static String mappedPath(String prefix, String path) {
        int length = prefix.length();
        if (length == 0 || "/".equals(prefix)) {
            return path;
        }

        if (prefix.charAt(length - 1) == '/') {
            // Make sure the mappedPath starts with '/'
            length -= 1;
        }
        return path.substring(length);
    }
Returns the path with its prefix removed.
core/src/main/java/com/linecorp/armeria/server/AbstractPathMapping.java