Java API to turn on debugging in a running JVM [duplicate]

Answer 1

This is not possible. The JVM has to know from the beginning that it is in debug mode. It runs a bit slower then but provides external processes with debug information and breakpoints which is not possible when the JVM already has been startet.

Answer 2

You can attach to any running JVM using Visual VM. Be sure to download version 1.3.2 and install all the plugins.

Answer 3

The debug port that the questioner refers to is for source code debugging, such as with an Eclipse debugger. The port for VisualVM is the JMX port, which takes a different set of JVM options. There are exceptions though: Mission Control for JRockit uses the jdwp port rather than the JMX port.

And yes, you can dynamically load the JMX debugger in code. Its complicated but OSGI can load this dynamically I believe. For example, here is a reference to Jetty project doing this.