web server - Borland Technical Publications

Client view of an enterprise bean
Locating the home interface
A client locates an enterprise bean's home interface using JNDI, as shown in the code
sample below. The client first needs to obtain a JNDI initial naming context. The code
instantiates a new javax.naming.Context object, which in our example it calls
initialContext. Then, the client uses the context lookup() method to resolve the name to
a home interface. Note that the initialization of the initial naming context factory is EJB
container/server specific.
A client application can also use logical names to access a resource such as the home
interface. Go to “Initializing the client” on page 85 for more information.
The context's lookup() method returns an object of type java.lang.Object. Your code
must cast this returned object to the expected type. The following code sample shows
a portion of the client code for the sort example. The main() routine begins by using the
JNDI naming service and its context lookup method to locate the home interface. You
pass the name of the remote interface, which in this case is sort, to the
context.lookup() method. Notice that the program eventually casts the results of the
context.lookup() method to SortHome, the type of the home interface.
// SortClient.java
import javax.naming.InitialContext;
import SortHome; // import the bean's home interface
import Sort; // import the bean's remote interface
public class SortClient {
...
public static void main(String[] args) throws Exception {
javax.naming.Context context;
// preferred JNDI context lookup
// get a JNDI context using a logical JNDI name in the local JNDI
context, i.e.,ejb-ref
javax.naming.Context context = new javax.naming.InitialContext();
Object ref = context.lookup("java:comp/env/ejb/Sort");
SortHome home = (SortHome) javax.rmi.PortableRemoteObject.narrow
(ref, SortHome.class);
Sort sort = home.create();
... //do the sort and merge work
sort.remove();
}
}
The main() routine of the client program throws the generic exception Exception. When
coded this way, the SortClient program does not have to catch any exceptions that
might occur, though if an exception occurs it will terminate the program.
Obtaining the remote interface
Now that we have obtained the home interface of an enterprise bean we can get a
reference to the enterprise bean's remote interface. To do this, we use the home
interface's create or finder methods. The exact method to invoke depends on the type
of the enterprise bean and the methods the enterprise bean provider has defined in the
home interface.
For example, the first code sample shows how SortClient obtains a reference to the
Sort remote interface. Once SortClient obtains the reference to the home interface and
casts it to its proper type (SortHome), then the code can create an instance of the bean
and call its methods. It calls the home interface's create() method, which returns a
reference to the bean's remote interface, Sort. (Because SortBean is a stateless
session bean, its home interface has only one create() method and that method by
definition takes no parameters.) SortClient can then call the methods defined on the
86 BES Developer’s Guide