• Kotlin collections

    This post should have been the 5th in the Scala vs Kotlin serie.

    Unfortunately, I must admit I have a hard time reading the documentation of Scala collections e.g.:

    trait LinearSeq [+A] extends Seq[A] with collection.LinearSeq[A] with GenericTraversableTemplate[A, LinearSeq] with LinearSeqLike[A, LinearSeq[A]]

    Hence, I will only describe collections from the Kotlin side.


    At the root of Kotlin’s Collection API lies the Iterator interface, similar to Java’s. But the similitude stops after that. java.util.ListIterator features are broken down into different contracts:

    1. ListIterator to move the iterator index forward and backward
    2. MutableIterator to remove content from the iterator
    3. MutableListIterator inherits from the 2 interfaces above to mimic the entire contract of java.util.ListIterator
    Iterator API

    Collection, List and Set

    The hierarchy of collections in Kotlin are very similar as in Java: Collection, List and Set. (I won’t detail maps, but they follow the same design). The only, but huge, difference is that it’s divided between mutable and immutable types. Mutable types have methods to change their contents (_e.g. add() and `set()), while immutable types don’t.

    Of course, the hierarchy is a bit more detailed compared to Java, but that’s expected from a language that benefits from its parent’s experience.

    Collection, List and Set


    IMHO, the important bit about Kotlin collections is not their hierarchy - though it’s important to understand about the difference between mutable and immutable.

    As Java developers know, there’s no such things as out-of-the-box immutable collection types in Java. When an immutable collection is required, the mutable collection must be wrapped into an unmodifiable type via a call to the relevant Collections.unmodifiableXXX(). But unmodifiable types are not public, they are private in Collections: types returned are generic ones (List or Set interfaces). It means they implement all methods of the standard collections. Immutability comes from the mutable-related methods throwing exceptions: at compile time, there’s no way to differentiate between a mutable and an immutable collection.

    On the opposite, Kotlin offers a clean separation between mutable and immutable types. It also provides dedicated functions to create objects of the relevant type:

    Collections-creating functions

    As opposed to Scala, Kotlin doesn’t implement its own collection types, it reuses those from Java. That means that even when the compile-time type is immutable, the runtime type is always mutable. The downside is that it’s possible to change the collection elements by casting it to the correct runtime type. IMHO, this is no more severe than what allows standard reflection. There are several advantages, though:

    1. Faster time-to-market
    2. Java collection types benefited from years of improvement
    3. The underlying implementation can be changed in the future with full backward compatibility
    Categories: Development Tags: API
  • A use-case for Google Fusion Tables

    I’ve been traveling somewhat during the last few years, and I wanted to check on a map which countries I already visited. There’s one requirement: I want the whole area of countries I’ve visited to be highlighted. There are a couple of solutions for that:

    The Elastic stack

    Data can be stored in ElasticSearch, and there’s one world map visualization available for the Kibana dashboard. This works, but:

    1. The visualization handles geo-location, but no highlighting an entire country
    2. It requires some setup, and I’m a developer - read that I’m lazy.
    Dedicated app

    To be honest, I didn’t search but I assume "there is an app for that". But by using a dedicated app, you’re not the owner of your own data anymore and that doesn’t suit me.

    Google Maps

    Google Maps allows to add layers, and dedicated data. This solution would be a great fit, if it was possible to easily highlight countries. And still, there’s still a lot of JavaScript to write.

    Fusion Tables is an experimental service offered by Google.

    Creating the table

    While it’s possible to input the data directly into Fusion Tables, it’s easier to do that in a simple Google Spreadsheet. The following is sample data:

    Date Country Place Type Event




















    Voxxed Days

    Such a spreadsheet can easily be imported into Fusion Tables.

    1. Connect Fusion Tables on Google Drive. From the Drive’s homepage, go on My Drive ▸ More ▸ Connect More Apps. Search for "fusion". Click on Connect.
      Connect Google Fusion Table on Drive
    2. Create a new Fusion Tables document. From the Drive’s homepage, click on New ▸ More ▸ Google Fusion Tables. Then select Google Spreadsheet.
      Import Google Spreadsheet into Fusion Tables
    3. Select the desired spreadsheet and click Select.
      Import new table
    4. Name the table accordingly and click Finish. It yields something akin to the following:
      Import new table

    Out-of-the-box, there’s a Map of Country tab that displays each data line on a world map. Unfortunately, it’s a simple dot at the center of the country. It doesn’t fulfil the initial requirement of highlighting the entire country area.

