Java Servlet Programming

The Server

A servlet can find out much about the server in which it is executing. It can learn the hostname, listening port, and server software, among other things. A servlet can display this information to a client, use it to customize its behavior based on a particular server package, or even use it to explicitly restrict the machines on which the servlet will run.

Getting Information About the Server

There are four methods that a servlet can use to learn about its server: two that are called using the ServletRequest object passed to the servlet and two that are called from the ServletContext object in which the servlet is executing. A servlet can get the name of the server and the port number for a particular request with getServerName() and getServerPort(), respectively:

public String ServletRequest.getServerName()
public int ServletRequest.getServerPort()

These methods are attributes of ServletRequest because the values can change for different requests if the server has more than one name (a technique called virtual hosting). The returned name might be something like "www.servlets.com" while the returned port might be something like "8080".

The getServerInfo() and getAttribute() methods of ServletContext provide information about the server software and its attributes:

public String ServletContext.getServerInfo()
public Object ServletContext.getAttribute(String name)

getServerInfo() returns the name and version of the server software, separated by a slash. The string returned ...