private static Boolean strictlyParseBoolean(String val) {
        if (!val.equals(Boolean.TRUE.toString()) && !val.equals(Boolean.FALSE.toString())) {
            throw new IllegalArgumentException(String.format("%s not in \"true\" or \"false\"", val));
        }
        return Boolean.valueOf(val);
    }
Implementation of {@link FlagsProvider} which provides values from JVM options to {@link Flags}.
core/src/main/java/com/linecorp/armeria/common/SystemPropertyFlagsProvider.java