BeanFlow

BeanFlow is a lightweight Java library for building flows using beans to orchestrate events. You can think of BeanFlow as a simple alternative to BPEL where the flows are all specified and implemented using Java code rather than declarative XML.

Motivation

When building highly concurrent or distributed applications it is very common for there to be many events happening; often asynchronously and in different threads and its very common to need to perform kinds of workflow or orchestration across these events.

Now you certainly can use things like BPEL to solve these kinds of problems. However often this is a bit heavy weight & complex and you just want to have a bean based flow using regular Java code to represent the flow.

Use cases

When working with concurrent or distributed applications there are many use cases for needing to orchestrate among multiple concurrent events. Here are a few examples from our use cases implementing ServiceMix and ActiveMQ

• starting dependent services; where a parent component is dependent on the child components starting; where the start process may be asynchronous in different threads. e.g. there may be a recovery process on startup which you need to wait for.
• implementing master-slave type protocols where you need to monitor the state of the master and slave to make decisions on what to do; together with dealing with transitions from Started to Recovering to Running then maybe to FailingOver etc.
• implementing message orchestration. You may want to implement some simple orchestrations, waiting for either a response to arrive or a timeout to fire etc

Flow overview

A flow is just a POJO which implements the Flow interface. A flow has a simple lifecycle, you can start them and stop them and ask their status.

Once a flow has been started via the start() method it can take an arbitrarily long time to complete; you can see if the flow has completed via the
isStopped() method. A flow could fail for some reason (such as it timed out or some error occurred) so there is a method isFailed() which can be used to easily inspect the flow.