BAEL-2378 Non-blocking Spring Boot with Kotlin Coroutines (#6966)

spring-boot-kotlin/README.md

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+### Relevant Articles:
+- [Non-blocking Spring Boot with Kotlin Coroutines](http://www.baeldung.com/non-blocking-spring-boot-with-kotlin-coroutines)

spring-boot-kotlin/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>spring-boot-kotlin</artifactId>
+    <name>spring-boot-kotlin</name>
+    <packaging>jar</packaging>
+    <description>Demo project showing how to use non-blocking in Kotlin with Spring Boot</description>
+
+    <parent>
+        <artifactId>parent-kotlin</artifactId>
+        <groupId>com.baeldung</groupId>
+        <version>1.0.0-SNAPSHOT</version>
+        <relativePath>../parent-kotlin</relativePath>
+    </parent>
+
+    <repositories>
+        <repository>
+            <id>spring-snapshots</id>
+            <name>Spring Snapshots</name>
+            <url>https://repo.spring.io/snapshot</url>
+            <snapshots>
+                <enabled>true</enabled>
+            </snapshots>
+        </repository>
+        <repository>
+            <id>spring-milestones</id>
+            <name>Spring Milestones</name>
+            <url>https://repo.spring.io/milestone</url>
+        </repository>
+    </repositories>
+
+
+    <dependencyManagement>
+        <dependencies>
+            <dependency>
+                <groupId>org.springframework.boot</groupId>
+                <artifactId>spring-boot-dependencies</artifactId>
+                <version>${spring-boot.version}</version>
+                <type>pom</type>
+                <scope>import</scope>
+            </dependency>
+        </dependencies>
+    </dependencyManagement>
+
+    <pluginRepositories>
+        <pluginRepository>
+            <id>spring-snapshots</id>
+            <name>Spring Snapshots</name>
+            <url>https://repo.spring.io/snapshot</url>
+            <snapshots>
+                <enabled>true</enabled>
+            </snapshots>
+        </pluginRepository>
+        <pluginRepository>
+            <id>spring-milestones</id>
+            <name>Spring Milestones</name>
+            <url>https://repo.spring.io/milestone</url>
+        </pluginRepository>
+    </pluginRepositories>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.jetbrains.kotlin</groupId>
+            <artifactId>kotlin-reflect</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.jetbrains.kotlin</groupId>
+            <artifactId>kotlin-stdlib-jdk8</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.jetbrains.kotlinx</groupId>
+            <artifactId>kotlinx-coroutines-core</artifactId>
+            <version>${kotlinx-coroutines.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.jetbrains.kotlinx</groupId>
+            <artifactId>kotlinx-coroutines-reactor</artifactId>
+            <version>${kotlinx-coroutines.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-webflux</artifactId>
+            <version>${spring-boot.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.fasterxml.jackson.module</groupId>
+            <artifactId>jackson-module-kotlin</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.data</groupId>
+            <artifactId>spring-data-r2dbc</artifactId>
+            <version>${r2dbc.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>io.r2dbc</groupId>
+            <artifactId>r2dbc-h2</artifactId>
+            <version>${h2-r2dbc.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>io.r2dbc</groupId>
+            <artifactId>r2dbc-spi</artifactId>
+            <version>${r2dbc-spi.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-test</artifactId>
+            <scope>test</scope>
+            <exclusions>
+                <exclusion>
+                    <groupId>junit</groupId>
+                    <artifactId>junit</artifactId>
+                </exclusion>
+            </exclusions>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-api</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-engine</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>io.projectreactor</groupId>
+            <artifactId>reactor-test</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.jetbrains.kotlin</groupId>
+                <artifactId>kotlin-maven-plugin</artifactId>
+                <configuration>
+                    <args>
+                        <arg>-Xjsr305=strict</arg>
+                    </args>
+                    <compilerPlugins>
+                        <plugin>spring</plugin>
+                    </compilerPlugins>
+                </configuration>
+                <dependencies>
+                    <dependency>
+                        <groupId>org.jetbrains.kotlin</groupId>
+                        <artifactId>kotlin-maven-allopen</artifactId>
+                        <version>${kotlin.version}</version>
+                    </dependency>
+                </dependencies>
+            </plugin>
+        </plugins>
+    </build>
+
+    <properties>
+        <kotlin.version>1.3.31</kotlin.version>
+        <r2dbc.version>1.0.0.M1</r2dbc.version>
+        <r2dbc-spi.version>1.0.0.M7</r2dbc-spi.version>
+        <h2-r2dbc.version>1.0.0.BUILD-SNAPSHOT</h2-r2dbc.version>
+        <kotlinx-coroutines.version>1.2.1</kotlinx-coroutines.version>
+        <spring-boot.version>2.2.0.M2</spring-boot.version>
+    </properties>
+
+</project>

