构建基于Lagom的微服务项目实践

### 构建基于 Lagom 的微服务项目实践 #### 1. 面包师服务（BakerService）的定义与实现 面包师服务（BakerService）定义了处理生面团（RawCookies）并返回烘焙好的饼干（ReadyCookies）的功能。以下是其定义与实现的详细内容： - **服务定义**： ```scala trait BakerService extends Service { def bake: ServiceCall[Source[RawCookies, NotUsed], Future[Source[ReadyCookies, NotUsed]]] override def descriptor: Descriptor = named("BakerService").withCalls(call(bake)) } ``` 这里定义了 `BakerService` 接收 `Source[RawCookies, NotUsed]` 类型的请求，并返回 `Future[Source[ReadyCookies, NotUsed]]` 类型的响应。这允许我们在生面团可用时写入，并在烘焙后得到成品饼干。 - **服务实现**： ```scala import play.api.Logger class BakerServiceImpl extends BakerService { private val logger = Logger("Baker") override def bake: ServiceCall[Source[RawCookies, NotUsed], Source[ReadyCookies, NotUsed]] = ServiceCall { dough => logger.info(s"Baking: $dough") Future.successful(dough.via(bakerFlow)) } private val bakerFlow: Flow[RawCookies, ReadyCookies, NotUsed] = Baker.bakeFlow.join(Oven.bakeFlow) } ``` 实现部分复用了 `Baker` 和 `Oven` 的流程定义，并将组合后的流程作为调用结果返回。同时，还展示了如何使用底层 Play 框架提供的日志记录器。 #### 2. 厨师服务（ChefService）的持久化实现 厨师服务在混合食材的过程中可能会花费一些时间，为了防止服务重启时工作丢失，我们使用 Lagom 框架提供的持久化功能。具体步骤如下： - **导入必要的包**： ```scala import ch15.model._ import java.util.UUID import akka.Done import com.lightbend.lagom.scaladsl.persistence._ import PersistentEntity.ReplyType import com.lightbend.lagom.scaladsl.playjson.JsonSerializer import play.api.libs.json._ ``` - **定义命令**： ```scala sealed trait ChefCommand final case class MixCommand(groceries: Groceries) extends ChefCommand with ReplyType[Done] final case class DoneCommand(id: UUID) extends ChefCommand with ReplyType[Done] ``` `MixCommand` 表示混合食材的请求，`DoneCommand` 表示混合完成的状态转换。 - **定义事件**： ```scala sealed trait ChefEvent final case class Mixing(id: UUID, groceries: Groceries) extends ChefEvent final case class MixingDone(id: UUID, dough: Dough) extends ChefEvent with AggregateEvent[MixingDone] { override def aggregateTag: AggregateEventTag[MixingDone] = ChefModel.EventTag } ``` `Mixing` 事件响应 `MixCommand`，`MixingDone` 事件响应 `DoneCommand`。 - **定义状态**： ```scala sealed trait ChefState { def batches: List[Mixing] } final case class MixingState(batches: List[Mixing]) extends ChefState ``` - **定义序列化器和事件标签**： ```scala object ChefModel { import play.api.libs.json._ implicit val mixingFormat = Json.format[Mixing] val serializers = List( JsonSerializer(mixingFormat), JsonSerializer(Json.format[MixingDone]), JsonSerializer(Json.format[MixingState]) ) val EventTag: AggregateEventTag[MixingDone] = AggregateEventTag[MixingDone]("MixingDone") } ``` - **配置 Cassandra 键空间**： 在 `application.conf` 中进行如下配置： ```plaintext user.cassandra.keyspace = chefprogress cassandra-journal.keyspace = ${user.cassandra.keyspace} cassandra-snapshot-store.keyspace = ${user.cassandra.keyspace} lagom.persistence.read-side.cassandra.keyspace = ${user.cassandra.keyspace} ``` - **定义服务接口**： ```scala trait ChefService extends Service { def mix: ServiceCall[Groceries, Done] def resultsTopic: Topic[Dough] override def descriptor: Descriptor = { named("ChefService") .withCalls(call(mix)) .withTopics(topic(ChefService.ResultsTopic, resultsTopic)) .withAutoAcl(true) } } object ChefService { val ResultsTopic = "MixedResults" } ``` - **服务实现**： ```scala class ChefServiceImpl(persistentEntities: PersistentEntityRegistry, as: ActorSystem) extends ChefService { private lazy val entity = wire[ChefPersistentEntity] persistentEntities.register(entity) override def mix: ServiceC ```