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Synchronous and Asynchronous Processes
Using Jdeveloper to develop BPEL - looking closely
qUsing Oracle BPEL Designer templates, you can start to create the BPEL services for:
nA synchronous service
nAn asynchronous service
nA One Way service
nBased on WSDL
nSubscribing to Events
nAn empty service
Developing a BPEL Service
In defining the BPEL standard, it was never intended to be a programming language, but instead it is a higher-level tool for developers to create the code necessary for orchestrating a set of heterogeneous services. In fact, each BPEL process is a service itself. A BPEL process can be created as:A synchronous serviceA asynchronous serviceAn empty service
Although the intrinsic structure of these types of services is different, they can all contain a sequence of activities to form a business process flow to orchestrate a set of services.
The BPEL source elements can be manually entered in a text editor. However, this is time consuming and error prone. By using a visual development tool like Oracle BPEL Process Designer you gain the benefit of rapid error free development through a sophisticated visual interface.
nIs to be used when an immediate response can
be returned
nA synchronous service would typically call
only synchronous services
nIts technically possible for a
synchronous client to call an asynchronous service, but the client may fail if
the service takes too long to respond
nExamples – stock quote service, weather
service, Account Service
From the perspective of client that invokes the Sync process
nThe client that invokes a synchronous service
would block until the service returns a response
nIf the client invoking synchronous process is
also a BPEL process
qthe Invoke activity is used for both sending
the request and receiving the reply.
Asynchronous Process
nUnlike a Synchronous process, an asynchronous
process is useful when it may not be possible to return a response quickly.
nAn asynchronous BPEL service can call other
synchronous as well as asynchronous services
nExample – Document Approval, Loan Approval,
RFQ process
From the perspective of client that invokes the Async process
nIf
the client invoking asynchronous processes is also a BPEL process
qthe Invoke activity
is used for sending a request, and the Receive activity is used for receiving the reply from the service.
qafter it has invoked the async
process, the client can continue to work through its process flow, until it
encounters a Receive activity. At this point it will wait for the response
from the async process
qTypically the client will also be a asynchronous process
nIts technically possible for a synchronous client to call an
asynchronous service, but the client may fail if the service takes too long to
respond
Initial Structure of a Synchronous process
Initial Structure of a Synchronous Service
In Oracle BPEL Process Designer when you choose to create a project with the "Synchronous BPEL Process" template, the initial BPEL process flow contains:
A client PartnerLlink representing the client who initiates this BPEL process as a service. This is shown as the client in the diagram.A receive activity, called receiveInput, to receive an request message from the client.
An reply activity, called replyOutput, for the BPEL process to return a synchronous response message to the client Note, it is not necessary or mandatory for a synchronous process to return something to its initiator. Hence, if required, we can delete the replyOutput activity.
nThe designer assists in creating the input
and output messages
nWhen we choose to create a sync or an asyn
process, it creates dummy messages on its own
nModify these if required
Initial Structure of an Asynchronous Service
Initial Structure of an Asynchronous ServiceIn Oracle BPEL Process Designer when you choose to create a project based on the "Asynchronous BPEL Process" template, the initial BPEL process flow contains:A client PartnerLlink representing the client who initiates this BPEL process as a service. This is shown as the client in the diagram.
Note: You will learn more about PartnerLinks later in this lesson.A receive activity, called receiveInput, to receive an request message from the client.An invoke activity, called callbackClient, so that the BPEL process can initiate an asynchronous callback to the client who initiate the process and send a response message to the client.
