Spring Batch 5 面接対策: パーティショニング・チャンク・フォールトトレランス

// Java 21 を用いた Spring Batch 5 のジョブ設定
@Configuration
public class BatchJobConfig {

    // JobRepository は実行メタデータを保存します
    // ジョブのリスタートと監視を可能にします
    private final JobRepository jobRepository;
    private final PlatformTransactionManager transactionManager;

    public BatchJobConfig(JobRepository jobRepository,
                          PlatformTransactionManager transactionManager) {
        this.jobRepository = jobRepository;
        this.transactionManager = transactionManager;
    }

    // Job はバッチプロセス全体をカプセル化します
    // 一つ以上の Step が順序付きで実行されます
    @Bean
    public Job importUserJob(Step processUsersStep, Step cleanupStep) {
        return new JobBuilder("importUserJob", jobRepository)
                .start(processUsersStep)      // メイン処理ステップ
                .next(cleanupStep)             // クリーンアップステップ
                .build();
    }

    // Step は独立した作業単位を表します
    // 二つのモデル: Tasklet(単一タスク)または Chunk(反復処理)
    @Bean
    public Step processUsersStep(ItemReader<UserRecord> reader,
                                  ItemProcessor<UserRecord, User> processor,
                                  ItemWriter<User> writer) {
        return new StepBuilder("processUsersStep", jobRepository)
                .<UserRecord, User>chunk(100, transactionManager)  // 100件ごとにコミット
                .reader(reader)       // 元データを読み取り
                .processor(processor) // 各アイテムを変換
                .writer(writer)       // 100件単位で書き込み
                .build();
    }
}

// Tasklet: 反復のない単一アクション
@Component
public class CleanupTasklet implements Tasklet {

    private final Path tempDirectory = Path.of("/tmp/batch-work");

    @Override
    public RepeatStatus execute(StepContribution contribution,
                                 ChunkContext chunkContext) throws Exception {
        // 処理に伴う一時ファイルをすべて削除
        try (var files = Files.walk(tempDirectory)) {
            files.filter(Files::isRegularFile)
                 .forEach(this::deleteQuietly);
        }

        // FINISHED は tasklet が処理を完了したことを示します
        // CONTINUABLE を返すと再実行されます(ポーリング向け)
        return RepeatStatus.FINISHED;
    }

    private void deleteQuietly(Path file) {
        try {
            Files.delete(file);
        } catch (IOException e) {
            // ログ出力して継続 - 1ファイルでジョブを失敗させない
        }
    }
}

// チャンク処理: 大量処理向け
@Configuration
public class ChunkProcessingConfig {

    @Bean
    public Step processOrdersStep(JobRepository jobRepository,
                                   PlatformTransactionManager transactionManager,
                                   ItemReader<OrderRecord> reader,
                                   ItemProcessor<OrderRecord, ProcessedOrder> processor,
                                   ItemWriter<ProcessedOrder> writer) {
        return new StepBuilder("processOrdersStep", jobRepository)
                // 500件のチャンク: 500件読み込み・処理・書き込み・コミット
                .<OrderRecord, ProcessedOrder>chunk(500, transactionManager)
                .reader(reader)
                .processor(processor)
                .writer(writer)
                // 進捗監視のリスナー
                .listener(new ChunkProgressListener())
                .build();
    }
}

// ItemReader: 一件ずつ読み取ります
@StepScope
@Component
public class OrderItemReader implements ItemReader<OrderRecord> {

    // @StepScope: Step 実行ごとに新しいインスタンス
    // 動的なジョブパラメーターを注入可能にします
    @Value("#{jobParameters['startDate']}")
    private LocalDate startDate;

    private Iterator<OrderRecord> orderIterator;

    @BeforeStep
    public void initializeReader(StepExecution stepExecution) {
        // Step 開始時にデータをロード
        List<OrderRecord> orders = fetchOrdersFromDate(startDate);
        this.orderIterator = orders.iterator();
    }

    @Override
    public OrderRecord read() {
        // データ終端を示すため null を返す
        // Spring Batch は null を受け取るまで read() を呼び続けます
        if (orderIterator.hasNext()) {
            return orderIterator.next();
        }
        return null;  // データセットの終端
    }

    private List<OrderRecord> fetchOrdersFromDate(LocalDate date) {
        // データソースから取得
        return List.of();  // 実際の実装
    }
}

