DDevelopment & Design

Activiti – are you ready for BPMN 2.0?

  • bympr
  • March 27, 2011
  • 5 minute read
From the beginning of this year I got quite involved in project called Activiti. It’s a “light-weight workflow and Business Process Management (BPM) Platform” (according to creators. The project is led by JBPM creators – Tom Bayens and Joram Barrez and is backed by Alfresco and several other companies. I also contributed some small features :) Activiti has already made some noise in BPM world – check this, this, or this, and of course InfoQ.
So, what’s the fuss all about? What makes Activiti special? Of course – it depends what are you comparing it with. My experience involves mainly working with open source BPEL implementation, but I think some points remain valid.

So, here is my list of distinctive features:

BPMN 2.0 support I took quite a lot of time for this spec to arrive, but it’s finally here. The biggest step ahead comparing with BPMN 1.x is execution model – no more BPEL, you can use the same diagram for modelling and execution, and it has proper xsd schema! Of course, it won’t solve all round-trip headaches, but I think it’s quite important improvement. XML describing BPMN 2.0 process consists of nodes definitions and transition definitions: Activiti is one of the first BPM engines offering BPMN 2.0 support. Currently not all nodes are supported, but the list includes:
* exclusive and paralell gateways  

  • timer boundary and intermediate events (timer start event almost ready)    

  • various tasks: script, user, service, manual, rules, receive    

  • error events and handling them    

  • subprocesses (both embedded or not)     Not all of these nodes are fully defined in spec – e.g. it does not describe how service task invocation should look like. Therefore, Activiti comes with a set of custom extensions. They are meant to be as non-intrusive as possible – to make processes more portable. One of most commonly used are ones for describing service task behaviour: Another useful extension enables to associate html form and candidate user with user task: One of nice features of BPMN 2.0 is also providing xml schema for describing process diagram – aka Diagram Interchange. This enables good engines (such as Activiti ;)) to generate process diagram just on the basis of xml definition – which makes importing processes modelled in some external tool much easier. It looks like this: Maybe not too beautiful, but usable.

Goal of supporting full BPM cycle

Do you (still) believe that future tools for creating business processes will allow users to get rid of developers? I do not… Unless of course, business people will learn how to code ;) Otherwise what we’ll be left with are some nice zero-coding tools which look great on 15minutes (or event 2hours if they’re exprensive enough) but after running into real-life problems will demand extensive hacking.
Activiti pursues different goal, and proposes developing process cycle layer. Key points of this proposition are:

  • zero coding solutions won’t work
  • analysts are needed to model the process, developers are needed to create executable processes, and operations are needed to deploy and monitor them
  • each of these groups have their own set of tools which they’re familiar with
  • so let’s not reinvent the wheel but encourage them to collaborate but use their set of tools

So, how to achieve this? By creating another web application, of course ;) It’s name is Activiti Cycle and it’s meant to encourage collaboration between business, developers and operations, while allowing each of them to use their own, specific tools in their daily job. It’s more like a federated repository of BPM assets, such as Visio Diagrams, BPMN process definitions, maven process projects, deployment packages and so on. These artifacts can be linked, commented and tracked by various process stakeholders and also transformed.

Easy to embed and extend, also by quasi-REST API

One of biggest pains of BPEL based solutions is that they force you to integrate with the rest of you app using webservices. Fortunately, this is no longer the case. You can embed activiti engine in your (for example) Spring application just by importing few jars and configuring it as any other Spring component:
This is of course great for running processes that handle some Java tasks. What about user tasks? Activiti comes with decent webapps for handling human tasks and monitoring process state: Activiti Explorer – screens shows the list of tasks for a given user:  

Activiti Probe – screen shows monitoring process instance:  

But what if you want to/have to use some other frontend technology? Webapps that I mentioned before are really thin clients – all logic is hidden behind Activiti’s quasi-REST API (I use the word quasi not to be beaten by RESTafarians who will surely point out that Activiti API is just RPC over HTTP…). That means you can embed Activiti in you webapps/OSGi container/any other environment and integrate with frontend webapps using handy JSON/HTTP communication. Which looks more or less like this:

