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A Maven plugin fails and to open an issue, I would like to explain inside how the NullPointerException encountered can appear

While compiling an opensource project, I encounter a problem with a Maven plugin that fails.
And I would like to open an issue about its problem. To be helpful to those who will search to solve it, I would like to explain how it might happen.
Execution default of goal pl.project13.maven:git-commit-id-plugin:4.0.3:revision failed. (pl.project13.maven:git-commit-id-plugin:4.0.3:revision:default:initialize)
org.apache.maven.plugin.PluginExecutionException: Execution default of goal pl.project13.maven:git-commit-id-plugin:4.0.3:revision failed.
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:148)
at org.eclipse.m2e.core.internal.embedder.MavenImpl.execute(MavenImpl.java:332)
at org.eclipse.m2e.core.internal.embedder.MavenImpl.lambda$8(MavenImpl.java:1380)
at [...]
Caused by: java.lang.NullPointerException
at pl.project13.maven.git.GitCommitIdMojo.execute(GitCommitIdMojo.java:441)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:137)
... 30 more
For that, I've red the involved line that causes the NullPointerException on its Git repository.
The content of the line 441 of GitCommitIdMojo.java is :
List<MavenProject> sortedProjects =
Optional.ofNullable(session.getProjectDependencyGraph())
.map(graph -> graph.getSortedProjects())
.orElseGet(() -> {
log.warn("Maven's dependency graph is null. Assuming project is the only one executed.");
return Collections.singletonList(session.getCurrentProject());
});
But I'm not so experienced with Optional and other inline functions. And I wonder from where the NullPointerException is really coming. I have no way to test it in Live, so I can only guess.
I've checked on the source file : session is a required attribute. It shouldn't be null.
I believe that the Optional.ofNullable(...) protects the content inside parenthesis and that the NullPointerException isn't coming from here.
But when entering the .orElseGet(...) part of the expression, it might fail on Collections.singletonList(session.getCurrentProject()) where session.getCurrentProject() would return null.
Am I right?
What other parts of this statement could lead to a NullPointerException under what conditions?

You're not looking at the right version of the code. The maven-error refers to 4.0.3 of git-commit-id-plugin, but the code you're displaying comes from the master branch, which is at 4.0.4-SNAPSHOT.
This is line 441 in version 4.0.3:
List sortedProjects = session.getProjectDependencyGraph().getSortedProjects();
The NullPointer can come from any of the three parts.

Class.forName() is not working with a particular class

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.

