From Mobile to Backend with Kotlin and Ktor | Generali Tech Conference 2023

As mobile developers, we often see the backend world as something magical that "does things". But what if I tell you that you can easily build a backend even if mobile is your thing?

With this talk, I want to show how it is possible to bring your mobile knowledge (and shift it a little bit) to build a backend with Kotlin and Ktor. I will show how to structure the project, set up Dependency Injection, connect to a database and test everything to have a working backend ready to be deployed.

Transcript

1. @marcoGomier From Mobile to Backend with Kotlin and Ktor 👨💻 Senior Android Engineer 
 Google Developer Expert for Kotlin Marco Gomiero
2. @marcoGomier 🤔 Why?
3. @marcoGomier • A career change 🤷 • Side project • Understand how things works “on the other side” • Help you teammates 🤔 Why?
4. @marcoGomier * based on a true story
5. @marcoGomier Ktor https://ktor.io/
6. @marcoGomier Ktor • Kotlin • Lightweight and flexible • Asynchronous with Coroutines • Unopinionated
7. @marcoGomier Unopinionated • Whatever architecture • Whatever pattern Knowledge Transfer
8. @marcoGomier Architecture
9. @marcoGomier Android Activity/Fragment ViewModel Repository Local Data Source Remote Data Source Application
10. @marcoGomier Resource* Repository Local Data Source Remote Data Source Application * or Controller Ktor
11. @marcoGomier Resource Repository Local Data Source Remote Data Source Application Activity/Fragment ViewModel Repository Local Data Source Remote Data Source Application
12. @marcoGomier Domain Data Resource Repository Local Data Source Remote Data Source Application Activity/Fragment ViewModel Repository Local Data Source Remote Data Source Application Presentation Application
13. @marcoGomier Application class MyApp : Application() { override fun onCreate() { super.onCreate() if (BuildConfig.DEBUG) { Timber.plant(Timber.DebugTree()) } initAnalytics() initCrashReporting() initRandomLib() } }
14. @marcoGomier Application fun Application.module() { install(Koin) { slf4jLogger() modules(koinModules) } setupConfig() setupDatabase() install(ContentNegotiation) { json() } install(CallLogging) { level = Level.INFO } install(Locations) routing { setupEndpoint() } }
15. @marcoGomier Application slf4jLogger() modules(koinModules) } setupConfig() setupDatabase() install(ContentNegotiation) { json() } install(CallLogging) { level = Level.INFO } install(Locations)
16. @marcoGomier Plugin https://ktor.io/docs/plugins.html • Add a specific feature to your backend • Highly customisable • No plugin activated by default
17. @marcoGomier Plugin https://ktor.io/docs/
18. @marcoGomier Application setupConfig() setupDatabase() install(ContentNegotiation) { json() } install(CallLogging) { level = Level.INFO }ㅤ install(Locations) routing { setupEndpoint() } }
19. @marcoGomier Application install(ContentNegotiation) { json() } install(CallLogging) { level = Level.INFO }ㅤ install(Locations) routing { setupEndpoint() } }
20. @marcoGomier Domain Data Presentation Application
21. @marcoGomier Presentation class MainActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) ... } }
22. @marcoGomier Presentation fun Route.jokeEndpoint() { val jokeRepository by inject<JokeRepository>() get<JokeEndpoint.Random> { call.respond(jokeRepository.getRandomJoke()) } post<JokeEndpoint.Watch> { apiCallParams -> val name = apiCallParams.name jokeRepository.watch(name) call.respond("Ok") } }
23. @marcoGomier Domain Data Presentation Application
24. @marcoGomier Domain class JokeRepositoryImpl( private val jokeLocalDataSource: JokeLocalDataSource ) : JokeRepository { override suspend fun getRandomJoke(): JokeDTO { // ... } }
25. @marcoGomier Domain Data Presentation Application
26. @marcoGomier @Entity(tableName = "allowed_app") data class AllowedApp( @PrimaryKey val packageName: String, @ColumnInfo val appName: String ) Room https://developer.android.com/training/data-storage/room Data
