Invoking component methods – PB Docs 2018

After a connection to the server has been established and a proxy
object or objects created, the client application can begin using the EJB
components. To invoke an EJB component method, you need to execute the
PowerScript statements required to perform these operations:

This procedure relies on the pbejbclient180.jar file, which is
included in the Java VM classpath automatically at design time and runtime
by the pbjvm180.dll.

Using the lookup method

The lookup method takes three string arguments: the name of the
proxy for the home interface, the JNDI name of the EJB component, and the
fully qualified home interface name of the EJB component.

The home interface name is the fully qualified class name of the EJB
home interface. For example, if the class’s location relative to the Java
naming context is ejbsample, the home interface name is
ejbsample.HelloEJBHome.

The following example shows the invocation of the lookup method for
HelloEJB on WebLogic.

Creating or finding an instance of an
EJB

A session bean is created in response to a client request. A client
usually has exclusive use of the session bean for the duration of that
client session. An entity bean represents persistent information stored in
a database. A client uses an entity bean concurrently with other clients.
Since an entity bean persists beyond the lifetime of the client, you must
use a primary key class name to find an instance of the entity bean if one
exists or create a new instance if it does not.

For a session bean, you use the proxy object’s create method to
create the instance of the EJB. The create method can throw
CreateException and RemoteException. Assuming that you have obtained a
reference to the home interface in homeobj, create is used in the same way
on all EJB servers:

For an entity bean, you provide a primary key. The
FindByPrimaryKey method can throw FinderException and RemoteException. In
this example, the key is the ID of a specific customer that is passed as
an argument to the function:

Invoking EJB component
methods

When the bean instance has been created or found, you can invoke its
methods. For example:

Creating an instance of a Java
class

If the bean has a method that accepts a Java class as an argument,
you use the CreateJavaInstance method of the JavaVM object to create it.
For example, if the primary key in a call to the findByPrimaryKey method
is a Java class, you would use the CreateJavaInstance method to create
that class, and then use a PowerBuilder proxy to communicate with
it.

In this example, the create method accepts a Java Integer class
argument. PowerBuilder creates a proxy called java_integer (the prefix
java_ is required to prevent a conflict with the PowerBuilder
integer type). The call to CreateJavaInstance sets the value of that
variable so you can call the EJB create method:

Downcasting return values

When Java code returns a common Java object that needs to be
downcast for use in Java programming, the Java method always sets the
return value as Java.lang.Object. In a PowerBuilder EJB client proxy,
java.lang.Object is mapped to the any datatype. At runtime, PowerBuilder
gets the correct Java object and indexes the generated mapping structure
to get the PowerBuilder proxy name. The any value is set as this proxy
object. If the returned Java object can map to a PowerBuilder standard
datatype, the any value is set as the PowerBuilder standard
datatype.

Suppose the remote interface includes the method:

and the home interface includes the method:

The return value java.lang.Object is really a java.lang.String at
runtime. PowerBuilder automatically downcasts the return value to the
PowerBuilder string datatype:

Dynamic casting

There are two scenarios in which a Java object returned from a call
to an EJB method can be represented by a proxy that does not provide the
methods you need:

The DynamicCast method allows you to cast the returned proxy object
to a proxy for the interface you require, or for the actual class of the
object returned at runtime so that the methods of that object can be
used.

You can obtain the actual class of the object using the
GetActualClass method. You can also use the DynamicCast method with the
GetSuperClass method, which returns the immediate parent of the Java
class, and the GetInterfaces method, which writes a list of interfaces
implemented by the class to an array of strings.

For example, given the following class:

GetActualClass returns java.util.LinkedList, GetSuperClass returns
java.util.AbstractSequentialList, and GetInterfaces returns 3 and writes
three strings to the referenced string array: java.util.List,
java.lang.Cloneable, and java.io.Serializable.

Java collection classes

EJB proxy generation generates Java common collection classes such
as Enumeration, Iterator, Vector, and so forth. PowerBuilder can
manipulate these collection classes in the same way as a Java
client.

For example, suppose the home interface includes the following
method with the return value java.util.Enumeration:

The following code shows how a PowerBuilder EJB client can
manipulate the enumeration class through the PowerBuilder proxy: