Any way to “reboot” the JVM?

Question

Is there any way to reboot the JVM? As in don\'t actually exit, but close and reload all classes, and run main from the top?

Answer 1

It's easy in JavaX: You can use the standard functions nohupJavax() or restart().

Answer 2

Your best bet is probably to run the java interpreter within a loop, and just exit. For example:

#!/bin/sh
while true
do
    java MainClass
done

If you want the ability to reboot or shutdown entirely, you could test the exit status:

#!/bin/sh
STATUS=0
while [ $STATUS -eq 0 ]
do
    java MainClass
    STATUS=$?
done

Within the java program, you can use System.exit(0) to indicate that you want to "reboot," and System.exit(1) to indicate that you want to stop and stay stopped.

Answer 3

IBM's JVM has a feature called "resettable" which allows you to effectively do what you are asking.

http://publib.boulder.ibm.com/infocenter/cicsts/v3r1/index.jsp?topic=/com.ibm.cics.ts31.doc/dfhpj/topics/dfhpje9.htm

Other than the IBM JVM, I don't think it is possible.

Answer 4

AFAIK there is no such way.

Notice that if there were a way to do that, it would highly depend on the current loaded code to properly release all held resources in order to provide a graceful restart (think about files, socket/tcp/http/database connections, threads, etc).

Some applications, like Jboss AS, capture Ctrl+C on the console and provide a graceful shutdown, closing all resources, but this is application-specific code and not a JVM feature.

Answer 5

If you're working in an application server, they typically come with built-in hot deployment mechanisms that'll reload all classes in your application (web app, enterprise app) when you redeploy it.

Otherwise, you'll have to look into commercial solutions. Java Rebel (http://www.zeroturnaround.com/javarebel/) is one such option.

Answer 6

I do something similar using JMX, I will 'unload' a module using JMX and then 'reload' it. Behind the scenes I am sure they are using a different class loader.