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PsiClass to java.lang.Class

I'm developing plugin for IntelliJ IDEA. How can plugin get the name and version of libraries that are imported to the project that is being checked by plugin? I have PsiClass of the project, but cannot convert it to java.lang.Class. Maybe there's the way to get ClassLoader from PsiElement?
super.visitImportStatement(psiImport);
Class importedClass = Class.forName(psiImport.getQualifiedName(), true, psiImport.getClass().getClassLoader());
PsiImport.getClass().GetClassLoader() - returns ClassLoader of class PsiImportStatementImpl instead of ClassLoader of class that I've imported.

IntelliJ does mostly static analysis on your code. In fact, the IDE and the projects you run/debug have completely different classpaths. When you open a project, your dependencies are not added to the IDE classpath. Instead, the IDE will index the JARs, meaning it will automatically discover all the declarations (classes, methods, interfaces etc) and save them for later in a cache.
When you write code in your editor, the static analysis tool will leverage the contents of this index to validate your code and show errors when you're trying to use unknown definitions for example.
On the other hand, when you run a Main class from your project, it will spawn a new java process that has its own classpath. This classpath will likely contain every dependency declared in your module.
Knowing this, you should now understand why you can't "transform" a PsiClass to a corresponding Class.
Back to your original question:
How can plugin get the name and version of libraries that are imported to the project that is being checked by plugin?
You don't need to access Class objects for this. Instead, you can use IntelliJ SDK libraries. Here's an example:
Module mod = ModuleUtil.findModuleForFile(virtualFile,myProject);
ModuleRootManager.getInstance(mod).orderEntries().forEachLibrary(library -> {
// do your thing here with `library`
return true;
});

NoSuchMethodError after cleaning the project

I'm currently getting this error:
java.lang.NoSuchMethodError: org.json.JSONObject.keySet()Ljava/util/Set;
at ee.ut.cs.Parser.accessLint(Parser.java:39)
I have tried cleaning the project to no awail.
I suspect I have an error in the src/plugin/parse-htmlraw/build.xml while creating the jar file but I'm not certain. I understand that this error is because the function does not exist at runtime, but the object is created which means that the class is there, just not that function. I decompiled the .class file in created jar and it has the necessary functions.
Code is available at https://github.com/jaansusi/WCAGgrader
Q: What is wrong with the build that produces this error?
The problem is that even if I put the necessary class files in the jar I create, they are not linked correctly and the class that's called in the jar can't locate functions inside the other classes. The class object JSONObject is created but the functions inside the JSONObject class can't be found.

If you do not find the problematic version, there is a possibility you get it (especially if you are using Spring) from the following dependency -
<artifactId>android-json</artifactId>
<groupId>com.vaadin.external.google</groupId>
excluding it worked for me,
An easy way of analyzing dependencies is the maven-helper plugin in Intellij, see here

Check for the version you have used.
There might be a case where 2 different versions are being used which in turn causes this error.

To their own maven local repository com\Google\code\gson\gson, see if there are two or more version about json, will have to do is to delete the old, and remember to look at any other place in the project is introduced into the old version of the dependence, if any, change the old version of the dependence to the new version is perfectly solved this problem

Class not found exception when using Java class in c#

I convert a java's class to dll using IKVM, by making a jar file for the this class and then I used IKVM to make the conversion operation. this operation is done successfully without errors or warnings. then I add the (DLL) with an 'IKVM.GNU.Classpath.dll' and 'IKVM.Runtime.dll' (DLLs) to my project. then I rebuilt the project, up to that point no errors, no warnings, no crashes happened. but when I tried to deserialized an arraylist of object from it is type, I get an exception is : java.lang.ClassNotFoundException: "MyClass" not found in java.lang.ClassLoader... my deserliazation. code is :
object deserializedObject = null;
java.io.ObjectInputStream ina = new java.io.ObjectInputStream(new java.io.FileInputStream(#"D:\130043674485690000.txt"));
deserializedObject = ina.readObject();
ina.close();

First: you should use the current version of IKVM for new projects. The file name show that you use a very old version of IKVM.
Second: you need to use all dlls from the IKVM. If all is working then you can remove some of the not used dlls.
Third: if you does reference the classes of your dll/jar file statically then you need load it dynamically. See the wiki for details.

