DDevelopment & Design

Multi module Gradle project with IDE support

This article is a short how-to about multi-module project setup with usage of the Gradle automation build tool. Here’s how Rich Seller, a StackOverflow user, describes Gradle: Gradle promises to hit the sweet spot between Ant and Maven. It uses Ivy’s approach for dependency resolution. It allows for convention over configuration but also includes Ant tasks as first class citizens. It also wisely allows you to use existing Maven/Ivy repositories. So why would one use yet another JVM build tool such as Gradle? The answer is simple: to avoid frustration involved by Ant or Maven. Short story I was fooling around with some fresh proof of concept and needed a build tool. I’m pretty familiar with Maven so created project from an artifact, and opened the build file, pom.xml for further tuning. I had been using Grails with its own build system (similar to Gradle, btw) already for some time up then, so after quite a time without Maven, I looked on the pom.xml and found it to be really repulsive. Once again I felt clearly: XML is not for humans. After quick googling I found Gradle. It was still in beta (0.8 version) back then, but it’s configured with Groovy DSL and that’s what a human likes :) Where are we In the time Ant can be met but among IT guerrillas, Maven is still on top and couple of others like for example Ivy conquer for the best position, Gradle smoothly went into its mature age. It’s now available in 1.3 version, released at 20th of November 2012. I’m glad to recommend it to anyone looking for relief from XML configured tools, or for anyone just looking for simple, elastic and powerful build tool. Lets build I have already written about basic project structure so I skip this one, reminding only the basic project structure: <project root> │ ├── build.gradle └── src ├── main │ ├── java │ └── groovy │ └── test ├── java └── groovy Have I just referred myself for the 1st time? Achievement unlocked! ;) Gradle as most build tools is run from a command line with parameters. The main parameter for Gradle is a ‘task name’, for example we can run a command: gradle build. There is no ‘create project’ task, so the directory structure has to be created by hand. This isn’t a hassle though. Java and groovy sub-folders aren’t always mandatory. They depend on what compile plugin is used. Parent project Consider an example project ‘the-app’ of three modules, let say: database communication layer domain model and services layer web presentation layer Our project directory tree will look like: the-app │ ├── dao-layer │ └── src │ ├── domain-model │ └── src │ ├── web-frontend │ └── src │ ├── build.gradle └── settings.gradle the-app itself has no src sub-folder as its purpose is only to contain sub-projects and build configuration. If needed it could’ve been provided with own src though. To glue modules we need to fill settings.gradle file under the-app directory with a single line of content specifying module names: include 'dao-layer', 'domain-model', 'web-frontend' Now the gradle projects command can be executed to obtain such a result: :projects ------------------------------------------------------------ Root project ------------------------------------------------------------ Root project 'the-app' +--- Project ':dao-layer' +--- Project ':domain-model' \--- Project ':web-frontend' …so we know that Gradle noticed the modules. However gradle build command won’t run successful yet because build.gradle file is still empty. Sub project As in Maven we can create separate build config file per each module. Let say we starting from DAO layer. Thus we create a new file the-app/dao-layer/build.gradle with a line of basic build info (notice the new build.gradle was created under sub-project directory): apply plugin: 'java' This single line of config for any of modules is enough to execute gradle build command under the-app directory with following result: :dao-layer:compileJava :dao-layer:processResources UP-TO-DATE :dao-layer:classes :dao-layer:jar :dao-layer:assemble :dao-layer:compileTestJava UP-TO-DATE :dao-layer:processTestResources UP-TO-DATE :dao-layer:testClasses UP-TO-DATE :dao-layer:test :dao-layer:check :dao-layer:build BUILD SUCCESSFUL Total time: 3.256 secs To use Groovy plugin slightly more configuration is needed: apply plugin: 'groovy' repositories { mavenLocal() mavenCentral() } dependencies { groovy 'org.codehaus.groovy:groovy-all:2.0.5' } At lines 3 to 6 Maven repositories are set. At line 9 dependency with groovy library version is specified. Of course plugin as ‘java’, ‘groovy’ and many more can be mixed each other. If we have settings.gradle file and a build.gradle file for each module, there is no need for parent the-app/build.gradle file at all. Sure that’s true but we can go another, better way. One file to rule them all Instead of creating many build.gradle config files, one per each module, we can use only the parent’s one and make it a bit more juicy. So let us move the the-app/dao-layer/build.gradle a level up to the-app/build-gradle and fill it with new statements to achieve full project configuration: def langLevel = 1.7 allprojects { apply plugin: 'idea' group = 'com.tamashumi' version = '0.1' } subprojects { apply plugin: 'groovy' sourceCompatibility = langLevel targetCompatibility = langLevel repositories { mavenLocal() mavenCentral() } dependencies { groovy 'org.codehaus.groovy:groovy-all:2.0.5' testCompile 'org.spockframework:spock-core:0.7-groovy-2.0' } } project(':dao-layer') { dependencies { compile 'org.hibernate:hibernate-core:4.1.7.Final' } } project(':domain-model') { dependencies { compile project(':dao-layer') } } project(':web-frontend') { apply plugin: 'war' dependencies { compile project(':domain-model') compile 'org.springframework:spring-webmvc:3.1.2.RELEASE' } } idea { project { jdkName = langLevel languageLevel = langLevel } } At the beginning simple variable langLevel is declared. It’s worth knowing that we can use almost any Groovy code inside build.gradle file, statements like for example if conditions, for/while loops, closures, switch-case, etc… Quite an advantage over inflexible XML, isn’t it? Next the allProjects block. Any configuration placed in it will influence – what a surprise – all projects, so the parent itself and sub-projects (modules). Inside of the block we have the IDE (Intellij Idea) plugin applied which I wrote more about in previous article (look under “IDE Integration” heading). Enough to say that with this plugin applied here, command gradle idea will generate Idea’s project files with modules structure and dependencies. This works really well and plugins for other IDEs are available too. Remaining two lines at this block define group and version for the project, similar as this is done by Maven. After that subProjects block appears. It’s related to all modules but not the parent project. So here the Groovy language plugin is applied, as all modules are assumed to be written in Groovy. Below source and target language level are set. After that come references to standard Maven repositories. At the end of the block dependencies to groovy version and test library – Spock framework. Following blocks, project(‘:module-name’), are responsible for each module configuration. They may be omitted unless allProjects or subProjects configure what’s necessary for a specific module. In the example per module configuration goes as follow: Dao-layer module has dependency to an ORM library – Hibernate Domain-model module relies on dao-layer as a dependency. Keyword project is used here again for a reference to other module. Web-frontend applies ‘war’ plugin which build this module into java web archive. Besides it referes to domain-model module and also use Spring MVC framework dependency. At the end in idea block is basic info for IDE plugin. Those are parameters corresponding to the Idea’s project general settings visible on the following screen shot. jdkName should match the IDE’s SDK name otherwise it has to be set manually under IDE on each Idea’s project files (re)generation with gradle idea command. Is that it? In the matter of simplicity – yes. That’s enough to automate modular application build with custom configuration per module. Not a rocket science, huh? Think about Maven’s XML. It would take more effort to setup the same and still achieve less expressible configuration quite far from user-friendly. Check the online user guide for a lot of configuration possibilities or better download Gradle and see the sample projects. As a tasty bait take a look for this short choice of available plugins: java groovy scala cpp eclipse netbeans ida maven osgi war ear sonar project-report signing and more, 3rd party plugins…

