IncludeUrlTests.java

import org.asciidoctor.Asciidoctor;
import org.asciidoctor.Attributes;
import org.asciidoctor.OptionsBuilder;
import org.asciidoctor.SafeMode;
import org.junit.Test;

import static org.assertj.core.api.Assertions.assertThat;

public class IncludeUrlsTests {

    @Test
    public void includeUrls() throws Exception {

        String testDoc = "== Example Title\n" +
                "\n" +
                "include::https://raw.githubusercontent.com/spring-guides/getting-started-macros/master/prereq_editor_jdk_buildtools.adoc[]";

        Asciidoctor engine = Asciidoctor.Factory.create();
        Attributes attributes = new Attributes();
        attributes.setAllowUriRead(true);
        String doc = engine.convert(testDoc, OptionsBuilder.options().safe(SafeMode.UNSAFE).attributes(attributes));

        assertThat(doc).contains("Example Title").contains("JDK");
    }
}

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.asciidoctorj.issues</groupId>
    <artifactId>asciidoctorj-includeurls</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <!-- Works with 1.5.3
        <dependency>
            <groupId>org.asciidoctor</groupId>
            <artifactId>asciidoctorj</artifactId>
            <version>1.5.3</version>
        </dependency>
        -->

        <!-- Fails with 1.5.4 -->
        <dependency>
            <groupId>org.asciidoctor</groupId>
            <artifactId>asciidoctorj</artifactId>
            <version>1.5.4</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
        <dependency>
            <groupId>org.assertj</groupId>
            <artifactId>assertj-core</artifactId>
            <version>3.3.0</version>
        </dependency>
    </dependencies>

</project>