I found a really weird bug within my Java Code
Even when i force a RuntimeException in my program it is not recognized by the JVM.
Here a demo of what I have written
private static void someMethod(){
//Some Code
if(true)
throw new RuntimeException();
// More Code
}
I added the if(true) to prevent the unreachable code message, just for testing.
But I think that the real problem is that there is some unhandled Exception in my code, which I cant really log, because the printStackTrace() is missing, or else i should get a console log.
Also I get the plain text: Exception while removing reference.
But its no System.err message, it just look like System.out
Are there any other methods of logging exception, excpect the default console, and what could cause a exception to be unhandled?
NOTE: I use following external libraries: JNativeHook, JLayer, Apache Commons IO
Full GitHub repo
The Exception should occur in CsgoSounds.java at line 944
OS: Windows 10, jre version: 1.8.0_60
There are checked Exceptions and unchecked ones (everything that extends runtime exception).
The compiler force you to deal with checked exceptions (with a try catch or a throws declaration). You are not forced to deal with Unchecked exceptions. But you can, just add a try catch around your code, then you can call printstacktrace on it.
JNativeHook was blocking all console outputs. I had to enable the function first.
Logger logger = Logger.getLogger(GlobalScreen.class.getPackage().getName());
logger.setLevel(Level.WARNING);
did the job.
Related
I work on a Java application that makes fairly heavy use of Javascript to form the business logic/glue. It runs using Graal. This all works fine, but we struggle with effective error handling.
This is essentially how the JS is executed:
try {
Context context = Context.newBuilder("js").allowAllAccess(true).build()
Source s = Source.newBuilder("js", src, "script").build();
context.eval(s);
} catch (Exception e) {
LOGGER.error("Exception occurred in JavaScript:...", e);
}
So when errors happen we log them somewhere so we can do some postmortem, etc. It's possible to get the JS stack trace in these logs out of the PolyglotException that Graal throws, which is great. However, things are more complicated when some JS code has called back into Java-land, and a Java exception has been thrown:
var x = callJavaFunction("invalid parameter"); // Throws a NoSuchElementException, for example
The PolyglotException has an asHostException() method that returns the original Java-land exception, and my code that executes the JS files is smart enough to understand this and produce a useful error log. The problem arises when the JS code has tried to catch this itself, for whatever reason:
try {
var x = callJavaFunction("invalid parameter"); // NoSuchElementException
} catch (e) {
doSomeCleanup();
throw e;
}
Now we have lost the original Exception, and even worse, the JS-stack trace now just shows us the catch block, instead of where the cause was. isHostException() returns false, because this is just a JS error now. I cannot find a way to get at the original cause, which makes diagnosing errors quite difficult, especially when they have come out of a production system. The original Java exception message ends up in the JS-error object, which is helpful, but we don't have the stack trace, which is not.
What approaches can I take to try and address this?
One thought I had: Can I hook into the GraalVM and get a callback whenever a host-exception is thrown? At least that way I could have a log saying "the following Java Exceptions were thrown during execution" which I could attach to the error report. So far I've not been able to find a way to achieve this.
I am trying to load with java reflection a bunch of classes. Everything seems working fine (I am handling the exception if the class is not found).
However there is a particular class that is raising another exception that is not thrown by call to the Class.forname() but by an internal method and so I cannot even catch it.
Here is my code:
try {
URL url = Class.forName(qualifiednameOfTheClass);
} catch (ClassNotFoundException ex) {
// ok class not found can be handled
} catch (Exception e){
// catch every other exception just to try to get the strange exception
}
So with this code everything is working, I am using it on lots of classes and it's working (sometimes it finds it sometimes it doesn't).
However there is one case that is not working properly and I cannot understand why. If qualifiednameOfTheClass = sun.security.krb5.SCDynamicStoreConfig my code is raising an exception:
Exception in thread "mythread-1" java.lang.UnsatisfiedLinkError: no
osx in java.library.path at
java.lang.ClassLoader.loadLibrary(ClassLoader.java:1886) at
java.lang.Runtime.loadLibrary0(Runtime.java:849) at
java.lang.System.loadLibrary(System.java:1088) at
sun.security.action.LoadLibraryAction.run(LoadLibraryAction.java:67)
at
sun.security.action.LoadLibraryAction.run(LoadLibraryAction.java:47)
at java.security.AccessController.doPrivileged(Native Method) at
sun.security.krb5.SCDynamicStoreConfig.(SCDynamicStoreConfig.java:39)
at java.lang.Class.forName0(Native Method) at
java.lang.Class.forName(Class.java:190) at
com.myclass.getJARFromClassForName(JavaId.java:510)
at com.myclass.getJARUrl(Id.java:550) at
com.myclass.collectInformation(Graph.java:366)
at
com.myclass.createNode(Graph.java:166)
at com.myclass.Graph.(Graph.java:143) at
com.myclass2.run(myclass2.java:246)
at java.lang.Thread.run(Thread.java:745)
So as you can see in the error we have this strange exception that cannot be caught even with a generic catch like in my code and I cannot understand why it has been raised and what actually is this osx library (I am on linux)
EDIT: The only thing that I found is this link http://www.straub.as/java/pocketapi/index7.html but is in german and so I read it with google translate and I don't know if I got it right but is saying that the classes listed there cannot be reproduced with Class.forname() itself.
Is it true? Is there a reason why this cannot be loaded with reflection or am I doing something wrong?
