Java Dynamic Management Kit 5.1 Tutorial

13.1.2 Defining Relation Types

We define a relation type in the relation service by associating a name for the relation type with a non-empty array of RoleInfo objects. These are the parameters to the service's createRelationType method that we call through the MBean server.

Example 13–3 Defining a Relation Type

try {
    String relTypeName = "myRelationType";

    Object[] params = new Object[2];
    params[0] = theRelTypeName;
    params[1] = theRoleInfoArray;
    String[] signature = new String[2];
    signature[0] = "java.lang.String";
    // get the string representing the "RoleInfo[]" object
    try {
         signature[1] =
                   (theRoleInfoArray.getClass()).getName();
         } catch (Exception exc) {
             throw exc;
         }
         server.invoke(theRelServObjName,
                         "createRelationType",
                         params,
                         signature);
    } catch (Exception e) {
         echo("\tCould not create the relation type " 
              + relTypeName);
         printException(e);
    }
}

The relation type name given by the calling process must be unique among all relation type names already created in the relation service. Relations will refer to this name to define their type, and the service will verify that the roles of the relation match the role information in this type.

The relation service provides methods for managing the list of relation types it stores. The removeRelationType removes the type's definition from the relation service and also removes all relation instances of this type. This mechanism is further covered in 13.2.3 Maintaining Consistency.

Other methods give the list of all currently defined relation types or the role information associated with a given type. Role information is always obtained through the name of the relation type where it is defined. Here we show the subroutine that our example uses to print out all role and type information.

Example 13–4 Retrieving Relation Types and Role Information

try {
    echo("\n-> Retrieve all relation types");
    Object[] params1 = new Object[0];
    String[] signature1 = new String[0];
    ArrayList relTypeNameList = (ArrayList)
    (server.invoke( relServObjName, "getAllRelationTypeNames",
                    params1, signature1));

    for (Iterator relTypeNameIter = relTypeNameList.iterator();
         relTypeNameIter.hasNext(); ) {
        String currRelTypeName = (String)(relTypeNameIter.next());
        echo("\n-> Print role info for relation type " +
             currRelTypeName);
        Object[] params2 = new Object[1];
        params2[0] = currRelTypeName;
        String[] signature2 = new String[1];
        signature2[0] = "java.lang.String";
        ArrayList roleInfoList = (ArrayList)
            (server.invoke( relServObjName,"getRoleInfos",
                            params2, signature2));
        printList(roleInfoList);
    }
} catch (Exception e) {
    echo("\tCould not browse the relation types");
    printException(e);
}