E4 RCP NoClassDefFoundError - eclipse-rcp

Question

I am trying to use classes from other projects in my E4 RCP application but I receive this error. I have a LoginHandler class that uses a LoginController class from another project to validate credentials however it seems it cant find the class and I don't know why.
Here is the log:
!ENTRY org.eclipse.e4.ui.workbench 4 0 2018-12-10 14:25:08.571
!MESSAGE Unable to load class 'com.kleinknecht.ui.parts.CloseHandler' from bundle '87'
!STACK 0
java.lang.ClassNotFoundException: com.kleinknecht.ui.parts.CloseHandler cannot be found by ATS_userManagement_RCP_1.0.0.qualifier
at org.eclipse.osgi.internal.loader.BundleLoader.findClassInternal(BundleLoader.java:484)
at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:395)
at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:387)
at org.eclipse.osgi.internal.loader.ModuleClassLoader.loadClass(ModuleClassLoader.java:150)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at org.eclipse.osgi.internal.framework.EquinoxBundle.loadClass(EquinoxBundle.java:564)
at org.eclipse.e4.ui.internal.workbench.ReflectionContributionFactory.createFromBundle(ReflectionContributionFactory.java:103)
at org.eclipse.e4.ui.internal.workbench.ReflectionContributionFactory.doCreate(ReflectionContributionFactory.java:74)
at org.eclipse.e4.ui.internal.workbench.ReflectionContributionFactory.create(ReflectionContributionFactory.java:56)
at org.eclipse.e4.ui.internal.workbench.addons.HandlerProcessingAddon.processActiveHandler(HandlerProcessingAddon.java:143)
at org.eclipse.e4.ui.internal.workbench.addons.HandlerProcessingAddon.postConstruct(HandlerProcessingAddon.java:53)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.eclipse.e4.core.internal.di.MethodRequestor.execute(MethodRequestor.java:55)
at org.eclipse.e4.core.internal.di.InjectorImpl.processAnnotated(InjectorImpl.java:990)
at org.eclipse.e4.core.internal.di.InjectorImpl.inject(InjectorImpl.java:124)
at org.eclipse.e4.core.internal.di.InjectorImpl.internalMake(InjectorImpl.java:399)
at org.eclipse.e4.core.internal.di.InjectorImpl.make(InjectorImpl.java:332)
at org.eclipse.e4.core.contexts.ContextInjectionFactory.make(ContextInjectionFactory.java:186)
at org.eclipse.e4.ui.internal.workbench.ReflectionContributionFactory.createFromBundle(ReflectionContributionFactory.java:108)
at org.eclipse.e4.ui.internal.workbench.ReflectionContributionFactory.doCreate(ReflectionContributionFactory.java:74)
at org.eclipse.e4.ui.internal.workbench.ReflectionContributionFactory.create(ReflectionContributionFactory.java:51)
at org.eclipse.e4.ui.internal.workbench.swt.E4Application.createE4Workbench(E4Application.java:282)
at org.eclipse.e4.ui.internal.workbench.swt.E4Application.start(E4Application.java:149)
at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:134)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:104)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:388)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:243)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:653)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:590)
at org.eclipse.equinox.launcher.Main.run(Main.java:1499)
at org.eclipse.equinox.launcher.Main.main(Main.java:1472)
!ENTRY org.eclipse.e4.ui.workbench 4 0 2018-12-10 14:25:13.308
!MESSAGE Internal Error
!STACK 0
java.lang.NoClassDefFoundError: com/klk/userManagement/controller/LoginController
at com.kleinknecht.ui.parts.LoginHandler.execute(LoginHandler.java:24)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.eclipse.e4.core.internal.di.MethodRequestor.execute(MethodRequestor.java:55)
at org.eclipse.e4.core.internal.di.InjectorImpl.invokeUsingClass(InjectorImpl.java:305)
at org.eclipse.e4.core.internal.di.InjectorImpl.invoke(InjectorImpl.java:239)
at org.eclipse.e4.core.contexts.ContextInjectionFactory.invoke(ContextInjectionFactory.java:132)
at org.eclipse.e4.core.commands.internal.HandlerServiceHandler.execute(HandlerServiceHandler.java:152)
at org.eclipse.core.commands.Command.executeWithChecks(Command.java:494)
at org.eclipse.core.commands.ParameterizedCommand.executeWithChecks(ParameterizedCommand.java:487)