spring-boot-kotlin/src/main/kotlin/com/baeldung/nonblockingcoroutines/SpringApplication.kt

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+package com.baeldung.nonblockingcoroutines
+
+import org.springframework.boot.SpringApplication.run
+import org.springframework.boot.autoconfigure.SpringBootApplication
+
+@SpringBootApplication
+class SpringApplication
+
+fun main(args: Array<String>) {
+    run(SpringApplication::class.java, *args)
+}

spring-boot-kotlin/src/main/kotlin/com/baeldung/nonblockingcoroutines/config/DatastoreConfig.kt

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+package com.baeldung.nonblockingcoroutines.config
+
+import io.r2dbc.h2.H2ConnectionConfiguration
+import io.r2dbc.h2.H2ConnectionFactory
+import io.r2dbc.spi.ConnectionFactory
+import org.springframework.beans.factory.annotation.Value
+import org.springframework.context.annotation.Bean
+import org.springframework.context.annotation.Configuration
+import org.springframework.data.r2dbc.config.AbstractR2dbcConfiguration
+import org.springframework.data.r2dbc.repository.config.EnableR2dbcRepositories
+
+@Configuration
+@EnableR2dbcRepositories
+class DatastoreConfig : AbstractR2dbcConfiguration() {
+    @Value("\${spring.datasource.username}")
+    private val userName: String = ""
+
+    @Value("\${spring.datasource.password}")
+    private val password: String = ""
+
+    @Value("\${spring.datasource.dbname}")
+    private val dbName: String = ""
+
+    @Bean
+    override fun connectionFactory(): ConnectionFactory {
+        return H2ConnectionFactory(H2ConnectionConfiguration.builder()
+          .inMemory(dbName)
+          .username(userName)
+          .password(password)
+          .build())
+    }
+}

spring-boot-kotlin/src/main/kotlin/com/baeldung/nonblockingcoroutines/config/RouterConfiguration.kt

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+package com.baeldung.nonblockingcoroutines.config
+
+import com.baeldung.nonblockingcoroutines.handlers.ProductsHandler
+import kotlinx.coroutines.FlowPreview
+import org.springframework.context.annotation.Bean
+import org.springframework.context.annotation.Configuration
+import org.springframework.web.reactive.function.server.coRouter
+
+@Configuration
+class RouterConfiguration {
+
+    @FlowPreview
+    @Bean
+    fun productRoutes(productsHandler: ProductsHandler) = coRouter {
+        GET("/", productsHandler::findAll)
+        GET("/{id}", productsHandler::findOne)
+        GET("/{id}/stock", productsHandler::findOneInStock)
+    }
+}

spring-boot-kotlin/src/main/kotlin/com/baeldung/nonblockingcoroutines/config/WebClientConfiguration.kt

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+package com.baeldung.nonblockingcoroutines.config
+
+import org.springframework.context.annotation.Bean
+import org.springframework.context.annotation.Configuration
+import org.springframework.web.reactive.function.client.WebClient
+
+@Configuration
+class WebClientConfiguration {
+
+    @Bean
+    fun webClient() = WebClient.builder().baseUrl("http://localhost:8080").build()
+}

spring-boot-kotlin/src/main/kotlin/com/baeldung/nonblockingcoroutines/controller/ProductController.kt

