverInfo.indexOf('/');
if(slash==-1)
return serverInfo;
else
return (String) serverInfo.subSequence(0,slash);
}
private String getServerInfoVersion(String serverInfo){

int slash = serverInfo.indexOf('/');
if(slash==-1)
return null;
else
return serverInfo.substring(slash + 1);
}}