DeepLearning4J NoSuchMethodError

I'm new to neural networks and NLP. I've found this library: DeepLearning4J. I'm trying to get it to work but whenever I execute this instruction:
Collection<String> similar = vec.wordsNearest("word_to_search", 10);
If the word I'm searching is mapped into the network I get the following exception:
java.lang.IllegalArgumentException: XERBLA: Error on argument 6 (LDA) in SGEMV
at org.jblas.NativeBlas.sgemv(Native Method)
at org.nd4j.linalg.jblas.blas.JblasLevel2.sgemv(JblasLevel2.java:25)
at org.nd4j.linalg.api.blas.impl.BaseLevel2.gemv(BaseLevel2.java:53)
at org.nd4j.linalg.api.ndarray.BaseNDArray.mmuli(BaseNDArray.java:2569)
at org.nd4j.linalg.api.ndarray.BaseNDArray.mmul(BaseNDArray.java:2377)
at org.deeplearning4j.models.embeddings.wordvectors.WordVectorsImpl.wordsNearest(WordVectorsImpl.java:290)
at org.deeplearning4j.models.embeddings.wordvectors.WordVectorsImpl.wordsNearest(WordVectorsImpl.java:337)
at word2vec.Word2VecTest.main(Word2VecTest.java:74)
Exception in thread "main" java.lang.NoSuchMethodError: org.nd4j.linalg.api.ndarray.INDArray.mean(I)Lorg/nd4j/linalg/api/ndarray/INDArray;
at org.deeplearning4j.models.embeddings.wordvectors.WordVectorsImpl.wordsNearest(WordVectorsImpl.java:283)
at word2vec.Word2VecTest.main(Word2VecTest.java:89)
I know that the NoSuchMethodError may be due to libraries different versions. In this specific case, this is probably caused by nd4j. I've checked the versions lots of time and this is what I'm importing at the moment:
akka-actor_2.11-2.4-M3.jar
akka-cluster_2.11-2.4-M3.jar
akka-remote_2.11-2.4-M3.jar
akka-slf4j_2.11-2.4-M3.jar
byte-buddy-0.6.15.jar
config-1.3.0.jar
deeplearning4j-core-0.0.3.3.4.alpha2.jar
deeplearning4j-nlp-0.0.3.3.4.alpha2.jar
deeplearning4j-scaleout-akka-0.0.3.3.4.alpha2.jar
deeplearning4j-ui-0.0.3.3.4.alpha2.jar
javassist-3.12.1.GA.jar
jblas-1.2.4.jar
jcublas-6.5.jar
lucene-analyzers-common-4.10.3.jar
lucene-core-4.10.3.jar
nd4j-api-0.4-rc3.4.jar
nd4j-bytebuddy-0.4-rc3.4.jar
nd4j-jblas-0.4-rc3.4.jar
nd4j-jcublas-common-0.4-rc3.4.jar
netty-3.10.4.Final.jar
protobuf-java-2.6.1.jar
reflections-0.9.10.jar
scala-library-2.12.0-M2.jar
selenium-server-standalone-2.47.1.jar
Can someone explain to me the problem?

The error is telling you that DeepLearning4J tried to call the method INDArray INDArray.mean(int value) but this method was not found.
Looking at nd4j 0.4-rc3.4 source code, you can see that the mean method actually takes a vararg int... as input. Since this is not int, the error is thrown.
This change was made by this commit when nd4j bumped version from 0.0.3.5.5.5 to 0.4-rc0.
As a result, you need to downgrade nd4j to version 0.0.3.5.5.5. With this downgrade, you will not have any more incompatibility since this is the actual version that DeepLearning4J is depending on. You can see that in the Maven dependencies of deeplearning4j-core-0.0.3.3.4.alpha2.

Java Play Mustache NPE Error

We are getting a mustache play error in production (amazon linux EC2 AMI) but not in development (MACs) and we have tried upgrading the jvm, using the jdk instead, and changing from a tomcat deploy model to match our development environments as much as possible but nothing is working. Please any help would be greatly appreciated. We have lots of shared code in java and javascript using mustache and it would be a big deal to rewrite everything if we had to ditch mustache on the java side.
20:48:52,403 ERROR ~
#6al2dd0po
Internal Server Error (500) for request GET /mystuff/people
Execution exception (In {module:mustache-0.2}/app/play/modules/mustache/MustacheTags.java around line 32)
NullPointerException occured : null
play.exceptions.JavaExecutionException
at play.templates.BaseTemplate.throwException(BaseTemplate.java:90)
at play.templates.GroovyTemplate.internalRender(GroovyTemplate.java:257)
at play.templates.Template.render(Template.java:26)
at play.templates.GroovyTemplate.render(GroovyTemplate.java:187)
at play.mvc.results.RenderTemplate.<init>(RenderTemplate.java:24)
at play.mvc.Controller.renderTemplate(Controller.java:660)
at play.mvc.Controller.renderTemplate(Controller.java:640)
at play.mvc.Controller.render(Controller.java:695)
at controllers.MyStuff.people(MyStuff.java:183)
at play.mvc.ActionInvoker.invokeWithContinuation(ActionInvoker.java:548)
at play.mvc.ActionInvoker.invoke(ActionInvoker.java:502)
at play.mvc.ActionInvoker.invokeControllerMethod(ActionInvoker.java:478)
at play.mvc.ActionInvoker.invokeControllerMethod(ActionInvoker.java:473)
at play.mvc.ActionInvoker.invoke(ActionInvoker.java:161)
at Invocation.HTTP Request(Play!)
Caused by: java.lang.NullPointerException
at play.modules.mustache.MustacheTags._template(MustacheTags.java:32)
at play.modules.mustache.MustacheTags$_template.call(Unknown Source)
at /app/views/User/people.html.(line:22)
at play.templates.GroovyTemplate.internalRender(GroovyTemplate.java:232)
... 13 more