27. @marcoGomier @Dao interface AllowedAppDAO { @Query("SELECT * FROM allowed_app") suspend fun getAllAllowedApps(): List<AllowedApp> } @Entity(tableName = "allowed_app") data class AllowedApp( @PrimaryKey val packageName: String, @ColumnInfo val appName: String )
28. @marcoGomier class LocalDatasource( private val db: RoomDatabase ) { suspend fun getAllowedApps(): List<AllowedApp> { return db.allowedAppDAO().getAllAllowedApps() } } @Entity(tableName = "allowed_app") data class AllowedApp( @PrimaryKey val packageName: String, @ColumnInfo val appName: String ) @Dao interface AllowedAppDAO { @Query("SELECT * FROM allowed_app") suspend fun getAllAllowedApps(): List<AllowedApp> }
29. @marcoGomier Exposed https://github.com/JetBrains/Exposed
30. @marcoGomier object JokeTable: IdTable<String>(name = "joke") { val createdAt = datetime("created_at") val updatedAt = datetime("updated_at") val value = text("value") override val id: Column<EntityID<String >> = varchar("joke_id", 255).entityId() override val primaryKey: PrimaryKey = PrimaryKey(id) }
31. @marcoGomier class Joke(id: EntityID<String>): Entity<String>(id) { companion object: EntityClass<String, Joke>(JokeTable) var createdAt by JokeTable.createdAt var updatedAt by JokeTable.updatedAt var value by JokeTable.value } object JokeTable: IdTable<String>(name = "joke") { val createdAt = datetime("created_at") val updatedAt = datetime("updated_at") val value = text("value") override val id: Column<EntityID<String >> = varchar("joke_id", 255).entityId() override val primaryKey: PrimaryKey = PrimaryKey(id) }
32. @marcoGomier class JokeLocalDataSourceImpl : JokeLocalDataSource { override suspend fun getAllJokes(): List<Joke> { val joke = newSuspendedTransaction { val query = JokeTable.selectAll() Joke.wrapRows(query).toList() } } } object JokeTable: IdTable<String>(name = "joke") { val createdAt = datetime("created_at") val updatedAt = datetime("updated_at") val value = text("value") override val id: Column<EntityID<String >> = varchar("joke_id", 255).entityId() override val primaryKey: PrimaryKey = PrimaryKey(id) } class Joke(id: EntityID<String>): Entity<String>(id) { companion object: EntityClass<String, Joke>(JokeTable) var createdAt by JokeTable.createdAt var updatedAt by JokeTable.updatedAt var value by JokeTable.value }
33. @marcoGomier class JokeLocalDataSourceImpl : JokeLocalDataSource { override suspend fun getAllJokes(): List<Joke> { val joke = newSuspendedTransaction { val query = JokeTable.selectAll() Joke.wrapRows(query).toList() } } } object JokeTable: IdTable<String>(name = "joke") { val createdAt = datetime("created_at") val updatedAt = datetime("updated_at") val value = text("value") override val id: Column<EntityID<String >> = varchar("joke_id", 255).entityId() override val primaryKey: PrimaryKey = PrimaryKey(id) } class Joke(id: EntityID<String>): Entity<String>(id) { companion object: EntityClass<String, Joke>(JokeTable) var createdAt by JokeTable.createdAt var updatedAt by JokeTable.updatedAt var value by JokeTable.value }
34. @marcoGomier object JokeTable: IdTable<String>(name = "joke") { val createdAt = datetime("created_at") val updatedAt = datetime("updated_at") val value = text("value") override val id: Column<EntityID<String >> = varchar("joke_id", 255).entityId() override val primaryKey: PrimaryKey = PrimaryKey(id) } class Joke(id: EntityID<String>): Entity<String>(id) { companion object: EntityClass<String, Joke>(JokeTable) var createdAt by JokeTable.createdAt var updatedAt by JokeTable.updatedAt var value by JokeTable.value } class JokeLocalDataSourceImpl : JokeLocalDataSource { override suspend fun getAllJokes(): List<Joke> { val joke = newSuspendedTransaction { val query = JokeTable.selectAll() Joke.wrapRows(query).toList() } } }