"Cannot be caught" because it's an Error, not an Exception. I'd recommend reviewing the object hierarchy in the JDK for Throwable.
Try changing that to Throwable and you'll have better luck catching. I don't know why the error is happening.
This looks like a JNI class that's using native code. I don't know what you're doing, but this looks like a bad idea to me.
This is not how this class expects to be loaded and loading this internal class directly doesn't appear to work. You need to load the class using the standard encryption API so that this class can be loaded as expected, or possibly not loaded at all (it could be code which will only work on OSX)
As you can see in the link you have provided, there are some classes where this method fails.
When calling this method on these objects, Java needs first to load additional stuff, as this is platform specific stuff which is not shipped by default. In your case, it is Kerberos, a security API.
As you can see in its Documentation, it searches for some files in specific paths (java.library.path). As it can not find it there, it throws an error.
Note that the error UnsatisfiedLinkError does not refer to finding the class name for sun.security.krb5.SCDynamicStoreConfig itself. It refers to not finding the native library in the paths provided by java.library.path.
This path itself points, for example on Windows, to C:Windows/system32/.
However, you may catch this error with catch(Error e), note that an Error is not an Exception (Throwable hierarchy).
Be aware that catching an Error in general is no good idead as you can not be sure if the JVM can recover from it.
Sorry for this very basic question, but I am stuck with this and m not able to find a solution.
I have a Core Java application (Java version is 1.6). From my application I am calling a method in a jar, which is throwing a custom runtime exception.
I am not catching this exception, but still JVM is not printing the stack trace.
Does JVM by default will not print the stack trace, when a runtime exception is thrown and not caught?
Or am I missing something which I can check?
Thanks in advance.
-Sandeep
AFAIK, JRE should print a stacktrace of an uncaught exception. But you can always do it yourself:
try {
someObject.someMethod();
} catch (Throwable t) {
t.printStackTrace();
throw t;
}
I've come across some really strange behaviour in my Java code. There is a exception shown on my Eclipse log console saying Exception:java.lang.NullPointerException with no reference to the code where it occurred.
On debugging I found out a line where this occurred and so put it in try-catch hoping I catch it. However it didn't return in catch block.
The strange part being even though there's exception thrown at the line immediately after it executes and the execution continues normally.
Can some one please tell me the probable cause?
I could have attached the source code but I have checked the parameters and all seem fine.
My main reason for this post is to learn about such behavior if any of you coders ever came across.
Probably a problem with Eclipse. I have seen that behaviour before, and restarting Eclipse solved the problem.
Please check whether your builder is activated and the changed source code is build automatically. Otherwise your code changes will never get it into your runtime application.
I am pretty sure, that the executed source code is different to the source code shown in your editor.
If you see the exception's message but no stack trace, that is caused by code that looks like this:
try
{
// something which causes the exception
}
catch (final Exception err)
{
System.out.println(err);
}
The problem with this code is that it only prints the result of the exception's .toString() method. For most exceptions this is just the exception class and the message. This code omits the stack trace, thus making it much harder to debug the problem.
If the exception is to be caught, then change the code to look like this for the stack trace to be included in the output:
try
{
// something which causes the exception
}
catch (final Exception err)
{
err.printStackTrace();
}
I'm using NetBeans as my IDE for developing Android.
However, when I get an exception, Netbeans does not break on the exception as I expect it to.
I have checked the box "Stop on uncaught exceptions" that can be found in Options --> Java Debugger --> Stop on uncaught exceptions but that doesn't help.
Furthermore, where can I see the actual exception message? I don't see anything. I have no clue where and when an exception occurs, just that it does occur.
I've read some on the netbeans.org site about a bug in 6.9.1 that was fixed, but it doesn't seem to be fixed in 7.0 that I have.
The debugging window doesn't say anything useful at all, gives some form of stack trace that is pointless as it doesn't specify any of my own code.
I switched from Eclipse because that IDE sucks, NetBeans is much leaner, but the debugging needs to be fixed to be useful.
I have this problem when I use netbeans too. To get the exception message, I use try-and-catch. In the catch() statement, call a function that contains some code and put a breakpoint on it. Then when the exception is given your breakpoint in the catch statement will be called and you can read the information (error message, stack, etc.) from the Exception obect.
try
{
// Doing something here
}
catch (Exception e1)
{
// This is called when an exception occurs
doSomething(); /// Put breakpoint here
}
UPDATE:
I am not sure if this will work for android but you could try entering a "New Breakpoint". When entering a new breakpoint to break on an exception, you need to know the
exact package/class exception name. For example, if you want to catch a
NullPointerException, then you go to Debug >> New Breakpoint to create a New Breakpoint and enter
java.lang.NullPointerException into the Exception Class Name field in the
Breakpoint Properties dialog. Choose whether to break on caught, uncaught or both, exceptions and it will hit a breakpoint if that type of exception ever occurs in the class/project.
I had such behavior where I had my source file that generated the exception NOT in "default package". When I moved everything to "default package" it started working fine and stop on exception automatically.
This answer actually also answers this question:
https://stackoverflow.com/a/2671390/415551
To quote user Finbarr:
Go to debug > New Breakpoint (alternatively CTRL+SHIFT+F8). Change the
breakpoint type to Exception in the top right hand drop down menu.
Type java.lang.NullPointerException in the Exception class field.
Choose whether to break on caught, uncaught or both.
Debug your code and watch the glorious auto breakpoint when the
Exception is thrown.
Simply change java.lang.NullPointerException to java.lang.Exception to break on any error.