RelationTypeSupport Class

A class must implement the RelationType interface in order to be considered a representation of a relation type. The methods of this interface are used to access the role information that makes up a relation type. Since relation types are immutable within the relation service, there are no methods for modifying the role information.

The RelationTypeSupport class is the implementation of this interface that is used internally by the relation service to represent a relation type. By extending this class, you can quickly write new relation type classes with all the required functionality. The class has a method for adding roles to the information that is exposed; this method can be called by the class constructor to initialize all roles. Our simple example does just this, and there is little other functionality that can be added to a relation type object.

Example 15–6 Extending the RelationTypeSupport Class

import javax.management.relation.*;

public class SimpleRelationType extends RelationTypeSupport {

    // Constructor
    public SimpleRelationType(String theRelTypeName) {

        super(theRelTypeName);

        // Defines the information for two roles
        // - primary: SimpleStandard class/read-write/cardinality=2
        // - secondary: SimpleStandard class/read-only/cardinality=2
        try {
            RoleInfo primaryRoleInfo =
                new RoleInfo("primary", "SimpleStandard",
                             true, true,
                             2, 2,
                             "Primary description");
            addRoleInfo(primaryRoleInfo);

            RoleInfo secondaryRoleInfo =
                new RoleInfo("secondary", "SimpleStandard",
                             true, false,
                             2, 2,
                             "Secondary description");
            addRoleInfo(secondaryRoleInfo);
        } catch (Exception exc) {
            throw new RuntimeException(exc.getMessage());
        }
    }
}

We now use our class to instantiate an object representing a relation type. We then call the relation service's addRelationType operation to make this type available in the relation service. Thereafter, it is manipulated through the service's operations and there is no way to distinguish it from other relation types that have been defined.

Example 15–7 Adding an Externally Defined Relation Type

String usrRelTypeName = "SimpleRelationType";
SimpleRelationType usrRelType =
    new SimpleRelationType("SimpleRelationType");
try {
    Object[] params = new Object[1];
    params[0] = usrRelType;
    String[] signature = new String[1];
    signature[0] = "javax.management.relation.RelationType";
    server.invoke( relServObjName, "addRelationType",
                   params, signature);
} catch(Exception e) {
    echo("\tCannot add user relation type");
    printException(e);
}

The role information defined by a relation type should never change once the type has been added to the relation service. This is why the RelationTypeSupport class is not an MBean: it would make no sense to manage it remotely. All of the information about its roles is available remotely through the relation service MBean.