Using (defacto) standards When you create application using Activiti chances are high that you know many (if not all) building blocks & techniques:

  • development? Eclipse plugin & maven
  • connecting components together? you can choose: spring or (for JEE6 lovers) CDI
  • testing? just do your normal TDD (you do it, right? ;)) using Activiti JUnit testing utils

Eclipse plugin includes visual modeler, which enables you to draw executable BPMN 2.0 processes, and fill all needed properties:

It uses Diagram Interchange format, so process diagram layout will remain the same when displaying process diagram in other applications. Testing is also pretty easy, as Activiti comes with good JUnit support. One of small, but important features is ability to simulate the clock – very handy when dealing with long running tasks.

Good integration capabilities

Activiti comes with capabilities allowing for integration with three most popular open source integration frameworks:

  • Mule ESB – integration is written by MuleSoft
  • SpringIntegration, contributed by SpringSource
  • last but cetainly not least: Apache Camel – which is contributed by TouK ;) – it’s still work in progress, but I hope to write a blog post soon about integrating Camel & Activiti

This allows to build processes that are closer to orchestration than simple workflows, containing only (or mostly) human tasks. Each of these integration frameworks comes with a vast collection of adapters using all popular (and not so popular) communication protocols. This allows process engine to concentrate on the process, and not on the communication details.

Summary I think it’s quite impressive set of features for a product that is less than year old. And what are Activiti plans for the future? Tom Bayens recently announced that Activiti is going to support some sort of Adaptive Case Management – which is one of top buzzwords in process world. Other goals include:

  • asynchronous continuations
  • moving towards full support of BPMN 2.0
  • extending Activiti Cycle – check Bernd’s Ruecker screencast showing Activiti Cycle approach to handling collaboration between analysts, developers and admins – it’s quite impressive

As for me, I’m finishing adding support for start timer tasks and hope to post something on Activiti-Camel intergration and running Activiti in OSGi environment soon – especially Apache Servicemix – so stay tuned. If you’ve found Activiti interesting, please start with 10 minutes 

Getting started guide, and if you know Polish, you can also have a look at my slides from Warsaw JUG presentation Thanks for reading my first post on this blog – hope you liked it.

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DDevelopment & Design

Using WsLite in practice

TL;DR

There is a example working GitHub project which covers unit testing and request/response logging when using WsLite.

Why Groovy WsLite ?

I’m a huge fan of Groovy WsLite project for calling SOAP web services. Yes, in a real world you have to deal with those - big companies have huge amount of “legacy” code and are crazy about homogeneous architecture - only SOAP, Java, Oracle, AIX…

But I also never been comfortable with XFire/CXF approach of web service client code generation. I wrote a bit about other posibilites in this post. With JAXB you can also experience some freaky classloading errors - as Tomek described on his blog. In a large commercial project the “the less code the better” principle is significant. And the code generated from XSD could look kinda ugly - especially more complicated structures like sequences, choices, anys etc.

Using WsLite with native Groovy concepts like XmlSlurper could be a great choice. But since it’s a dynamic approach you have to be really careful - write good unit tests and log requests. Below are my few hints for using WsLite in practice.

Unit testing

Suppose you have some invocation of WsLite SOAPClient (original WsLite example):

def getMothersDay(long _year) {
    def response = client.send(SOAPAction: action) {
       body {
           GetMothersDay('xmlns':'http://www.27seconds.com/Holidays/US/Dates/') {
              year(_year)
           }
       }
    }
    response.GetMothersDayResponse.GetMothersDayResult.text()
}

How can the unit test like? My suggestion is to mock SOAPClient and write a simple helper to test that builded XML is correct. Example using great SpockFramework: 

void setup() {
   client = Mock(SOAPClient)
   service.client = client
}

def "should pass year to GetMothersDay and return date"() {
  given:
      def year = 2013
  when:
      def date = service.getMothersDay(year)
  then:
      1 * client.send(_, _) >> { Map params, Closure requestBuilder ->
            Document doc = buildAndParseXml(requestBuilder)
            assertXpathEvaluatesTo("$year", '//ns:GetMothersDay/ns:year', doc)
            return mockResponse(Responses.mothersDay)
      }
      date == "2013-05-12T00:00:00"
}

