org.zalando.riptide.opentracing.span.HeaderExtractor Maven / Gradle / Ivy

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package org.zalando.riptide.opentracing.span;

import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Optional;
import java.util.function.Predicate;

import static java.lang.String.join;

final class HeaderExtractor {

    Optional extract(
            final Map> headers,
            final List names) {

        return names.stream()
                .map(headers::get)
                .filter(Objects::nonNull)
                .filter(not(List::isEmpty))
                .findFirst()
                .map(list -> join("\n", list));
    }

    private static  Predicate not(final Predicate predicate) {
        return predicate.negate();
    }

}