How to simplify JPA and Hibernate integration testing using Java 8 lambdas

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Introduction

Hibernate 5.2 has migrated to Java 1.8. In this article, I’m going to show you how easily you can now test JPA logic using Java 1.8 lambdas.

Integration testing

Hibernate has thousands of integration tests, and each unit test runs in isolation. Traditionally, every test required to open an EntityManager, as well as to coordinate the underlying database transaction by calling begin, commit, and rollback.

EntityManager entityManager = getOrCreateEntityManager();
entityManager.getTransaction().begin();
try {
    entityManager.persist( item );
    assertTrue( entityManager.contains( item ) );
    entityManager.getTransaction().commit();
}
catch (Exception e){
    if ( entityManager.getTransaction() != null &&
         entityManager.getTransaction().isActive() ) {
        entityManager.getTransaction().rollback();
    }
    throw e;
}
finally {
    entityManager.close();
}

That’s very verbose because we need to ensure that the EntityManager always gets closed so that connections are released back to the pool. More, the database transaction must be rolled back on every failure as otherwise locks might be held, therefore preventing a schema-drop process.

For this reason, we decided to extract the whole EntityManager and JPA transaction management logic into a common utility class:

import static org.hibernate.testing.transaction.TransactionUtil.*;

What’s great about these utilities is that you don’t even need to create them. We’ve got you covered!

You only have to add the following dependency to your Maven pom.xml:

<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-testing</artifactId>
    <version>5.2.2.Final</version>
</dependency>

Therefore, the previous test case is reduced to four lines of code:

doInJPA( this::entityManagerFactory, entityManager -> {
    entityManager.persist( item );
    assertTrue( entityManager.contains( item ) );
} );

Brilliant!

The aforementioned example relies on the presence of the entityManagerFactory() method that returns an EntityManagerFactory instance.

If you prefer the Hibernate native API, you can do it as follows:

doInHibernate( this::sessionFactory, session -> {
    session.persist( item );
    assertTrue( session.contains( item ) );
} );

Analogous to the previous example, a sessionFactory() method is assumed to be existing in the test class. However, you can name these methods any way you like and just make sure to update the first argument of the doInJPA or doInHibernate methods.