This uses a real cool feature of Spock - even when you mock the invocation with “any mark” (_), you are able to get actual arguments. So we can build XML that would be passed to SOAPClient's send method and check that specific XPaths are correct:

void setup() {
    engine = XMLUnit.newXpathEngine()
    engine.setNamespaceContext(new SimpleNamespaceContext(namespaces()))
}

protected Document buildAndParseXml(Closure xmlBuilder) {
    def writer = new StringWriter()
    def builder = new MarkupBuilder(writer)
    builder.xml(xmlBuilder)
    return XMLUnit.buildControlDocument(writer.toString())
}

protected void assertXpathEvaluatesTo(String expectedValue,
                                      String xpathExpression, Document doc) throws XpathException {
    Assert.assertEquals(expectedValue,
            engine.evaluate(xpathExpression, doc))
}

protected Map namespaces() {
    return [ns: 'http://www.27seconds.com/Holidays/US/Dates/']
}

The XMLUnit library is used just for XpathEngine, but it is much more powerful for comparing XML documents. The NamespaceContext is needed to use correct prefixes (e.g. ns:GetMothersDay) in your Xpath expressions.

Finally - the mock returns SOAPResponse instance filled with envelope parsed from some constant XML:

protected SOAPResponse mockResponse(String resp) {
    def envelope = new XmlSlurper().parseText(resp)
    new SOAPResponse(envelope: envelope)
}

Request and response logging

The WsLite itself doesn’t use any logging framework. We usually handle it by adding own sendWithLogging method:

private SOAPResponse sendWithLogging(String action, Closure cl) {
    SOAPResponse response = client.send(SOAPAction: action, cl)
    log(response?.httpRequest, response?.httpResponse)
    return response
}

private void log(HTTPRequest request, HTTPResponse response) {
    log.debug("HTTPRequest $request with content:\n${request?.contentAsString}")
    log.debug("HTTPResponse $response with content:\n${response?.contentAsString}")
}

This logs the actual request and response send through SOAPClient. But it logs only when invocation is successful and errors are much more interesting… So here goes withExceptionHandler method:

private SOAPResponse withExceptionHandler(Closure cl) {
    try {
        cl.call()
    } catch (SOAPFaultException soapEx) {
        log(soapEx.httpRequest, soapEx.httpResponse)
        def message = soapEx.hasFault() ? soapEx.fault.text() : soapEx.message
        throw new InfrastructureException(message)
    } catch (HTTPClientException httpEx) {
        log(httpEx.request, httpEx.response)
        throw new InfrastructureException(httpEx.message)
    }
}
def send(String action, Closure cl) {
    withExceptionHandler {
        sendWithLogging(action, cl)
    }
}

XmlSlurper gotchas

Working with XML document with XmlSlurper is generally great fun, but is some cases could introduce some problems. A trivial example is parsing an id with a number to Long value:

def id = Long.valueOf(edit.'@id' as String)

The Attribute class (which edit.'@id' evaluates to) can be converted to String using as operator, but converting to Long requires using valueOf.

The second example is a bit more complicated. Consider following XML fragment:

<edit id="3">
   <params>
      <param value="label1" name="label"/>
      <param value="2" name="param2"/>
   </params>
   <value>123</value>
</edit>
<edit id="6">
   <params>
      <param value="label2" name="label"/>
      <param value="2" name="param2"/>
   </params>
   <value>456</value>
</edit>

We want to find id of edit whose label is label1. The simplest solution seems to be:

def param = doc.edit.params.param.find { it['@value'] == 'label1' }
def edit = params.parent().parent()

But it doesn’t work! The parent method returns multiple edits, not only the one that is parent of given param…

Here’s the correct solution:

doc.edit.find { edit ->
    edit.params.param.find { it['@value'] == 'label1' }
}

Example

The example working project covering those hints could be found on GitHub.