// ItemProcessor: 各アイテムを個別に変換
@Component
public class OrderItemProcessor implements ItemProcessor<OrderRecord, ProcessedOrder> {

    private final PricingService pricingService;
    private final ValidationService validationService;

    public OrderItemProcessor(PricingService pricingService,
                               ValidationService validationService) {
        this.pricingService = pricingService;
        this.validationService = validationService;
    }

    @Override
    public ProcessedOrder process(OrderRecord item) {
        // null を返すとアイテムをフィルタ(書き込まれない)
        if (!validationService.isValid(item)) {
            return null;  // アイテムを除外
        }

        // ビジネス変換
        BigDecimal finalPrice = pricingService.calculatePrice(item);

        return new ProcessedOrder(
                item.orderId(),
                item.customerId(),
                finalPrice,
                LocalDateTime.now()
        );
    }
}

// ItemWriter: チャンク全体を一回の操作で書き込み
@Component
public class OrderItemWriter implements ItemWriter<ProcessedOrder> {

    private final JdbcTemplate jdbcTemplate;

    public OrderItemWriter(JdbcTemplate jdbcTemplate) {
        this.jdbcTemplate = jdbcTemplate;
    }

    @Override
    public void write(Chunk<? extends ProcessedOrder> chunk) {
        // チャンクは処理済みの全アイテムを保持
        // 最適なパフォーマンスのためバッチ書き込み
        List<? extends ProcessedOrder> items = chunk.getItems();

        jdbcTemplate.batchUpdate(
                "INSERT INTO processed_orders (order_id, customer_id, final_price, processed_at) VALUES (?, ?, ?, ?)",
                items,
                items.size(),
                (ps, order) -> {
                    ps.setLong(1, order.orderId());
                    ps.setLong(2, order.customerId());
                    ps.setBigDecimal(3, order.finalPrice());
                    ps.setTimestamp(4, Timestamp.valueOf(order.processedAt()));
                }
        );
    }
}

// チャンクサイズの動的設定
@Configuration
public class ChunkSizingConfig {

    // 多くの場合に妥当なデフォルト値
    private static final int DEFAULT_CHUNK_SIZE = 100;

    // 軽量アイテム(フィールドが少ない)向け
    private static final int LIGHT_ITEMS_CHUNK_SIZE = 500;

    // 重量アイテム(blob、ドキュメント)向け
    private static final int HEAVY_ITEMS_CHUNK_SIZE = 25;

    @Bean
    public Step processLightDataStep(JobRepository jobRepository,
                                      PlatformTransactionManager txManager,
                                      ItemReader<LightRecord> reader,
                                      ItemWriter<LightRecord> writer) {
        return new StepBuilder("processLightDataStep", jobRepository)
                // 軽量アイテム: コミット回数を減らすため大きめのチャンク
                .<LightRecord, LightRecord>chunk(LIGHT_ITEMS_CHUNK_SIZE, txManager)
                .reader(reader)
                .writer(writer)
                .build();
    }

    @Bean
    public Step processDocumentsStep(JobRepository jobRepository,
                                      PlatformTransactionManager txManager,
                                      ItemReader<Document> reader,
                                      ItemProcessor<Document, ProcessedDocument> processor,
                                      ItemWriter<ProcessedDocument> writer) {
        return new StepBuilder("processDocumentsStep", jobRepository)
                // 重いドキュメント: メモリ抑制のため小さめのチャンク
                .<Document, ProcessedDocument>chunk(HEAVY_ITEMS_CHUNK_SIZE, txManager)
                .reader(reader)
                .processor(processor)
                .writer(writer)
                .build();
    }
}

// パーティション化されたジョブの設定
@Configuration
public class PartitionedJobConfig {

    private final JobRepository jobRepository;
    private final PlatformTransactionManager transactionManager;

    public PartitionedJobConfig(JobRepository jobRepository,
                                 PlatformTransactionManager transactionManager) {
        this.jobRepository = jobRepository;
        this.transactionManager = transactionManager;
    }

    @Bean
    public Job partitionedImportJob(Step partitionedStep) {
        return new JobBuilder("partitionedImportJob", jobRepository)
                .start(partitionedStep)
                .build();
    }

    // マネージャー Step: パーティションを統制
    @Bean
    public Step partitionedStep(Partitioner partitioner,
                                 Step workerStep,
                                 TaskExecutor taskExecutor) {
        return new StepBuilder("partitionedStep", jobRepository)
                // Partitioner で作業を分割
                .partitioner("workerStep", partitioner)
                // 各パーティションで実行する Step
                .step(workerStep)
                // 8 並列スレッド
                .taskExecutor(taskExecutor)
                // 作成するパーティション数
                .gridSize(8)
                .build();
    }