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+package com.baeldung.nonblockingcoroutines.controller
+
+import com.baeldung.nonblockingcoroutines.model.Product
+import com.baeldung.nonblockingcoroutines.repository.ProductRepository
+import org.springframework.beans.factory.annotation.Autowired
+import org.springframework.http.MediaType
+import org.springframework.web.bind.annotation.GetMapping
+import org.springframework.web.bind.annotation.PathVariable
+import org.springframework.web.reactive.function.client.WebClient
+import org.springframework.web.reactive.function.client.bodyToMono
+import reactor.core.publisher.Flux
+import reactor.core.publisher.Mono
+
+class ProductController {
+    @Autowired
+    lateinit var webClient: WebClient
+    @Autowired
+    lateinit var productRepository: ProductRepository
+
+    @GetMapping("/{id}")
+    fun findOne(@PathVariable id: Int): Mono<Product> {
+        return productRepository
+          .getProductById(id)
+    }
+
+    @GetMapping("/{id}/stock")
+    fun findOneInStock(@PathVariable id: Int): Mono<ProductStockView> {
+        val product = productRepository.getProductById(id)
+
+        val stockQuantity = webClient.get()
+          .uri("/stock-service/product/$id/quantity")
+          .accept(MediaType.APPLICATION_JSON)
+          .retrieve()
+          .bodyToMono<Int>()
+        return product.zipWith(stockQuantity) { productInStock, stockQty ->
+            ProductStockView(productInStock, stockQty)
+        }
+    }
+
+    @GetMapping("/stock-service/product/{id}/quantity")
+    fun getStockQuantity(): Mono<Int> {
+        return Mono.just(2)
+    }
+
+    @GetMapping("/")
+    fun findAll(): Flux<Product> {
+        return productRepository.getAllProducts()
+    }
+}

spring-boot-kotlin/src/main/kotlin/com/baeldung/nonblockingcoroutines/controller/ProductControllerCoroutines.kt

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+package com.baeldung.nonblockingcoroutines.controller
+
+import com.baeldung.nonblockingcoroutines.model.Product
+import com.baeldung.nonblockingcoroutines.repository.ProductRepositoryCoroutines
+import kotlinx.coroutines.Deferred
+import kotlinx.coroutines.FlowPreview
+import kotlinx.coroutines.GlobalScope
+import kotlinx.coroutines.async
+import kotlinx.coroutines.flow.Flow
+import org.springframework.beans.factory.annotation.Autowired
+import org.springframework.http.MediaType.APPLICATION_JSON
+import org.springframework.web.bind.annotation.GetMapping
+import org.springframework.web.bind.annotation.PathVariable
+import org.springframework.web.reactive.function.client.WebClient
+import org.springframework.web.reactive.function.client.awaitBody
+import org.springframework.web.reactive.function.client.awaitExchange
+
+class ProductControllerCoroutines {
+    @Autowired
+    lateinit var webClient: WebClient
+
+    @Autowired
+    lateinit var productRepository: ProductRepositoryCoroutines
+
+    @GetMapping("/{id}")
+    suspend fun findOne(@PathVariable id: Int): Product? {
+        return productRepository.getProductById(id)
+    }
+
+    @GetMapping("/{id}/stock")
+    suspend fun findOneInStock(@PathVariable id: Int): ProductStockView {
+        val product: Deferred<Product?> = GlobalScope.async {
+            productRepository.getProductById(id)
+        }
+        val quantity: Deferred<Int> = GlobalScope.async {
+            webClient.get()
+              .uri("/stock-service/product/$id/quantity")
+              .accept(APPLICATION_JSON)
+              .awaitExchange().awaitBody<Int>()
+        }
+        return ProductStockView(product.await()!!, quantity.await())
+    }
+
+    @FlowPreview
+    @GetMapping("/")
+    fun findAll(): Flow<Product> {
+        return productRepository.getAllProducts()
+    }
+}

spring-boot-kotlin/src/main/kotlin/com/baeldung/nonblockingcoroutines/controller/ProductStockView.kt

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+package com.baeldung.nonblockingcoroutines.controller
+
+import com.baeldung.nonblockingcoroutines.model.Product
+
+class ProductStockView(product: Product, var stockQuantity: Int) {
+    var id: Int = 0
+    var name: String = ""
+    var price: Float = 0.0f
+
+    init {
+        this.id = product.id
+        this.name = product.name
+        this.price = product.price
+    }
+}

spring-boot-kotlin/src/main/kotlin/com/baeldung/nonblockingcoroutines/handlers/ProductsHandler.kt