Package contains object and package with same name

I am having problems compiling some Scala with Maven or Eclipse where I try to import a class from a Java jar which contains both a namespace and class of the same name.
I can compile with scalac, however.
E.g. the Java project (jar) contains:
src/foo/bar.java
src/foo/bar/some_resource.txt
-> foobar.jar
Scala project references foobar.jar
Foobartest.scala:
import foo.bar
class foobartest {
}
The compiler complains with:
package foo contains object and package with same name: bar
one of them needs to be removed from classpath
Using Maven 3.0.03/Eclipse 3.7.1 with Scala 2.9.0.1 (and maven-scala-plugin).
The jar which I am having problems with is jenkins-core-1.399.jar - it definitely contains several instances where there is a namespace and object of the same name.
I am attempting to write a Jenkins plugin in Scala (I could do this in Java but would prefer scala since all of our libraries are in scala), which is dependent on using Maven -
https://wiki.jenkins-ci.org/display/JENKINS/Plugin+tutorial.

That kind of limitation was outlined in SI-4695: package object misbehaves in the presence of classfiles.
As suggested in SI-2089 (naming restriction makes some jars unusable), you could try and use the "resolve-term-conflict", as implemented in changeset 25145:
Added a -Y option to resolve namespace collisions between package and object.
It's a blunt instrument: if people have lots of these conflicts they need to resolve in individually nuanced fashion, they'll probably remain out of luck.
val termConflict = ChoiceSetting ("-Yresolve-term-conflict", "strategy", "Resolve term conflicts", 113 List("package", "object", "error"), "error")
// Some jars (often, obfuscated ones) include a package and
// object with the same name. Rather than render them unusable,
// offer a setting to resolve the conflict one way or the other.
// This was motivated by the desire to use YourKit probes, which
// require `yjp.jar` at runtime. See SI-2089.

The actual compiler option is "-Yresolve-term-conflict:strategy" where strategy is either package, object, error.

Java "NoSuchMethodError"

I'm getting:
NoSuchMethodError: com.foo.SomeService.doSmth()Z
Am I understanding correctly that this 'Z' means that return type of doSmth() method is boolean? If true, then that kind of method really does not exist because this method returns some Collection. But on the other hand if I call this method, I'm not assigning its return value to any variable. I just call this method like this:
service.doSmth();
Any ideas why this error occurs? All necessary JAR files exist and all other methods from this class seems to exist.

Looks like method exists in classpath during compilation, but not during running of your application.
I don't think return type is a problem. If it was, it wouldn't compile. Compiler throws error when method call is ambiguous, and it is when two methods differ only by return type.

Normally, this error is caught by the compiler; this error can only occur at run time if the definition of a class has incompatibly changed.
In short - a class/jar file at runtime is not the same that you used at compile time.

This is probably a difference between your compile-time classpath and you run-time classpath.
Here is what seems to be going on:
The code is compiled with a class path that defines the doSmth() method returning a boolean. The byte-code refers to the doSmth()Z method.
At runtime, the doSmth()Z method isn't found. A method returning a Collection is found instead.
To correct this problem, check your (compile time) classpath.

The current reply just tell you why is failing. Usually is even nicer to know how to fix problems. As it is mentioned, the problem usually is that you built your program but when running or exporting it, the library is not included. So the solution is...
If you are running, check the the run configuration
Select Run tab -> Run configurations -> Select the configuration you are running -> Check the Classpath tab -> Ensure the libraries you need are there
If you are exporting (for example a war file), follow this
Select project -> Select properties -> Select Deployment Assembly -> Press Add -> Select Java Build Path Entries -> Select the libraries you want to be included in your exported file (for example a war file)
In both cases, ensure the library which you are referencing in included.
Other frequent problems for this error are not the right type of parameters or visibility but then, the compiler will detect the error before running. In this case, just check the documentation to match the function and package visibility, and ensure that the library is found in Java Build Path in your project properties.

Maybe still can help somebody, but this exception can happen also when you have on the classpath two classes in different jar files that have the same exact signature but they haven't the same public methods.
For example:
On file mylibrary1.jar you have class com.mypackage.mysubpackage.MyClass with method doSmth()
On file mylibrary2.jar you have class com.mypackage.mysubpackage.MyClass without method doSmth()
When searching the class, the classloader may find first mylibrary2.jar depending on the path precedence but can't find the method on that class.
Be sure you don't have the same package + class on two different files.

I noticed this problem occurring while testing some experimental changes in multiple linked projects, after updating them from SVN in Eclipse.
Specifically, I updated all projects from SVN, and reverted the .classpath file rather than edit it manually to keep things simple.
Then I re-added the linked projects to the path, but forgot to remove the related jars. This was how the problem occurred for me.
So apparently the run time used the jar file while the compiler used the project files.

Another way this can happen and is difficult to find:
If a signature of a method in an external jar changes in a way that there is no error found in the IDE because it's still compatible with how you call it the class might not be re-compiled.
If your build checks the files for changes and only then recompiles them, the class might not be recompiled during the build process.
So when you run it this might lead to that problem. Although you have the new jar, your own code expects still the old one but does never complain.
To make it harder it depends on the jvm if it can handle such cases. So in the worst case it runs on the test server but not on the live machine.