    // 並列実行用の TaskExecutor
    @Bean
    public TaskExecutor batchTaskExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(8);
        executor.setMaxPoolSize(16);
        executor.setQueueCapacity(50);
        executor.setThreadNamePrefix("batch-partition-");
        executor.initialize();
        return executor;
    }
}

// ID 範囲ベースの Partitioner
@Component
public class RangePartitioner implements Partitioner {

    private final JdbcTemplate jdbcTemplate;

    public RangePartitioner(JdbcTemplate jdbcTemplate) {
        this.jdbcTemplate = jdbcTemplate;
    }

    @Override
    public Map<String, ExecutionContext> partition(int gridSize) {
        // データセットの境界を取得
        Long minId = jdbcTemplate.queryForObject(
                "SELECT MIN(id) FROM orders WHERE status = 'PENDING'", Long.class);
        Long maxId = jdbcTemplate.queryForObject(
                "SELECT MAX(id) FROM orders WHERE status = 'PENDING'", Long.class);

        if (minId == null || maxId == null) {
            return Map.of();  // 処理対象データなし
        }

        // 各パーティションのサイズを計算
        long range = (maxId - minId) / gridSize + 1;
        Map<String, ExecutionContext> partitions = new HashMap<>();

        for (int i = 0; i < gridSize; i++) {
            ExecutionContext context = new ExecutionContext();
            long start = minId + (i * range);
            long end = Math.min(start + range - 1, maxId);

            // 各パーティションが境界値を受け取る
            context.putLong("minId", start);
            context.putLong("maxId", end);
            context.putInt("partitionNumber", i);

            partitions.put("partition" + i, context);
        }

        return partitions;
    }
}

// メッセージングを用いたリモートパーティショニング設定
@Configuration
public class RemotePartitioningConfig {

    @Bean
    public Step managerStep(JobRepository jobRepository,
                             Partitioner partitioner,
                             MessageChannelPartitionHandler partitionHandler) {
        return new StepBuilder("managerStep", jobRepository)
                .partitioner("workerStep", partitioner)
                // リモート worker と通信するハンドラ
                .partitionHandler(partitionHandler)
                .build();
    }

    // PartitionHandler は ExecutionContext を worker へ送信
    @Bean
    public MessageChannelPartitionHandler partitionHandler(
            MessagingTemplate messagingTemplate,
            JobExplorer jobExplorer) {
        MessageChannelPartitionHandler handler = new MessageChannelPartitionHandler();
        handler.setStepName("workerStep");
        handler.setGridSize(4);
        handler.setMessagingOperations(messagingTemplate);
        handler.setJobExplorer(jobExplorer);
        // worker の完了待ちタイムアウト
        handler.setPollInterval(5000L);
        return handler;
    }
}

// worker 側の設定
@Configuration
public class WorkerConfiguration {

    private final JobRepository jobRepository;
    private final PlatformTransactionManager transactionManager;

    public WorkerConfiguration(JobRepository jobRepository,
                                PlatformTransactionManager transactionManager) {
        this.jobRepository = jobRepository;
        this.transactionManager = transactionManager;
    }

    // worker はパーティションを受け取り Step を実行
    @Bean
    public Step workerStep(ItemReader<OrderRecord> reader,
                            ItemProcessor<OrderRecord, ProcessedOrder> processor,
                            ItemWriter<ProcessedOrder> writer) {
        return new StepBuilder("workerStep", jobRepository)
                .<OrderRecord, ProcessedOrder>chunk(100, transactionManager)
                // パーティションパラメーターを受け取るため @StepScope を設定
                .reader(reader)
                .processor(processor)
                .writer(writer)
                .build();
    }

    // パーティション境界を使う Reader
    @Bean
    @StepScope
    public JdbcCursorItemReader<OrderRecord> partitionedReader(
            DataSource dataSource,
            @Value("#{stepExecutionContext['minId']}") Long minId,
            @Value("#{stepExecutionContext['maxId']}") Long maxId) {
        return new JdbcCursorItemReaderBuilder<OrderRecord>()
                .name("partitionedOrderReader")
                .dataSource(dataSource)
                .sql("SELECT * FROM orders WHERE id BETWEEN ? AND ? AND status = 'PENDING'")
                .preparedStatementSetter(ps -> {
                    ps.setLong(1, minId);
                    ps.setLong(2, maxId);
                })
                .rowMapper(new OrderRecordRowMapper())
                .build();
    }
}

