Bug 31556 Export jar from Navigator view fails
(M5 build) In Navigator view (resource perspective), right-click on a src/ directory containing your sources, select export->jar file and the package selector opens with no resource selected (and finish button disabled); but it seems that the src/ dir is really selected, because if you re-select it in the window, it ends up with a "jar creation failed" and a lot of duplicate entries in the error log. If you try the same from the Projects view (Java browsing perspective), it works fine.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/jarpackager/JarPackageWizardPage.java
if (getControl() == null)
			return;
		
		
		fJarPackage.setElements(getSelectedElements());
		fJarPackage.setExportClassFiles(fExportClassFilesCheckbox.getSelection());
		fJarPackage.setExportJavaFiles(fExportJavaFilesCheckbox.getSelection());
		
		String comboText= fDestinationNamesCombo.getText();
		IPath path= new Path(comboText);
		if (!new File(comboText).isAbsolute())
			
			path= getWorkspaceLocation().append(path);
		if (path.segmentCount() > 0 && ensureTargetFileIsValid(path.toFile()) && path.getFileExtension() == null) 
			
			path= path.addFileExtension(JarPackagerUtil.JAR_EXTENSION);
		fJarPackage.setJarLocation(path);
		
		fJarPackage.setCompress(fCompressCheckbox.getSelection());
		fJarPackage.setOverwrite(fOverwriteCheckbox.getSelection());
	}
	/**
	 * Returns a boolean indicating whether the passed File handle is
	 * is valid and available for use.
	 *
	 * @return boolean
	 */
	protected boolean ensureTargetFileIsValid(File targetFile) {
		if (targetFile.exists() && targetFile.isDirectory() && fDestinationNamesCombo.getText().length() > 0) {
			setErrorMessage(JarPackagerMessages.getString("JarPackageWizardPage.error.exportDestinationMustNotBeDirectory"));