Akka HTTP does not currently provide a Java API for XML support. If you need to produce and consume XML, you can write a custom marshaller using Jackson, which is also the library used for providing JSON support.

copysourceimport java.io.IOException;
import java.util.List;
import java.util.Arrays;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.dataformat.xml.XmlMapper;
import akka.http.javadsl.model.*;
import akka.http.javadsl.marshalling.Marshaller;
import akka.http.javadsl.unmarshalling.Unmarshaller;

public class JacksonXmlSupport {
  private static final ObjectMapper DEFAULT_XML_MAPPER =
    new XmlMapper().enable(SerializationFeature.WRAP_ROOT_VALUE);
  private static final List<MediaType> XML_MEDIA_TYPES = Arrays.asList(MediaTypes.APPLICATION_XML, MediaTypes.TEXT_XML);

  public static <T> Marshaller<T, RequestEntity> marshaller() {
    return Marshaller.wrapEntity(
      u -> toXML(DEFAULT_XML_MAPPER, u),
      Marshaller.stringToEntity(),
      MediaTypes.APPLICATION_XML
    );
  }

  public static <T> Unmarshaller<HttpEntity, T> unmarshaller(Class<T> expectedType) {
    return Unmarshaller.forMediaTypes(XML_MEDIA_TYPES, Unmarshaller.entityToString())
                       .thenApply(xml -> fromXML(DEFAULT_XML_MAPPER, xml, expectedType));
  }

  private static <T> String toXML(ObjectMapper mapper, T object) {
    try {
      return mapper.writeValueAsString(object);
    } catch (IOException e) {
      throw new IllegalArgumentException("Cannot marshal to XML: " + object, e);
    }
  }

  private static <T> T fromXML(ObjectMapper mapper, String xml, Class<T> expectedType) {
    try {
      return mapper.readerFor(expectedType).readValue(xml);
    } catch (IOException e) {
      throw new IllegalArgumentException("Cannot unmarshal XML as " + expectedType.getSimpleName(), e);
    }
  }
}

The custom XML (un)marshalling code shown above requires that you depend on the jackson-dataformat-xml library.

The Akka dependencies are available from Akka’s library repository. To access them there, you need to configure the URL for this repository.

sbt

resolvers += "Akka library repository".at("https://repo.akka.io/maven")

Gradle

repositories {
    mavenCentral()
    maven {
        url "https://repo.akka.io/maven"
    }
}

Maven

<project>
  ...
  <repositories>
    <repository>
      <id>akka-repository</id>
      <name>Akka library repository</name>
      <url>https://repo.akka.io/maven</url>
    </repository>
  </repositories>
</project>

Additionally, add the dependency as below.

sbt

libraryDependencies += "com.fasterxml.jackson.dataformat" % "jackson-dataformat-xml" % "2.15.4"

Gradle

dependencies {
  implementation "com.fasterxml.jackson.dataformat:jackson-dataformat-xml:2.15.4"
}

Maven

<dependencies>
  <dependency>
    <groupId>com.fasterxml.jackson.dataformat</groupId>
    <artifactId>jackson-dataformat-xml</artifactId>
    <version>2.15.4</version>
  </dependency>
</dependencies>