Normally we use IDE for remote debugging a Java application, but it's also possible to use a command line tool to do this.
There is a jdb tool included in the JDK: http://docs.oracle.com/javase/7/docs/technotes/tools/windows/jdb.html
We should compile and run the Java file first.
When compiling the Java source, we need to pass -g to keep local varible names for debugging (otherwise the names will be changed to some shorter names).
javac -g HelloWorld.java
Then run it with enabling remote debugging:
java -Xdebug -Xrunjdwp:transport=dt_socket,server=y,address=9999 HelloWorld
It:
- listenning on port
9999 - won't run any code until client connect (
server=y)
$ jdb -attach 9999
Set uncaught java.lang.Throwable
Set deferred uncaught java.lang.Throwable
Initializing jdb ...
>
VM Started: No frames on the current call stack
Also we can speicify the ip to connect a remote host:
jdb -attach <some-ip>:<port>
Set a breakpoint:
main[1] stop at HelloWorld:4
Deferring breakpoint HelloWorld:4.
It will be set after the class is loaded.
Run to the (next) breakpoint:
main[1] next
> Set deferred breakpoint HelloWorld:4
Breakpoint hit: "thread=main", HelloWorld.main(), line=4 bci=3
4 name = "BBB";
Print a varible value:
main[1] print name
name = "AAA"
Run to the next line:
main[1] step
>
Step completed: "thread=main", HelloWorld.main(), line=5 bci=6
5 name = "CCC";
Print the name variable again:
main[1] print name
name = "BBB"
Next breakpoint (actually run to end now):
main[1] next
>
Step completed: "thread=main", HelloWorld.main(), line=6 bci=9
6 System.out.println(name);
Show threads:
main[1] threads
Group system:
(java.lang.ref.Reference$ReferenceHandler)0x14d Reference Handler cond. waiting
(java.lang.ref.Finalizer$FinalizerThread)0x14c Finalizer cond. waiting
(java.lang.Thread)0x14b Signal Dispatcher running
Group main:
(java.lang.Thread)0x1 main running
main[1]