    Default world map view

    Changing the Location field to "Place" instead of "Country" will place dots at the correct location instead of the country center, but still no highlighting.

    Merging multiple Fusion Tables

    Fusion Tables support geometries that can be defined using the Keyhole Markup Language format. That can fulfil the highlighting requirement. Yet, that would mean defining the geometry of each country visited manually; it requires an effort I’m not prepared to make. Fortunately, it’s possible to "join" multiple tables - it’s called merging. Merging creates a new table, with both tables associated in it. Even better, if any of the initial table data changes, it’s reflected in the merged table.

    Good news: there’s an existing publicly accessible table defining all country geographies. Let’s merge the existing table with it in File ▸ Merge. In the Or paste a web address here field, paste the URL from the world countries above. Click Next. The opening pop-up requires to define the "join" columns of the tables.

    Default world map view

    Click Next. In the opening pop-up, tick the checkboxes of columns that will be part of the merged table. Click Merge. Wait for the merge to happen. Click View table.

    Now, on the world map tab, changing the Location field to "geometry" yields the expected result.

    Highlighted world map view

    At this point, the requirement is fulfilled. Further refinements would be to access the data via its REST API.


    Fusion Tables is a no-fluff, just-stuff cloud service that allows to easily display data in various ways. With its ability to join on other tables, it’s easy to re-use existing tabular data.

    Categories: Technical Tags: databasedata visualization
  • Scala vs Kotlin: Multiple Inheritance and the Diamond problem

    This post is the 4th part in the serie dedicated to comparing Scala and Kotlin:

    1. Pimp my library
    2. Operator overloading
    3. inline and infix

    Inheritance is one of the basic tenet of Object-Oriented Programming, along with encapsulation and polymorphism. Alongside simple inheritance, there is multiple inheritance:

    Multiple inheritance is a feature of some object-oriented computer programming languages in which an object or class can inherit characteristics and features from more than one parent object or parent class. It is distinct from single inheritance, where an object or class may only inherit from one particular object or class.

    C++ is famous for allowing multiple inheritance, and describing the diamond problem. It states that there’s an issue when a child class inherits from multiple classes that have the same method.

    C++ has its own way of coping with the diamond problem. In order to avoid it, Java completely disallows multiple-inheritance. Let’s check how Scala and Kotlin fare.


    Scala doesn’t allow for multiple inheritance per se, but allows to extends multiple traits.

    Traits are used to share interfaces and fields between classes. They are similar to Java 8’s interfaces. Classes and objects can extend traits but traits cannot be instantiated and therefore have no parameters.
    --Scala Documentation

    The above diagram translates into the following code:

    trait Openable {
      def open() { ... }
    trait Window extends Openable {
      def open() { ... }
    trait Door extends Openable {
      def open() { ... }
    class WindowDoor extends Door with Window {

    Scala resolves the diamond problem by defining one main super trait - whose code will be used, among all super traits. The main one is set with the extends keyword, while other are with with.

    Hence, in the above example, WindowDoor.open() will by default use code from Door.open(). Of course, nothing prevents us from overriding the method.


    As in Scala, Kotlin doesn’t allow to extend multiple super classes. Yet, interfaces can have concrete functions.

    Interfaces in Kotlin are very similar to Java 8. They can contain declarations of abstract methods, as well as method implementations. What makes them different from abstract classes is that interfaces cannot store state.
    --Kotlin Documentation

    The following is the code above translated in Kotlin:

    interface Openable {
        fun open() { ... }
    interface Window : Openable {
        override fun open() { ... }
    interface Door : Openable {
        override fun open() { ... }
    class WindowDoor : Door, Window {
        override fun open() { ... }

    Kotlin takes another path to solve the diamond problem: explicit overriding. The compiler detects diamond occurrences, and fires an error if a function is implemented by multiple parent classes. To fix this, the developer must explicitly code the desired behavior.