// 包括的なフォールトトレランス設定
@Configuration
public class FaultTolerantStepConfig {

    @Bean
    public Step faultTolerantStep(JobRepository jobRepository,
                                   PlatformTransactionManager transactionManager,
                                   ItemReader<DataRecord> reader,
                                   ItemProcessor<DataRecord, ProcessedRecord> processor,
                                   ItemWriter<ProcessedRecord> writer,
                                   SkipPolicy customSkipPolicy) {
        return new StepBuilder("faultTolerantStep", jobRepository)
                .<DataRecord, ProcessedRecord>chunk(100, transactionManager)
                .reader(reader)
                .processor(processor)
                .writer(writer)
                // フォールトトレラントモードを有効化
                .faultTolerant()
                // SKIP: 検証エラーを最大 10 件まで無視
                .skipLimit(10)
                .skip(ValidationException.class)
                .skip(DataIntegrityViolationException.class)
                // 一部のエラーは決してスキップしない
                .noSkip(FatalBatchException.class)
                // RETRY: 一時的なエラーをリトライ
                .retryLimit(3)
                .retry(TransientDataAccessException.class)
                .retry(DeadlockLoserDataAccessException.class)
                // リトライ間の指数バックオフ
                .backOffPolicy(exponentialBackOffPolicy())
                // スキップを記録するリスナー
                .listener(skipListener())
                .build();
    }

    @Bean
    public BackOffPolicy exponentialBackOffPolicy() {
        ExponentialBackOffPolicy policy = new ExponentialBackOffPolicy();
        policy.setInitialInterval(1000);  // 1 秒
        policy.setMultiplier(2.0);         // リトライごとに倍
        policy.setMaxInterval(10000);      // 最大 10 秒
        return policy;
    }

    @Bean
    public SkipListener<DataRecord, ProcessedRecord> skipListener() {
        return new SkipListener<>() {
            @Override
            public void onSkipInRead(Throwable t) {
                // 読み取り不能アイテムをログ
            }

            @Override
            public void onSkipInProcess(DataRecord item, Throwable t) {
                // 処理に失敗したアイテムをログ
            }

            @Override
            public void onSkipInWrite(ProcessedRecord item, Throwable t) {
                // 書き込みに失敗したアイテムをログ
            }
        };
    }
}

// 高度な業務ロジックを持つ SkipPolicy
@Component
public class AdaptiveSkipPolicy implements SkipPolicy {

    private static final int MAX_SKIP_COUNT = 100;
    private static final double MAX_SKIP_PERCENTAGE = 0.05;  // 最大 5%

    private final AtomicInteger totalProcessed = new AtomicInteger(0);
    private final AtomicInteger skipCount = new AtomicInteger(0);

    @Override
    public boolean shouldSkip(Throwable exception, long skipCountSoFar) {
        // 致命的エラーは決してスキップしない
        if (exception instanceof FatalBatchException
                || exception instanceof OutOfMemoryError) {
            return false;
        }

        // スキップ数の絶対上限
        if (skipCountSoFar >= MAX_SKIP_COUNT) {
            return false;  // ジョブを停止
        }

        // パーセンテージ上限
        int total = totalProcessed.get();
        if (total > 1000) {  // ウォームアップ後にのみ適用
            double skipPercentage = (double) skipCountSoFar / total;
            if (skipPercentage > MAX_SKIP_PERCENTAGE) {
                return false;  // 比率としてエラーが多すぎる
            }
        }

        // 検証・データエラーをスキップ
        return exception instanceof ValidationException
                || exception instanceof DataFormatException
                || exception instanceof IllegalArgumentException;
    }

    // リスナーから呼ばれ進捗を追跡
    public void incrementProcessed() {
        totalProcessed.incrementAndGet();
    }
}

// ジョブリスタート管理サービス
@Service
public class JobRestartService {

    private final JobLauncher jobLauncher;
    private final JobExplorer jobExplorer;
    private final JobRepository jobRepository;
    private final Job importJob;

    public JobRestartService(JobLauncher jobLauncher,
                              JobExplorer jobExplorer,
                              JobRepository jobRepository,
                              @Qualifier("importJob") Job importJob) {
        this.jobLauncher = jobLauncher;
        this.jobExplorer = jobExplorer;
        this.jobRepository = jobRepository;
        this.importJob = importJob;
    }

    public JobExecution restartFailedJob(Long jobExecutionId) throws Exception {
        // 失敗した実行を取得
        JobExecution failedExecution = jobExplorer.getJobExecution(jobExecutionId);

        if (failedExecution == null) {
            throw new IllegalArgumentException("Job execution not found: " + jobExecutionId);
        }

