java正则表达式分析替换字符串

public static void main(String[] args){
		
		String regex = "\\$\\{(.+?)\\}";
		String str = "<a onclick=\"showUserName('${session.user.username}','${session.user.password}');\" >linkme</a>" ;
		Pattern pattern = Pattern.compile(regex);
		System.out.println(pattern);
		Matcher matcher = pattern.matcher(str);
		StringBuffer sb = new StringBuffer();
		while (matcher.find()) {
			System.out.println(">>>>> replace sequence : " + matcher.group(0));
			System.out.println(">>>>> index range : (" + matcher.start() + ", " + matcher.end() + ")");
			System.out.println(">>>>> sub : " + str.substring(matcher.start(), matcher.end()));
			matcher.appendReplacement(sb, "123");
			System.out.println("-----------------");
		}
		matcher.appendTail(sb);
		System.out.println(">>>> sb : " + sb.toString());

	}

输出：

\$\{(.+?)\}
>>>>> replace sequence : ${session.user.username}
>>>>> index range : (26, 50)
>>>>> sub : ${session.user.username}
-----------------
>>>>> replace sequence : ${session.user.password}
>>>>> index range : (53, 77)
>>>>> sub : ${session.user.password}
-----------------
>>>> sb : <a onclick="showUserName('123','123');" >linkme</a>