Bug 26699 Create Jar fails with no warning if jar read-only
Once *.jardesc has been created, if I invoke "Create JAR" from the context menu and the jar file already exists and is read-only, the progress dialog flashes and nothing more happens. Please add check for this condition and at least an error message should be displayed. Even better, ask something like "Jar file read-only, overwrite?" Y/N and overwrite the file on yes (similar to what the option "warn if jar file exists" does).
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/jarpackager/JarFileExportOperation.java
String message= ex.getLocalizedMessage();
		if (message == null || message.length() < 1) {
			message= JarPackagerMessages.getString("JarFileExportOperation.coreErrorDuringExport"); 
			status= new Status(status.getSeverity(), status.getPlugin(), status.getCode(), message, ex);
		}		
		fStatus.add(status);
	}
	/**
	 * Adds a new info to the list with the passed information.
	 * Normally the export operation continues after a warning.
	 * @param	message		the message
	 * @param	exception	the throwable that caused the warning, or <code>null</code>
	 */
	protected void addInfo(String message, Throwable error) {
		fStatus.add(new Status(IStatus.INFO, JavaPlugin.getPluginId(), JavaStatusConstants.INTERNAL_ERROR, message, error));
	}
	/**
	 * Adds a new warning to the list with the passed information.
	 * Normally the export operation continues after a warning.
	 * @param	message		the message
	 * @param	exception	the throwable that caused the warning, or <code>null</code>
	 */
	protected void addWarning(String message, Throwable error) {
		fStatus.add(new Status(IStatus.WARNING, JavaPlugin.getPluginId(), JavaStatusConstants.INTERNAL_ERROR, message, error));
	}
	
	/**
	 * Adds a new error to the list with the passed information.
	 * Normally an error terminates the export operation.
	 * @param	message		the message