Programming WebLogic Resource Adapters

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Message and Transactional Inflow

This section discusses how WebLogic resource adapters use inbound connections to handle message inflow and transactional inflow.


Overview of Message and Transactional Inflow

Message inflow refers to inbound communication from an EIS to the application server, using a resource adapter. Inbound messages can be part of a transaction that is governed by a Transaction Manager that is external to WebLogic Server and the resource adapter, as described in Transactional Inflow.

The following diagram provides an overview of how messaging and transaction inflow occurs within a resource adapter and the role played by the Work Manager.

Figure 7-1 Messaging and Transactional Inflow Architecture

Messaging and Transactional Inflow Architecture

Architecture Components

Figure 7-1 contains the following components:

Inbound Communication Scenario

This section describes a basic inbound communication scenario that may be described using the diagram, showing how inbound messages originate in an EIS, flow into the resource adapter, and are handled by a Message-driven Bean. For related information, see Figure 2-1.

A typical simplified inbound sequence involves the following steps:

  1. The EIS sends a message to the resource adapter.
  2. The resource adapter inspects the message and determines what type of message it is.
  3. The resource adapter may create a Work object and submit it to the Work Manager. The Work Manager performs the succeeding work in a separate Thread, while the resource adapter can continue waiting for other incoming messages.
  4. Based on the message type, the resource adapter (either directly or as part of a Work instance) looks up the correct message endpoint to which it will send the message.
  5. Using the message endpoint factory corresponding to the type of message endpoint it needs, the resource adapter creates a message endpoint (which is a proxy to a message-driven bean instance from the MDB pool).
  6. The resource adapter invokes the message listener method on the endpoint, passing it message content based on the message it received from the EIS.
  7. The message is handled by the MDB in one of several possible ways:
    1. the MDB may handle the message directly and possibly return a result to the EIS through the resource adapter
    2. the MDB may distribute the message to some other application component
    3. the MDB may place the message on a queue to be picked up by the client
    4. the MDB may directly communicate with the client application.


How Message Inflow Works

A resource adapter that supports inbound communication from an EIS to the application server typically includes the following:

Handling Inbound Messages

A resource adapter may handle an inbound message in a variety of ways. For example, it may:

Inbound messages may return a result to the EIS that is sending the message. A message requiring an immediate response is referred to as synchronous (the sending system waits for a response). This is also referred to as request-response messaging. A message that does not expect a response as part of the same exchange with the resource adapter is referred to as asynchronous or event notification-based communication. A resource adapter can support asynchronous or synchronous communications for all three destinations listed above.

Depending upon the transactional capabilities of the resource adapter and the EIS, inbound messages can be either part of a transaction (XA) or not (non-transactional). If the messages are XA, the controlling transaction may be coordinated by an external Transaction Manager (transaction inflow) or by the application server’s Transaction Manager. See Transactional Inflow.

In most cases, inbound messages in a resource adapter are dispatched through a Work instance in a separate thread. The resource adapter wraps the work to be done in a Work instance and submits it to the application server’s Work Manager for execution and management. A resource adapter can submit a Work instance using the doWork(), startWork(), or scheduleWork() methods depending upon the scheduling requirements of the work.

Proprietary Communications Channel and Protocol

The resource adapter can expose connection configuration information to the deployer by various means; for example, as properties on the ResourceAdapter bean or properties on the ActivationSpec object. An alternative is to use the same communication channel for inbound as well as outbound traffic. Thus you can also set configuration information on the outbound connection pool.


Message Inflow to Message Endpoints (Message-driven Beans)

Prior to EJB 2.1, a message-driven bean (MDB) supported only Java Message Service (JMS) messaging. That is, an MDB had to implement the javax.jms.MessageListener interface, including the onMessage(javax.jms.Message) message listener method. MDBs were bound to JMS components and the JMS subsystem delivered the messages to MDBs by invoking the onMessage() method on an instance of the MDB.

With EJB 2.1, the JMS-only MDB restriction has been lifted to accommodate the delivery of messages from inbound resource adapters. The main ingredients for message delivery to an MDB by way of a resource adapter are:

For more information about message-driven Beans, see “Message-Driven EJBs” in Programming WebLogic Enterprise JavaBeans.

Deployment-Time Binding Between an MDB and a Resource Adapter

A resource adapter can be deployed independently (as a standalone RAR) or as part of an enterprise application (EAR). An MDB can also be deployed independently (as a standalone JAR) or as part of an enterprise application (EAR). In either case, an MDB whose messages are derived from a resource adapter must be bound to the resource adapter. The following sections describe binding the MDB and resource adapter and subsequent messaging operations.

Binding an MDB and a Resource Adapter

To bind an MDB and a resource adapter, you must:

  1. Set the jndi-name element in the weblogic-ra.xml deployment descriptor for the resource adapter. See jndi-name.
  2. Set the adapter-jndi-name element in the weblogic-ejb-jar.xml deployment descriptor to match the value set in the corresponding jndi-name element in the resource adapter.
  3. Assume that the resource adapter is deployed prior to the MDB. (The MDB could be deployed before the resource adapter is deployed; in that case, the deployed MDB polls until the resource adapter is deployed.) When the resource adapter is deployed, the ResourceAdapter bean is bound into JNDI using the name specified.
  4. The MDB is deployed, and the MDB container invokes an application server-specific API that looks up the resource adapter by its JNDI name and invokes the specification-mandated endpointActivation(MessageEndpointFactory, ActivationSpec) method on the resource adapter.
  5. The MDB container provides the resource adapter with a configured ActivationSpec (containing configuration information) and a factory for the creation of message endpoint instances.
  6. The resource adapter saves this information for later use in message delivery. The resource adapter thereby knows what message listener interface the MDB implements. This information is important for determining what kind of messages to deliver to the MDB.