        // ジョブが再開可能か確認
        if (!failedExecution.getStatus().equals(BatchStatus.FAILED)) {
            throw new IllegalStateException("Only FAILED jobs can be restarted");
        }

        // 元の実行と同じパラメーターを使用
        JobParameters originalParams = failedExecution.getJobParameters();

        // ジョブを再起動 - 最終チェックポイントから自動再開
        return jobLauncher.run(importJob, originalParams);
    }

    public List<JobExecution> findRestartableJobs() {
        // 再開未実施の FAILED 実行を一覧化
        return jobExplorer.findJobInstancesByJobName(importJob.getName(), 0, 100)
                .stream()
                .flatMap(instance -> jobExplorer.getJobExecutions(instance).stream())
                .filter(exec -> exec.getStatus() == BatchStatus.FAILED)
                .filter(this::isRestartable)
                .toList();
    }

    private boolean isRestartable(JobExecution execution) {
        // より新しい成功実行が存在しないことを確認
        JobInstance instance = execution.getJobInstance();
        return jobExplorer.getJobExecutions(instance).stream()
                .noneMatch(exec -> exec.getStatus() == BatchStatus.COMPLETED);
    }
}

// マルチスレッド Step: 複数スレッドが同じデータセットを処理
@Configuration
public class MultiThreadedStepConfig {

    @Bean
    public Step multiThreadedStep(JobRepository jobRepository,
                                   PlatformTransactionManager transactionManager,
                                   ItemReader<Record> reader,
                                   ItemProcessor<Record, ProcessedRecord> processor,
                                   ItemWriter<ProcessedRecord> writer,
                                   TaskExecutor taskExecutor) {
        return new StepBuilder("multiThreadedStep", jobRepository)
                .<Record, ProcessedRecord>chunk(100, transactionManager)
                // 注意: reader はスレッドセーフでなければならない
                .reader(synchronizedReader(reader))
                .processor(processor)
                .writer(writer)
                // 4 スレッドが並列にチャンクを処理
                .taskExecutor(taskExecutor)
                .throttleLimit(4)
                .build();
    }

    // reader をスレッドセーフにするラッパー
    private ItemReader<Record> synchronizedReader(ItemReader<Record> reader) {
        SynchronizedItemStreamReader<Record> syncReader = new SynchronizedItemStreamReader<>();
        syncReader.setDelegate((ItemStreamReader<Record>) reader);
        return syncReader;
    }
}

// 独立 Step を並列実行
@Configuration
public class ParallelStepsConfig {

    @Bean
    public Job parallelJob(JobRepository jobRepository,
                            Step loadCustomersStep,
                            Step loadProductsStep,
                            Step loadOrdersStep,
                            Step processDataStep) {
        // 並列フロー: customers と products を同時にロード
        Flow loadCustomersFlow = new FlowBuilder<Flow>("loadCustomersFlow")
                .start(loadCustomersStep)
                .build();

        Flow loadProductsFlow = new FlowBuilder<Flow>("loadProductsFlow")
                .start(loadProductsStep)
                .build();

        Flow loadOrdersFlow = new FlowBuilder<Flow>("loadOrdersFlow")
                .start(loadOrdersStep)
                .build();

        // Split がフローを並列実行
        return new JobBuilder("parallelJob", jobRepository)
                .start(new FlowBuilder<Flow>("parallelLoadFlow")
                        .split(new SimpleAsyncTaskExecutor())
                        .add(loadCustomersFlow, loadProductsFlow, loadOrdersFlow)
                        .build())
                // 並列ロード後に逐次処理
                .next(processDataStep)
                .build()
                .build();
    }
}

// Micrometer による監視設定
@Configuration
public class BatchMetricsConfig {

    private final MeterRegistry meterRegistry;

    public BatchMetricsConfig(MeterRegistry meterRegistry) {
        this.meterRegistry = meterRegistry;
    }

    @Bean
    public JobExecutionListener metricsJobListener() {
        return new JobExecutionListener() {

            private Timer.Sample jobTimer;

            @Override
            public void beforeJob(JobExecution jobExecution) {
                // ジョブ時間タイマーを開始
                jobTimer = Timer.start(meterRegistry);
                Counter.builder("batch.job.started")
                        .tag("job", jobExecution.getJobInstance().getJobName())
                        .register(meterRegistry)
                        .increment();
            }