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+package com.baeldung.nonblockingcoroutines.handlers
+
+import com.baeldung.nonblockingcoroutines.controller.ProductStockView
+import com.baeldung.nonblockingcoroutines.model.Product
+import com.baeldung.nonblockingcoroutines.repository.ProductRepositoryCoroutines
+import kotlinx.coroutines.Deferred
+import kotlinx.coroutines.FlowPreview
+import kotlinx.coroutines.GlobalScope
+import kotlinx.coroutines.async
+import org.springframework.beans.factory.annotation.Autowired
+import org.springframework.http.MediaType
+import org.springframework.stereotype.Component
+import org.springframework.web.reactive.function.client.WebClient
+import org.springframework.web.reactive.function.client.awaitBody
+import org.springframework.web.reactive.function.client.awaitExchange
+import org.springframework.web.reactive.function.server.ServerRequest
+import org.springframework.web.reactive.function.server.ServerResponse
+import org.springframework.web.reactive.function.server.bodyAndAwait
+import org.springframework.web.reactive.function.server.json
+
+@Component
+class ProductsHandler(
+  @Autowired var webClient: WebClient,
+  @Autowired var productRepository: ProductRepositoryCoroutines) {
+
+    @FlowPreview
+    suspend fun findAll(request: ServerRequest): ServerResponse =
+      ServerResponse.ok().json().bodyAndAwait(productRepository.getAllProducts())
+
+    suspend fun findOneInStock(request: ServerRequest): ServerResponse {
+        val id = request.pathVariable("id").toInt()
+
+        val product: Deferred<Product?> = GlobalScope.async {
+            productRepository.getProductById(id)
+        }
+        val quantity: Deferred<Int> = GlobalScope.async {
+            webClient.get()
+              .uri("/stock-service/product/$id/quantity")
+              .accept(MediaType.APPLICATION_JSON)
+              .awaitExchange().awaitBody<Int>()
+        }
+        return ServerResponse.ok().json().bodyAndAwait(ProductStockView(product.await()!!, quantity.await()))
+    }
+
+    suspend fun findOne(request: ServerRequest): ServerResponse {
+        val id = request.pathVariable("id").toInt()
+        return ServerResponse.ok().json().bodyAndAwait(productRepository.getProductById(id)!!)
+    }
+}

spring-boot-kotlin/src/main/kotlin/com/baeldung/nonblockingcoroutines/model/Product.kt

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+package com.baeldung.nonblockingcoroutines.model
+
+data class Product(
+  var id: Int = 0,
+  var name: String = "",
+  var price: Float = 0.0f
+)

spring-boot-kotlin/src/main/kotlin/com/baeldung/nonblockingcoroutines/repository/ProductRepository.kt

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+package com.baeldung.nonblockingcoroutines.repository
+
+import com.baeldung.nonblockingcoroutines.model.Product
+import org.springframework.data.r2dbc.function.DatabaseClient
+import org.springframework.stereotype.Repository
+import reactor.core.publisher.Flux
+import reactor.core.publisher.Mono
+
+@Repository
+class ProductRepository(private val client: DatabaseClient) {
+
+    fun getProductById(id: Int): Mono<Product> {
+        return client.execute().sql("SELECT * FROM products WHERE id = $1")
+          .bind(0, id)
+          .`as`(Product::class.java)
+          .fetch()
+          .one()
+    }
+
+    fun addNewProduct(name: String, price: Float): Mono<Void> {
+        return client.execute()
+          .sql("INSERT INTO products (name, price) VALUES($1, $2)")
+          .bind(0, name)
+          .bind(1, price)
+          .then()
+    }
+
+    fun getAllProducts(): Flux<Product> {
+        return client.select().from("products")
+          .`as`(Product::class.java)
+          .fetch()
+          .all()
+    }
+}

spring-boot-kotlin/src/main/kotlin/com/baeldung/nonblockingcoroutines/repository/ProductRepositoryCoroutines.kt

