DDevelopment & Design

What is NoSQL good for?

… or how I ended up writing a CouchDB proof of concept app?

Once upon a time I set out on a journey to discover the NoSQL land. I’ve decided that doing simple queries wouldn’t be interesting enough. That’s why I’ve chose to create an app that would be based on some NoSQL database. The main idea was to create an app, that would dynamically update itself with geographic data flowing in. Since there are myriads of geo-data that are available on the internet, you can pick your favorite one and load them into your SQL database of choice. In my case the primary source of data was a proprietary database, or more specifically – one table in it continuously updated with new data. To make that data visible on my map I needed to: * buffer the huge amount of those records – so as not to overhoul other services with large traffic, and not to flood the frontend * convert then to my representation * display them – have presentation layer in a browser – since browser-based frontend was the easiest and fastest to develop The idea of the front-end HTML page was to show new points on the map. From the moment of opening the page records that appear in database table should be shown interactively on the screen.

Toys used

For the first step I chose to use RabbitMQ broker. A queue on the broker would receive messages – one message per database table’s row. Then I’d use some simple groovy middle ware to convert the data to appropriate format and put it onto another db – this time db specific to my app. You may ask why incorporate another database. It would be good for separating environments – assuming the original data contains some vulnerable content that should be anatomised, or we just don’t feel comfortable exposing the whole database of some XYZ-system just to have access to its one table. Since for my presentation layer I chose HTML+JS without any application server-based back-end I’ve decided on CouchDB . This seemed like a perfect match for this scenario. Why? – ease of use, REST API, with JSON responses – just great for interacting with my simple front-end. The flow of things was as shown on the image below:

diagram

Avro – for the beginning

As you can see, I’ve chosen JSON as my data-format. I’ve been considering Apache Avro in the first place but using it was a real pain in the ass. Avro itself is used in Apache Hadoop as a serialization layer, so it would seem OK, but it has virtually no documentation. But once you tear through the unintuitive interface and manage to handle all those unthinkable exceptions you get a few pros for this library. It’s great in that it does not require code generation – I like it being made on the fly. It also offers sending data in binary format, which was not necessary, but never the less is a nice feature. What I certainly didn’t like about it was its orientation on the files rather than chunks of data – so it was not so obvious how should I send data through the wire. Than I found out it can produce JSON output, which would work for me, except the output could not have been parsed by other JSON libraries :) (I’ve asked on stackoverflow about that, but with no luck). If my whining haven’t put you back and still would like to see how to use Avro, try this unit test in project’s GitHub repo: AvroSimpleTest.groovy

Svenson

I’ve dropped Avro in favour of a simple JSON lib called (Svenson and that was painless. The only thing I was forced to do was create my model class in Java – the rest of the project is written in Groovy. I’ve no idea why was that necessary, and didn’t want to look into it.

RabbitMQ

Further on the way is RabbitMQ, to which records are filled by a feeding middle-ware written in Groovy. Since I use ActiveMQ on a day-to-day basis, I’ve decided to try something new. This broker is a really nice piece of software. Being written in Erlang makes it really fast. What’s more it has some extensive capabilities and is easy to approach for anyone similar with messaging (JMS and friends). For such a lightweight product it is really powerful – implements AMQP!

CouchDB

From the broker’s queue messages are again fetched by a middle-ware just to be put into CouchDB view. This database is also written in Erlang. It’s very reliable, however the way it handles refreshing view isn’t the most pleasant one – performance-wise. Word of advice – if you’re on Debian derivative, be cautious with apt-repository version. It’s rather _ancient_. Also remember to add allow_jsonp = true to you config file /opt/couchbase/etc/couchdb/local.ini. It’s not enabled by default, and not having this set would result with empty responses from the CouchDB server. The problem here is, that the browser doesn’t allow quering a web server with hostname other than the one the script originates. More on this case here. Seems like my problem could be overcame by changing url in index.html and hostname couchdb listens on to the same address. I’ve also created a view, that would expose an event by key: view code

Presenting the dots

As a back-end I’ve done some JQuery based AJAX calls – nothing too fancy. All things necessary for presentation layer are in this file.

