How to kill a java thread using VisualVM or using a unix command?

It's not true. You can always attach to the JVM process with GDB and do a call pthread_kill if you know the thread id. You only need to translate from the java thread dump (do a kill -3) which gives you a hex id, (native id), then look into the list of threads in GDB (info threads) and locate the real thread id.

This is proven to work.

Dan Woods documented how to kill a thread in this blog entry... https://web.archive.org/web/20160302023213/http://www.rhcedan.com/2010/06/22/killing-a-java-thread The steps he performed involved using a debugger (JDB) and injecting an exception in the thread's execution. Specifically...

1. Ensure that your java program is started with the following parameters:

   -Dcom.sun.management.jmxremote.port=50199
   -Dcom.sun.management.jmxremote.authenticate=false
   -Dcom.sun.management.jmxremote.ssl=false
   -Xrunjdwp:transport=dt_socket,address=50100,server=y,suspend=n

   This will allow us to attach the java debugger to the running process, after we identify which Thread is causing the problem. Also, make sure that you have your iptables setup appropriately so as to only allow connections on 50100 and 50199 from the hosts/workstations that you manage.

2. Identify the offending thread:

3. Kill the thread. In this example, the ThreadName is “btpool0-0?. Fire up the java debugger (also shipped with the JDK distribution), and attach to the running JVM…

   [root@host ~]# jdb -attach 50100

Get a list of the running threads — this will also give us the thread id as the JVM sees it:

> threads  
--snip--  
(org.mortbay.thread.BoundedThreadPool$PoolThread)0x25cb
btpool0-0 running  
--snip--

The thread id that we’re going to kill is “0x25cb”. The first step of killing the thread is to jump into it, and suspend it…

thread 0x25cb
btpool0-0[1] suspend 0x25cb
btpool0-0[1] step
Step completed: <... snip ...>
btpool0-0[1] kill 0x25cb new java.lang.Exception()
killing thread: btpool0-0
btpool0-0[1] instance of 
com.site.package.name(name='btpool0-0', id=9675) killed btpool0-0[1]

Exit the java debugger, and you’re done!

There is no safe way to "kill" a thread without killing the process it is in. It not something you would do deliberately. For testing purposes I would add code to your application to support this.