EntityManagerUtil.java

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import java.sql.SQLException;
import java.util.Random;

public class EntityManagerUtil {
    @FunctionalInterface
    public interface TransactionalAction {
        void action(EntityManager entityManager) throws Exception;
    }

    @FunctionalInterface
    public interface TransactionalFunction<T> {
        T apply(EntityManager entityManager) throws Exception;
    }

    @FunctionalInterface
    public interface RetryRequired {
        boolean required(Exception e);
    }

    @FunctionalInterface
    public interface RetryIntervalFunction {
        int interval(int currentRetryNumber, int maxRetryCount);
    }

    public static final int DEFAULT_RETRY_COUNT = 10;

    private static EntityManagerFactory entityManagerFactory;

    public static void setEntityManagerFactory(EntityManagerFactory entityManagerFactory) {
        EntityManagerUtil.entityManagerFactory = entityManagerFactory;
    }

    public static <T> T txFunction(TransactionalFunction<T> function,
                                   RetryRequired retryRequired,
                                   int maxRetryCount, RetryIntervalFunction retryIntervalFunction) {
        EntityManager entityManager = entityManagerFactory.createEntityManager();
        entityManager.getTransaction().begin();

        int retryNumber = 0;

        while (true) {
            T result = null;
            Exception exception = null;
            try {
                result = function.apply(entityManager);
            } catch (Exception e) {
                exception = e;
                entityManager.getTransaction().setRollbackOnly();
            }
            try {
                if (entityManager.getTransaction().getRollbackOnly()) {
                    entityManager.getTransaction().rollback();
                } else {
                    entityManager.getTransaction().commit();
                }
                entityManager.close();
            } catch (Exception e) {
                if (exception != null) {
                    exception.addSuppressed(e);
                } else {
                    exception = e;
                }
            }

            if (exception != null) {
                if (retryNumber >= maxRetryCount) {
                    throw runtimeException(exception);
                }
                if (retryRequired.required(exception)) {
                    try {
                        Thread.sleep(retryIntervalFunction.interval(retryNumber, maxRetryCount));
                    } catch (InterruptedException ignored) {
                        Thread.currentThread().interrupt();
                        throw runtimeException(exception);
                    }
                    retryNumber++;
                } else {
                    throw runtimeException(exception);
                }
            } else {
                return result;
            }
        }
    }

    public static <T> T txFunction(TransactionalFunction<T> function) {
        return txFunction(function, 
                EntityManagerUtil::defaultRetryRequired,
                DEFAULT_RETRY_COUNT, EntityManagerUtil::defaultRetryInterval);
    }
    
    public static void txAction(TransactionalAction action) {
        txFunction(new TransactionActionWrapper(action),
                EntityManagerUtil::defaultRetryRequired,
                DEFAULT_RETRY_COUNT, EntityManagerUtil::defaultRetryInterval);
    }

    private static RuntimeException runtimeException(Exception e) {
        return e instanceof RuntimeException ? (RuntimeException) e : new RuntimeException(e.getMessage(), e);
    }

    private static final Random DEFAULT_RETRY_INTERVAL_RANDOM = new Random();

    public static int defaultRetryInterval(int currentRetryNumber, int maxRetryCount) {
        return (maxRetryCount - currentRetryNumber) * 1000 + DEFAULT_RETRY_INTERVAL_RANDOM.nextInt(1000);
    }

    public static boolean defaultRetryRequired(Throwable exception) {
        if (exception == null) {
            return false;
        }
        if (exception instanceof SQLException) {
            SQLException sqlException = (SQLException) exception;
            if ("40P01".equals(sqlException.getSQLState())) {
                return true;
            }
        }
        if (defaultRetryRequired(exception.getCause())) {
            return true;
        }
        for (Throwable suppressedException : exception.getSuppressed()) {
            if (defaultRetryRequired(suppressedException)) {
                return true;
            }
        }
        return false;
    }

    public static class TransactionActionWrapper implements TransactionalFunction<Void> {
        private final TransactionalAction action;

        public TransactionActionWrapper(TransactionalAction action) {
            this.action = action;
        }

        @Override
        public Void apply(EntityManager entityManager) throws Exception {
            action.action(entityManager);
            return null;
        }
    }
}