DDevelopment & Design

33rd Degree day 3 review

At the last day of the conference, I’ve decided to skip the first presentations, and get some sleep instead. I was afraid that Venkat’s show is going to be too basic, I will see Jacek Laskowski talking about closure at 4Developers, which I’m kind of s…
At the last day of the conference, I’ve decided to skip the first presentations, and get some sleep instead. I was afraid that Venkat’s show is going to be too basic, I will see Jacek Laskowski talking about closure at 4Developers, which I’m kind of supervising from the Java perspective. As an afterthought, I should have gone to see “Static Code Analysis and AST Transformations” by Hamlet D’Arcy, as I really like this guy and the topic is intriguing at least, but I didn’t want to intoxicate myself more with coffee, and really needed to get some sleep.

MongoDB: Scaling Web Application

The first talk I’ve seen was by Ken Sipe. It was a very interesting case study, and I love case studies. They give you a real perspective, unlike the product-half-marketing that some authors are doing, and unlike self-marketing that some “professional” speakers perform. 
Ken had an interesting project at hand: a Facebook like social service, that deals with politic, named GoVote. Half of the presentation was a bit basic, with simple CRUD syntax, but when Ken started to talk about modeling, it got interesting.
Ken used Grails as the web framework and went through several plugins/libs to get him to the performance and efficiency he needed. Every one of them failed, except for GSP, which is a thing worth reflecting about. His lesson was not really surprising: you should not use any abstracts (ORM?), when playing with document databases. He sticked to GORM because of how fast his problems were solved on the mailing list and bug tracker, but GORM doesn’t really give you the resolution you want, when dealing with tree structures composed of documents.
My favourite part, albeit short, was about modeling. Ken managed to get ONE hit to DB per dynamic web page, something I’ve always dreamed of. His advice was to focus on use cases, and design document model with use cases in mind. You get a sign of bad design, when you find nested joins (hitting more than once for the data), and you can usually get away with tags, instead. Interesting stuff, I hope to verify that soon.

HTML5 For Developers

Nathaniel Schutta had a large presentation at hand, nothing he kind fit into only one hour, so he gave us a choice: what do we want to hear about. It turned out, the audience was most interested into Web Workers, local web storage and Canvas. Each had their caveats. 
Web workers allow to get some much needed concurrency  into heavy GUI (or game engines, I guess), work with a simple API where you can handle errors and spawn new workers.
Local storage is unfortunately limited by default to 5MB, and you may get unsuccessful persuading the user to change it. Apart from that, it’s a simple key-value store (both Strings), with storage events (think on-insert etc.), but current implementations handle those not without some problems.
Canvas was quite interesting. Though it has a very simple API, and only basic primitives implemented, I’ve already bought a 500 pages long book about it (and that’s without any info on all the libs build on top of it).

Ending keynotes

There were three ending keynotes, one from Nathaniel Schutta, Jurgen Appelo and the last from Robert C. Martin. As expected, those were entertaining, though unless you’ve been sleeping through the last three years in a cave, you would not be surprised by both craftsman. Jurgen, however, was quite a different animal.
His talk, titled “How to Change the World”, was based on his book “Management 3.0” and his work afterwards. I’ve been interested in the mechanics of change, since I’ve been trying to change with more or less luck, all the companies I’ve worked for. Jurgen has a lot to say in that matter, and I’ve been wrong on so many levels in my attitude towards change, that the talk was very refreshing.
You can take a look at his presentation here:
How to Change the World
Overall, while it’s too early to say whether that was the best JVM conference in Poland this year, I can recommend 33rd on all grounds. I feel I can bet blindly on it next year. Grzegorz Duda delivers enormous knowledge in so little time and so little money.

Solution Architect @ TouK

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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.