如果要显示新信息，如何使servlet刷新jsp页面？

Question

I am making a web application that receives pictures from an android smartphone and then displayes them in a .jsp page.

I need a mechanism to reload the .jsp page if there is new pictures in the server. Kinda like facebook where we dont need to refresh to see new content.

Does facebook just refreshs from time to time or there is some mechanism that realizes there is new information to be displayed and notifies the page to refresh itself?

Answer 1

The servlet only informs that there is new information then, the jsp refreshes itself. The other option is to use AJAX so that the servlet returns you the new information let's say in a JSON format. And then by using javascript you update your webpage with the new information (and without refreshing the page because of AJAX).

Answer 2

As the other folks answered, with HTTP the client (web browser) must initiate the message exchange. In other words. the server (JSP is a server process) cannot send a message to a web browser. The web browser must start the process (by sending a request). The server can only respond the web browser's request.

So as the other folks pointed out. Face book probably sends a javascript program to the web browser. The javascript program running in the web browser every few seconds sends a message to server. The message asks the server whether there is new information to display.

Hope that makes sense. You need to add javascript that runs in the browser. That javascript runs in a loop, polling the server for new info. The server does not poll the web browser. It's the other way around. The web browser polls the server.

Hope that helps :) Good Luck.