Client-side programming tips for the Java Object Request Broker service

This article includes programming tips for applications that communicate with the client-side ORB that is part of the Java ORB service.

 

Resolution of initial references to services

Client applications can use the properties ORBInitRef and ORBDefaultInitRef to configure the network location that the Java ORB service uses to find a service such as naming. Once set, these properties are included in the parameters used to initialize the ORB, as follows 

org.omg.CORBA.ORB.init(java.lang.String[] args, 
                       java.util.Properties props)

Set these properties in client code or by command-line argument. It is possible to specify more than one service location by using multiple ORBInitRef property settings (one for each service), but only a single value for ORBDefaultInitRef may be specified. For more information about the two properties and the order of precedence that the ORB uses to locate services, read the CORBA/IIOP specification, cited in "Resources for learning."

For setting in client code, these properties are com.ibm.CORBA.ORBInitRef.service_name and com.ibm.CORBA.ORBDefaultInitRef, respectively. For example, to specify that the naming service (NameService) is located in sample.server.com at port 2809, set the com.ibm.CORBA.ORBInitRef.NameService property to corbaloc::sample.server.com:2809/NameService.

For setting by command-line argument, these properties are -ORBInitRef and -ORBDefaultInitRef, respectively. To locate the same naming service specified previously, use the following Java command (split here for publication only) 

java program -ORBInitRef 
     NameService=corbaloc::sample.server.com:2809/NameService

After these properties have been set for services supported by the ORB, J2EE applications obtain the initial reference to a given service by calling the resolve_initial_references function on the ORB as defined in the CORBA/IIOP specification.

 

Preferred API for obtaining an ORB instance

For J2EE applications, you can use either of the following approaches. However, it is strongly recommended that you use the JNDI approach to ensure that the same ORB instance is used throughout the client application; you will avoid the unintended inconsistencies that might occur when different ORB instances are used.

JNDI approach: For J2EE applications (including enterprise beans, J2EE clients and servlets), you can obtain an ORB instance by creating a JNDI InitialContext object and looking up the ORB under the name java:comp/ORB, as follows 

javax.naming.Context ctx = new javax.naming.InitialContext();
org.omg.CORBA.ORB orb = 
   (org.omg.CORBA.ORB)javax.rmi.PortableRemoteObject.narrow(ctx.lookup("java:comp/ORB"), 
                                                            org.omg.CORBA.ORB.class);

The ORB instance obtained using JNDI is a singleton object, shared by all J2EE components running in the same JVM process.

CORBA approach: Because thin-client applications do not run in a J2EE container, they cannot use JNDI interfaces to look up the ORB. In this case, you can obtain an ORB instance by using CORBA programming interfaces, as follows 

java.util.Properties props = new java.util.Properties();
java.lang.String[] args = new java.lang.String[0];
org.omg.CORBA.ORB orb = org.omg.CORBA.ORB.init(args, props);

In contrast to the JNDI approach, the CORBA specification requires that a new ORB instance be created each time the ORB.init method is called. If necessary to change the ORB's default settings, you can add ORB property settings to the Properties object that is passed in the ORB.init() call.

The use of com.ibm.ejs.oa.EJSORB.getORBinstance(), supported in previous releases of WAS, has been deprecated.

 

API restrictions with sharing an ORB instance among J2EE application components

For performance reasons, it often makes sense to share a single ORB instance among components in a J2EE application. As required by the J2EE Specification, Version 1.3, all web and EJB containers provide an ORB instance in the JNDI namespace as java:comp/ORB. Each container can share this instance among application components but is not required to. For proper isolation between application components, application code must comply with the following restrictions...

In addition, an ORB instance should not be shared among application components in different J2EE applications.

 

Required use of rmic and idlj shipped with the IBM Developer Kit

The Java Runtime Environment (JRE) used by WAS includes the tools rmic and idlj. You use the tools to generate Java language bindings for the CORBA/IIOP protocol.

During product installation, the tools are installed in the directory $WAS_INSTALL/java/ibm_bin, where $WAS_INSTALL is the installation directory for the product. Versions of these tools included with Java development kits in $JAVA_HOME/bin other than the IBM Developer Kit installed with WAS are incompatible with WAS.

When you install WAS, the directory $WAS_INSTALL/java/ibm_bin is included in the $PATH search order to enable use of the rmic and idlj scripts provided by IBM. Because the scripts are in $WAS_INSTALL/java/ibm_bin instead of the JRE standard location $WAS_INSTALL/java/bin, it is unlikely that you will overwrite them when applying maintenance to a JRE not provided by IBM.

In addition to the rmic and idlj tools, the JRE also includes Interface Definition Language (IDL) files. The files are based on those defined by the Object Management Group and can be used by applications that need an IDL definition of selected ORB interfaces. The files are placed in the $WAS_INSTALL/java/ibm_lib directory.

Before using either the rmic or idlj tool, ensure that the $WAS_INSTALL/java/ibm_bin directory is included in the proper PATH variable search order in the environment. If your application will use IDL files in the $WAS_INSTALL/java/ibm_lib directory, also ensure that the directory is included in the PATH variable.

 

See Also

Object Request Brokers: Resources for learning