<location>${project.basedir}/javadoc-link/j2objc-annotations</location>
            </offlineLink>
            <!-- The JDK doc must be listed after JSR305 (and as an <offlineLink>, not a <link>) so that JSR305 "claims" javax.annotation. -->
            <offlineLink>
              <url>https://docs.oracle.com/javase/9/docs/api/</url>

                   Failed to check signatures: Bad class file .../CollectionFuture$ListFuture.class

                   One way of dealing with that would be to disable
                   animal-sniffer. And that would be fine for our -jre builds:
                   If we're building with JDK8, then clearly we're sticking to
                   JDK8 APIs. However, I assume (but did not confirm) that we'd

              <location>${project.basedir}/javadoc-link/j2objc-annotations</location>
            </offlineLink>
            <!-- The JDK doc must be listed after JSR305 (and as an <offlineLink>, not a <link>) so that JSR305 "claims" javax.annotation. -->
            <offlineLink>
              <url>https://docs.oracle.com/javase/9/docs/api/</url>

        <configuration>
          <excludes>
            <!-- Yes, we want to exclude ForceGuavaCompilation 4 times: -->
            <!-- (And we might as well exclude DummyJavadocClass 3 times (though it would be harmless to include).) -->
            <!-- 1. Don't compile it (since that requires a *non-test* dep on gwt-user. -->
            <exclude>**/ForceGuavaCompilation*</exclude>
            <exclude>**/DummyJavadocClass*</exclude>