This article is a short how-to about multi-module project setup with usage of the Gradle automation build tool.

Here’s how Rich Seller, a StackOverflow user, describes Gradle:

Gradle promises to hit the sweet spot between Ant and Maven. It uses Ivy’s approach for dependency resolution. It allows for convention over configuration but also includes Ant tasks as first class citizens. It also wisely allows you to use existing Maven/Ivy repositories.

So why would one use yet another JVM build tool such as Gradle? The answer is simple: to avoid frustration involved by Ant or Maven.

Short story

I was fooling around with some fresh proof of concept and needed a build tool. I’m pretty familiar with Maven so created project from an artifact, and opened the build file, pom.xml for further tuning.
I had been using Grails with its own build system (similar to Gradle, btw) already for some time up then, so after quite a time without Maven, I looked on the pom.xml and found it to be really repulsive.

Once again I felt clearly: XML is not for humans.

After quick googling I found Gradle. It was still in beta (0.8 version) back then, but it’s configured with Groovy DSL and that’s what a human likes :)

Where are we

In the time Ant can be met but among IT guerrillas, Maven is still on top and couple of others like for example Ivy conquer for the best position, Gradle smoothly went into its mature age. It’s now available in 1.3 version, released at 20th of November 2012. I’m glad to recommend it to anyone looking for relief from XML configured tools, or for anyone just looking for simple, elastic and powerful build tool.

Lets build

I have already written about basic project structure so I skip this one, reminding only the basic project structure:

<project root>
│
├── build.gradle
└── src
    ├── main
    │   ├── java
    │   └── groovy
    │
    └── test
        ├── java
        └── groovy

Have I just referred myself for the 1st time? Achievement unlocked! ;)

Gradle as most build tools is run from a command line with parameters. The main parameter for Gradle is a ‘task name’, for example we can run a command: gradle build.
There is no ‘create project’ task, so the directory structure has to be created by hand. This isn’t a hassle though.
Java and groovy sub-folders aren’t always mandatory. They depend on what compile plugin is used.

Parent project

Consider an example project ‘the-app’ of three modules, let say:

  1. database communication layer
  2. domain model and services layer
  3. web presentation layer

Our project directory tree will look like:

the-app
│
├── dao-layer
│   └── src
│
├── domain-model
│   └── src
│
├── web-frontend
│   └── src
│
├── build.gradle
└── settings.gradle

the-app itself has no src sub-folder as its purpose is only to contain sub-projects and build configuration. If needed it could’ve been provided with own src though.

To glue modules we need to fill settings.gradle file under the-app directory with a single line of content specifying module names:

include 'dao-layer', 'domain-model', 'web-frontend'

Now the gradle projects command can be executed to obtain such a result:

:projects
------------------------------------------------------------
Root project
------------------------------------------------------------
Root project 'the-app'
+--- Project ':dao-layer'
+--- Project ':domain-model'
\--- Project ':web-frontend'

…so we know that Gradle noticed the modules. However gradle build command won’t run successful yet because build.gradle file is still empty.

Sub project

As in Maven we can create separate build config file per each module. Let say we starting from DAO layer.
Thus we create a new file the-app/dao-layer/build.gradle with a line of basic build info (notice the new build.gradle was created under sub-project directory):

apply plugin: 'java'

This single line of config for any of modules is enough to execute gradle build command under the-app directory with following result:

:dao-layer:compileJava
:dao-layer:processResources UP-TO-DATE
:dao-layer:classes
:dao-layer:jar
:dao-layer:assemble
:dao-layer:compileTestJava UP-TO-DATE
:dao-layer:processTestResources UP-TO-DATE
:dao-layer:testClasses UP-TO-DATE
:dao-layer:test
:dao-layer:check
:dao-layer:build

BUILD SUCCESSFUL

Total time: 3.256 secs

To use Groovy plugin slightly more configuration is needed:

apply plugin: 'groovy'

repositories {
    mavenLocal()
    mavenCentral()
}

dependencies {
    groovy 'org.codehaus.groovy:groovy-all:2.0.5'
}

At lines 3 to 6 Maven repositories are set. At line 9 dependency with groovy library version is specified. Of course plugin as ‘java’, ‘groovy’ and many more can be mixed each other.

If we have settings.gradle file and a build.gradle file for each module, there is no need for parent the-app/build.gradle file at all. Sure that’s true but we can go another, better way.