    While Scala’s approach is more elegant, Kotlin’s is consistent with its philosophy: being explicit and readable before being concise.

    Categories: Development Tags: scalakotlin
  • Managing publications with Jekyll

    Jekyll logo

    Some time ago, I migrated my WordPress blog to Jekyll for different reasons including performance, security, and hosting costs - but mainly because I lost too much time maintaining the platform and the plugins up-to-date. So far, I’m very happy about the result.

    But I had to change the way I’m writing posts I intend to publish later. In WordPress, the process is very simple: write a draft anytime you want; edit it to your heart’s content and when ready, hit publish. Done.

    Jekyll is quite different. The site is generated statically so that there’s no magical button to click in order to publish. Posts are written in Markdown (or Asciidoc): in order to get the HTML, the site needs to be generated.

    There are several ways to manage the management of publications with Jekyll. This post is dedicated to a few of them.

    Using future dates

    Posts are stored in a specific _posts folder. Each post is tagged with a publish date. When generating the HTML site, only posts whose publish date are not after the date of the day are generated.

    Given the above behavior, the easiest way to publish is just to create posts with a date set in the future. That way, on D-day, re-generating the site will publish the new post.

    In order to preview the generated post before that date, the generation process can be launched with the --future option.

    This strategy requires to know the date a post will be published in advance. If no publication date can be planned, the next strategy is useful.

    Using drafts

    In order for a post to be generated, it needs to have its type meta-data set to…​ post. This is the case by default.

    But if the type is set to draft, they won’t be generated unless Jekyll build is launched with the --drafts option. For better management, all such drafts can (should?) be stored in a _drafts folder.

    When one wants to publish a draft, change the type from draft to post - and optionally move it to the main posts folder.

    Using a VCS

    When using a Version Control System - and I do hope it’s the case, posts/drafts can also be written in a specific publication branch e.g. feature/new_posts.

    Changing branch will preview those new posts with no consequence to the master branch. Publishing requires just cherry-picking the commit of the wanted post. Of course, it’s possible to combine cherry-picking with the above options to achieve full flexibility.

    As an added benefit to cherry-pick new publications from a dedicated branch, this branch can be cleaned up from time to time to keep the number of posts low, and the generation time as well.

    My way

    That’s currently how I manage my publishing flow:

    If I planned a specific publication date
    1. Commit the new post in the publication branch, feature/new_posts
    2. Cherry-pick it the day of the publication
    3. Generate the site
    If there’s none
    1. Same as above
    2. Optionally move the file from the _drafts to the _posts folder
    3. Amend the cherry-pick to:
      • Change the type from draft to post
      • Add the correct date
    4. Generate the site as above
    This way works quite well for multiple writers, with the editing process handled through Pull Requests.
    Categories: Technical Tags: jekyll
  • A SonarQube plugin for Kotlin - Creating the plugin proper

    SonarQube Continuous Inspection logo

    This is the 3rd post in a serie about creating a SonarQube plugin for the Kotlin language:

    • The first post was about creating the parsing code itself.
    • The 2nd post detailed how to use the parsing code to check for two rules.

    In this final post, we will be creating the plugin proper using the code of the 2 previous posts.

    The Sonar model

    The Sonar model is based on the following abstractions:

    Entry-point for plugins to inject extensions into SonarQube
    A plugin points to the other abstraction instances to make the SonarQube platform load them
    Pretty self-explanatory. Represents a language - Java, C#, Kotlin, etc.
    Define a profile which is automatically registered during sonar startup
    A profile is a mutable set of fully-configured rules. While not strictly necessary, having a Sonar profile pre-registered allows users to analyze their code without further configuration. Every language plugin offered by Sonar has at least one profile attached.
    Defines some coding rules of the same repository
    Defines an immutable set of rule definitions into a repository. While a rule definition defines available parameters, default severity, etc. the rule (from the profile) defines the exact value for parameters, a specific severity, etc. In short, the rule implements the role definition.
    A sensor is invoked once for each module of a project, starting from leaf modules. The sensor can parse a flat file, connect to a web server... Sensors are used to add measure and issues at file level.
    The sensor is the entry-point where the magic happens.

