Use the “Service Locator” Design Pattern with the J2EE Architechture

This tip is an extension of a Design Pattern called “Service Locator” for the J2EE architecture. Generally, the “Service Locator” pattern returns a home object by merely accepting a string, usually a mapping for a JNDI name.

This tip creates a pure factory for stateless session beans (a method which accepts a string?in JNDI, the name of the stateless session bean) and returns the appropriate remote objects (called EJBObject) without actually type-casting the appropriate home object (called EJBHome) or executing the create method. The following code demonstrates:

Accounts valAccounts= ((AccountsHome)home).create();

This easiest way to call a subclass method without actually type-casting it is by using reflection:

Method m = homeBase.getMethod("create", null);remoteObject = (EJBObject) m.invoke(home, null);

Here’s the sample code:

/* Sample code */public class ResourceLocator{   public static EJBObect getResourceInstance(String jndiName)   {      Context ctx = new InitialContext();      Object o = ctx.lookup(jndiName);      //Need not type cast home object to appropriate Home Interface      home = (EJBHome) PortableRemoteObject.narrow(o, Class.forName("javax.ejb.EJBHome"));    //Need not type cast home object to appropriate Remote Interface    Class homeBase = home.getClass();    Method m = homeBase.getMethod("create", null);    remoteObject = (EJBObject) m.invoke(home, null);    return remoteObject;   }}

Whichever JNDI name is provided, the above code generalizes and achieves a perfect factory pattern for a stateless session bean.

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