By default OpenStack4j uses Jersey 2. You can break this out to allow usage of any of the following connectors Jersey 2, Resteasy, Apache HttpClient or OKHttp.
Instead of depending on the normal "openstack4j" artifactId, change the dependency to be "openstack4j-core" like below:
<dependency>
<groupId>org.pacesys</groupId>
<artifactId>openstack4j-core</artifactId>
<version>2.0.0-SNAPSHOT</version>
</dependency>
Now choose a connector by adding the applicable dependency below:
Jersey 2
<dependency>
<groupId>org.pacesys.openstack4j.connectors</groupId>
<artifactId>openstack4j-jersey2</artifactId>
<version>2.0.0-SNAPSHOT</version>
</dependency>
Resteasy
<dependency>
<groupId>org.pacesys.openstack4j.connectors</groupId>
<artifactId>openstack4j-resteasy</artifactId>
<version>2.0.0-SNAPSHOT</version>
</dependency>
Apache HttpClient
<dependency>
<groupId>org.pacesys.openstack4j.connectors</groupId>
<artifactId>openstack4j-httpclient</artifactId>
<version>2.0.0-SNAPSHOT</version>
</dependency>
OKHttp
<dependency>
<groupId>org.pacesys.openstack4j.connectors</groupId>
<artifactId>openstack4j-okhttp</artifactId>
<version>2.0.0-SNAPSHOT</version>
</dependency>