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
fDestinationNamesCombo.setFocus();
			return false;
		}
		if (targetFile.exists()) {
			if (!targetFile.canWrite()) {
				setErrorMessage(JarPackagerMessages.getString("JarPackageWizardPage.error.jarFileExistsAndNotWritable")); 
				fDestinationNamesCombo.setFocus();
				return false;
			}
		}
		return true;
	}
	/*
	 * Overrides method from WizardExportPage
	 */
	protected void createDestinationGroup(Composite parent) {
		
		initializeDialogUnits(parent);
		
		
		Composite destinationSelectionGroup= new Composite(parent, SWT.NONE);
		GridLayout layout= new GridLayout();
		layout.numColumns= 3;
		destinationSelectionGroup.setLayout(layout);
		destinationSelectionGroup.setLayoutData(new GridData(GridData.HORIZONTAL_ALIGN_FILL | GridData.VERTICAL_ALIGN_FILL));
		new Label(destinationSelectionGroup, SWT.NONE).setText(getDestinationLabel());
		
		fDestinationNamesCombo= new Combo(destinationSelectionGroup, SWT.SINGLE | SWT.BORDER);
		fDestinationNamesCombo.addListener(SWT.Modify, this);
		fDestinationNamesCombo.addListener(SWT.Selection, this);