Force exception while debugging

Question

Is it possible to force an exception to be thrown while debugging.

Let me give you an example: I am debugging some code where I download a page from the internet. When the Internet connection is lost, or network card is down, an IOException should be thrown, BUT instead the execution is blocking (on the second line)

URLConnection connection = requestURL.openConnection();
BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));

I need a way to force throwing an exception while debugging when the code is blocking so I can jump to the catch block.

I am using netbeans BTW.

While Debugging = added manually when the execution thread is paused.

EDIT: In other words, I need to inject - Invoke an exception while running, without affecting current code !

Thank you.

You can write a unit test reproducing your issue and debug it. However if your system is tightly coupled this might be a difficult task. — Alex Nikolaenkov
– Alex Nikolaenkov, Commented Mar 5, 2011 at 17:35

luk2302 · Accepted Answer · 2016-07-15 11:56:13Z

22

I would find the variable that is being waited on, and in the expression window in eclipse, call notify on that variable, then i would null out that variable, so that the synchronized block would throw a NullPointerException.

edited Jul 15, 2016 at 11:56

luk2302

57.5k24 gold badges108 silver badges151 bronze badges

answered Mar 5, 2011 at 17:34

MeBigFatGuy

28.7k8 gold badges64 silver badges68 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Jayan Over a year ago

! This idea can be extended to throw any type of exception. :)

Axel Knauf Over a year ago

Using Eclipse you can also add a break point somewhere and a watch expression "throw new FooBarException". Only problem is, it will be evaluated every time the VM is suspended.

Patrick Over a year ago

@Axel you mark the expression as disabled, and then anytime you want it to be thrown you just right click on it and 'Reevaluate Watch Expression' and it gets thrown a single time.

user443854 · Accepted Answer · 2012-11-29 15:39:28Z

19

In eclipse Debug perspective, in Expressions view, just add new expression: throw new Exception("test"). I suppose NetBeans has something similar.

answered Nov 29, 2012 at 15:39

user443854

7,54313 gold badges56 silver badges64 bronze badges

1 Comment

Aleksandr Dubinsky Over a year ago

NetBeans seems to not have that.

mericano1 · Accepted Answer · 2011-03-15 11:54:56Z

2

I think what you need to do is wrap that code in a FutureTask with a time out and have the main thread waiting for either the time out or the completion of the task.

You can also use some additional system properties to only throw the exception if in test mode

Have a look at this post (Disclaimer, I wrote it)

Hope it helps

edited Mar 15, 2011 at 11:54

user50049

answered Mar 6, 2011 at 1:42

mericano1

2,9131 gold badge19 silver badges25 bronze badges

Comments

mdm · Accepted Answer · 2011-03-05 17:21:40Z

0

Why not just modify the code temporarily so that it generates an exception? (throw new IOException(...)). Or, disconnect from the internet and try and run it.

answered Mar 5, 2011 at 17:21

mdm

12.7k5 gold badges36 silver badges53 bronze badges

3 Comments

firas Over a year ago

When the internet is disconnected, or the ntwork card is down, the thread blocks on the second line, JUST LIKE I SAID in the question :)

mdm Over a year ago

It may block while the request times out, so just wait. There is also nothing to stop you from throwing your own IOException.

firas Over a year ago

In other words, I need to inject - Invoke an exception while running, without affecting current code !

Bozho · Accepted Answer · 2011-03-05 17:37:10Z

0

If you thread is waiting (blocked), you can't do much with it. You'd have to interrupt() the waiting thread. The JVM appears to have this option, you just have to find it in the debugger.

answered Mar 5, 2011 at 17:37

Bozho

599k147 gold badges1.1k silver badges1.2k bronze badges

Comments

Community · Accepted Answer · 2017-05-23 12:02:51Z

0

JDB has a kill thread command where the developer can specify the thread id and the exception to be used to kill the thread.

I found two references that use the command line jdb debugger. See StackOverflow - Is it possible view/pause/kill a particular thread from a different java program running on the same JVM?, How do I use kill call in JDB?

I couldn't find any info on a similar method from Eclipse Java debugger.

edited May 23, 2017 at 12:02

CommunityBot

11 silver badge

answered Mar 5, 2011 at 17:57

typo.pl

8,9302 gold badges31 silver badges29 bronze badges

Comments

wil · Accepted Answer · 2022-07-24 01:22:47Z

0

You can also throw Exceptions with coditional breakpoints. With this way is not necessary modify your code.

answered Jul 24, 2022 at 1:22

wil

112 bronze badges

Collectives™ on Stack Overflow

Force exception while debugging

7 Answers 7

3 Comments

1 Comment

Comments

3 Comments

Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

7 Answers 7

3 Comments

1 Comment

Comments

3 Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related