35. @marcoGomier object JokeTable: IdTable<String>(name = "joke") { val createdAt = datetime("created_at") val updatedAt = datetime("updated_at") val value = text("value") override val id: Column<EntityID<String >> = varchar("joke_id", 255).entityId() override val primaryKey: PrimaryKey = PrimaryKey(id) } class Joke(id: EntityID<String>): Entity<String>(id) { companion object: EntityClass<String, Joke>(JokeTable) var createdAt by JokeTable.createdAt var updatedAt by JokeTable.updatedAt var value by JokeTable.value } class JokeLocalDataSourceImpl : JokeLocalDataSource { override suspend fun getAllJokes(): List<Joke> { val joke = newSuspendedTransaction { val query = JokeTable.selectAll() Joke.wrapRows(query).toList() } } }
36. @marcoGomier Joke.new { this.createdAt = LocalDateTime.now() this.updatedAt = LocalDateTime.now() value = "A Joke" }
37. @marcoGomier EmailTable.deleteWhere { EmailTable.account.eq(account.id.value) and EmailTable.id.eq(emailId) }
38. @marcoGomier EmailTable.deleteWhere { EmailTable.account.eq(account.id.value) and EmailTable.id.eq(emailId) } EmailThreadTable.join(EmailFolderTable, JoinType.INNER, additionalConstraint = { (EmailThreadTable.id eq EmailFolderTable.threadId).and( EmailThreadTable.account eq EmailFolderTable.accountId ) }) .select { EmailThreadTable.account eq account.id.value and (EmailFolderTable.folderId eq folderId) } .orderBy(EmailThreadTable.lastEmailDate, SortOrder.DESC) .limit(n = pageSize)
39. @marcoGomier Dependency Injection
40. @marcoGomier https://insert-koin.io/docs/quickstart/ktor Koin
41. @marcoGomier val appModule = module { single<HelloRepository> { HelloRepositoryImpl() } factory { MySimplePresenter(get()) } }
42. @marcoGomier class MyApplication : Application() { override fun onCreate() { super.onCreate() startKoin { androidLogger() androidContext(this@MyApplication) modules(appModule) } } }
43. @marcoGomier class MainActivity : AppCompatActivity() { val firstPresenter: MySimplePresenter by inject() override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) ... } }
44. @marcoGomier val appModule = module { single<JokeLocalDataSource> { JokeLocalDataSourceImpl() } single<JokeRepository> { JokeRepositoryImpl(get()) } }
45. @marcoGomier fun Application.module() { install(Koin) { slf4jLogger() modules(koinModules) } ... }
46. @marcoGomier fun Route.jokeEndpoint() { val jokeRepository by inject<JokeRepository>() get<JokeEndpoint.Random> { call.respond(jokeRepository.getRandomJoke()) } post<JokeEndpoint.Watch> { apiCallParams -> val name = apiCallParams.name jokeRepository.watch(name) call.respond("Ok") } }
47. @marcoGomier Logging
48. @marcoGomier Timber class MyApplication : Application() { override fun onCreate() { super.onCreate() if (BuildConfig.DEBUG) { Timber.plant(Timber.DebugTree()) } else { // Log to somewhere else } } } https://github.com/JakeWharton/timber
49. @marcoGomier Timber https://github.com/JakeWharton/timber Timber.d(“Message") Timber.v("Message") Timber.i("Message") Timber.w("Message") Timber.wtf("Message") Timber.e(exception)
50. @marcoGomier SLF4J http://www.slf4j.org/index.html fun Application.module(testing: Boolean = false) { log.info("Hello from module!") }
51. @marcoGomier SLF4J http://www.slf4j.org/index.html routing { get("/api/v1") { call.application.environment.log.info("Hello from /api/v1!") } } fun Application.module(testing: Boolean = false) { log.info("Hello from module!") }
52. @marcoGomier SLF4J http://www.slf4j.org/index.html routing { get("/api/v1") { call.application.environment.log.info("Hello from /api/v1!") } } fun Application.module(testing: Boolean = false) { log.info("Hello from module!") } val logger = LoggerFactory.getLogger(MyClass :: class.java)
53. @marcoGomier val logger = LoggerFactory.getLogger(MyClass :: class.java) inline fun <reified T> T.getLogger(): Logger { return LoggerFactory.getLogger(T :: class.java) } class MyClass { private val logger = getLogger() fun main() { logger.info("Hello World") } }
54. @marcoGomier logger.trace("Message") logger.debug("Message") logger.info("Message") logger.warn("Message") logger.error("Message") SLF4J
55. @marcoGomier logback.xml