            @Override
            public void afterJob(JobExecution jobExecution) {
                // 合計時間を記録
                jobTimer.stop(Timer.builder("batch.job.duration")
                        .tag("job", jobExecution.getJobInstance().getJobName())
                        .tag("status", jobExecution.getStatus().toString())
                        .register(meterRegistry));

                // ステータス別ジョブカウンタ
                Counter.builder("batch.job.completed")
                        .tag("job", jobExecution.getJobInstance().getJobName())
                        .tag("status", jobExecution.getStatus().toString())
                        .register(meterRegistry)
                        .increment();
            }
        };
    }

    @Bean
    public StepExecutionListener metricsStepListener() {
        return new StepExecutionListener() {

            @Override
            public void afterStep(StepExecution stepExecution) {
                String jobName = stepExecution.getJobExecution().getJobInstance().getJobName();
                String stepName = stepExecution.getStepName();

                // スループットメトリクス
                Gauge.builder("batch.step.read.count", stepExecution, StepExecution::getReadCount)
                        .tag("job", jobName)
                        .tag("step", stepName)
                        .register(meterRegistry);

                Gauge.builder("batch.step.write.count", stepExecution, StepExecution::getWriteCount)
                        .tag("job", jobName)
                        .tag("step", stepName)
                        .register(meterRegistry);

                Gauge.builder("batch.step.skip.count", stepExecution, StepExecution::getSkipCount)
                        .tag("job", jobName)
                        .tag("step", stepName)
                        .register(meterRegistry);

                return null;
            }
        };
    }
}

// 実際に負荷を均すパーティショナー
@Component
public class BalancedPartitioner implements Partitioner {

    private final JdbcTemplate jdbcTemplate;

    public BalancedPartitioner(JdbcTemplate jdbcTemplate) {
        this.jdbcTemplate = jdbcTemplate;
    }

    @Override
    public Map<String, ExecutionContext> partition(int gridSize) {
        // 処理対象アイテム総数を取得
        Integer totalCount = jdbcTemplate.queryForObject(
                "SELECT COUNT(*) FROM orders WHERE status = 'PENDING'", Integer.class);

        if (totalCount == null || totalCount == 0) {
            return Map.of();
        }

        // パーティションごとの目標サイズを算出
        int itemsPerPartition = (int) Math.ceil((double) totalCount / gridSize);

        Map<String, ExecutionContext> partitions = new HashMap<>();

        // OFFSET/LIMIT でバランスの取れたパーティションを生成
        // 範囲指定よりコストは高いが均衡を保証
        for (int i = 0; i < gridSize; i++) {
            ExecutionContext context = new ExecutionContext();
            context.putInt("offset", i * itemsPerPartition);
            context.putInt("limit", itemsPerPartition);
            context.putInt("partitionNumber", i);

            partitions.put("partition" + i, context);
        }

        return partitions;
    }
}

// OffsetBasedReader.java
// オフセットベースのパーティショニングと互換のリーダー
@StepScope
@Component
public class OffsetBasedReader implements ItemReader<OrderRecord>, ItemStream {

    private final JdbcTemplate jdbcTemplate;
    private Iterator<OrderRecord> iterator;

    @Value("#{stepExecutionContext['offset']}")
    private int offset;

    @Value("#{stepExecutionContext['limit']}")
    private int limit;

    public OffsetBasedReader(JdbcTemplate jdbcTemplate) {
        this.jdbcTemplate = jdbcTemplate;
    }

    @Override
    public void open(ExecutionContext executionContext) {
        // このパーティションに割り当てられた範囲だけをロード
        List<OrderRecord> records = jdbcTemplate.query(
                "SELECT * FROM orders WHERE status = 'PENDING' ORDER BY id LIMIT ? OFFSET ?",
                new OrderRecordRowMapper(),
                limit, offset
        );
        this.iterator = records.iterator();
    }

    @Override
    public OrderRecord read() {
        return iterator.hasNext() ? iterator.next() : null;
    }

    @Override
    public void update(ExecutionContext executionContext) {
        // 必要ならリスタート用に状態を保存
    }