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+package com.baeldung.nonblockingcoroutines.repository
+
+
+import com.baeldung.nonblockingcoroutines.model.Product
+import kotlinx.coroutines.FlowPreview
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.reactive.awaitFirstOrNull
+import kotlinx.coroutines.reactive.flow.asFlow
+import org.springframework.data.r2dbc.function.DatabaseClient
+import org.springframework.stereotype.Repository
+
+@Repository
+class ProductRepositoryCoroutines(private val client: DatabaseClient) {
+
+    suspend fun getProductById(id: Int): Product? =
+      client.execute().sql("SELECT * FROM products WHERE id = $1")
+        .bind(0, id)
+        .`as`(Product::class.java)
+        .fetch()
+        .one()
+        .awaitFirstOrNull()
+
+    suspend fun addNewProduct(name: String, price: Float) =
+      client.execute()
+        .sql("INSERT INTO products (name, price) VALUES($1, $2)")
+        .bind(0, name)
+        .bind(1, price)
+        .then()
+        .awaitFirstOrNull()
+
+    @FlowPreview
+    fun getAllProducts(): Flow<Product> =
+      client.select()
+        .from("products")
+        .`as`(Product::class.java)
+        .fetch()
+        .all()
+        .log()
+        .asFlow()
+}

spring-boot-kotlin/src/main/resources/application.properties

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+logging.level.org.springframework.data.r2dbc=DEBUG
+logging.level.org.springframework.web.reactive.function.client.ExchangeFunctions=TRACE
+spring.http.log-request-details=true
+spring.h2.console.enabled=true
+spring.datasource.username=sa
+spring.datasource.url=jdbc:h2:mem:testdb
+spring.datasource.password=
+spring.datasource.dbname=testdb

spring-boot-kotlin/src/main/resources/logback.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
+            </pattern>
+        </encoder>
+    </appender>
+
+    <root level="INFO">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>

spring-boot-kotlin/src/test/kotlin/com/baeldung/nonblockingcoroutines/ProductHandlerTest.kt

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+package com.baeldung.nonblockingcoroutines
+
+import com.baeldung.nonblockingcoroutines.config.RouterConfiguration
+import com.baeldung.nonblockingcoroutines.handlers.ProductsHandler
+import com.baeldung.nonblockingcoroutines.model.Product
+import com.baeldung.nonblockingcoroutines.repository.ProductRepositoryCoroutines
+import kotlinx.coroutines.FlowPreview
+import kotlinx.coroutines.reactive.flow.asFlow
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.mockito.BDDMockito.given
+import org.springframework.beans.factory.annotation.Autowired
+import org.springframework.boot.autoconfigure.security.reactive.ReactiveSecurityAutoConfiguration
+import org.springframework.boot.autoconfigure.security.reactive.ReactiveUserDetailsServiceAutoConfiguration
+import org.springframework.boot.test.autoconfigure.web.reactive.WebFluxTest
+import org.springframework.boot.test.mock.mockito.MockBean
+import org.springframework.test.context.junit4.SpringRunner
+import org.springframework.test.web.reactive.server.WebTestClient
+import org.springframework.test.web.reactive.server.expectBodyList
+import org.springframework.web.reactive.function.client.WebClient
+import reactor.core.publisher.Flux
+import org.springframework.test.context.ContextConfiguration
+
+@WebFluxTest(
+    excludeAutoConfiguration = [ReactiveUserDetailsServiceAutoConfiguration::class, ReactiveSecurityAutoConfiguration::class]
+)
+@RunWith(SpringRunner::class)
+@ContextConfiguration(classes = [ProductsHandler::class, RouterConfiguration::class])
+class ProductHandlerTest {
+
+    @Autowired
+    private lateinit var client: WebTestClient
+
+    @MockBean
+    private lateinit var webClient: WebClient
+
+    @MockBean
+    private lateinit var productsRepository: ProductRepositoryCoroutines
+
+
+    @FlowPreview
+    @Test
+    public fun `get all products`() {
+        val productsFlow = Flux.just(
+          Product(1, "product1", 1000.0F),
+          Product(2, "product2", 2000.0F),
+          Product(3, "product3", 3000.0F)
+        ).asFlow()
+        given(productsRepository.getAllProducts()).willReturn(productsFlow)
+        client.get()
+          .uri("/")
+          .exchange()
+          .expectStatus()
+          .isOk
+          .expectBodyList<Product>()
+    }
+
+}