Feeds

Programming constructs in BPEL

Part 3: BPELJ and Compensation

Boost IT visibility and business value

In this column in our series examining BPEL and its use within Service Oriented Architecture (SOA) systems, I'll will be looking at BPELJ and Compensation.

BPELJ is an extension to the core BPEL (Business Process Execution Language), which allows the direct inclusion of Java code within a BPEL script. Compensation is actually a core element of BPEL that provides an undo-like facility for situations where part of a BPEL script fails and other parts require their effects to be undone.

BPELJ

The aim of BPELJ is to let you embed Java and J2EE processes in a BPEL process. The intention is to allow portable integration of Java and J2EE applications into BPEL across application servers. In practice, most BPEL engines have allowed integration with programming languages such as Java in one form or another for some time, but via their own proprietary extensions. Thus, there have been BPEL extensions without portability, which I personally find extremely frustrating - because I need to support multiple application server environments.

BPELJ offers a glimmer of hope, in that it aims to provide a standard extension to BPEL for inline Java. The aim of BPELJ is to combine the power of a general purpose programming language such as Java with the orchestration and integration facilities of BPEL. By doing this, developers are free to select the appropriate "programming" language for the level of task they are implementing.

The Design of BPELJ

The design of BPELJ allows Java code to be embedded directly within a BPEL script in similar way to the embedding of Java within a JSP page. That is, BPELJ allows sections of Java code, called Java snippets, to be included in BPEL process definitions. Snippets are expressions or small blocks of Java code used for such things as loop conditions, branching conditions, variable initialisation, calling methods on Java objects etc.

Within BPEL standard extension points are used to support BPELJ. For example, a new partner link type is defined that references Java code; variables can now be typed as being of a specific Java class; and BPELJ code snippets can contain valid Java code statements, with the ability to invoke methods on Java classes from within BPEL statements.

BPELJ Examples

The following BPEL script illustrates the concepts presented in the above section. I've omitted much of this example for clarity, however, the core BPELJ elements remain:


<process name="BookCheck" 

expressionLanguage="http://jcp.org/java"

bpelj:package="com.regdev.example"

xmlns="http://schemas.xmlsoap.org/ws/2003/03/business-process/"

targetNamespace="http://regdev.com/bp/BookCheck"

xmlns:bpelj="http://schemas.xmlsoap.org/ws/2003/03/business-process/java"

xmlns:pq="http://regdev.com/ws/external/BookCheck">

<partnerLinks>

      ...

      <partnerLink name="lookup"  

              partnerLinkType="bpelj:com.regdev.BookLookup"/>

<variables>

   ....

   <variable name="message" type="bpelj:com.regdev.TextMessage"/>

</variables>

<sequence>

...

<flow>

...

</flow>

<bpelj:snippet name="Calculate Total">

   <bpelj:code>

      ...

      subtotal = subtotal * (1 – discount.getRate());

      response.setSubtotal(subtotal);

      float taxes = subtotal * taxRate;

      float total = subtotal + taxes;

      response.setTax(taxes);

      response.setTotal(total);

      ...

   </bpelj:code>

</bpelj:snippet>

...

<invoke partnerLink="BookLookup" operation="checkRegistration">

    <input part="Title" variable="title"/>

    <input part="ISBN" variable="isbn"/>

</invoke>

...

</sequence>

</process>

The Essential Guide to IT Transformation

Next page: Compensation

More from The Register

next story
NO MORE ALL CAPS and other pleasures of Visual Studio 14
Unpicking a packed preview that breaks down ASP.NET
KDE releases ice-cream coloured Plasma 5 just in time for summer
Melty but refreshing - popular rival to Mint's Cinnamon's still a work in progress
Leaked Windows Phone 8.1 Update specs tease details of Nokia's next mobes
New screen sizes, dual SIMs, voice over LTE, and more
Another day, another Firefox: Version 31 is upon us ALREADY
Web devs, Mozilla really wants you to like this one
Put down that Oracle database patch: It could cost $23,000 per CPU
On-by-default INMEMORY tech a boon for developers ... as long as they can afford it
Mozilla keeps its Beard, hopes anti-gay marriage troubles are now over
Plenty on new CEO's todo list – starting with Firefox's slipping grasp
Apple: We'll unleash OS X Yosemite beta on the MASSES on 24 July
Starting today, regular fanbois will be guinea pigs, it tells Reg
prev story

Whitepapers

Implementing global e-invoicing with guaranteed legal certainty
Explaining the role local tax compliance plays in successful supply chain management and e-business and how leading global brands are addressing this.
The Essential Guide to IT Transformation
ServiceNow discusses three IT transformations that can help CIO's automate IT services to transform IT and the enterprise.
Consolidation: The Foundation for IT Business Transformation
In this whitepaper learn how effective consolidation of IT and business resources can enable multiple, meaningful business benefits.
How modern custom applications can spur business growth
Learn how to create, deploy and manage custom applications without consuming or expanding the need for scarce, expensive IT resources.
Build a business case: developing custom apps
Learn how to maximize the value of custom applications by accelerating and simplifying their development.