Dispatching a Message

When a message arrives from the EIS to the resource adapter, the resource adapter determines where to dispatch it. The following is a possible sequence of events:

  1. A message arrives from the EIS to the resource adapter.
  2. The resource adapter examines the message and determines its type by looking it up in an internal table. The resource adapter determines the message type corresponds to a particular pair (MessageEndpointFactory, ActivationSpec).
  3. The resource adapter determines the message should be dispatched to an MDB.
  4. Using the MessageEndpointFactory for that type of message endpoint (one to be dispatched to an MDB), the resource adapter creates an MDB instance by invoking createEndpoint() on the factory.
  5. The resource adapter then invokes the message listener method on the MDB instance, passing any required information (such as the body of the incoming message) to the MDB.
  6. If the message listener does not return a value, the message dispatching process is complete.
  7. If the message listener returns a value, the resource adapter determines how to handle that value. This may or may not result in further communication with the EIS, depending upon the contract with the EIS.

Activation Specifications

A resource adapter is configured with a mapping of message types and activation specifications. The activation specification is a JavaBean that implements javax.resource.spi.ActivationSpec. The resource adapter has an ActivationSpec class for each supported message type. The mapping of message types and activation specifications is configured in the ra.xml deployment descriptor, as described in Configuring Inbound Connections. For more information about ActivationSpecs, see Chapter 12, “Message Inflow” in the J2CA 1.5 Specification.

Administered Objects

As described in section of the J2CA 1.5 Specification, a resource adapter may provide the Java class name and the interface type of an optional set of JavaBean classes representing administered objects that are specific to a messaging style or message provider. You configure administered objects in the admin-objects elements of the ra.xml and weblogic-ra.xml deployment descriptor files. As with outbound connections and other WebLogic resource adapter configuration elements, you can define administered objects at three configuration scope levels:


Transactional Inflow

This section discusses how transactions flow into WebLogic Server from an EIS and a resource adapter. A transaction inflow contract allows the resource adapter to handle transaction completion and crash recovery calls initiated by an EIS. It also ensures that ACID properties of the imported transaction are preserved. For more information on transaction inflow, see Chapter 14, “Transaction Inflow” of the J2CA 1.5 Specification.

When an EIS passes a message through a resource adapter to the application server, it may pass a transactional context under which messages are delivered or work is performed. The inbound transaction will be controlled by a transaction manager external to the resource adapter and application server. See Message Inflow to Message Endpoints (Message-driven Beans).

A resource adapter may act as a bridge between the EIS and the application server for transactional control. That is, the resource adapter receives messages that it interprets as XA callbacks for participating in a transaction with a external Transaction Manager.

WebLogic Server can function as an XA resource to a external Transaction Manager through its interposed Transaction Manager. The WebLogic Server Transaction Manager maps external transaction IDs to WebLogic Server-specific transaction IDs for such transactions.

The WebLogic Server Transaction Manager is subordinate to the external Transaction Manager, which means that the external Transaction Manager ultimately determines whether the transaction succeeds or is rolled back. See Participating in Transactions Managed by a Third-Party Transaction Manager” in Programming WebLogic JTA. As part of the J2EE 1.5 Connector Architecture, the ability for a resource adapter to participate in such a transaction is now exposed through a J2EE standard API.

The following illustrates how a resource adapter would participate in a external transaction. For more information, see section 14.4, “Transaction Inflow Model” of the J2CA 1.5 Specification.

  1. The resource adapter receives an inbound message with a new external transaction ID.
  2. The resource adapter decodes the external transaction ID and constructs an Xid (javax.transaction.xa.Xid).
  3. The resource adapter creates an instance of an ExecutionContext (, setting the Xid it created and also setting a transaction timeout value.
  4. The resource adapter creates a new Work object to process the incoming message and deliver it to a message endpoint.
  5. The resource adapter submits the Work object and the ExecutionContext to the Work Manager for processing. At this point, the Work Manager performs the necessary work to enlist the transaction and start it with the WebLogic Server Transaction Manager.
  6. Subsequent XA calls from the external Transaction Manager are sent through the resource adapter and communicated to the WebLogic Server Transaction Manager. In this way, the resource adapter acts as a bridge for the XA calls between the external Transaction Manager and the WebLogic Server Transaction Manager, which is acting as a resource manager.

Using the Transactional Inflow Model for Locally Managed Transactions

When the resource adapter receives requests from application components running in the same server instance as the resource adapter that need to be delivered to an MDB as part of the same transaction as the resource adapter request, the transaction ID must be obtained from the transaction on the current thread and placed in an ExecutionContext.

In this case, WebLogic Server does not use the Interposed Transaction Manager but simply passes the transaction on to the Work Thread used for message delivery to the MDB.

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