CORBA ORB

This chapter supplements the information in package org.omg.CORBA by providing the following topics:

• Initializing the ORB, which includes the section "Passing the Address of the IIOP Listener"

• Initializing the ORB for Native and Remote Clients

  Note: For details about the API for package org.omg.CORBA, see the Java IDL document published by the Sun Microsystems, Inc. and distributed with the JDK 1.2.

Initializing the ORB

[This section is reprinted from the package information for org.omg.CORBA, as published by Sun Microsystems, Inc. for the JDK 1.2.]

An application or applet gains access to the CORBA environment by initializing itself into an ORB using one of three init methods. Two of the three methods use the properties (associations of a name with a value) shown in the following table:

These properties allow a different vendor's ORB implementation to be "plugged in."

When an ORB instance is being created, the class name of the ORB implementation is located using the following standard search order:

1. Check in Applet parameter or application string array, if any.

2. Check in properties parameter, if any.

3. Check in the System properties (currently applications only).

4. Fall back on a hardcoded default behavior (use the Java IDL implementation).

Note that the WebLogic Enterprise ORB provides a default implementation for the fully functional ORB and for the Singleton ORB. When the init method is given no parameters, the default Singleton ORB is returned. When the init method is given parameters but no ORB class is specified, the Java IDL ORB implementation is returned.

The following code fragment creates an ORB object initialized with the default ORB Singleton. This ORB has a restricted implementation to prevent malicious applets from doing anything beyond creating typecodes. It is called a Singleton because there is only one instance for an entire virtual machine.

ORB orb = ORB.init();

The following code fragment creates an ORB object and a Singleton ORB object for an application.

Properties p = new Properties();
p.put("org.omg.CORBA.ORBClass", "com.sun.CORBA.iiop.ORB");
p.put("org.omg.CORBA.ORBSingletonClass","com.sun.CORBA.idl.ORBSingleton");
System.setProperties(p);
ORB orb = ORB.init(args, p);

In the preceding code fragment, note the following:

• The ORB class is to be initialized as com.sun.CORBA.iiop.ORB.

• The SingletonORB class is to be initialized as com.sun.CORBA.idl.ORBSingleton.

• The statement System.setProperties(p) sets the system properties based on the value of p.

• The parameter args represents the arguments supplied to the application's main method. If p is null, and the arguments do not specify an ORB class, the new ORB is initialized with the default Java IDL implementation.

  Note: Due to the security restrictions on applets, you will probably not be able to invoke the System.setProperties method from within an applet. Instead, you can set the org.omg.CORBA.ORBClass and org.omg.CORBA.ORBSingletonClass parameters via HTML before starting the applet.

The following code fragment creates an ORB object for the applet supplied as the first parameter. If the given applet does not specify an ORB class, the new ORB will be initialized with the default WebLogic Enterprise ORB implementation.

ORB orb = ORB.init(myApplet, null);

An application or applet can be initialized in one or more ORBs. ORB initialization is a bootstrap call into the CORBA world.

Passing the Address of the IIOP Listener

When you compile WebLogic Enterprise client and server applications, use the -DTOBJADDR option to specify the host and port of the IIOP Listener. This allows you, in the application code, to specify null as a host and port string in invocations to:

• The ORB.init method

• The local Bootstrap object

By keeping host and port specifications out of your client and server application code, you maximize the portability and reusability of your application code.

Initializing the ORB for Native and Remote Clients

WebLogic Enterprise provides two methods on the com.beasys.Tobj_Bootstrap object that client applications use to initialize the ORB, depending on whether the client is native (that is, on a process that is inside the WebLogic Enterprise domain) or remote (that is, on a machine that needs to communicate to the server application via the IIOP Listener/Handler).

These two methods are:

• The getNativeProperties method

  This method returns a set of properties that need to be passed in a subsequent invocation of the org.omg.CORBA.ORB.init method. This subsequent invocation causes BEA's Java ORB to be initialized. The getNativeProperties method also initializes the WebLogic Enterprise infrastructure.

  The getNativeProperties method must be invoked before any attempt is made to access any class in the org.omg.CORBA package; otherwise, errors will occur when receiving CORBA exceptions from the server.

• The getRemoteProperties method

  This method returns the properties needed to initialize the ORB for remote clients. The getRemoteProperties method is specified for symmetry and always returns null.

  Note: In WLE 4.2, Java native clients are not supported.