Jakarta EE: Multitenancy with JPA on WildFly, Part 1

In this two-part series, I demonstrate two approaches to multitenancy with the Jakarta Persistence API (JPA) running on WildFly. In the first half of this series, you will learn how to implement multitenancy using a database. In the second half, I will introduce you to multitenancy using a schema. I based both examples on JPA and Hibernate.

Because I have focused on implementation examples, I won't go deeply into the details of multitenancy, though I will start with a brief overview. Note, too, that I assume you are familiar with Java persistence using JPA and Hibernate.

Multitenancy architecture

Multitenancy is an architecture that permits a single application to serve multiple tenants, also known as clients. Although tenants in a multitenancy architecture access the same application, they are securely isolated from each other. Furthermore, each tenant only has access to its own resources. Multitenancy is a common architectural approach for software-as-a-service (SaaS) and cloud computing applications. In general, clients (or tenants) accessing a SaaS are accessing the same application, but each one is isolated from the others and has its own resources.

A multitenant architecture must isolate the data available to each tenant. If there is a problem with one tenant's data set, it won't impact the other tenants. In a relational database, we use a database or a schema to isolate each tenant's data. One way to separate data is to give each tenant access to its own database or schema. Another option, which is available if you are using a relational database with JPA and Hibernate, is to partition a single database for multiple tenants. In this article, I focus on the standalone database and schema options. I won't demonstrate how to set up a partition.

In a server-based application like WildFly, multitenancy is different from the conventional approach. In this case, the server application works directly with the data source by initiating a connection and preparing the database to be used. The client application does not spend time opening the connection, which improves performance. On the other hand, using Enterprise JavaBeans (EJBs) for container-managed transactions can lead to problems. As an example, the server-based application could do something to generate an error to commit or roll the application back.

Implementation code

Two interfaces are crucial to implementing multitenancy in JPA and Hibernate:

• MultiTenantConnectionProvider is responsible for connecting tenants to their respective databases and services. We will use this interface and a tenant identifier to switch between databases for different tenants.
• CurrentTenantIdentifierResolver is responsible for identifying the tenant. We will use this interface to define what is considered a tenant (more about this later). We will also use this interface to provide the correct tenant identifier to MultiTenantConnectionProvider.

In JPA, we configure these interfaces using the persistence.xml file. In the next sections, I'll show you how to use these two interfaces to create the first three classes we need for our multitenancy architecture: DatabaseMultiTenantProvider, MultiTenantResolver, and DatabaseTenantResolver.

DatabaseMultiTenantProvider

DatabaseMultiTenantProvider is an implementation of the MultiTenantConnectionProvider interface. This class contains logic to switch to the database that matches the given tenant identifier. In WildFly, this means switching to different data sources. The DatabaseMultiTenantProvider class also implements the ServiceRegistryAwareService, which allows us to inject a service during the configuration phase.

Here's the code for the DatabaseMultiTenantProvider class:

public class DatabaseMultiTenantProvider implements MultiTenantConnectionProvider, ServiceRegistryAwareService{
    private static final long serialVersionUID = 1L;
    private static final String TENANT_SUPPORTED = "DATABASE";
    private DataSource dataSource;
    private String typeTenancy ;

    @Override
    public boolean supportsAggressiveRelease() {
        return false;
    }
    @Override
    public void injectServices(ServiceRegistryImplementor serviceRegistry) {

        typeTenancy = (String) ((ConfigurationService)serviceRegistry
                .getService(ConfigurationService.class))
                .getSettings().get("hibernate.multiTenancy");

        dataSource = (DataSource) ((ConfigurationService)serviceRegistry
                .getService(ConfigurationService.class))
                .getSettings().get("hibernate.connection.datasource");


    }
    @SuppressWarnings("rawtypes")
    @Override
    public boolean isUnwrappableAs(Class clazz) {
        return false;
    }
    @Override
    public <T> T unwrap(Class<T> clazz) {
        return null;
    }
    @Override
    public Connection getAnyConnection() throws SQLException {
        final Connection connection = dataSource.getConnection();
        return connection;

    }
    @Override
    public Connection getConnection(String tenantIdentifier) throws SQLException {

        final Context init;
        //Just use the multi-tenancy if the hibernate.multiTenancy == DATABASE
        if(TENANT_SUPPORTED.equals(typeTenancy)) {
            try {
                init = new InitialContext();
                dataSource = (DataSource) init.lookup("java:/jdbc/" + tenantIdentifier);
            } catch (NamingException e) {
                throw new HibernateException("Error trying to get datasource ['java:/jdbc/" + tenantIdentifier + "']", e);
            }
        }

        return dataSource.getConnection();
    }

    @Override
    public void releaseAnyConnection(Connection connection) throws SQLException {
        connection.close();
    }
    @Override
    public void releaseConnection(String tenantIdentifier, Connection connection) throws SQLException {
        releaseAnyConnection(connection);
    }
}

As you can see, we call the injectServices method to populate the datasource and typeTenancy attributes. We use the datasource attribute to get a connection from the data source, and we use the typeTenancy attribute to find out if the class supports the multiTenancy type. We call the getConnection method to get a data source connection. This method uses the tenant identifier to locate and switch to the correct data source.

