//向后匹配
String a = "I paid $90 for 10 oranges, 12 pears and 8 apples. I saved $5 on ";
		 Pattern p = Pattern.compile("(?<=\\$)\\d+");
		 Matcher m = p.matcher(a);
		 while (m.find ())
		 {
			 String group = m.group ();
			 System.out.println (group);
		 }
向前匹配
		 a = "https://mail.huawei.com ";
		 p = Pattern.compile(".+(?=:)");
		 m = p.matcher(a);
		 while (m.find ())
		 {
			 String group = m.group ();
			 System.out.println (group);
		 }
Java 正则表达式 向前、向后匹配,布布扣,bubuko.com
原文:http://www.cnblogs.com/kevinge/p/3829679.html