Add product classes into domain.

demo-domain/build.gradle.kts

@@ -0,0 +1,8 @@
+plugins {
+    kotlin("jvm")
+    id("java")
+}
+
+dependencies {
+    implementation(kotlin("stdlib"))
+}

demo-domain/src/main/kotlin/com/example/demo/domain/product/model/Product.kt

@@ -0,0 +1,9 @@
+package com.example.demo.domain.product.model
+
+import java.util.UUID
+
+data class Product(
+    val id: UUID,
+    val name: String,
+    val type: ProductType
+)

demo-domain/src/main/kotlin/com/example/demo/domain/product/model/ProductType.kt

@@ -0,0 +1,7 @@
+package com.example.demo.domain.product.model
+
+enum class ProductType {
+    SOLID,
+    LIQUID,
+    GAS
+}

demo-domain/src/main/kotlin/com/example/demo/domain/product/port/ProductPort.kt

@@ -0,0 +1,12 @@
+package com.example.demo.domain.product.port
+
+import com.example.demo.domain.product.model.Product
+import java.util.UUID
+
+interface ProductPort {
+    fun getById(id: UUID): Product?
+
+    fun getAll(): List<Product>
+
+    fun save(product: Product)
+}