Things to consider

Please bear in mind that this whole application is rather a playground, not a full-fledged project!! After creating all the parts I have some doubts about some architectural decisions I made. I don’t think the security have been taken into account seriously enough. Also scalability was never an issue ;-) If you have some thoughts about any of the aspects mentioned in this post, please feel free to comment or contact me directly :) And also you may try the application by yourself – it’s on GitHub.

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DDevelopment & Design

How to automate tests with Groovy 2.0, Spock and Gradle

This is the launch of the 1st blog in my life, so cheers and have a nice reading!

y u no test?

Couple of years ago I wasn't a big fan of unit testing. It was obvious to me that well prepared unit tests are crucial though. I didn't known why exactly crucial yet then. I just felt they are important. My disliking to write automation tests was mostly related to the effort necessary to prepare them. Also a spaghetti code was easily spotted in test sources.

Some goodies at hand

Now I know! Test are crucial to get a better design and a confidence. Confidence to improve without a hesitation. Moreover, now I have the tool to make test automation easy as Sunday morning... I'm talking about the Spock Framework. If you got here probably already know what the Spock is, so I won't introduce it. Enough to say that Spock is an awesome unit testing tool which, thanks to Groovy AST Transformation, simplifies creation of tests greatly.

An obstacle

The point is, since a new major version of Groovy has been released (2.0), there is no matching version of Spock available yet.

What now?

Well, in a matter of fact there is such a version. It's still under development though. It can be obtained from this Maven repository. We can of course use the Maven to build a project and run tests. But why not to go even more "groovy" way? XML is not for humans, is it? Lets use Gradle.

The build file

Update: at the end of the post is updated version of the build file.
apply plugin: 'groovy'

apply plugin: 'idea'


def langLevel = 1.7


sourceCompatibility = langLevel

targetCompatibility = langLevel


group = 'com.tamashumi.example.testwithspock'

version = '0.1'


repositories {

    mavenLocal()

    mavenCentral()

    maven { url 'http://oss.sonatype.org/content/repositories/snapshots/' }

}


dependencies {

    groovy 'org.codehaus.groovy:groovy-all:2.0.1'

    testCompile 'org.spockframework:spock-core:0.7-groovy-2.0-SNAPSHOT'

}


idea {

    project {

        jdkName = langLevel

        languageLevel = langLevel

    }

}
As you can see the build.gradle file is almost self-explanatory. Groovy plugin is applied to compile groovy code. It needs groovy-all.jar - declared in version 2.0 at dependencies block just next to Spock in version 0.7. What's most important, mentioned Maven repository URL is added at repositories block.

Project structure and execution

Gradle's default project directory structure is similar to Maven's one. Unfortunately there is no 'create project' task and you have to create it by hand. It's not a big obstacle though. The structure you will create will more or less look as follows: 
<project root>

│

├── build.gradle

└── src

    ├── main

    │   ├── groovy

    └── test

        └── groovy
To build a project now you can type command gradle build or gradle test to only run tests.

How about Java?

You can test native Java code with Spock. Just add src/main/java directory and a following line to the build.gradle: 
apply plugin: 'java'
This way if you don't want or just can't deploy Groovy compiled stuff into your production JVM for any reason, still whole goodness of testing with Spock and Groovy is at your hand.

A silly-simple example

Just to show that it works, here you go with a basic example.