    Starting to code the plugin

    Every abstraction above needs a concrete subclass. Note that the API classes themselves are all fairly decoupled. It’s the role of the Plugin child class to bind them together.

    class KotlinPlugin : Plugin {
        override fun define(context: Context) {

    Most of the code is mainly boilerplate, but for ANTLR code.

    Wiring the ANTLR parsing code

    On one hand, the parsing code is based on generated listeners. On the other hand, the sensor is the entry-point to the SonarQube parsing. There’s a need for a bridge between the 2.

    In the first article, we used an existing grammar for Kotlin to generate parsing code. SonarQube provides its own lexer/parser generating tool (SonarSource Language Recognizer). A sizeable part of the plugin API is based on it. Describing the grammar is no small feat for any real-life language, so I preferred to design my own adapter code instead.

    Subclass of the generated ANTLR KotlinParserBaseListener. It has an attribute to store violations, and a method to add such a violation.
    The violation only contains the line number, as the rest of the required information will be stored into a KotlinCheck instance.
    Abstract class that wraps an AbstractKotlinParserListener. Defines what constitutes a violation. It handles the ANTLR boilerplate code itself.

    This can be represented as the following:

    The sensor proper

    The general pseudo-code should look something akin to:

    FOR EACH source file
        FOR EACH rule
            Check for violation of the rule
            FOR EACH violation
                Call the SonarQube REST API to create a violation in the datastore

    This translates as:

    class KotlinSensor(private val fs: FileSystem) : Sensor {
        val sources: Iterable<InputFile>
            get() = fs.inputFiles(MAIN)
        override fun execute(context: SensorContext) {
            sources.forEach { inputFile: InputFile ->
                KotlinChecks.checks.forEach { check ->
                    val violations = check.violations(inputFile.file())
                    violations.forEach { (lineNumber) ->
                        with(context.newIssue().forRule(check.ruleKey())) {
                            val location = newLocation().apply {

    Finally, the run

    Let’s create a dummy Maven project with 2 classes, Test1 and Test2 in one Test.kt file, with the same code as last week. Running mvn sonar:sonar yields the following output:

    Et voilà, our first SonarQube plugin for Kotlin, checking for our custom-developed violations.

    Of course, it has (a lot of) room for improvements:

    • Rules need to be activated through the GUI - I couldn’t find how to do it programmatically
    • Adding new rules needs updates to the plugin. Rules in 3rd-party plugins are not added automatically, as could be the case for standard SonarQube plugins.
    • So far, code located outside of classes seems not to be parsed.
    • The walk through the parse tree is executed for every check. An obvious performance gain would be to walk only once and do every check from there.
    • A lof of the above improvements could be achieved by replacing ANTLR’s grammar with Sonar’s internal SSLR
    • No tests…

    That still makes the project a nice starting point for a full-fledged Kotlin plugin. Pull requests are welcome!

    Categories: Technical Tags: code qualitySonarQubeKotlinpluginANTLR
  • A SonarQube plugin for Kotlin - Analyzing with ANTLR

    SonarQube Continuous Inspection logo

    Last week, we used ANTLR to generate a library to be able to analyze Kotlin code. It’s time to use the generated API to check for specific patterns.

    API overview

    Let’s start by having a look at the generated API:

    • KotlinLexer: Executes lexical analysis.
    • KotlinParser: Wraps classes representing all Kotlin tokens, and handles parsing errors.
    • KotlinParserVisitor: Contract for implementing the Visitor pattern on Kotlin code. KotlinParserBaseVisitor is its empty implementation, to ease the creation of subclasses.
    • KotlinParserListener: Contract for callback-related code when visiting Kotlin code, with KotlinParserBaseListener its empty implementation.

