Debugging Applications with Separate 'jdb' Sessions

Java Tools Tutorials - Herong's Tutorial Notes - Version 5.32, by Dr. Herong Yang

Java Tools Tutorials - Herong's Tutorial Notes

∟Debugging Applications with Separate 'jdb' Sessions

This section provides a tutorial example on how to run a Java application and the 'jdb' debugger separately in shared memory mode.

If you ask "Can I launch the debugger ('jdb') and the target application separately?", the answer is "Yes, you can.". Since Java 5 (JDK 1.5), both "jdb" and "java" have been enhanced to use the latest JPDA (Java Platform Debugger Architecture) technology to give you the following options:

                     Debugger                 Target
Option                    jdb                   java

     1   Shared memory client   Shared memory server
     2   Shared memory server   Shared memory client
     3          Socket client          Socket server   
     4          Socket server          Socket client

The shared memory options requires that the debugger and the target application to be on the same machine. Of course, the socket options allow you to run them remotely.

Let's try option #1 first. Open a command window on a windows system and run:

C:\herong>java -agentlib:jdwp=transport=dt_shmem,address=MyHello,server=y,
   suspend=y Hello

Listening for transport dt_shmem at address: MyHello

The target application is launched in "shared memory server" mode. Its execution is suspended. Now open another command window and run:

C:\herong>jdb -attach MyHello
Set uncaught java.lang.Throwable
Set deferred uncaught java.lang.Throwable
Initializing jdb ...
>
VM Started: No frames on the current call stack

main[1] stop in Hello.main
Deferring breakpoint Hello.main.
It will be set after the class is loaded.

main[1] cont
> Set deferred breakpoint Hello.main

Breakpoint hit: "thread=main", Hello.main(), line=3 bci=0
3          System.out.println("Hello world!");

main[1] list
1    public class Hello {
2       public static void main(String[] a) {
3 =>       System.out.println("Hello world!");
4       }
5    }

main[1] cont
>
The application exited

As you can see, the debugger successfully connected to the target application.

Last update: 2015.

Table of Contents

About This Book

Java Tools Terminology

Installing Java 8 on Windows

'javac' - The Java Program Compiler

'java' - The Java Program Launcher

►'jdb' - The Java Debugger

'jdb' - Java Debugger Command and Options

Starting a Debugging Session with 'jdb'

►Debugging Applications with Separate 'jdb' Sessions