Java Reference
In-Depth Information
Expression Language
Expression Language
The robust support for jPDL within the JBoss suite of products means that developers can
take advantage of integration with Seam/Web beans. Using the Expression Language, you
can integrate your process with any named object in any Seam context.
Human tasks
Human tasks
jPDL offers support for defining business processes that are composed in part of steps that
humans must complete. In BPEL, human tasks are not handled directly, and require an ex-
tension.The competing specifications in the BPEL realm are WS-HumanTask and an IBM
whitepaper called “BPEL4People.” WS-HumanTask was published by a consortium, in-
cluding Oracle, SAP, Active Endpoints, IBM, and Adobe in June 2007.
Embeddable
Embeddable
Because it is pure Java, jPDL can be embedded easily in libraries, databases, or other Java-
based tools.
Ultimately, I think that the difference between BPEL and jPDL comes down to this: jPDL is
about task management in Java, and BPEL is focused on creating composite applications in
XML. You might consider using jPDL when you have existing Java POJOs (Plain Old Java
Objects) that you want to combine within a task management flow, and BPEL when your pro-
cess steps need to be executed by external web services. Because of the growing popularity
of BPMN, and the fact that it exports (if roughly) to BPEL, we won't cover jPDL much fur-
ther in this topic. However, it's an interesting and useful technology. It is also worth noting
that JBoss's jBPM platform supports not only jPDL, but also BPEL, pageflows, and others be-
cause its runtime is implemented on top of a “process virtual machine.” Which is pretty slick.
BPEL
We're going to be spending a lot of time covering BPEL, so I won't rehash its features here.
BPEL is the focus of this chapter because it is written in an XML grammar and does not re-
quire you to write Java code, which is a potential advantage over jPDL in flexibility. Also,
despite solid support for jPDL from vendors such as JBoss/RedHat, BPEL is more widely
supported.
NOTE
Microsoft products such as BizTalk can execute BPEL, as can a variety of Java engines.