Initial Structure of an Empty ServiceIn Oracle BPEL Process Designer when you choose to create a project with the "Empty BPEL Process" template, the initial BPEL process flow does not contain any activities.This is useful when we want the BPEL process to be initiated when a adapter is listening to a system – say a DB, a directory, a Queue or a Oracle Apps system
BPEL Process Variables
nProcess variables:
qCommunicate data between
activities and processes
qUseful for storing information
BPEL Process VariablesWhen design a BPEL process you must manage the input message data received from the client and returned to the client. In addition the data may need to be transformed and passed to services that you invoke. BPEL process variables need to be created to hold the data shared between activities and invoked services.The BPEL Process source defines the BPEL process variables, whose structure can be specified as:
Built-in data type, such as String, Boolean etcXML Element types, which are either defined directly in the BPEL process WSDL or an XML schema document Message type defined in the WSDL document.
Note: Message types are structured from element type specifications defined directly in the WSDL document located in an imported XML schema. It is more common to import an XML schema to define element types for message structures.When you create an Synchronous or an Asynchronous BPEL Process in Oracle BPEL Process Designer, it automatically creates an inputVariable for the request message from its client PartnerLink, and an outputVariable for the response message to be returned to the client.
Variable Types
nWhen it comes to what type the variable represents, we have three
options
1.Built-in type – string, int, boolean etc
2.Element type - based on a schema
3.Message type - Based on message in WSDL
JDeveloper creates input/output for the BPEL process automatically
qWhen you create an Synchronous or
an Asynchronous BPEL Process, JDeveloper automatically creates an inputVariable for the request message from its
client PartnerLink, and an outputVariable for the response message to be
returned to the client.
qQuestion : Is it possible to specify some other
input/output format, instead of using the defaults given by JDeveloper
qAnswer: Yes
Understanding Partner Links
nPartner
links are an external service that can be called by the BPEL process, or call
into the BPEL process.
qThe latter is known as a callback activity.
nPartner
links are BPEL components that are used to define the communication between the
BPEL engine and external components. Examples of external components include:
qWeb services
qJ2EE applications
qDatabases applications
qAdapters
nPartner
links define the communication interfaces, such as input variables, output
variables, and roles.
In the BPEL source document, the <partnerLink> element signifies the channel used to interact with the client and services.
Partner links are defined and created in the development environment, and run as part of the BPEL process.
Including a Partner LinkTo include a partner link within your process, drag a PartnerLink activity, from the Process Activities of the Component Palette, and drop it into the left or right Partner Links column the Diagram View.
Configuring the Partner
Link Activity
nThe WSDL does not specify a partnerrole. Hence JDeveloper will create a wrapper wsdl for
this service.
nTab out.
nThe partner link type is automatically
populated with randomQuote_PL.
nFor the Partner role, select randomQuote_Role.
Notes:
In asynchronous services, the My Role field is needed to allow the provider a mechanism for calling back the process that called it. The WSDL in this example is a free service available on the Internet. However, this WSDL does not have partner link definition (remember this is a BPEL extension to WSDL). This is so because this service is not developed using BPEL and partnerlink is a BPEL concept. Hence JDeveloper creates a copy of that WSDL and additionally adds the BPEL extension to WSDL – the partnerlink definition <plnk:partnerLinkType name="randomQuote_PL"> <plnk:role name="randomQuote_Role"> <plnk:portType name="impl:randomQuote"/> </plnk:role> </plnk:partnerLinkType>
Dissecting the Partnerlink configuration
nThe PartnerLinkType defines which WSDL PortType is used in a relationship with some partner
and which PortType is used when a partner interacts with the
process itself (remembering that the process is exposed as a service and
therefore has its own WSDL interface).
qAn important aspect of this is that the use of PortTypes means that WS-BPEL only refers
to services in an abstract way and it is up to an execution engine to determine
what port (and therefore binding) should be used for each PortType.
nThese
two relationships are defined in the partnerRole and myRole attributes of the PartnerLinkType.
nFor
two way relationships both roles are specified. In other words, in asynchronous
services, the My Role field is needed to allow the provider a mechanism for
calling back the process that called it.
Invoking the partnerlink
nTo call the webservice, we need to ‘invoke’ it.
nFrom the Process Activities, drop an Invoke
activity between receiveInput and replyOutput
Reviewing the Source Code
