@Nullable
    private static <T, U> RoutingPredicate<T> parseContainRoutingPredicate(
            String predicateExpr, Function<String, U> nameConverter,
            Function<U, Predicate<T>> containsPredicate) {
        final Matcher containMatcher = CONTAIN_PATTERN.matcher(predicateExpr);
        if (containMatcher.matches()) {
            final U name = nameConverter.apply(containMatcher.group(2));
            final Predicate<T> predicate = containsPredicate.apply(name);
            if ("!".equals(containMatcher.group(1))) {
                return negated(containMatcher.group(2), predicate);
            } else {
                return from(predicateExpr, predicate);
            }
        }
        return null;
    }
Patterns used to parse a given predicate. The predicate can be one of the following forms:
<ul>
    <li>{@code some-name=some-value} which means that the request must have a
    {@code some-name=some-value} header or parameter</li>
    <li>{@code some-name!=some-value} which means that the request must not have a
    {@code some-name=some-value} header or parameter</li>
    <li>{@code some-name} which means that the request must contain a {@code some-name} header or
    parameter</li>
    <li>{@code !some-name} which means that the request must not contain a {@code some-name} header or
    parameter</li>
    <li>{@code some-name=some-value || some-other-value} which means that the request must have
    a {@code some-name=some-value} or a {@code some-other-value} header or parameter</li>
</ul>
core/src/main/java/com/linecorp/armeria/server/RoutingPredicate.java