SE452: Conditional Get [16/20]

One thing we can use these headers for is conditional get. When the request header If-Modified-Since is present in a request, it is called a conditional get. The browser sends this header.

Advantage: reduce network traffic and server load.

Web brower (client):

• A browser may cache the pages it has visited.
• When a user request a page that has been cached, the browser sends a conditional get.

Web server:

• When a conditional get is recieved, if the requested page is modified after the date, the page is sent to the client.
• Otherwise, sends status code 304 (Not Modified)

A servlet may take advantage of the conditional get.

Explicitly setting the Last-Modified header

        long t= System.currentTimeMillis();
        response.setDateHeader("Last-Modified", t)
        

Overriding the getLastModified() method in class HttpServlet

	long getLastModified( HttpServletRequest request) {
		return System.currentTimeMillis();
	}