56. @marcoGomier <configuration> <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender"> <encoder> <pattern>%d{YYYY-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n </ pattern> </ encoder> </ appender> <appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender"> <file>${LOG_DEST}/ktor-chuck-norris-sample.log </ file> <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy"> <!-- daily rollover --> <fileNamePattern>${LOG_DEST}/ktor-chuck-norris-sample.%d{yyyy-MM-dd}.log </ fileNamePattern> <!-- keep 90 days' worth of history capped at 3GB total size --> <maxHistory>${LOG_MAX_HISTORY} </ maxHistory> <totalSizeCap>3GB </ totalSizeCap> </ rollingPolicy> <encoder> <pattern>%d{YYYY-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n </ pattern> </ encoder> </ appender> <root level="info"> <appender-ref ref="STDOUT" /> <appender-ref ref="FILE" /> </ root> <logger name="org.eclipse.jetty" level="INFO" /> <logger name="io.netty" level="INFO" /> <logger name="org.quartz" level="INFO" /> </ configuration> logback.xml
57. @marcoGomier <configuration> <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender"> <encoder> <pattern>%d{YYYY-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n </ pattern> </ encoder> </ appender> <appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender"> <file>${LOG_DEST}/ktor-chuck-norris-sample.log </ file> <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy"> <!-- daily rollover --> <fileNamePattern>${LOG_DEST}/ktor-chuck-norris-sample.%d{yyyy-MM-dd}.log </ fileNamePattern> <!-- keep 90 days' worth of history capped at 3GB total size --> <maxHistory>${LOG_MAX_HISTORY} </ maxHistory> <totalSizeCap>3GB </ totalSizeCap> </ rollingPolicy> logback.xml
58. <pattern>%d{YYYY-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n </ pattern> </ encoder> </ appender> <appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender"> <file>${LOG_DEST}/ktor-chuck-norris-sample.log </ file> <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy"> <!-- daily rollover --> <fileNamePattern>${LOG_DEST}/ktor-chuck-norris-sample.%d{yyyy-MM-dd}.log </ fileNamePattern> <!-- keep 90 days' worth of history capped at 3GB total size --> <maxHistory>${LOG_MAX_HISTORY} </ maxHistory> <totalSizeCap>3GB </ totalSizeCap> </ rollingPolicy> <encoder> <pattern>%d{YYYY-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n </ pattern> </ encoder> </ appender> <root level="info"> <appender-ref ref="STDOUT" /> />
59. @marcoGomier <encoder> <pattern>%d{YYYY-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{36} - % </ pattern> </ encoder> </ appender> <root level="info"> <appender-ref ref="STDOUT" /> <appender-ref ref="FILE" /> </ root> <logger name="org.eclipse.jetty" level="INFO" /> <logger name="io.netty" level="INFO" /> <logger name="org.quartz" level="INFO" /> </ configuration>
60. @marcoGomier Secrets
61. @marcoGomier local.properties tmdbKey="private_key"
62. @marcoGomier build.gradle.kts val String.byProperty: String? get() { val local = java.util.Properties() val localProperties: File = rootProject.file("local.properties") if (localProperties.exists()) { localProperties.inputStream().use { local.load(it) } return local.getProperty(this) } return null } tmdbKey="private_key" buildConfigField("String", "TMDB_KEY", "\"${"tmdbKey".byProperty ?: "")}\"")
63. @marcoGomier NetworkApiInterceptor.kt tmdbKey="private_key" buildConfigField("String", "TMDB_KEY", "\"${"tmdbKey".byProperty ?: "")}\"") val myKey: String = BuildConfig.TMDB_KEY
64. @marcoGomier application.conf
65. @marcoGomier ktor { deployment { port = 8080 port = ${?PORT} }ㅤ application { modules = [com.prof18.ktor.chucknorris.sample.ApplicationKt.module] }ㅤ server { isProd = false } database { driverClass = "com.mysql.cj.jdbc.Driver" url = "jdbc:mysql: / / localhost:3308/chucknorris?useUnicode=true&characterEncoding=UTF-8" user = "root" password = "password" maxPoolSize = 3 } } application.conf