at org.eclipse.e4.core.commands.internal.HandlerServiceImpl.executeHandler(HandlerServiceImpl.java:210)
at org.eclipse.e4.core.commands.internal.HandlerServiceImpl.executeHandler(HandlerServiceImpl.java:196)
at com.kleinknecht.ui.parts.LoginDialog$1.widgetSelected(LoginDialog.java:86)
at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:249)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:86)
at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4428)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1079)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4238)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3817)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$5.run(PartRenderingEngine.java:1150)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:336)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1039)
at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:153)
at org.eclipse.e4.ui.internal.workbench.swt.E4Application.start(E4Application.java:162)
at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:134)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:104)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:388)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:243)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:653)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:590)
at org.eclipse.equinox.launcher.Main.run(Main.java:1499)
at org.eclipse.equinox.launcher.Main.main(Main.java:1472)
Caused by: java.lang.ClassNotFoundException: com.klk.userManagement.controller.LoginController cannot be found by ATS_userManagement_RCP_1.0.0.qualifier
at org.eclipse.osgi.internal.loader.BundleLoader.findClassInternal(BundleLoader.java:484)
at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:395)
at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:387)
at org.eclipse.osgi.internal.loader.ModuleClassLoader.loadClass(ModuleClassLoader.java:150)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 39 more
Here is the LoginHandler code and the classpath of my RCP project:
<?xml version="1.0" encoding="UTF-8"?>
<classpath>
<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-1.8"/>
<classpathentry kind="con" path="org.eclipse.pde.core.requiredPlugins"/>
<classpathentry kind="src" path="src"/>
<classpathentry kind="output" path="bin"/>
<classpathentry combineaccessrules="false" kind="src" path="/ATS_core"/>
<classpathentry combineaccessrules="false" kind="src" path="/ATS_errorList"/>
<classpathentry combineaccessrules="false" kind="src" path="/ATS_gui"/>
<classpathentry combineaccessrules="false" kind="src" path="/ATS_model"/>
<classpathentry combineaccessrules="false" kind="src" path="/ATS_update"/>
<classpathentry combineaccessrules="false" kind="src" path="/ATS_userAuthentication"/>
<classpathentry combineaccessrules="false" kind="src" path="/ATS_userManagement"/>
</classpath>
The controllers are located in the ATS_userAuthentication path

Answer 1

The classpath is not used by Eclipse plug-ins. Only the MANIFEST.MF is consulted to find out what other plug-ins and classes to use. Plug-ins can only use classes in other plug-ins.
The MANIFEST.MF of the plug-in that wants to use something in another plug-in must use the Require-Bundle entry to reference the plug-in or use the Import-Package entry to let Eclipse find the package in any installed plug-in.
The MANIFEST.MF of the plug-in that provides a class must export the package that contains the class using Export-Package
So, for example, I have a greg.music.core plug-in which exports various packages:
Export-Package: greg.music.core.common,
greg.music.core.databinding,
greg.music.core.e4util,
greg.music.core.editor,
greg.music.core.expression,
greg.music.core.preferences,
greg.music.core.progress,
greg.music.core.services,
greg.music.core.showin,
greg.music.core.util,
greg.music.core.views,
greg.music.core.xml
And another plug-in which imports from that plug-in:
Require-Bundle: greg.music.core
Note: For testing inside Eclipse you do also have to have the classpath set up. The MANIFEST.MF editor will do this for you.