    @Override
    public void close() {
        // クリーンアップ
    }
}

// ジョブ間依存管理
@Service
public class JobDependencyService {

    private final JobExplorer jobExplorer;
    private final JobLauncher jobLauncher;
    private final Map<String, Job> jobs;

    public JobDependencyService(JobExplorer jobExplorer,
                                  JobLauncher jobLauncher,
                                  Map<String, Job> jobs) {
        this.jobExplorer = jobExplorer;
        this.jobLauncher = jobLauncher;
        this.jobs = jobs;
    }

    public JobExecution runWithDependencies(String jobName,
                                             JobParameters params,
                                             List<String> dependsOn) throws Exception {
        // すべての依存が成功しているか確認
        for (String dependency : dependsOn) {
            if (!hasSuccessfulExecution(dependency, params)) {
                throw new JobExecutionException(
                        "Dependency not satisfied: " + dependency);
            }
        }

        Job job = jobs.get(jobName);
        if (job == null) {
            throw new IllegalArgumentException("Unknown job: " + jobName);
        }

        return jobLauncher.run(job, params);
    }

    private boolean hasSuccessfulExecution(String jobName, JobParameters params) {
        // 同じ業務パラメーターで COMPLETED になった実行を探す
        return jobExplorer.findJobInstancesByJobName(jobName, 0, 1)
                .stream()
                .flatMap(instance -> jobExplorer.getJobExecutions(instance).stream())
                .filter(exec -> exec.getStatus() == BatchStatus.COMPLETED)
                .anyMatch(exec -> matchesBusinessParams(exec.getJobParameters(), params));
    }

    private boolean matchesBusinessParams(JobParameters actual, JobParameters expected) {
        // 業務パラメーターを比較(実行タイムスタンプは無視)
        String actualDate = actual.getString("businessDate");
        String expectedDate = expected.getString("businessDate");
        return Objects.equals(actualDate, expectedDate);
    }
}

// Processor のユニットテスト
@ExtendWith(MockitoExtension.class)
class OrderProcessorTest {

    @Mock
    private PricingService pricingService;

    @Mock
    private ValidationService validationService;

    @InjectMocks
    private OrderItemProcessor processor;

    @Test
    void shouldProcessValidOrder() {
        // Given
        OrderRecord input = new OrderRecord(1L, 100L, BigDecimal.TEN);
        when(validationService.isValid(input)).thenReturn(true);
        when(pricingService.calculatePrice(input)).thenReturn(new BigDecimal("12.50"));

        // When
        ProcessedOrder result = processor.process(input);

        // Then
        assertThat(result).isNotNull();
        assertThat(result.finalPrice()).isEqualTo(new BigDecimal("12.50"));
    }

    @Test
    void shouldFilterInvalidOrder() {
        // Given
        OrderRecord input = new OrderRecord(1L, 100L, BigDecimal.TEN);
        when(validationService.isValid(input)).thenReturn(false);

        // When
        ProcessedOrder result = processor.process(input);

        // Then - null はフィルタを意味
        assertThat(result).isNull();
        verify(pricingService, never()).calculatePrice(any());
    }
}

// ジョブ全体の統合テスト
@SpringBatchTest
@SpringBootTest
@ActiveProfiles("test")
class ImportJobIntegrationTest {

    @Autowired
    private JobLauncherTestUtils jobLauncherTestUtils;

    @Autowired
    private JobRepositoryTestUtils jobRepositoryTestUtils;

    @Autowired
    private JdbcTemplate jdbcTemplate;

    @BeforeEach
    void setup() {
        // テスト間でメタデータを掃除
        jobRepositoryTestUtils.removeJobExecutions();
        // テストデータを初期化
        jdbcTemplate.execute("DELETE FROM processed_orders");
        jdbcTemplate.execute("DELETE FROM orders");
    }

    @Test
    void shouldCompleteJobSuccessfully() throws Exception {
        // Given - テストデータ
        insertTestOrders(100);

        // When
        JobParameters params = new JobParametersBuilder()
                .addLocalDate("businessDate", LocalDate.now())
                .addLong("run.id", System.currentTimeMillis())
                .toJobParameters();

        JobExecution execution = jobLauncherTestUtils.launchJob(params);

        // Then
        assertThat(execution.getStatus()).isEqualTo(BatchStatus.COMPLETED);
        assertThat(countProcessedOrders()).isEqualTo(100);
    }

    @Test
    void shouldHandleEmptyDataset() throws Exception {
        // Given - データなし

        // When
        JobExecution execution = jobLauncherTestUtils.launchJob();

        // Then - データなしでもジョブは成功
        assertThat(execution.getStatus()).isEqualTo(BatchStatus.COMPLETED);
    }