66. ktor { deployment { port = 8080 port = ${?PORT} }ㅤ application { modules = [com.prof18.ktor.chucknorris.sample.ApplicationKt.module] }ㅤ server { isProd = false } database { driverClass = "com.mysql.cj.jdbc.Driver" // application.conf
67. @marcoGomier ktor { deployment { port = 8080 port = ${?PORT} }ㅤ application { modules = [com.prof18.ktor.chucknorris.sample.ApplicationKt.module] }ㅤ server { isProd = false } database { driverClass = "com.mysql.cj.jdbc.Driver" url = "jdbc:mysql: // localhost:3308/chucknorris?useUnicode=true&characterEncoding=UT user = "root" password = "password" maxPoolSize = 3 } }
68. @marcoGomier }ㅤ application { modules = [com.prof18.ktor.chucknorris.sample.ApplicationKt.module] }ㅤ server { isProd = false } database { driverClass = "com.mysql.cj.jdbc.Driver" url = "jdbc:mysql: // localhost:3308/chucknorris?useUnicode=true&characterEncoding=UT user = "root" password = "password" maxPoolSize = 3 } }
69. @marcoGomier data class ServerConfig( val isProd: Boolean )
70. @marcoGomier data class ServerConfig( val isProd: Boolean ) class AppConfig { lateinit var serverConfig: ServerConfig // Place here other configurations }
71. @marcoGomier data class ServerConfig( val isProd: Boolean ) class AppConfig { lateinit var serverConfig: ServerConfig // Place here other configurations } fun Application.setupConfig() { val appConfig by inject<AppConfig>() // Server val serverObject = environment.config.config("ktor.server") val isProd = serverObject.property("isProd").getString().toBoolean() appConfig.serverConfig = ServerConfig(isProd) }
72. @marcoGomier fun Application.module() { ... setupConfig() val appConfig by inject<AppConfig>() ... }
73. @marcoGomier java -jar ktor-backend.jar -config=/config-folder/application.conf
74. @marcoGomier Testing
75. @marcoGomier • Unit Test -> Just regular Kotlin Unit tests • androidTest -> TestEngine Testing https://ktor.io/docs/testing.html
76. @marcoGomier @Test fun testRoot() = testApplication { val response = client.get("/") assertEquals(HttpStatusCode.OK, response.status) assertEquals("Hello, world!", response.bodyAsText()) } https://ktor.io/docs/testing.html
77. @marcoGomier Deploy
78. @marcoGomier • aar • apk • aab Deploy
79. @marcoGomier ./gradlew assembleRelease ./gradlew bundleRelease
80. @marcoGomier • Fat JAR • Executable JVM application • WAR • GraalVM Deploy https://ktor.io/docs/deploy.html
81. @marcoGomier • Fat JAR • Executable JVM application • WAR • GraalVM Deploy https://ktor.io/docs/deploy.html
82. @marcoGomier https://github.com/ktorio/ktor-build-plugins build.gradle.kts plugins { ... id("io.ktor.plugin") version "2.3.0" }
83. @marcoGomier https://github.com/ktorio/ktor-build-plugins build.gradle.kts application { mainClass.set("io.ktor.server.netty.EngineMain") }
84. @marcoGomier https://github.com/ktorio/ktor-build-plugins ./gradlew buildFatJar
85. @marcoGomier
86. @marcoGomier Conclusions
87. @marcoGomier • Ktor is flexible and unopinionated -> Knowledge Transfer • Mobile knowledge can be adapted • Effective scaling and deploying can be hard • “Going to the other side” enrich your dev vision Conclusions
88. @marcoGomier https://github.com/prof18/ktor-chuck-norris-sample
89. Bibliography / Useful Links • https: / / ktor.io/ • https: / / ktor.io/learn/ • https: / / ktor.io/docs/welcome.html • https: / / ktor.io/docs/migrating-2.html • https: / / github.com/JetBrains/Exposed/wiki • https: / / www.marcogomiero.com/posts/2021/ktor-project-structure/ • https: / / www.marcogomiero.com/posts/2021/ktor-logging-on-disk/ • https: / / www.marcogomiero.com/posts/2021/ktor-in-memory-db-testing/ • https: / / www.marcogomiero.com/posts/2022/ktor-migration-liquibase/ • https: / / www.marcogomiero.com/posts/2022/ktor-setup-documentation/ • https: / / www.marcogomiero.com/posts/2022/ktor-jobs-quartz/ • https: / / www.marcogomiero.com/posts/2022/backend-from-mobile-ktor/
90. @marcoGomier Thank you! > Twitter: @marcoGomier 
 > Github: prof18 
 > Website: marcogomiero.com 
 > Mastodon: androiddev.social/@marcogom Marco Gomiero 👨💻 Senior Android Engineer 
 Google Developer Expert for Kotlin