In Java, Portable Object Adaptor (POA)-based Dynamic Skeleton Interface (DSI)
servants inherit from the standard DynamicImplementation
class, which
inherits from the Servant
class. The native Servant
type is
defined by the PortableServer
module for the POA. In Java, the
Servant
type is mapped to the Java
org.omg.PortableServer.Servant
class.
It serves as the base class for all POA servant
implementations and provides a number of methods that may
be invoked by the application programmer, as well as methods
which are invoked by the POA itself and may be overridden by
the user to control aspects of servant behavior.
For a precise list of supported sections of official OMG specifications with which the Java[tm] Platform, Standard Edition 6 complies, see Official Specifications for CORBA support in Java[tm] SE 6.
The PortableServer
module defines the following POA-related interfaces:
POA
POAManager
ServantManager
ServantActivator
ServantLocator
AdapterActivator
ThreadPolicy
LifespanPolicy
IdUniquenessPolicy
IdAssignmentPolicy
ImplicitActivationPolicy
ServantRetentionPolicy
RequestProcessingPolicy
Current
In addition, the POA defines the Servant
native type.
Each of the interfaces listed above has an associated Operations
interface.
The Operations
interface is generated by the idlj
compiler and
contains the method signatures for methods defined in its associated interface.
The Operations
interface can be accessed by both the client and the server,
while its associated interface can only be called by the client.
PolicyValue
provide the values used
for the create_POA
call, which sets the policy for the POA. See
the sample code below for a demonstration.
PolicyValue
files include the following:
IdAssignmentPolicyValue
IdUniquenessPolicyValue
ImplicitActivationPolicyValue
LifespanPolicyValue
RequestProcessingPolicyValue
ServantRetentionPolicyValue
ThreadPolicyValue
Helper classes, which are generated for all user-defined types in an OMG IDL
interface, supply static methods needed to manipulate those types.
There is only one method in a helper class that an application programmer uses:
the narrow
method. Only Java interfaces mapped from IDL interfaces
will have a helper class that includes a narrow
method, so in
the PortableServer
package, only the following classes have a narrow
method:
ForwardRequestHelper
ServantActivatorHelper
ServantLocatorHelper
POA classes are used to implement the ServantActivator
or ServantLocator
.
The ForwardRequest
exception indicates to the ORB
that it is responsible for delivering the current request and
subsequent ForwardRequest
requests to the object denoted in the
forward_reference
member of the exception.
Most of what PortableServer
does is transparent to the user.
The result is that programmers will use only a few of the interfaces mentioned above.
The remaining interfaces will be provided by the ORB implementation.
The interfaces of interest to application programmers are the following:
AdapterActivator
Adapter activators are associated with POAs.
An adapter activator supplies a POA with the ability to create child POAs on demand,
as a side-effect of receiving a request that names the child POA (or one of its children),
or when find_POA
is called with an activate parameter value of TRUE
.
An application server that creates all its needed POAs at the beginning of execution
does not need to use or provide an adapter activator; it is necessary
only for the case in which POAs need to be created during request processing.
ServantLocator
When the POA has the NON_RETAIN
policy,
it uses servant managers that are ServantLocator
s.
ServantActivator
When the POA has the RETAIN
policy,
it uses servant managers that are ServantActivator
s.
org.omg.PortableServer.ServantLocatorPackage
This package supplies a CookieHolder
class for passing
the Cookie
type as an out
parameter. The CookieHolder
class
follows exactly the same pattern as the other holder classes for basic types.
For an overview of Java IDL, please see: Java IDL home page.
import javax.naming.InitialContext; import javax.naming.Context; import javax.rmi.PortableRemoteObject ; import com.sun.corba.se.impl.poa.POAORB; import org.omg.PortableServer.*; import java.util.*; import org.omg.CORBA.*; import javax.rmi.CORBA.Stub; import javax.rmi.CORBA.Util; public class HelloServer { public HelloServer(String[] args) { try { Properties p = System.getProperties(); // p.put("org.omg.CORBA.ORBClass", "com.sun.corba.ee.internal.POA.POAORB"); ORB orb = ORB.init( args, p ); POA rootPOA = (POA)orb.resolve_initial_references("RootPOA"); Policy[] tpolicy = new Policy[3]; tpolicy[0] = rootPOA.create_lifespan_policy( LifespanPolicyValue.TRANSIENT ); tpolicy[1] = rootPOA.create_request_processing_policy( RequestProcessingPolicyValue.USE_ACTIVE_OBJECT_MAP_ONLY ); tpolicy[2] = rootPOA.create_servant_retention_policy( ServantRetentionPolicyValue.RETAIN); POA tpoa = rootPOA.create_POA("MyTransientPOA", null, tpolicy); String ObjectId = "MyObjectId"; byte[] oid = ObjectId.getBytes(); org.omg.CORBA.Object obj = tpoa.create_reference_with_id(oid, new _HelloImpl_Tie()._all_interfaces(tpoa, oid)[0]); HelloInterface helloRef = (HelloInterface)PortableRemoteObject.narrow( obj, HelloInterface.class ); Context initialNamingContext = new InitialContext(); initialNamingContext.rebind("HelloService", helloRef); System.out.println("Hello Server: Ready..."); orb.run(); } catch (Exception e) { System.out.println("Trouble: " + e); e.printStackTrace(); } } public static void main(String args[]) { new HelloServer( args ); } }@since 1.4