Java OpenNebula Cloud API

This page contains the OpenNebula Cloud API Specification for Java. It has been designed as a wrapper for the XML-RPC methods, with some basic helpers. This means that you should be familiar with the XML-RPC API and the XML formats returned by the OpenNebula core. As stated in the XML-RPC documentation, you can download the XML Schemas (XSD) here.


You can download the .jar file compiled using Java 1.8, the required libraries, and the javadoc packaged in a tar.gz file following this link in the OpenNebula version you have installed.

You can also consult the javadoc online.


To use the OpenNebula Cloud API for Java in your Java project, you have to add to the classpath the org.opennebula.client.jar file and the XML-RPC libraries located in the lib directory.

Code Sample

This is a small code snippet. As you can see, the code flow would be as follows:

  • Create a org.opennebula.client.Client object, setting up the authorization string and the endpoint. You only need to create it once.

  • Create a pool (e.g. HostPool) or element (e.g. VirtualNetwork) object.

  • You can perform “actions” over these objects right away, like myVNet.delete();

  • If you want to query any information (like what objects the pool contains, or one of the element attributes), you have to issue an info() call before, so the object retrieves the data from OpenNebula.

For more complete examples, please check the examples available at the official repository.

// First of all, a Client object has to be created.
// Here the client will try to connect to OpenNebula using the default
// options: the auth. file will be assumed to be at $ONE_AUTH, and the
// endpoint will be set to the environment variable $ONE_XMLRPC.
Client oneClient;

    oneClient = new Client();

    // We will try to create a new virtual machine. The first thing we
    // need is an OpenNebula virtual machine template.

    // This VM template is a valid one, but it will probably fail to run
    // if we try to deploy it; the path for the image is unlikely to
    // exist.
    String vmTemplate =
          "NAME     = vm_from_java    CPU = 0.1    MEMORY = 64\n"
        + "#DISK     = [\n"
        + "#\tsource   = \"/home/user/vmachines/ttylinux/ttylinux.img\",\n"
        + "#\ttarget   = \"hda\",\n"
        + "#\treadonly = \"no\" ]\n"
        + "# NIC     = [ NETWORK = \"Non existing network\" ]\n"
        + "FEATURES = [ acpi=\"no\" ]";

    // You can try to uncomment the NIC line, in that case OpenNebula
    // won't be able to insert this machine in the database.

    System.out.println("Virtual Machine Template:\n" + vmTemplate);

    System.out.print("Trying to allocate the virtual machine... ");
    OneResponse rc = VirtualMachine.allocate(oneClient, vmTemplate);

    if( rc.isError() )
        System.out.println( "failed!");
        throw new Exception( rc.getErrorMessage() );

    // The response message is the new VM's ID
    int newVMID = Integer.parseInt(rc.getMessage());
    System.out.println("ok, ID " + newVMID + ".");

    // We can create a representation for the new VM, using the returned
    // VM-ID
    VirtualMachine vm = new VirtualMachine(newVMID, oneClient);

    // Let's hold the VM, so the scheduler won't try to deploy it
    System.out.print("Trying to hold the new VM... ");
    rc = vm.hold();

        throw new Exception( rc.getErrorMessage() );

    // And now we can request its information.
    rc =;

        throw new Exception( rc.getErrorMessage() );

            "This is the information OpenNebula stores for the new VM:");
    System.out.println(rc.getMessage() + "\n");

    // This VirtualMachine object has some helpers, so we can access its
    // attributes easily (remember to load the data first using the info
    // method).
    System.out.println("The new VM " +
            vm.getName() + " has status: " + vm.status());

    // And we can also use xpath expressions
    System.out.println("The path of the disk is");
    System.out.println( "\t" + vm.xpath("template/disk/source") );

    // Let's delete the VirtualMachine object.
    vm = null;

    // The reference is lost, but we can ask OpenNebula about the VM
    // again. This time however, we are going to use the VM pool
    VirtualMachinePool vmPool = new VirtualMachinePool(oneClient);
    // Remember that we have to ask the pool to retrieve the information
    // from OpenNebula
    rc =;

        throw new Exception( rc.getErrorMessage() );

            "\nThese are all the Virtual Machines in the pool:");
    for ( VirtualMachine vmachine : vmPool )
        System.out.println("\tID : " + vmachine.getId() +
                           ", Name : " + vmachine.getName() );

        // Check if we have found the VM we are looking for
        if ( vmachine.getId().equals( ""+newVMID ) )
            vm = vmachine;

    // We have also some useful helpers for the actions you can perform
    // on a virtual machine, like suspend:
    rc = vm.suspend();
    System.out.println("\nTrying to suspend the VM " + vm.getId() +
                        " (should fail)...");

    // This is all the information you can get from the OneResponse:
    System.out.println("\tOpenNebula response");
    System.out.println("\t  Error:  " + rc.isError());
    System.out.println("\t  Msg:    " + rc.getMessage());
    System.out.println("\t  ErrMsg: " + rc.getErrorMessage());

    rc = vm.terminate();
    System.out.println("\nTrying to terminate the VM " +
                        vm.getId() + "...");

    System.out.println("\tOpenNebula response");
    System.out.println("\t  Error:  " + rc.isError());
    System.out.println("\t  Msg:    " + rc.getMessage());
    System.out.println("\t  ErrMsg: " + rc.getErrorMessage());

catch (Exception e)


To compile the Java OCA, untar the OpenNebula source, cd to the java directory and use the build script:

cd src/oca/java
./ -d
Compiling java files into class files...
Packaging class files in a jar...
Generating javadocs...

This command will compile and package the code in jar/org.opennebula.client.jar, and the javadoc will be created in share/doc/.

You might want to copy the .jar files to a more convenient directory. You could use /usr/lib/one/java/

sudo mkdir /usr/lib/one/java/
sudo cp jar/* lib/* /usr/lib/one/java/