Java parsing and extract String from pattern String
There's a simpler way:

Pattern p = Pattern.compile("\\w+@\\{(\\w+)\\}");
Matcher m = p.matcher(targetStr);
while (m.find()) {
    parsed.add(m.group(1));
}


Instead of matching the opening and closing braces separately, the above pattern matches a whole expression of the form aaa@{bbb} at once. And when it finds the expression, it remembers the part inside the braces. This is done via a capturing group (the parentheses).

To learn more about each of the characters in the pattern, read the Javadoc of the Pattern class.