Do Applets use Browser for HTTP Requests?

My testing with Windows 7, Java 1.6.23 and Firefox, Chrome and Internet Explorer is that HttpURLConnections from within an applet's JVM interact in no way with the browser. They don't use the cache, and don't have cookie headers added.

Applets are executed by the Java Plugin, which is a browser plugin. The applet is indeed part of an HTML page loaded by the browser, can communicate with the browser DOM and with JavaScript code in the page, and uses the browser to send requests to its originating server.

See http://docs.oracle.com/javase/tutorial/deployment/applet/appletExecutionEnv.html and http://docs.oracle.com/javase/tutorial/deployment/applet/server.html for more information.

Applets do not share the session information by default, but you can pass the session ID via Applet parameter while initializing. And use the session ID for each HTTP request.

I think it depends on the Java plugin. My experience is that usually it uses the browser cache for network connections, and usually it transmits the cookies. I have had to empty the browser cache before to get a new file in an applet.

If you look at the Oracle Java 7 Plugin Control Panel, you will see an option in the network parameters to use direct connections for the applets, but the default is to use "browser parameters".

As for the cookies, I have seen in the past some Java plugins that did not transmit the session cookies, in particular on MacOS X (Apple even suggested a workaround). But most developers now assume that they are transmitted, and in practice it usually works.