Lagom学习 （二）

以一个官方的例子，开启lagom的学习之旅。

1：   git clone https://github.com/lagom/activator-lagom-java-chirper.git。

2：   下载后进入目录，运行mvn lagom:runAll。

 3： 浏览器输入：localhost:9000

4:  模块：

　　Chirp service: 负责存储聊天，提供存储接口服务。
　　Friend service: 负责用户存储，管理朋友关系。
　　Activity Stream service: 为聊天提供流数据的支持，依赖于 Chirp与Friend 服务。
　　Front-End service: 提供前台用户UI。

5： 

• An api project：   that contains a service interface through which consumers can interact with the service.
• An impl project：  that contains the service implementation.

ActivityStreamService.java

/*
 * Copyright (C) 2016 Lightbend Inc. <http://www.lightbend.com>
 */
package sample.chirper.activity.api;

import sample.chirper.chirp.api.Chirp;

import akka.stream.javadsl.Source;

import akka.NotUsed;
import com.lightbend.lagom.javadsl.api.ServiceCall;
import com.lightbend.lagom.javadsl.api.Descriptor;
import com.lightbend.lagom.javadsl.api.Service;
import static com.lightbend.lagom.javadsl.api.Service.*;

public interface ActivityStreamService extends Service {

  ServiceCall<NotUsed, Source<Chirp, ?>> getLiveActivityStream(String userId);

  ServiceCall<NotUsed, Source<Chirp, ?>> getHistoricalActivityStream(String userId);

  @Override
  default Descriptor descriptor() {
    // @formatter:off
    return named("activityservice").withCalls(
        pathCall("/api/activity/:userId/live", this::getLiveActivityStream),
        pathCall("/api/activity/:userId/history", this::getHistoricalActivityStream)
      ).withAutoAcl(true);
    // @formatter:on
  }
}

Service interface (ActivityStreamService.java):

• 这个自定义的服务继承自 Service， 并且提供了一个Service.descriptor方法的实现。
• Service.descriptor 返回 Descriptor，定义了服务的名称，并且定义了提供的REST API。
• 提供了两个接口：getLiveActivityStream  /  getHistoricalActivityStream
• 关于 Service descriptor详细信息，https://www.lagomframework.com/documentation/1.4.x/java/ServiceDescriptors.html

Service implementation(ActivityStreamServiceImpl.java)

         提供了对ActivityStreamService.java的实现

/*
 * Copyright (C) 2016 Lightbend Inc. <http://www.lightbend.com>
 */
package sample.chirper.activity.impl;

import akka.NotUsed;
import com.lightbend.lagom.javadsl.api.ServiceCall;
import java.time.Duration;
import java.time.Instant;
import java.util.concurrent.CompletionStage;
import javax.inject.Inject;
import org.pcollections.PSequence;
import sample.chirper.activity.api.ActivityStreamService;
import sample.chirper.chirp.api.Chirp;
import sample.chirper.chirp.api.ChirpService;
import sample.chirper.chirp.api.HistoricalChirpsRequest;
import sample.chirper.chirp.api.LiveChirpsRequest;
import sample.chirper.friend.api.FriendService;

import akka.stream.javadsl.Source;

public class ActivityStreamServiceImpl implements ActivityStreamService {

  private final FriendService friendService;
  private final ChirpService chirpService;

  @Inject
  public ActivityStreamServiceImpl(FriendService friendService, ChirpService chirpService) {
    this.friendService = friendService;
    this.chirpService = chirpService;
  }

  @Override
  public ServiceCall<NotUsed, Source<Chirp, ?>> getLiveActivityStream(String userId) {
    return req -> {
      return friendService.getUser(userId).invoke().thenCompose(user -> {
        PSequence<String> userIds = user.friends.plus(userId);
        LiveChirpsRequest chirpsReq =  new LiveChirpsRequest(userIds);
        // Note that this stream will not include changes to friend associates,
        // e.g. adding a new friend.
        CompletionStage<Source<Chirp, ?>> result = chirpService.getLiveChirps().invoke(chirpsReq);
        return result;
      });
    };
  }

  @Override
  public ServiceCall<NotUsed, Source<Chirp, ?>> getHistoricalActivityStream(String userId) {
    return req ->
      friendService.getUser(userId).invoke().thenCompose(user -> {
        PSequence<String> userIds = user.friends.plus(userId);
        // FIXME we should use HistoricalActivityStreamReq request parameter
        Instant fromTime = Instant.now().minus(Duration.ofDays(7));
        HistoricalChirpsRequest chirpsReq = new HistoricalChirpsRequest(fromTime, userIds);
        CompletionStage<Source<Chirp, ?>> result = chirpService.getHistoricalChirps().invoke(chirpsReq);
        return result;
      });
  }

}