Standalone Application Invocation into a Remote Session EJB

Internal

• EJB Concepts - Invoking into EJBs

Overview

This example describes how a standalone Java application looks up a remote EJB and makes a remote invocation.

GitHub Example

TODO: the example is not fully implemented and may be confusing, though it can be used as a base for the second iteration. Re-iterate next time I need it.

https://github.com/NovaOrdis/playground/tree/master/jee/ejb/stateless-and-standalone-jboss-application

The Business Interface Must be Market as @Remote

The business interface must be marked with the @Remote annotation, otherwise the EJB won't be accessible remotely. If the business interface is not annotated with @Remote, the JNDI lookup on the client side, even if using the correct EJB client context, will fail to locate the EJB.

Business Interface Type Access

The calling application needs the business interface type to make the call, so the classes related to the business interface will have to be made accessible on the standalone application's classpath. Since those classes are also needed in the EJB deployment unit, the best strategy is to develop those as part of shared "common-types" Maven module, and pull its artifact in the EJB JAR, then makes accessible on the standalone application's classpath. The example linked above showcases this approach. A Maven "recipe" to include some dependencies in a simple JAR artifact is described here: Include Dependencies in JAR Artifact.

EJB Lookup

Configure EJB Client Context in jboss-ejb-client.properties

The standalone application needs a way to look up the EJB reference that has been deployed on a remote JBoss instance. This is done internally by using a JBoss-specific mechanism named EJB client context. In order to use the EJB client context that knows how to invoke into the remote JBoss instance, the standalone application must have access to a jboss-ejb-client.properties on its classpath.

More details about jboss-ejb-client.properties are available here:

jboss-ejb-client.properties

More details about the EJB client context are available here:

EJB Client Context

Use a Specific JNDI Name

Use a JNDI name that complies with the following pattern:

ejb:[/<application-name>/]<module-name>/<bean-name>!<view-class>

Example:

ejb:/stateless-ejb-example/SimpleStatelessBean!io.novaordis.playground.jee.ejb.stateless.SimpleStateless

The "ejb:" name space is essential, it is what seems to be engaging the correct EJB client context, if "java:global" is used, the look up will fail.

The !<view-class> part is also essential, if not used, the JNDI lookup will return an org.jboss.ejb.client.naming.ejb.EjbNamingContext instance, instead of a business interface type.

JNDI Lookup Code

The code that does the JNDI lookup is similar to:

SimpleStateless bean = null;

...

try {

   InitialContext  ic = new InitialContext();
   SimpleStateless bean = (SimpleStateless)ic.lookup(
       "ejb:/stateless-ejb-example/SimpleStatelessBean!io.novaordis.playground.jee.ejb.stateless.SimpleStateless");
}
catch(Exception e) {
    ...
}

EJB Invocation

Once the EJB reference is obtained from JNDI, business interface methods can be called on its reference:

...
bean.methodOne("something from servlet");