MultiTenantResolver

MultiTenantResolver is an abstract class that implements the CurrentTenantIdentifierResolver interface. This class aims to provide a setTenantIdentifier method to all CurrentTenantIdentifierResolver implementations:

public abstract class MultiTenantResolver implements CurrentTenantIdentifierResolver {

    protected String tenantIdentifier;

    public void setTenantIdentifier(String tenantIdentifier) {
        this.tenantIdentifier = tenantIdentifier;
    }
}

This abstract class is simple. We only use it to provide the setTenantIdentifier method.

DatabaseTenantResolver

DatabaseTenantResolver also implements the CurrentTenantIdentifierResolver interface. This class is the concrete class of MultiTenantResolver:

public class DatabaseTenantResolver extends MuiltiTenantResolver {

    private Map<String, String> regionDatasourceMap;

    public DatabaseTenantResolver(){
        regionDatasourceMap = new HashMap();
        regionDatasourceMap.put("default", "MyDataSource");
        regionDatasourceMap.put("america", "AmericaDB");
        regionDatasourceMap.put("europa", "EuropaDB");
        regionDatasourceMap.put("asia", "AsiaDB");
    }

    @Override
    public String resolveCurrentTenantIdentifier() {


        if(this.tenantIdentifier != null
                && regionDatasourceMap.containsKey(this.tenantIdentifier)){
            return regionDatasourceMap.get(this.tenantIdentifier);
        }

        return regionDatasourceMap.get("default");

    }

    @Override
    public boolean validateExistingCurrentSessions() {
        return false;
    }

}

Notice that DatabaseTenantResolver uses a Map to define the correct data source for a given tenant. The tenant, in this case, is a region. Note, too, that this example assumes we have the data sources java:/jdbc/MyDataSource, java:/jdbc/AmericaDB, java:/jdbc/EuropaDB, and java:/jdbc/AsiaDB configured in WildFly.

Configure and define the tenant

Now we need to use the persistence.xml file to configure the tenant:

<persistence>
    <persistence-unit name="jakartaee8">

        <jta-data-source>jdbc/MyDataSource</jta-data-source>
        <properties>
            <property name="javax.persistence.schema-generation.database.action" value="none" />
            <property name="hibernate.dialect" value="org.hibernate.dialect.PostgresPlusDialect"/>
            <property name="hibernate.multiTenancy" value="DATABASE"/>
            <property name="hibernate.tenant_identifier_resolver" value="net.rhuanrocha.dao.multitenancy.DatabaseTenantResolver"/>
            <property name="hibernate.multi_tenant_connection_provider" value="net.rhuanrocha.dao.multitenancy.DatabaseMultiTenantProvider"/>
        </properties>

    </persistence-unit>
</persistence>

Next, we define the tenant in the EntityManagerFactory:

@PersistenceUnit
protected EntityManagerFactory emf;


protected EntityManager getEntityManager(String multitenancyIdentifier){

    final MuiltiTenantResolver tenantResolver = (MuiltiTenantResolver) ((SessionFactoryImplementor) emf).getCurrentTenantIdentifierResolver();
    tenantResolver.setTenantIdentifier(multitenancyIdentifier);

    return emf.createEntityManager();
}

Note that we call the setTenantIdentifier before creating a new instance of EntityManager.

Conclusion

I have presented a simple example of multitenancy in a database using JPA with Hibernate and WildFly. There are many ways to use a database for multitenancy. My main point has been to show you how to implement the CurrentTenantIdentifierResolver and MultiTenantConnectionProvider interfaces. I've shown you how to use JPA's persistence.xml file to configure the required classes based on these interfaces.

Keep in mind that for this example, I have assumed that WildFly manages the data source and connection pool and that EJB handles the container-managed transactions. In the second half of this series, I will provide a similar introduction to multitenancy, but using a schema rather than a database. If you want to go deeper with this example, you can find the complete application code and further instructions on my GitHub repository.