DDevelopment & Design

Tired of exporting your OSGI metatype to client manually?

Feel my pain

We use OSGi, but we don’t deploy our bundles further than testing environment. It is our client who deploys it to production. However, they rarely read the metatypes – as metatype files are hidden deep inside jars and their format is not very user-friendly (who wants to read XMLs?). This is why they don’t know how to configure the application.

Sharing metatypes

If you work with OSGi metatype files, you have to find some way of informing your client what configuration is necessary for your application. There are a few ways of sharing this information:

  • You can send configuration options by e-mail or Jira/Redmine/(paste your issue tracker here). However, this might cause a big mess, searching is horrible, and it becomes outdated faster than you can say I hate sending metatypes.
  • You can share your repository with the client so that they always have up-to-date XMLs. Nevertheless, XML files are difficult to read and are scattered across whole modules.
  • You can keep your configuration in some document (e.g. Markdown), providing easy access for the client, but you must remember to synchronize it every time you change metatype.

metatype-exporter-maven-plugin to the rescue!

Our new Maven plugin allows us to automatically generate Markdown file from metatype files. Just add the plugin and enjoy automatically generated configuration created without any effort. Sample configuration may look like below.

<project ...>

    ...

    <pluginRepositories>
        <pluginRepository>
            <id>touk</id>
            <url>https://philanthropist.touk.pl/nexus/content/repositories/releases</url>
            <!-- we are not on central, but we are going to be there soon -->
        </pluginRepository>
    </pluginRepositories>
    <build>
        <plugins>
            <plugin>
                <groupId>pl.touk.osgi</groupId>
                <artifactId>metatype-exporter-maven-plugin</artifactId>
                <version>@metatype-exporter-maven-plugin.version@</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>export</goal>
                        </goals>
                    </execution>
                </executions>
                <configuration>
                    <destination>${project.build.directory}/classes/documentation</destination>
                    <outputFileName>ConfigurationDescription.md</outputFileName>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

 

Markdown produced by this configuration may look like this:

# Properties name (theseAreProperties) for pid this.is.first.pid

Description goes here

| ID  | Name  | Required | Type    | Default value | Options                         | Description |
| --- | ----- | -------- | ------- | ------------- | ------------------------------- | ----------- |
| id1 | name1 | Yes      | String  |               |                                 | desc1       |
| id2 |       | No       | Long    | 123           |                                 | desc2       |
| id3 |       | Yes      | Integer |               | <ul><li>15</li><li>30</li></ul> |             |

# Properties name (secondProps) for pid this.is.second.pid

| ID  | Required | Type   |
| --- | -------- | ------ |
| id1 | Yes      | String |

Markdown files are great because many git repositories like Gitlab or Github render Markdown files nicely. You can view the above file here: https://gist.github.com/piotrekfus91/ba36404341664c48df19576350a2340f.

Definitely more readable, huh?

Change language if your client doesn’t speak English

If you want to change the language of generated files, just add a resource bundle named MarkdownBundle, change locale in plugin configuration and enjoy your custom language. English and Polish are available out of the box.

<project ...>

    ...

    <build>
        <plugins>
            <plugin>
                <groupId>pl.touk.osgi</groupId>
                <artifactId>metatype-exporter-maven-plugin</artifactId>
                <version>@metatype-exporter-maven-plugin.version@</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>export</goal>
                        </goals>
                    </execution>
                </executions>
                <configuration>
                    <language>de</language>
                    <country>DE</country>
                </configuration>
                <depenedencies>
                    <dependency>
                        <!-- maven coordinates of the jar with resource bundle -->
                    </dependency>
                <depenedencies>
            </plugin>
        </plugins>
    </build>
</project>

Resource bundle (for example MarkdownBundle_de.properties)

forPid=...
attributeHeaderId=...
attributeHeaderName=...
attributeHeaderDescription=...
attributeHeaderOptions=...
attributeHeaderType=...
attributeHeaderDefaultValue=...
attributeHeaderRequired=...
attributeRequiredTrue=...
attributeRequiredFalse=...

Summary

Our problem – client doesn’t know how to configure the application – was solved with our new Maven plugin. The sources may be found on https://github.com/TouK/metatype-exporter-maven-plugin.

What’s next?

We are planning to add other output formats or enable users to provide custom templates. If you have any suggestions for enhancements or found a bug, just let us know in a Github issue.

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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.