Imagine if you could ping a running JVM over HTTP to obtain realtime diagnostic info. That seems to be what Sun has in mind with U.S. Patent 7,039,691, "Java Virtual Machine Configurable to Perform as a Web Server," granted to Sun Microsystems last month.
Abstract: A virtual machine, such as a Java(tm) virtual machine, is configured to operate as a web server so that users, using a browser, can make general-purpose inquiries into the state of the virtual machine or, in some cases, mutate the state of the VM. A "browsable" VM contains a network traffic worker, such as an HTTP thread, a services library, and a VM operations thread, which is an existing component in most virtual machines. The network traffic worker and the VM operations thread communicate through a request data structure. The VM operations thread generates a reply to the request upon receiving a request data structure from the traffic worker. Such a reply can be in the form of an HTTP response containing HTML or XML pages. These pages are transmitted back to the browser/user by the network traffic worker.