Lightweight workflow engine for Java

I agree with the guys that already posted responses here, or part of their responses anyway :P, but as here in the company where I am currently working we had a similar challenge I took the liberty of adding my opinion, based on our experience.

We needed to migrate an application that was using the jBPM workflow engine in a production related applications and as there were quite a few challenges in maintaining the application we decided to see if there are better options on the market. We came to the list already mentioned:

• Activiti (planned to try it through a prototype)
• Bonita (planned to try it through a prototype)
• jBPM (disqualified due to past experience)

We decided not to use jBPM anymore as our initial experience with it was not the best, besides this the backwards compatibility was broken with every new version that was released.

Finally the solution that we used, was to develop a lightweight workflow engine, based on annotations having activities and processes as abstractions. It was more or less a state machine that did it's job.

Another point that is worth mentioning when discussing about workflow engine is the fact they are dependent on the backing DB - it was the case with the two workflow engines I have experience with (SAG webMethods and jPBM) - and from my experience that was a little bit of an overhead especially during migrations between versions.

So, I would say that using an workflow engine is entitled only for applications that would really benefit from it and where most of the workflow of the applications is spinning around the workflow itself otherwise there are better tools for the job:

• wizards (Spring Web Flow)
• self built state machines

Regarding state machines, I came across this response that contains a rather complete collection of state machine java frameworks.

Hope this helps.

This really depends on your requirements. First, see if you really need a workflow engine (this or other sources). Unless you really need it, probably you should avoid it.

If you really need what provides a workflow engine, I would pick one that is already built. People who works with jbpm or activiti have much more experience than you in building workflow engines, so it is probably already tunned to improve performance.

I recently open sourced Piper (https://github.com/creactiviti/piper) a distributed and very light weight, Spring-based, workflow engine.

Java based workflow engines like Activiti, Bonita or jBPM support a wide range of the BPMN 2.0 specification. Therefore, you can model processes in a graphical way. In addition, some of those engines have simulation capabilities like Activiti (with Activiti Crystalball). If you code the processes on your own, you aren´t as flexible when you need to change the process. Therefore, I would also advice to use a java based BPM engine.

I did a research concerning BPMN 2.0 based Open Source Engines. Here are the key-points which were relevant for our concrete use case:

1. Bonita:

Bonita has a zero-coding approach which means that they provide an easy to use IDE to build your processes without the need for coding. To achieve that, Bonita has the concept of connectors. For example, if you want to consume a web service, they provide you with a graphical wizzard. The downside is that you have to write the plain XML SOAP-envelope manually and copy it in a graphical textbox. The problem with this approach is that you only can realize use cases which are intended by Bonita. If you want to integrate a system which Bonita did not developed a connector for, you have to code such a connector on your own which is very painful. For example, Bonita offers a SOAP connector for consuming SOAP web services. This connector only works with SOAP 1.2, but not for SOAP 1.1 (http://community.bonitasoft.com/answers/consume-soap-11-webservices-bonita-secure-web-service-connector). If you have a legacy application with SOAP 1.1, you cannot integrate this system easily in your process. The same is true for databases. There are only a few database connectors for dedicated database versions. If you have a version not matching to a connector, you have to code this on your own.

In addition, Bonita has no support for LDAP or Active Directory Sync in the free community edition which is quite a showstopper for a production environment. Another thing to consider is that Bonita is licensed under the GPL / LGPL license which could cause problems when you want to integrate Bonita in another enterprise application. In addition, the community support is very weak. There are several posts which are more than 2 years old and those posts are still not answered.

Another important thing is Business-IT-Alignment. Modelling processes is a collaborative discipline in which IT AND the business analysts are involed. That is why you need adequate tools for both user groups (e.g. an Eclipse Plugin for the developers and an easy to use web modeler for the business people). Bonita only offers Bonita Studio, which needs to be installed on your machine. This IDE is quite technical and not suitable for business users. Therefore, it is very hard to realize Business-IT-Alignment with Bonita.

Bonita is a BPM tool for very trivial and easy processes. Because of the zero-coding approach, the lerning curve is very low and you can start modelling very fast. You need less programming skills and you are able to realize your processes without the need of coding. But as soon as your processes become very complex, Bonita might not be the best solution because of the lack of flexibility. You only can realize use cases which are intended by Bonita.

2. jBPM:

jBPM is a very powerful Open Source BPM Engine which has a lot of features. The web modeler even supports prefabricated models of some van der Aalst workflow patterns (workflowpatterns.com). Business-IT-Alignment is realizable because jBPM offers an Eclipse integration as well as a web-based modeler. A bit tricky is that you only can define forms in the web modeler, but not in the Eclipse Plugin, as far as I know. To sum up, jBPM is a good candidate for using in a company. Our showstopper was the scalability. jBPM is based on the Rules-Engine Drools. This leads to the fact that whole process instances are persisted as BLOBS in the database. This is a critial showstopper when you consider searching and scalability.

In addition, the learning curve is very high because of the complexity. jBPM does not offer a Service Task like the BPMN-Standard suggests In contrast, you have to define your own Java Service tasks and you have to register them manually in the engine, which results in quite low level programming.

3. Activiti:

In the end, we went with Activiti because this is a very easy to use framework-based engine. It offers an Eclipse Plugin as well as a modern AngularJS Web-Modeler. In this way, you can realize Business-IT-Alignment. The REST-API is secured by Spring Security which means that you can extend the Engine very easily with Single Sign-on features. Because of the Apache License 2.0, there is no copyleft which means you are completely free in terms of usage and extensibility which is very important in a productive environment.

In addition, the BPMN-coverage is very good. Not all BPMN-elements are realized, but I do not know any engine which does that.

The Activiti Explorer is a demo frontend which demonstrates the usage of the Activiti APIs. Since this frontend is based on VAADIN, it can be extended very easily. The community is very active which means that you can get help very fast if you have any problems.

Activiti offers good integration points for external form-technologies which is very important for a productive usage. The form-technologies of all candidates are very restrictive. Therefore, it makes sense to use a standard form-technology like XForms in combination with the Engine. Even such more complex things are realizable via the formKey-Attribute.

Activiti does not follow the zero-coding approach which means that you will need a bit of coding if you want to orchestrate services. But even the communication with SOAP services can be achieved by using a Java Service Task and Apache CXF. The coding effort is low.

I hope that my key points can help by taking a decision. To be clear, this is no advertisment for Activiti. The right product choice depends on the concrete use cases. I only want to point out the most important points in our project