One file to rule them all

Instead of creating many build.gradle config files, one per each module, we can use only the parent’s one and make it a bit more juicy. So let us move the the-app/dao-layer/build.gradle a level up to the-app/build-gradle and fill it with new statements to achieve full project configuration:

pipeline {
    agent any
    stages {
        stage('Unit Test') {
            steps {
                sh 'mvn clean test'
            }
        }
        stage('Deploy Standalone') {
            steps {
                sh 'mvn deploy -P standalone'
            }
        }
        stage('Deploy AnyPoint') {
            environment {
                ANYPOINT_CREDENTIALS = credentials('anypoint.credentials')
            }
            steps {
                sh 'mvn deploy -P arm -Darm.target.name=local-4.0.0-ee -Danypoint.username=${ANYPOINT_CREDENTIALS_USR}  -Danypoint.password=${ANYPOINT_CREDENTIALS_PSW}'
            }
        }
        stage('Deploy CloudHub') {
            environment {
                ANYPOINT_CREDENTIALS = credentials('anypoint.credentials')
            }
            steps {
                sh 'mvn deploy -P cloudhub -Dmule.version=4.0.0 -Danypoint.username=${ANYPOINT_CREDENTIALS_USR} -Danypoint.password=${ANYPOINT_CREDENTIALS_PSW}'
            }
        }
    }
}

At the beginning simple variable langLevel is declared. It’s worth knowing that we can use almost any Groovy code inside build.gradle file, statements like for example if conditions, for/while loops, closures, switch-case, etc… Quite an advantage over inflexible XML, isn’t it?

Next the allProjects block. Any configuration placed in it will influence – what a surprise – all projects, so the parent itself and sub-projects (modules). Inside of the block we have the IDE (Intellij Idea) plugin applied which I wrote more about in previous article (look under “IDE Integration” heading). Enough to say that with this plugin applied here, command gradle idea will generate Idea’s project files with modules structure and dependencies. This works really well and plugins for other IDEs are available too.
Remaining two lines at this block define group and version for the project, similar as this is done by Maven.

After that subProjects block appears. It’s related to all modules but not the parent project. So here the Groovy language plugin is applied, as all modules are assumed to be written in Groovy.
Below source and target language level are set.
After that come references to standard Maven repositories.
At the end of the block dependencies to groovy version and test library – Spock framework.

Following blocks, project(‘:module-name’), are responsible for each module configuration. They may be omitted unless allProjects or subProjects configure what’s necessary for a specific module. In the example per module configuration goes as follow:

  • Dao-layer module has dependency to an ORM library – Hibernate
  • Domain-model module relies on dao-layer as a dependency. Keyword project is used here again for a reference to other module.
  • Web-frontend applies ‘war’ plugin which build this module into java web archive. Besides it referes to domain-model module and also use Spring MVC framework dependency.

At the end in idea block is basic info for IDE plugin. Those are parameters corresponding to the Idea’s project general settings visible on the following screen shot.

jdkName should match the IDE’s SDK name otherwise it has to be set manually under IDE on each Idea’s project files (re)generation with gradle idea command.

Is that it?

In the matter of simplicity – yes. That’s enough to automate modular application build with custom configuration per module. Not a rocket science, huh? Think about Maven’s XML. It would take more effort to setup the same and still achieve less expressible configuration quite far from user-friendly.

Check the online user guide for a lot of configuration possibilities or better download Gradle and see the sample projects.
As a tasty bait take a look for this short choice of available plugins:

  • java
  • groovy
  • scala
  • cpp
  • eclipse
  • netbeans
  • ida
  • maven
  • osgi
  • war
  • ear
  • sonar
  • project-report
  • signing

and more, 3rd party plugins…

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Next article —

Use XMLs not groovy scripts with db migration plugin!

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DDevelopment & Design

Grails session timeout without XML

This article shows clean, non hacky way of configuring featureful event listeners for Grails application servlet context. Feat. HttpSessionListener as a Spring bean example with session timeout depending on whether user account is premium or not.

