Enable java remote debug in code

Question

For example, we can enable java remote debug by adding following to command line.

-agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=5005

But my application is running in yarn, I'm not sure which port is available.

So I want enable java debug in my code.

First I detect a available port and log in my program, then I can use this port to debug my application.

Does this answer your question? Debug a java application without starting the JVM with debug arguments — Vadzim
– Vadzim, Commented Feb 28, 2020 at 22:38

Florian Fray · Accepted Answer · 2017-09-30 10:23:03Z

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The address property specifies host (optionally) and port (only the port if host is left out). So address=5005 specifies the port 5005 in your case. If you want your program to wait until you connect your debugger, switch suspend=n to suspend=y.

Edit: Maybe I misunderstood your question. In case you want to enable debugging programmatically, this won't be possible as the debugging facility JPDA is not exposing a Java API nor any other way to start and stop it programmatically.

edited Sep 30, 2017 at 10:23

answered Sep 30, 2017 at 10:05

Florian Fray

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2 Comments

yunfan Over a year ago

So it is impossible to do this?

Florian Fray Over a year ago

As stated: No, it's not possible to start a debugger after the JVM has started your program. Same is true for stopping the debugger.

brain99 · Accepted Answer · 2017-09-30 10:25:29Z

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I'm not sure this can be done from code; however according to an answer to this old question, it is possible to enable debugging for an already-running JVM using jsadebugd

As mentioned in said answer, the feature is marked experimental and unsupported so your mileage may vary.

answered Sep 30, 2017 at 10:25

brain99

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1 Comment

Florian Fray Over a year ago

jsadebugd enables remote connection of some debugging tools like jmap, jinfo and jstack. They help in some areas of debugging, but not the in the same way jpda jdb do. BTW it is possible to connect jdb to any running process (regardless of -agentlib:jdwp... setting), but that can be used to inspect few things and freezes the running application. Uncertain if that is what the author of this question wanted to do.

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