    @Test
    void shouldRestartFromFailurePoint() throws Exception {
        // Given - 処理中のエラーをシミュレート
        insertTestOrders(100);
        insertPoisonOrder(50);  // エラー発生

        // When - 1 回目の実行は失敗
        JobExecution firstExecution = jobLauncherTestUtils.launchJob();
        assertThat(firstExecution.getStatus()).isEqualTo(BatchStatus.FAILED);

        // データを修正
        removePoisonOrder(50);

        // When - リスタート
        JobExecution restartExecution = jobLauncherTestUtils.launchJob(
                firstExecution.getJobParameters());

        // Then - 失敗地点から再開
        assertThat(restartExecution.getStatus()).isEqualTo(BatchStatus.COMPLETED);
    }

    private void insertTestOrders(int count) {
        for (int i = 1; i <= count; i++) {
            jdbcTemplate.update(
                    "INSERT INTO orders (id, customer_id, amount, status) VALUES (?, ?, ?, 'PENDING')",
                    i, i * 10, BigDecimal.valueOf(i * 10));
        }
    }

    private int countProcessedOrders() {
        return jdbcTemplate.queryForObject(
                "SELECT COUNT(*) FROM processed_orders", Integer.class);
    }
}

// 大量データ向けに最適化された Writer
@Component
public class OptimizedJdbcWriter implements ItemWriter<ProcessedOrder> {

    private final JdbcTemplate jdbcTemplate;
    private final DataSource dataSource;

    public OptimizedJdbcWriter(JdbcTemplate jdbcTemplate, DataSource dataSource) {
        this.jdbcTemplate = jdbcTemplate;
        this.dataSource = dataSource;
    }

    @Override
    public void write(Chunk<? extends ProcessedOrder> chunk) throws Exception {
        List<? extends ProcessedOrder> items = chunk.getItems();

        if (items.isEmpty()) {
            return;
        }

        // バッチで PreparedStatement を使用
        try (Connection connection = dataSource.getConnection();
             PreparedStatement ps = connection.prepareStatement(
                     "INSERT INTO processed_orders (order_id, customer_id, final_price, processed_at) " +
                             "VALUES (?, ?, ?, ?)")) {

            for (ProcessedOrder order : items) {
                ps.setLong(1, order.orderId());
                ps.setLong(2, order.customerId());
                ps.setBigDecimal(3, order.finalPrice());
                ps.setTimestamp(4, Timestamp.valueOf(order.processedAt()));
                ps.addBatch();
            }

            // すべての INSERT を 1 回のネットワーク操作で実行
            ps.executeBatch();
        }
    }
}

// StagingTableWriter.java
// 超大量データ向けのステージングテーブルパターン
@Component
public class StagingTableWriter implements ItemWriter<ProcessedOrder>, StepExecutionListener {

    private final JdbcTemplate jdbcTemplate;
    private String stagingTable;

    public StagingTableWriter(JdbcTemplate jdbcTemplate) {
        this.jdbcTemplate = jdbcTemplate;
    }

    @Override
    public void beforeStep(StepExecution stepExecution) {
        // この Step 用に一時テーブルを作成
        stagingTable = "staging_orders_" + stepExecution.getId();
        jdbcTemplate.execute(
                "CREATE TEMP TABLE " + stagingTable + " (LIKE processed_orders INCLUDING ALL)");
    }

    @Override
    public void write(Chunk<? extends ProcessedOrder> chunk) {
        // ステージングテーブルへ書き込み(FK 制約なし)
        String sql = "INSERT INTO " + stagingTable +
                " (order_id, customer_id, final_price, processed_at) VALUES (?, ?, ?, ?)";

        jdbcTemplate.batchUpdate(sql, chunk.getItems(), chunk.size(),
                (ps, order) -> {
                    ps.setLong(1, order.orderId());
                    ps.setLong(2, order.customerId());
                    ps.setBigDecimal(3, order.finalPrice());
                    ps.setTimestamp(4, Timestamp.valueOf(order.processedAt()));
                });
    }

    @Override
    public ExitStatus afterStep(StepExecution stepExecution) {
        if (stepExecution.getStatus() == BatchStatus.COMPLETED) {
            // 最終テーブルへバルクコピー
            jdbcTemplate.execute(
                    "INSERT INTO processed_orders SELECT * FROM " + stagingTable);
        }
        // ステージングテーブルを掃除
        jdbcTemplate.execute("DROP TABLE IF EXISTS " + stagingTable);
        return stepExecution.getExitStatus();
    }
}