Common approaches

Speaking of session timeout config in Grails, a default approach is to install templates with a command. This way we got direct access to web.xml file. Also more unnecessary files are created. Despite that unnecessary files are unnecessary, we should also remember some other common knowledge: XML is not for humans.

Another, a bit more hacky, way is to create mysterious scripts/_Events.groovy file. Inside of which, by using not less enigmatic closure: eventWebXmlEnd = { filename -> ... }, we can parse and hack into web.xml with a help of XmlSlurper.
Even though lot of Grails plugins do it similar way, still it’s not really straightforward, is it? Besides, where’s the IDE support? Hello!?

Examples of both above ways can be seen on StackOverflow.

Simpler and cleaner way

By adding just a single line to the already generated init closure we have it done:
class BootStrap {


    def init = { servletContext ->    

        servletContext.addListener(OurListenerClass)    

    }    

}

Allrighty, this is enough to avoid XML. Sweets are served after the main course though :)

Listener as a Spring bean

Let us assume we have a requirement. Set a longer session timeout for premium user account.
Users are authenticated upon session creation through SSO.

To easy meet the requirements just instantiate the CustomTimeoutSessionListener as Spring bean at resources.groovy. We also going to need some source of the user custom session timeout. Let say a ConfigService.
beans = {    

    customTimeoutSessionListener(CustomTimeoutSessionListener) {    

        configService = ref('configService')    

    }    

}

With such approach BootStrap.groovy has to by slightly modified. To keep control on listener instantation, instead of passing listener class type, Spring bean is injected by Grails and the instance passed:
class BootStrap {


    def customTimeoutSessionListener


    def init = { servletContext ->    

        servletContext.addListener(customTimeoutSessionListener)

    }    

}

An example CustomTimeoutSessionListener implementation can look like:
import javax.servlet.http.HttpSessionEvent    

import javax.servlet.http.HttpSessionListener    

import your.app.ConfigService    


class CustomTimeoutSessionListener implements HttpSessionListener {    


    ConfigService configService


    @Override    

    void sessionCreated(HttpSessionEvent httpSessionEvent) {    

        httpSessionEvent.session.maxInactiveInterval = configService.sessionTimeoutSeconds

    }    


    @Override    

    void sessionDestroyed(HttpSessionEvent httpSessionEvent) { /* nothing to implement */ }    

}
Having at hand all power of the Spring IoC this is surely a good place to load some persisted user’s account stuff into the session or to notify any other adequate bean about user presence.

Wait, what about the user context?

Honest answer is: that depends on your case. Yet here’s an example of getSessionTimeoutMinutes() implementation using Spring Security:
import org.springframework.security.core.context.SecurityContextHolder    


class ConfigService {


    static final int 3H = 3 * 60 * 60

    static final int QUARTER = 15 * 60


    int getSessionTimeoutSeconds() {    


        String username = SecurityContextHolder.context?.authentication?.principal    

        def account = Account.findByUsername(username)    


        return account?.premium ? 3H : QUARTER

    }    

}
This example is simplified. Does not contain much of defensive programming. Just an assumption that principal is already set and is a String - unique username. Thanks to Grails convention our ConfigService is transactional so the Account domain class can use GORM dynamic finder.
OK, config fetching implementation details are out of scope here anyway. You can get, load, fetch, obtain from wherever you like to. Domain persistence, principal object, role config, external file and so on...

Any gotchas?

There is one. When running grails test command, servletContext comes as some mocked class instance without addListener method. Thus we going to have a MissingMethodException when running tests :(

Solution is typical:
def init = { servletContext ->

    if (Environment.current != Environment.TEST) {    

        servletContext.addListener(customTimeoutSessionListener)    

    }    

}
An unnecessary obstacle if you ask me. Should I submit a Jira issue about that?

TL;DR

Just implement a HttpSessionListener. Create a Spring bean of the listener. Inject it into BootStrap.groovy and call servletContext.addListener(injectedListener).