Create Your Kotlin Library

Create Your Kotlin Library

Learn how to create, package, and publish your own Kotlin library for others to use.

Basic Library Structure

Project Setup

// build.gradle.kts
plugins {
    kotlin("jvm") version "1.8.0"
    `maven-publish`
}

group = "com.example"
version = "1.0.0"

repositories {
    mavenCentral()
}

dependencies {
    implementation(kotlin("stdlib"))
    testImplementation(kotlin("test"))
}

publishing {
    publications {
        create<MavenPublication>("maven") {
            from(components["java"])
        }
    }
}

Library Code

// src/main/kotlin/com/example/mylib/MyLibrary.kt
package com.example.mylib

class MyLibrary {
    fun greet(name: String): String {
        return "Hello, $name!"
    }

    fun calculate(a: Int, b: Int): Int {
        return a + b
    }
}

Advanced Library Features

Public API

// Public API
package com.example.mylib

interface DataProcessor {
    fun process(data: String): String
}

class DefaultDataProcessor : DataProcessor {
    override fun process(data: String): String {
        return data.uppercase()
    }
}

// Factory
object DataProcessorFactory {
    fun create(): DataProcessor {
        return DefaultDataProcessor()
    }
}

Extension Functions

package com.example.mylib

fun String.toTitleCase(): String {
    return split(" ").joinToString(" ") { word ->
        word.lowercase().replaceFirstChar { it.uppercase() }
    }
}

fun Int.isEven(): Boolean {
    return this % 2 == 0
}

Publishing to Maven Central

Sonatype Setup

// build.gradle.kts
plugins {
    kotlin("jvm") version "1.8.0"
    `maven-publish`
    signing
}

publishing {
    publications {
        create<MavenPublication>("maven") {
            from(components["java"])

            pom {
                name.set("My Library")
                description.set("A useful Kotlin library")
                url.set("https://github.com/username/mylib")

                licenses {
                    license {
                        name.set("Apache License 2.0")
                        url.set("https://www.apache.org/licenses/LICENSE-2.0")
                    }
                }

                developers {
                    developer {
                        id.set("username")
                        name.set("Your Name")
                        email.set("your.email@example.com")
                    }
                }
            }
        }
    }

    repositories {
        maven {
            name = "OSSRH"
            url = uri("https://s01.oss.sonatype.org/service/local/staging/deploy/maven2/")
            credentials {
                username = System.getenv("OSSRH_USERNAME")
                password = System.getenv("OSSRH_PASSWORD")
            }
        }
    }
}

Best Practices

1. Clear API design
2. Comprehensive documentation
3. Version management
4. Dependency management
5. Testing coverage

Common Patterns

Builder Pattern

class ConfigBuilder {
    private var timeout: Int = 30
    private var retries: Int = 3
    private var debug: Boolean = false

    fun timeout(value: Int) = apply { timeout = value }
    fun retries(value: Int) = apply { retries = value }
    fun debug(value: Boolean) = apply { debug = value }

    fun build() = Config(timeout, retries, debug)
}

data class Config(
    val timeout: Int,
    val retries: Int,
    val debug: Boolean
)

// Usage
val config = ConfigBuilder()
    .timeout(60)
    .retries(5)
    .debug(true)
    .build()

Factory Pattern

interface Connection {
    fun connect()
    fun disconnect()
}

class DatabaseConnection : Connection {
    override fun connect() { /* ... */ }
    override fun disconnect() { /* ... */ }
}

class NetworkConnection : Connection {
    override fun connect() { /* ... */ }
    override fun disconnect() { /* ... */ }
}

object ConnectionFactory {
    fun create(type: String): Connection {
        return when (type) {
            "database" -> DatabaseConnection()
            "network" -> NetworkConnection()
            else -> throw IllegalArgumentException("Unknown connection type")
        }
    }
}

Performance Considerations

• API design impact
• Memory usage
• Thread safety
• Resource management
• Error handling

Common Mistakes

1. Poor API design
2. Missing documentation
3. Version conflicts
4. Dependency issues
5. Testing gaps

Conclusion

Creating a Kotlin library requires careful planning and attention to detail. Focus on creating a clean, well-documented API that others can easily use and maintain.