MultiTenantProvider.java

package yourpackage.util.hibernate.multitenancy;

import java.sql.Connection;
import java.sql.SQLException;
import java.util.Map;

import org.hibernate.HibernateException;
import org.hibernate.service.config.spi.ConfigurationService;
import org.hibernate.service.jdbc.connections.internal.C3P0ConnectionProvider;
import org.hibernate.service.jdbc.connections.spi.MultiTenantConnectionProvider;
import org.hibernate.service.spi.ServiceRegistryAwareService;
import org.hibernate.service.spi.ServiceRegistryImplementor;

public class MultiTenantProvider implements MultiTenantConnectionProvider, ServiceRegistryAwareService  {

	private static final long serialVersionUID = 4368575201221677384L;
	
	private C3P0ConnectionProvider connectionProvider = null;

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

	@Override
	public void injectServices(ServiceRegistryImplementor serviceRegistry) {
		Map lSettings = serviceRegistry.getService(ConfigurationService.class).getSettings();
		
		connectionProvider = new C3P0ConnectionProvider();
		connectionProvider.injectServices(serviceRegistry);
		connectionProvider.configure(lSettings);
	}

	@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 = connectionProvider.getConnection();
		return connection;
	}

	@Override
	public Connection getConnection(String tenantIdentifier) throws SQLException {
		final Connection connection = getAnyConnection();
		try {
			connection.createStatement().execute("SET SCHEMA '" + tenantIdentifier + "'");
		}
		catch (SQLException e) {
			throw new HibernateException("Could not alter JDBC connection to specified schema [" + tenantIdentifier + "]", e);
		}
		return connection;
	}

	@Override
	public void releaseAnyConnection(Connection connection) throws SQLException {
		try {
			connection.createStatement().execute("SET SCHEMA 'public'");
		}
		catch (SQLException e) {
			throw new HibernateException("Could not alter JDBC connection to specified schema [public]", e);
		}
		connectionProvider.closeConnection(connection);
	}

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

persistence.xml

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
	<persistence-unit name="default">
		<properties>
			<property name="javax.persistence.provider" value="org.hibernate.ejb.HibernatePersistence" />

			<property name="javax.persistence.jdbc.driver" value="org.postgresql.Driver" />
			<property name="javax.persistence.jdbc.url" value="jdbc:postgresql://localhost:5432/mydatabase" />
			<property name="javax.persistence.jdbc.user" value="postgres" />
			<property name="javax.persistence.jdbc.password" value="" />

			<property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQLDialect" />
			<property name="hibernate.archive.autodetection" value="class, hbm" />
			<property name="hibernate.show_sql" value="true" />
			<property name="hibernate.format_sql" value="true" />
			 
			<property name="hibernate.multiTenancy" value="SCHEMA"/>
			<property name="hibernate.tenant_identifier_resolver" value="yourpackage.util.hibernate.multitenancy.SchemaResolver"/>
			<property name="hibernate.multi_tenant_connection_provider" value="yourpackage.util.hibernate.multitenancy.MultiTenantProvider"/>
 
			<property name="hibernate.hbm2ddl.auto" value="create-drop" />
		</properties>
	</persistence-unit>
</persistence>

SchemaResolver.java

package yourpackage.util.hibernate.multitenancy;

import org.hibernate.context.spi.CurrentTenantIdentifierResolver;

public class SchemaResolver implements CurrentTenantIdentifierResolver {

	@Override
	public String resolveCurrentTenantIdentifier() {
		return "master"; //TODO: Implement service to identify tenant like: userService.getCurrentlyAuthUser().getTenantId();
	}

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