openxava / documentation / Configuration for Kotlin

Since v7.0 you can easily develop OpenXava projects with Kotlin using OpenXava Studio, Eclipse, IntelliJ IDEA and others. Kotlin is the most used language in Android applications and can be developed on JVM or JS. One of the Kotlin's features is that it's designed to fully interoperate with Java syntax, it means that you can compile both codes and have them interact with each other without any problems.

Add dependencies in pom.xml

After created an OpenXava project (how to), you must define the Kotlin version in properties in the pom.xml file located in the root folder of the project:

<properties>
    <kotlin.version>1.8.0</kotlin.version>
</properties>

Add the following dependency in dependencies to use the Kotlin library:

<dependencies>
    <dependency>
        <groupId>org.jetbrains.kotlin</groupId>
        <artifactId>kotlin-stdlib-jdk8</artifactId>
        <version>${kotlin.version}</version>
    </dependency>
</dependencies>

To build projects that include Kotlin and Java code, add the following in build:

<build>
    <plugins>
        <plugin>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-maven-plugin</artifactId>
            <version>${kotlin.version}</version>
            <executions>
                <execution>
                    <id>compile</id>
                    <goals>
                        <goal>compile</goal>
                    </goals>
                    <configuration>
                        <sourceDirs>
                            <sourceDir>${project.basedir}/src/main/kotlin</sourceDir>
                            <sourceDir>${project.basedir}/src/main/java</sourceDir>
                        </sourceDirs>
                    </configuration>
                </execution>
                <execution>
                    <id>test-compile</id>
                    <goals> <goal>test-compile</goal> </goals>
                    <configuration>
                        <sourceDirs>
                            <sourceDir>${project.basedir}/src/test/kotlin</sourceDir>
                            <sourceDir>${project.basedir}/src/test/java</sourceDir>
                        </sourceDirs>
                    </configuration>
                </execution>
            </executions>
        </plugin>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.5.1</version>
            <executions>
                <!-- Replacing default-compile as it is treated specially by maven -->
                <execution>
                    <id>default-compile</id>
                    <phase>none</phase>
                </execution>
                <!-- Replacing default-testCompile as it is treated specially by maven -->
                <execution>
                    <id>default-testCompile</id>
                    <phase>none</phase>
                </execution>
                <execution>
                    <id>java-compile</id>
                    <phase>compile</phase>
                    <goals>
                        <goal>compile</goal>
                    </goals>
                </execution>
                <execution>
                    <id>java-test-compile</id>
                    <phase>test-compile</phase>
                    <goals>
                        <goal>testCompile</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

Test with a simple entity

Create the kotlin folder in src/main to store Kotlin codes, in the same folder create com.yourcompany.invoicing.model package for OpenXava entities. You may need to do a Reload project in Maven so that you can create packages in the kotlin folder.

Create a Kotlin class in the model package with the name Customer (or Customer.kt file in Eclipse/OpenXava Studio):

package com.yourcompany.invoicing.model

import org.openxava.annotations.Required
import javax.persistence.Column
import javax.persistence.Entity
import javax.persistence.Id

@Entity
class Customer {

    @Id
    @Column(length = 6)
    var number : Int ?= null

    @Required
    @Column(length = 50)
    var name : String ?= null

}

Package and run your project

Before running your project for the first time, you must make a mvn package, in the next ones mvn compile is enough. Then find the invoicing class inside the package com.yourcompany.invoicing.run in src/main/java, and run it. In the browser go to http://localhost:8080/invoicing and log in with admin/admin as username/password to see the results.

Other codes examples

To create a simple button (action) where it displays a message, put the Kotlin ShowMessageAction (ShowMessageAction.kt) class in the com.yourcompany.invoicing.action package of the kotlin folder:

package com.yourcompany.invoicing.action

import org.openxava.actions.ViewBaseAction

class ShowMessageAction : ViewBaseAction() {

    @Throws(Exception::class)
    override fun execute() {
        addMessage("Hello world!")
    }

 }

Remember that you have to declare the action in controllers.xml in src/main/resources/xava:

<controller name ="Customer">
    <extends controller ="Typical"/>
    <action name ="showMessage" class ="com.yourcompany.invoicing.action.ShowMessageAction" mode="detail"/>
</controller>

An entity with more features:

package com.yourcompany.invoicing.model

import org.openxava.annotations.*
import org.openxava.calculators.CurrentLocalDateCalculator
import org.openxava.calculators.CurrentYearCalculator
import org.openxava.model.Identifiable
import java.time.LocalDate
import javax.persistence.*

@Entity
@View(members="""
	year, number, date,
        data {
        	customer;
        	details;
        	remarks 
	}
	"""
)
class Invoice  : Identifiable() {

    @Column(length = 4)
    @DefaultValueCalculator(CurrentYearCalculator::class)
    var year : Int? = null

    @Column(length = 6)
    var number : Int? = null

    @Required
    @DefaultValueCalculator(CurrentLocalDateCalculator::class)
    var date:  LocalDate? = null

    @ManyToOne(fetch = FetchType.LAZY, optional = false)
    @ReferenceView("Simple")
    var customer: Customer? = null

    @ElementCollection
    @ListProperties("product.number, product.description, quantity")
    var details: Collection<Detail>? = null

    @TextArea
    var remarks: String? = null

 }

If you decide to develop your OpenXava project with Kotlin, we recommend use IntelliJ IDEA, because it comes with Kotlin included which offers autocompletion, code coloring, automatic compilation, etc.
You can find more details about Kotlin in its documentation and how to integrate Kotlin into maven projects.
You can also see more about how to use OpenXava in our course developed in Java.