Konvert

This is a kotlin compiler plugin (using KSP) to generate mapping code from one class to another.

This README provides a basic overview, for more details have a look at the documentation.

Usage

Gradle

To use Konvert with Gradle, you have to do the following steps:

1. Add konvert-api as a dependency:

   dependencies {
      implementation("io.mcarle:konvert-api:$konvertVersion")
   }

2. Add the KSP plugin matching your Kotlin version:

   plugins {
       id("com.google.devtools.ksp").version("2.0.21-1.0.27")
   }

3. Add konvert as a ksp dependency:

   dependencies {
      ksp("io.mcarle:konvert:$konvertVersion")
   }

Maven

To use Konvert with Maven, you have to do the following steps:

1. Add konvert-api as a dependency:

   <dependency>
       <groupId>io.mcarle</groupId>
       <artifactId>konvert-api</artifactId>
       <version>${konvert.version}</version>
   </dependency>

2. Configure the kotlin-maven-plugin to use Konvert:

   <plugin>
       <groupId>org.jetbrains.kotlin</groupId>
       <artifactId>kotlin-maven-plugin</artifactId>
       <configuration>
           <jvmTarget>17</jvmTarget>
           <compilerPlugins>
               <plugin>ksp</plugin>
           </compilerPlugins>
       </configuration>
       <dependencies>
           <dependency>
               <groupId>com.dyescape</groupId>
               <artifactId>kotlin-maven-symbol-processing</artifactId>
               <version>1.6</version>
           </dependency>
           <dependency>
               <groupId>io.mcarle</groupId>
               <artifactId>konvert</artifactId>
               <version>${konvert.version}</version>
           </dependency>
       </dependencies>
   </plugin>

Code

For a simple example project have a look into the example directory.

There are three different ways to use Konvert:

1. Using @KonvertTo:

   @KonvertTo(PersonDto::class)
   class Person(val firstName: String, val lastName: String)
   data class PersonDto(val firstName: String, val lastName: String)

   This will generate the following extension function

   fun Person.toPersonDto(): PersonDto =
      PersonDto(firstName = firstName, lastName = lastName)

2. Using @KonvertFrom (especially useful, if you cannot change the code of the source class)

   class Person(val firstName: String, val lastName: String) {
      @KonvertFrom(PersonDto::class)
      companion object
   }
   data class PersonDto(val firstName: String, val lastName: String)

   This will generate the following extension function

   fun Person.Companion.fromPersonDto(personDto: PersonDto): Person =
      Person(firstName = personDto.firstName, lastName = personDto.lastName)

3. Using @Konverter:

   class Person(val firstName: String, val lastName: String)
   data class PersonDto(val firstName: String, val lastName: String)
   
   @Konverter
   interface PersonMapper {
      fun toDto(person: Person): PersonDto
   }

   This will generate the following object

   object PersonMapperImpl: PersonMapper {
      override fun toDto(person: Person): PersonDto
         = PersonDto(firstName = person.firstName, lastName = person.lastName)
   }

Type mappings

For simple type mappings, like from Instant to Date, there already is a type converter provided with Konvert:

@KonvertTo(PersonDto::class)
class Person(val name: String, val birthday: Instant)
data class PersonDto(val name: String, val birthday: Date)

This will generate the following extension function

fun Person.toPersonDto(): PersonDto = PersonDto(
   name = name,
   birthday = birthday.let { java.util.Date.from(it) }
)

Have a look at the documentation for a list of provided type converters.

🛈: You can also create your own type converter library by implementing TypeConverter and register it using SPI.

Fine tuning

Most of the time, the source and target classes might not have the same property names and types. You can configure specific mappings and rename the generated extension function like this:

@KonvertTo(
   PersonDto::class,
   mappings = [
      Mapping(source = "firstName", target = "givenName"),
      Mapping(source = "lastName", target = "familyName")
   ],
   mapFunctionName = "asDto"
)
class Person(val firstName: String, val lastName: String)
data class PersonDto(val givenName: String, val familyName: String)

This will generate the following extension function

fun Person.asDto(): PersonDto = PersonDto(
   givenName = firstName,
   familyName = lastName
)

For further functionality, have a look into the documentation the KDocs of the annotations, the example project or the tests.

Further information

• Konvert is primarily compiled and tested with JDK >=17. It should also work with anything below JDK 17, but is not guaranteed to.
• Konvert is able to convert classes from and to classes written in Java (and probably also in other JVM languages).

Building

Gradle

To build the project, simply run

gradle build

Run all tests

By default, only a subset of available tests are executed, which should verify most of Konvert's functionality. To run all tests, append the property runAllTests, e.g.:

gradle test -PrunAllTests

Documentation

To serve the Jekyll site locally, simply run the following command inside docs:

docker run --rm -it -v "$PWD":/srv/jekyll -p 4000:4000 jekyll/jekyll jekyll serve

CI

GitHub Actions are used to:

• build and test
• release and publish to a Maven repository
• generate documentation and deploy it to GitHub Pages.

Changelog

The changelog contains all notable changes.

License

Copyright 2023 Marcel Carlé

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.