Seems the issue is with the threadlocal. In Prod as per my logs, the session gets initialized with the main thread.
[2012-06-30 18:35:38,102] INFO 10097[**main**] - Mustache module initialized
However, MustacheTag tries to access with various thread like this during request.
[2012-06-30 17:48:44,669] INFO 66048[**play-thread-1**] - [{module:mustache-0.2}/app/play/modules/mustache/MustacheTags.java:46] _meta() :: MustachePlugin.session():null
So I changed the implementation of MustachePlugin like this.Changed line commented out:
//private static ThreadLocal<MustacheSession> session_ = new ThreadLocal<MustacheSession>();
private static MustacheSession _session = null;
public static MustacheSession session(){
//return session_.get();
return _session;
}
public void onConfigurationRead(){
// some code
_session = new MustacheSession(compiler, root);
// some code
}
And it is working fine now in prod mode! I see no reason why it should have been in a ThreadLocal in the first place as the session gets initialized at startup!

your issue is difficult to reproduce so i'll give few pointers here. you have tried to eliminate of issue being env issue. so other possible issues could be
data issue: many times reason for production issue is usually difference in actual data and test data. check if its data issue which is casuing NPE.
code issue: Is there something at people.html.(line:22) causing issue. first try removing / altering that to check if thats causing issue. Or can you get source code of mustache (exact version which you are using) and see what object its trying to create and where its failing.
Properties file for different environments: do you have different proprties file for each env? If yes, have u missed on any property for prod env?

You have a NullPointerException on MustacheTags.java at line 32.
This means that you are probably calling a method of the Mustache library and passing a null value.
Try logging all the parameters you transfer to this method (MyStuff.java line 183?).
You can look at the source code of MustacheTags here, it might help you understand what values you are passing and what should be passed.

Exception breakpoint occurred at EventDispatchThread.java

we are getting this error at the end of running application. I search in google buti don't know what cause this error and what this means. What to do and how to solve it?
i even don't know what raise this exception...
Exception breakpoint occurred at line 145 of EventDispatchThread.java.
java.lang.NullPointerException:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at oracle.jbo.uicli.jui.JUTableBinding$JUTableModel$2.run(JUTableBinding.java:1209)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:461)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:163)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:157)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:149)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)

Don't know what kind of searches you have performed on Google. I would suggest looking up each error (or rather each class where error occurs). Starting from the beginning as subsequent errors may be a due to error propagation. Two searches for EventDispatchThread and JUTableBinding.java may provide some insight at what went wrong.
http://www.docjar.org/docs/api/java/awt/EventDispatchThread.html
It seems that this class deals with AWT components ("takes events off the EventQueue and dispatches them to the appropriate AWT components")
For the JUTableBinding.java there are quite a few pages that say about NullPointerException
https://forums.oracle.com/forums/thread.jspa?threadID=515213
https://forums.oracle.com/forums/thread.jspa?threadID=2343921
https://kr.forums.oracle.com/forums/thread.jspa?threadID=503593
Some of them say that the problem may be with jdk version (seems 1.6 and above throw errors). I would assume that may be the case. Try to recompile using earlier versions of jdk and check whether error is still there. If it is not this then we will investigate further.
"I've looked into the code and found out that JUTableBinding.JUTableModel calls
mScrollUnit = control.getScrollableUnitIncrement(null,
SwingConstants.VERTICAL, 0);
(Line 947)
This was okay in Java 5, since JTable's getScrollableUnitIncrement just returned the row height."
"I changed the line to:
mScrollUnit = control.getScrollableUnitIncrement(
control.getVisibleRect(), SwingConstants.VERTICAL, 0);
and everything works fine on Java 6..."
Hope it helps.