JPA without persistence.xml

Question

I'm trying to get started with using Guice Persist and JPA, which recommends using configuration via persistence.xml. Coming from a native Hibernate background where configuration was obtained programmatically, is there a simple way to configure a JpaPersistModule without a persistence.xml file, or will a rump persistence.xml always have to exist?

If no such option exists, it might be the case where I might have to play around with PersistenceProvider (assuming the "default" parses persistence.xml somehow). Any tutorials on working with the JPA SPI?

Answer 1

There is no need for persistence.xml if you are using a Spring version higher than 3.1 and you have already defined your entities classes.

@Configuration
@ComponentScan(basePackages = { "com.demoJPA.model" })
@EnableTransactionManagement
public class DemoJPAConfig {

    @Bean
    public DataSource dataSource() throws PropertyVetoException {
        ComboPooledDataSource dataSource = new ComboPooledDataSource();
        dataSource.setDriverClass("org.gjt.mm.mysql.Driver");
        dataSource.setJdbcUrl("jdbc:mysql://localhost:3306/cimto");
        dataSource.setUser("user");
        dataSource.setPassword("pass");

        return dataSource;
    }

    @Bean
    public LocalContainerEntityManagerFactoryBean entityManagerFactory() throws PropertyVetoException {
        LocalContainerEntityManagerFactoryBean em = new LocalContainerEntityManagerFactoryBean();
        em.setDataSource(dataSource());
        em.setJpaVendorAdapter(vendorAdapter());
        em.setPersistenceUnitName("cimtoPU");
        em.setJpaPropertyMap(getJpaProperties());

        return em;
    }

    public Map<String, ?> getJpaProperties() {
    return new HashMap<String, Object>();
    }

    @Bean
    public PlatformTransactionManager transactionManager(EntityManagerFactory emf) {
        JpaTransactionManager transactionManager = new JpaTransactionManager();
        transactionManager.setEntityManagerFactory(emf);

        return transactionManager;
    }

    public JpaVendorAdapter vendorAdapter() {
        HibernateJpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();
        vendorAdapter.setDatabase(Database.MYSQL);
    vendorAdapter.setDatabasePlatform("org.hibernate.dialect.MySQL5Dialect");
        vendorAdapter.setShowSql(true);

        return vendorAdapter;
    }
}

Note: com.demoJPA.model package must contain your entities classes.

Answer 2

Assuming that you have a PersistenceProvider implementation (e.g. Hibernate), you can use the PersistenceProvider#createContainerEntityManagerFactory(PersistenceUnitInfo info, Map map) method to bootstrap an EntityManagerFactory without needing a persistence.xml.

However, it's annoying that you have to implement the PersistenceUnitInfo interface, so you are better off using Spring or Hibernate which both support bootstrapping JPA without a persistence.xml file:

this.nativeEntityManagerFactory = provider.createContainerEntityManagerFactory(
    this.persistenceUnitInfo, 
    getJpaPropertyMap()
);

Where the PersistenceUnitInfo is implemented by the Spring-specific MutablePersistenceUnitInfo class.

Check out this article for a nice demonstration of how you can achieve this goal with Hibernate.

Answer 3

Depending on what you want to achieve and in what context (ApplicationServer vs CLI, CMT transactions vs EntityTransactions), it may be possible to use JPA without a persistence.xml. I did this in a CLI Java application, where I had different databases with the same structure. For that I constructed the EntityManagerFactory manually.

PS: The config file is there to make your life easier, so if you can, just use it.