include regexp

gistfile1.txt

import java.util.regex.*;

String hocon = """
include "a.conf"
include file("b.conf")
include required("c.conf")
include required file("bad.conf")
include required "also.bad.conf"
""";

Pattern p = Pattern.compile(
    "(?m)^\\s*include\\s+(?:required\\(([^)]*)\\)|(?:file|url|classpath|resource)?\\(?\"?([^\"\\s)]+)\"?\\)?)"
);
Matcher m = p.matcher(hocon);

while (m.find()) {
    String inner = m.group(1) != null ? m.group(1) : m.group(2);
    System.out.println("FOUND: " + inner);
}