[Spring Batch 마스터 클래스] Chapter 1: Spring Batch가 뭐고, 왜 필요한가?

@Component
class OrderReportScheduler(
    private val orderRepository: OrderRepository
) {
    
    @Scheduled(cron = "0 0 2 * * *")  // 매일 새벽 2시
    fun createDailyReport() {
        // 1. 어제 날짜의 모든 주문 조회
        val yesterday = LocalDate.now().minusDays(1)
        val orders = orderRepository.findByDate(yesterday)
        
        // 2. 주문 데이터 집계
        orders.forEach { order ->
            // 복잡한 비즈니스 로직...
        }
        
        // 3. 리포트 생성
        // 4. 이메일 발송
    }
}

@Bean
fun orderReportJob(jobRepository: JobRepository): Job {
    return JobBuilder("orderReportJob", jobRepository)
        .start(step1())
        .build()
}

@Bean
fun processOrderStep(
    jobRepository: JobRepository,
    transactionManager: PlatformTransactionManager
): Step {
    return StepBuilder("processOrderStep", jobRepository)
        .chunk<Order, OrderReport>(1000, transactionManager)  // 1000건씩 처리
        .reader(orderReader())
        .processor(orderProcessor())
        .writer(orderWriter())
        .build()
}

@Bean
fun parallelStep(
    jobRepository: JobRepository,
    partitioner: Partitioner
): Step {
    return StepBuilder("parallelStep", jobRepository)
        .partitioner("workerStep", partitioner)
        .gridSize(4)  // 4개 스레드로 병렬 처리
        .build()
}

dependencies {
    implementation("org.springframework.boot:spring-boot-starter-batch")
    implementation("org.springframework.boot:spring-boot-starter-data-jpa")
    implementation("org.jetbrains.kotlin:kotlin-reflect")
    runtimeOnly("com.h2database:h2")
    testImplementation("org.springframework.batch:spring-batch-test")
}

@SpringBootApplication
@EnableBatchProcessing  // Spring Boot 3.x에서는 이 어노테이션이 필수가 아님
class BatchApplication

fun main(args: Array<String>) {
    runApplication<BatchApplication>(*args)
}

spring:
  datasource:
    url: jdbc:h2:mem:testdb
    driver-class-name: org.h2.Driver
    username: sa
    password:
    
  batch:
    jdbc:
      initialize-schema: always  # 배치 메타 테이블 자동 생성
    job:
      enabled: false  # 애플리케이션 시작 시 자동 실행 방지
    
  h2:
    console:
      enabled: true  # H2 콘솔 활성화
      
  jpa:
    hibernate:
      ddl-auto: create-drop
    show-sql: true

@Configuration
class HelloBatchConfig {
    
    @Bean
    fun helloJob(
        jobRepository: JobRepository,
        helloStep: Step
    ): Job {
        return JobBuilder("helloJob", jobRepository)
            .start(helloStep)
            .build()
    }
    
    @Bean
    fun helloStep(
        jobRepository: JobRepository,
        transactionManager: PlatformTransactionManager
    ): Step {
        return StepBuilder("helloStep", jobRepository)
            .tasklet({ _, _ ->
                println("Hello, Spring Batch! 🎉")
                RepeatStatus.FINISHED
            }, transactionManager)
            .build()
    }
}

@RestController
@RequestMapping("/batch")
class BatchController(
    private val jobLauncher: JobLauncher,
    private val helloJob: Job
) {
    
    @PostMapping("/run")
    fun runBatch(): String {
        val jobParameters = JobParametersBuilder()
            .addLocalDateTime("requestTime", LocalDateTime.now())
            .toJobParameters()
            
        val execution = jobLauncher.run(helloJob, jobParameters)
        
        return "Batch job started with id: ${execution.id}"
    }
}

2025-07-27 10:00:00 INFO  --- [main] o.s.b.c.l.support.SimpleJobLauncher : Job: [helloJob] launched
2025-07-27 10:00:00 INFO  --- [main] o.s.batch.core.job.SimpleStepHandler : Executing step: [helloStep]
Hello, Spring Batch! 🎉
2025-07-27 10:00:00 INFO  --- [main] o.s.b.c.l.support.SimpleJobLauncher : Job: [helloJob] completed