Getting Started with Kotlin‑Java Mixed Development for Android

The author, previously focused on Android, decided to explore mixed Java‑Kotlin development and built a basic project to demonstrate the process.

Project creation

A standard Java project is created using the usual steps (see screenshot).

pom.xml configuration

The pom.xml is updated to include Kotlin libraries, selecting version 1.2.50. The added dependencies are:

<dependency>
    <groupId>org.jetbrains.kotlin</groupId>
    <artifactId>kotlin-reflect</artifactId>
    <version>${kotlin.version}</version>
</dependency>
<dependency>
    <groupId>org.jetbrains.kotlin</groupId>
    <artifactId>kotlin-runtime</artifactId>
    <version>${kotlin.version}</version>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.module</groupId>
    <artifactId>jackson-module-kotlin</artifactId>
    <version>2.9.6</version>
</dependency>
<dependency>
    <groupId>org.jetbrains.kotlin</groupId>
    <artifactId>kotlin-stdlib-jdk8</artifactId>
    <version>${kotlin.version}</version>
</dependency>
<dependency>
    <groupId>org.jetbrains.kotlin</groupId>
    <artifactId>kotlin-test</artifactId>
    <version>${kotlin.version}</version>
    <scope>test</scope>
</dependency>

With the dependencies in place, the author proceeds to write Kotlin code.

Controller code development

Kotlin variable definitions resemble JavaScript; they use var and do not require a trailing semicolon, e.g., var coupon = Coupon().

Method signatures differ from Java: the type follows the variable name, separated by a colon, and the return type follows the parameter list, also after a colon.

open fun homeList(type : String?, couponName : String?, couponType : String?, @RequestParam status: String): String {

The method defines four parameters— type, couponName, couponType, and status —and returns a String.

/**
 * 优惠券列表
 */
@RequestMapping(value="lists")
open fun homeList(type : String?, couponName : String?, couponType : String?, @RequestParam status: String): String {
    var coupon = Coupon()
    if (!StringUtils.isEmpty(type)) {
        coupon.type = type?.toInt()
    }
    coupon.title = couponName
    coupon.status = status.toInt()
    coupon.couponType = couponType?.toInt()
    val pageInfo = couponService.test()
    return "success"
}

The example demonstrates creating a Coupon object, setting its fields based on the incoming parameters, invoking a service method, and returning a success string.

The basic Java‑Kotlin mixed project is now complete.