Java simple example class:

public class SimpleJavaClass {


    public int sumAll(int... args) {


        int sum = 0;


        for (int arg : args){

            sum += arg;

        }


        return sum;

    }

}

Groovy simple example class:

class SimpleGroovyClass {


    String concatenateAll(char separator, String... args) {


        args.join(separator as String)

    }

}

The test, uhm... I mean the Specification:

class JustASpecification extends Specification {


    @Unroll('Sums integers #integers into: #expectedResult')

    def "Can sum different amount of integers"() {


        given:

            def instance = new SimpleJavaClass()


        when:

            def result = instance.sumAll(* integers)


        then:

            result == expectedResult


        where:

            expectedResult | integers

            11             | [3, 3, 5]

            8              | [3, 5]

            254            | [2, 4, 8, 16, 32, 64, 128]

            22             | [7, 5, 6, 2, 2]

    }


    @Unroll('Concatenates strings #strings with separator "#separator" into: #expectedResult')

    def "Can concatenate different amount of integers with a specified separator"() {


        given:

            def instance = new SimpleGroovyClass()


        when:

            def result = instance.concatenateAll(separator, * strings)


        then:

            result == expectedResult


        where:

            expectedResult     | separator   | strings

            'Whasup dude?'     | ' ' as char | ['Whasup', 'dude?']

            '2012/09/15'       | '/' as char | ['2012', '09', '15']

            'nice-to-meet-you' | '-' as char | ['nice', 'to', 'meet', 'you']

    }

}
To run tests with Gradle simply execute command gradle test. Test reports can be found at <project root>/build/reports/tests/index.html and look kind a like this.


Please note that, thanks to @Unroll annotation, test is executed once per each parameters row in the 'table' at specification's where: block. This isn't a Java label, but a AST transformation magic.

IDE integration

Gradle's plugin for Iintellij Idea

I've added also Intellij Idea plugin for IDE project generation and some configuration for it (IDE's JDK name). To generate Idea's project files just run command: gradle idea There are available Eclipse and Netbeans plugins too, however I haven't tested them. Idea's one works well.

Intellij Idea's plugins for Gradle

Idea itself has a light Gradle support built-in on its own. To not get confused: Gradle has plugin for Idea and Idea has plugin for Gradle. To get even more 'pluginated', there is also JetGradle plugin within Idea. However I haven't found good reason for it's existence - well, maybe excluding one. It shows dependency tree. There is a bug though - JetGradle work's fine only for lang level 1.6. Strangely all the plugins together do not conflict each other. They even give complementary, quite useful tool set.

Running tests under IDE

Jest to add something sweet this is how Specification looks when run with jUnit  runner under Intellij Idea (right mouse button on JustASpecification class or whole folder of specification extending classes and select "Run ...". You'll see a nice view like this.

Building web application

If you need to build Java web application and bundle it as war archive just add plugin by typing the line 
apply plugin: 'war'
in the build.gradle file and create a directory src/main/webapp.

Want to know more?

If you haven't heard about Spock or Gradle before or just curious, check the following links:

What next?

The last thing left is to write the real production code you are about to test. No matter will it be Groovy or Java, I leave this to your need and invention. Of course, you are welcome to post a comments here. I'll answer or even write some more posts about the subject.

Important update

Spock version 0.7 has been released, so the above build file doesn't work anymore. It's easy to fix it though. Just remove last dash and a word SNAPSHOT from Spock dependency declaration. Other important thing is that now spock-core depends on groovy-all-2.0.5, so to avoid dependency conflict groovy dependency should be changed from version 2.0.1 to 2.0.5.
Besides oss.sonata.org snapshots maven repository can be removed. No obstacles any more and the build file now looks as follows: 
apply plugin: 'groovy'

apply plugin: 'idea'


def langLevel = 1.7


sourceCompatibility = langLevel

targetCompatibility = langLevel


group = 'com.tamashumi.example.testwithspock'

version = '0.1'


repositories {

    mavenLocal()

    mavenCentral()

}


dependencies {

    groovy 'org.codehaus.groovy:groovy-all:2.0.5'

    testCompile 'org.spockframework:spock-core:0.7-groovy-2.0'

}


idea {

    project {

        jdkName = langLevel

        languageLevel = langLevel

    }

}