    Class diagrams are not the greatest diagrams to ease the writing of code. The following snippet is a very crude analysis implementation. I’ll be using Kotlin, but any JVM language interoperable with Java could be used:

    val stream = CharStreams.fromString("fun main(args : Array<String>) {}")
    val lexer = KotlinLexer(stream)
    val tokens = CommonTokenStream(lexer)
    val parser = KotlinParser(tokens)
    val context = parser.kotlinFile()
    ParseTreeWalker().apply {
        walk(object : KotlinParserBaseListener() {
            override fun enterFunctionDeclaration(ctx: KotlinParser.FunctionDeclarationContext) {
        }, context)

    Here’s the explanation:

    1. Create a CharStream to feed the lexer on the next line. The CharStreams offers plenty of static fromXXX() methods, each accepting a different type (String, InputStream, etc.)
    2. Instantiate the lexer, with the stream
    3. Instantiate a token stream over the lexer. The class provides streaming capabilities over the lexer.
    4. Instantiate the parser, with the token stream
    5. Define the entry point into the code. In that case, it’s a Kotlin file - and probably will be for the plugin.
    6. Create the overall walker that will visit each node in turn
    7. Start the visiting process by calling walk and passing the desired behavior as an object
    8. Override the desired function. Here, it will be invoked every time a function node is entered
    9. Do whatever is desired e.g. print the function name

    Obviously, lines 1 to 7 are just boilerplate to wire all components together. The behavior that need to be implemented should replace lines 8 and 9.

    First simple check

    In Kotlin, if a function returns Unit - nothing, then explicitly declaring its return type is optional. It would be a great rule to check that there’s no such explicit return. The following snippets, both valid Kotlin code, are equivalent - one with an explicit return type and the other without:

    fun hello1(): Unit {
    fun hello2() {

    Let’s use grun to graphically display the parse tree (grun was explained in the previous post). It yields the following:

    As can be seen, the snippet with an explicit return type has a type branch under functionDeclaration. This is confirmed by the snippet from the KotlinParser ANTLR grammar file:

      : modifiers 'fun' typeParameters?
          (type '.' | annotations)?
          typeParameters? valueParameters (':' type)?

    The rule should check that if such a return type exists, then it shouldn’t be Unit. Let’s update the above code with the desired effect:

    ParseTreeWalker().apply {
        walk(object : KotlinParserBaseListener() {
            override fun enterFunctionDeclaration(ctx: KotlinParser.FunctionDeclarationContext) {
                if (ctx.type().isNotEmpty()) {
                    val typeContext = ctx.type(0)
                    with(typeContext.typeDescriptor().userType().simpleUserType()) {
                        val typeName = this[0].SimpleName()
                        if (typeName.symbol.text == "Unit") {
                            println("Found Unit as explicit return type " +
                            	"in function ${ctx.SimpleName()} at line ${typeName.symbol.line}")
        }, context)

    Here’s the explanation:

    • Line 4: Check there’s an explicit return type, whatever it is
    • Line 5: Strangely enough, the grammar allows for a multi-valued return type. Just take the first one.
    • Line 6: Follow the parse tree up to the final type name - refer to the above parse tree screenshot for a graphical representation of the path.
    • Line 8: Check that the return type is Unit
    • Line 9: Prints a message in the console. In the next step, we will call the SonarQube API there.

    Running the above code correctly yields the following output:

    Found Unit as explicit return type in function hello1 at line 1

    A more advanced check

    In Kotlin, the following snippets are all equivalent:

    fun hello1(name: String): String {
        return "Hello $name"
    fun hello2(name: String): String = "Hello $name"
    fun hello3(name: String) = "Hello $name"

    Note that in the last case, the return type can be inferred by the compiler and omitted by the developer. That would make a good check: in the case of a expression body, the return type should be omitted. The same technique as above can be used:

    1. Display the parse tree from the snippet using grun:

    2. Check for differences. Obviously:
      • Functions that do not have an explicit return type miss a type node in the functionDeclaration tree, as above
      • Functions with an expression body have a functionBody whose first child is = and whose second child is an expression
    3. Refer to the initial grammar, to make sure all cases are covered.
        : block
        | '=' expression
    4. Code!
    ParseTreeWalker().apply {
        walk(object : KotlinParserBaseListener() {
            override fun enterFunctionDeclaration(ctx: KotlinParser.FunctionDeclarationContext) {
                val bodyChildren = ctx.functionBody().children
                if (bodyChildren.size > 1
                        && bodyChildren[0] is TerminalNode && bodyChildren[0].text == "="
                        && ctx.type().isNotEmpty()) {
                    val firstChild = bodyChildren[0] as TerminalNode
                    println("Found explicit return type for expression body " +
                            "in function ${ctx.SimpleName()} at line ${firstChild.symbol.line}")
        }, context)

