Architecture of the COM connector
To illustrate the architecture of the connector, this
section describes request processing at a high-level, as illustrated
in Figure 1, and then the details
of how the connector works, as illustrated in Figure 2.
Figure 1. Request processing in the connector for COM
- The connector receives a business object request from the integration
broker.
- The connector creates a proxy object instance of the business
object. The proxy object instance acts as a representation of the
COM object to which the connector is sending the request. For details
about how the connector creates and processes the proxy object,
see How the connector works.
- The connector processes the proxy object by using it to invoke
the corresponding COM object running on COM server and write data
to the COM application.
- The connector updates the proxy object by reading, or getting,
data from COM server object.
- The adapter returns a message to the integration broker indicating
that the original object request was either successful or unsuccessful
(a FAIL status). If the request was successful, the connector also
returns the updated business object to the broker.
How the connector works
This section describes how the different parts of the
connector process a business object, as illustrated in Figure 2.
Figure 2. The connector for COM
-
When you first start up the connector,
the connector's Agent class performs the following initialization processes:
- Instantiates the OLE environment.
- Does one of the following, depending on how the connector properties
have been set. For details about the connector properties and how
they affect each of the following scenarios, see Connector-specific properties.
-
Scenario 1: Creates
a connection factory object instance, which is an object that refers
to an application. The factory object is persistent for the life
of the connector and creates connections that are placed in the
connection pool. The number of connections created depends on the
value specified in the connector PoolSize property.
- Scenario 2: Creates connection objects
only that are placed in the connection pool. The number of connections
depends on the value specified in the PoolSize property. No factory object is created in this scenario.
- Scenario 3: Creates a factory proxy object
against which the business object will call methods (the factory
class matches the proxy class ASI of the BO). In this scenario,
no connections are created.
- The integration broker sends a request, in the form of a business
object, to the connector.
- The connector's BO handler receives the object.
- The doVerbFor() method of the BO handler calls the Dispatch() method, which reads the BO ASI to obtain the proxy class
name. The Dispatch() method gets the proxy class name and sends it to the Loader.
-
The Loader uses the proxy class name to
load the proxy class (qualified using valid Java class notation,
ie. Mypackage.myclass) and create a proxy object instance, loading it in the per-call
object pool. The Loader checks to see if the object is one of the
following:
- Is it a connection? If so, retrieve it as a connection object
from the connection pool.
- Is it a factory object? If so, retrieve it as a static object
from the connection factory.
- Dispatch then reads through the BO's verb ASI and builds
a list of methods. The verb ASI is an ordered list of attribute
names. Each attribute represents a method on the proxy object. In
other words, the verb ASI is not a list of methods, but a list of
attributes, each one having a value that represents a proxy object method.
-
For each method on the verb ASI list, the InvokeMethods() method of the BO handler calls InvokeMethod() to do one of the following:
- Call Invoker, if the method is a regular method. If the argument
is marked as a foreign key, store it in the per-call object pool.
If the attribute is not populated, check the attribute ASI for use_attribute_value. If the use_attribute_value ASI is present, attempt to pull the object from the per-call
object pool.
- Call the Load (LoadFromProxy function) and Store (WriteToProxy
function) operations of Synchronizer (the BO handler's
object synchronization process) against all attributes on the proxy object.
The operation called depends on what is in the verb ASI. LoadFromProxy
(Load) and WriteToProxy (Store) are pre-defined functions that you
can include in the verb ASI. Their purpose is to synchronize a business
object's simple attributes to a COM component's
public properties.
- Call Load or Store operations against a single, specific attribute
(LoadFromProxy gets the proxy property and sets the BO property
to that value; WriteToProxy sets the proxy property with values from
the BO).
Note:
If the verb ASI is empty, the BO handler will search
for a method on the BO with populated parameters and call that.
Only one method can have populated parameters. Otherwise, if multiple
methods are populated and the verb ASI is empty, then the connector
logs an error and returns a FAIL code.
- For each method of the proxy object, Invoker constructs the
parameters and arguments of the method by doing the following:
- If it encounters a BO type (rather than a simple data type,
such as a String) in the attribute, Invoker recursively calls the Dispatch() method on the active BO handler.
- Dispatch() returns a proxy object that the parent method can use to
invoke its method call.
- The BO handler's synchronization process, called Synchronizer,
invokes WriteToProxy to store (set) a value in each property of
the COM component (proxy object), thus updating data on the COM
server. The value stored is from the corresponding attribute on
the business object that the COM component corresponds to.
- When values are returned from the COM server, the LoadFromProxy
function calls the "getters" of the proxy object
and loads the data returned from the proxy object onto the BO.
- The connector returns the business object to the integration
broker.
