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
if (container == null || !container.isAccessible())
			return new HashMap(0);
		/*
		 * XXX: Bug 6584: Need a way to get class files for a java file (or CU)
		 */
		org.eclipse.jdt.internal.compiler.classfmt.ClassFileReader cfReader;
		IResource[] members= container.members();
		Map map= new HashMap(members.length);
		for (int i= 0;  i < members.length; i++) {
			if (isClassFile(members[i])) {
				IFile classFile= (IFile)members[i];
				try {
					cfReader= org.eclipse.jdt.internal.compiler.classfmt.ClassFileReader.read(classFile.getLocation().toFile());
				} catch (org.eclipse.jdt.internal.compiler.classfmt.ClassFormatException ex) {
					addWarning(JarPackagerMessages.getFormattedString("JarFileExportOperation.invalidClassFileFormat", classFile.getLocation().toFile()), ex); 
					continue;
				} catch (IOException ex) {
					addWarning(JarPackagerMessages.getFormattedString("JarFileExportOperation.ioErrorDuringClassFileLookup", classFile.getLocation().toFile()), ex); 
					continue;
				}
				if (cfReader != null) {
					if (cfReader.sourceFileName() == null) {
						/*
						 * Can't fully build the map because one or more
						 * class file does not contain the name of its 
						 * source file.
						 */
						addWarning(JarPackagerMessages.getFormattedString("JarFileExportOperation.classFileWithoutSourceFileAttribute", classFile.getLocation().toFile()), null); 
						return null;