    The code is pretty self-explanatory and yields the following:

    Found explicit return type for expression body in function hello2 at line 5
    Categories: Technical Tags: code qualitySonarQubeKotlinplugin
  • A SonarQube plugin for Kotlin - Paving the way

    SonarQube Continuous Inspection logo

    Since I started my journey into Kotlin, I wanted to use the same libraries and tools I use in Java. For libraries - Spring Boot, Mockito, etc., it’s straightforward as Kotlin is 100% interoperable with Java. For tools, well, it depends. For example, Jenkins works flawlessly, while SonarQube lacks a dedicated plugin. The SonarSource team has limited resources: Kotlin, though on the rise - and even more so since Google I/O 17, is not in their pipe. This post serie is about creating such a plugin, and this first post is about parsing Kotlin code.


    In the realm of code parsing, ANTLR is a clear leader in the JVM world.

    ANTLR (ANother Tool for Language Recognition) is a powerful parser generator for reading, processing, executing, or translating structured text or binary files. It’s widely used to build languages, tools, and frameworks. From a grammar, ANTLR generates a parser that can build and walk parse trees.

    Designing the grammar

    ANTLR is able to generate parsing code for any language thanks to a dedicated grammar file. However, creating such a grammar from scratch for regular languages is not trivial. Fortunately, thanks to the power of the community, a grammar for Kotlin already exists on Github.

    With this existing grammar, ANTLR is able to generate Java parsing code to be used by the SonarQube plugin. The steps are the following:

    • Clone the Github repository
      git clone git@github.com:antlr/grammars-v4.git
    • By default, classes will be generated under the root package, which is discouraged. To change that default:
      • Create a src/main/antlr4/<fully>/<qualified>/<package> folder such as src/main/antlr4/ch/frankel/sonarqube/kotlin/api
      • Move the g4 files there
      • In the POM, remove the sourceDirectory and includes bits from the antlr4-maven-plugin configuration to use the default
    • Build and install the JAR in the local Maven repo
      cd grammars-v4/kotlin
      mvn install

    This should generate a KotlinLexer and a KotlinParser class, as well as several related classes in target/classes. As Maven goes, it also packages them in a JAR named kotlin-1.0-SNAPSHOT.jar in the target folder - and in the local Maven repo as well.

    Testing the parsing code

    To test the parsing code, one can use the grun command. It’s an alias for the following:

    java -Xmx500M -cp "<path/to/antlr/complete/>.jar:$CLASSPATH" org.antlr.v4.Tool

    Create the alias manually or install the antlr package via Homebrew on OSX.

    With grun, Kotlin code can parsed then displayed in different ways, textual and graphical. The following expects an input in the console:

    cd target/classes
    grun Kotlin kotlinFile -tree

    After having typed valid Kotlin code, it yields its parse tree in text. By replacing the -tree option with the -gui option, it displays the tree graphically instead. For example, the following tree comes from this snippet:

    fun main(args : Array<String>) { 
        val firstName : String = "Adam"
        val name : String? = firstName 

    In order for the JAR to be used later in the SonarQube plugin, it has been deployed on Bintray. In the next post, we will be doing proper code analysis to check for violations.

    Categories: Technical Tags: code qualitySonarQubeKotlinpluginANTLR
  • It depends

    Light bulb

    In the industry, there’s this widespread joke. Whatever the question you ask a consultant, the answer will be:

    It depends.

    This joke is meant to highlight that consultants never give a straight answer to a simple question, because they don’t want to take any responsibility. While I understand the frustration of the business when faced with this situation, I’d like to write about the other side of the fence.

    Let’s enlarge the scope: in the IT industry, it’s probably more about every developer rather than only consultants. But why is this answer so common? For one single reason: if the question - deemed simple by the person asking, doesn’t provide enough context - and they rarely do, then the answer cannot be any other.

    Let’s highlight that with a simple question:

    What’s the best transportation?

