JAva String日付をDateに変更し、月1を減らします.

String date1 = "2007-01-10";
		
		DateFormat df = new SimpleDateFormat("yyyy-MM");
		try {
			Date d1 = df.parse(date1);
			System.out.println("d1=="+df.format(d1));
			Calendar  g = Calendar.getInstance();
			g.setTime(d1);
			g.add(Calendar.MONTH,-1);			
			Date d2 = g.getTime();
			System.out.println("d2======="+df.format(d2));
		} catch (ParseException e) {			
			e.printStackTrace();
		}