    Guess what? There’s no right answer to that, because no context has been provided. For example, context parameters that could help refine the answer include:

    • the distance, do you expect to move 200 meters or 200 kilometers?
    • the nature of the terrain, road vs. land vs. water
    • the time constraint
    • the expected comfort level
    • the cost
    • the physical condition - it’s hard to consider running/biking when in bad shape
    • for some, the pollution
    • etc.

    I hope this pretty down-to-earth example makes those who ask questions realize that the quality of the answer is heavily constrained by the quality of the question - garbage in, garbage out.

    I could stop there and everyone would ponder how stupid the business is, but every coin has 2 sides. In general, developers don’t react in a constructive way to context-less questions: "It depends", "I don’t know", "I have no clue", "Nobody can answer that", or even "That’s a stupid question" are comments I’ve heard already. If you’re a developer and reading this post, know it’s your job to guide the business. What do they know about scalability, databases, and so on? Probably nothing because it’s not their job. So, pro-actively guide them through questions. With the example above, the following could be an actual dialog:

    "What’s the best transportation?
    - Where do you want to go?
    - Munich
    - Ok, what’s your starting point?
    - Home
    - Ah…​ Where’s you home located?
    - Germany
    - Which city in Germany?
    - etc."

    I’m very aware that most developers - including myself, don’t like to talk to the business so much. I mean, that’s the reason most of us chose to work in IT, because we are more comfortable talking to computers than people. But in essence, it changes nothing.

    Be professional, ask for context instead of ditching the question.

    Categories: Miscellaneous Tags: communication
  • What archive format should you use, WAR or JAR?

    Female hitting a male with boxing gloves on

    Some time ago, RAM and disk space were scarce resources. At that time, the widespread strategy was to host different applications onto the same platform. That was the golden age of the application server. I wrote in an earlier post that the current tendency toward cheaper resources will make it obsolete, in the short or long term. However, a technology trend might bring it back in favor.

    Having an application server is good when infrastructure resources are expensive, and sharing them across apps brings a significant cost decrease. On the down side, it requires a deep insight into the load of each application sharing the same resources, as well as skilled sysadmins that can deploy on the same app server applications that are compatible. For old-timers, does an application requiring to be run alone because it mismanages resources ring a bell? When infrastructure costs decrease, laziness and aversion to risk take precedence over them, and hosting a single app on an application server become the norm. At that point, the next logical step is to consider why application servers as dedicated components are still required. It seems the Spring guys came to the same conclusion, for Spring Boot applications' default mode is to package executable JARs - also known as Fat JARs. Those apps can be run as java -jar fat.jar. Hence the famous:

    Make JAR, not WAR

    — Josh Long

    I’m still not completely sold on that, as I believe it too easily discards the expertise of most Ops teams regarding application servers' management. However, one compelling argument about Fat JARs is that since the booting technology is in charge of app management from the start, it can handle load classes in any way it wants. For example, with Dev Tools, Spring Boot provides a mechanism based on two classloaders, one for libraries and one for classes, so that classes can be changed and reloaded without restarting the whole JVM - a neat trick that gives a very fast feedback loop at each code change.

    It wrongly thought that application server providers were still stuck with the legacy way - thanks to Ivar Grimstad for making me aware of this option (a good reason to visit talks that do not necessarily target your interest at conferences). Wildlfy, TomEE and other app server implementers can be configured to package Fat JARs as well, albeit with one huge difference: there’s nothing like Spring Dev Tools, so the restart of the whole app server is still required when code changes. The only alternative for faster feedback regarding those changes is to work at a lower level e.g. JRebel licenses for the whole team. However, there’s still one reason to use WAR archives, and that reason is Docker. By providing a common app server Docker image as a base image, one just needs to add one’s WAR on top of it, thus making the WAR image quite lightweight. And this cannot be achieved (yet?) with the JAR approach.

    Note that it’s not Spring Boot vs JavaEE but mostly JAR vs WAR, as Spring Boot is perfectly able to package either format, while many app server providers as well. As I pointed out above, the only missing piece is for the later to reload classes instead of restarting the whole JVM when a change occurs - but I believe it will happen at some point.

    Choosing between the WAR and the JAR approaches is highly dependent whether the company values more fast feedback cycles during development or more optimized and manageable Docker images.

    Categories: Java Tags: WARJARJavaEESpring Bootarchive
  • Why are you testing your software?

    Burned bus at a bus stop

    15 years ago, automated tests didn’t exist in the Java ecosystem. One had to build the application and painfully test it manually by using it. I was later introduced to the practice of adding a main method to every class and putting some testing code there. That was only marginally better, as it still required to manually run the methods. Then came JUnit, the reference unit testing framework in Java which brought test execution automation. At that point, I had to convince teams I was part of that we had to use it to create an automated tests harness to prevent regression bugs. Later, this became an expectation: no tests meant no changes in the code for fear of breaking something.

    More recently, however, it happened that I sometimes have to advocate for the opposite: not write too many tests. Yes, you read that well, and yet I’m no turncoat. The reason for this lies in the title of the post: why are you testing your software? It may sound like the answer to this question is pretty obvious - but it’s not, and the answer is tightly coupled to the concept of quality.

    In the context of software engineering, software quality refers to two related but distinct notions that exist wherever quality is defined in a business context:

    • Software functional quality reflects how well it complies with or conforms to a given design, based on functional requirements or specifications. That attribute can also be described as the fitness for purpose of a piece of software or how it compares to competitors in the marketplace as a worthwhile product. It is the degree to which the correct software was produced.
    • Software structural quality refers to how it meets non-functional requirements that support the delivery of the functional requirements, such as robustness or maintainability. It is the degree to which the software was produced correctly.
    — Wikipedia

    Before answering the question of the why, let’s consider some reason why not I’ve already been confronted to:

    • Because everyone does it
    • Because the boss/the lead/colleagues/authority figures say so
    • To achieve 100% of code coverage
    • To achieve more code coverage than another team/colleague
    • And so on, and so forth

    All in all, those "reasons" boil down to either plain cargo culting or mistaking a metric for the goal. Which brings us back to the question, why do you test software?

    The only valid reason for testing is that resources spent in making sure the software conforms to non-/functional requirements will be less over the course of time than the resources spent if not done.

    That’s pure and simple Return Over Investment. If ROI is positive, do test; if it’s negative, don’t. It’s as simple as that.

    Perfect is the enemy of good

    The real difficulty lies in estimating the cost of testing vs the cost of not testing. The following is a non-exhaustive list of ROI-influencing parameters:


    No bugs are allowed in some industries e.g. medical, airplanes, banks without serious consequences to the business, while this is less critical for others such as mobile gaming.

    Estimated lifespan of the app

    the longer the lifespan of an app, the better the ROI because the same amount of testing code will yield more times e.g. nearly no tests for one-shot single-event apps vs. more traditional testing for tradition business apps running for a decade or so.

    Nature of the app

    some technologies are more mature than others, allowing for easier automated testing. The testing echosystem around webapps is richer than around native or mobile apps.

    Architecture of the app

    The more distributed the app, the harder it is to test. In particular, the migration from monoliths to microservices has some interesting side-effects on the testing side. It’s easier to test each component separately, but harder to test the whole system. Also, testing specific scenarios in clustered/distributed environments, such as node failure in a cluster, increase the overall cost.

    Nature and number of infrastructure dependencies

    The higher the number of dependencies, the more test doubles are required to test the app in isolation, which in turns drive up testing costs. Also, some dependencies are more widespread e.g. databases and web services, with many available tools while some are not e.g. FTP servers.

    Size of the app

    Of course, the bigger the size of the app, the bigger the number of possible combinations that needs to be tested.

    Maturity of the developers, and the size of the team(s)

    Obviously, developers range from the ones who don’t care about testing to those who integrate testing requirements in their code from the start. Also, just for developers, adding more testers is subject to the law of diminishing returns.

    Nature of the tests

    I don’t want to start a war, suffice to say there are many kinds of tests - unit, integration, end-to-end, performance, penetration, etc. Each one is good at one specific thing, and has pros and cons. Get to know them and use them wisely.

    Strength of the type system

    Developing in dynamically-typed languages require more tests to handle the job of the compiler in comparison to more statically-typed languages.

    While it’s good to listen to other’s advices - including well-established authority figures and this post, it’s up to every delivery team to draw the line between not enough testing and too much testing according to its own context.

    Categories: Java Tags: code qualitytestingcode coverage