/**
* Uses the JPA configuration to emit the schema creation script.
*/
/*
* The deprecation can not be avoided, as it appears that Ejb3Configuration was
* deprecated before its substitute has been implemented (the JIRA issues
* referenced by the deprecation notice have been rescheduled for Hibernate 5).
* Also, as of hibernate 4.1.2, hibernate still uses Ejb3Configuration to create
* an EntityManagerFactory.
*/
@SuppressWarnings("deprecation")
public class ExportSchema {

    private static final String persistenceUnitName = "main";
   
    public static final String outputFileName = "target/populate_schema.sql";
   
    /**
     * @param dialectClass the dialect to be used by the sql script
     */
    public static void export(Class<? extends Dialect> dialectClass) {
        new File(outputFileName).getParentFile().mkdirs();

        Ejb3Configuration cfg = new Ejb3Configuration();
        if (beanValidationInClasspath()) {
            injectBeanValidationConstraintToDdlTranslator(cfg, dialectClass);
        }
        cfg.configure(persistenceUnitName, null);
        cfg.setProperty("hibernate.dialect", dialectClass.getName());
       
        SchemaExport exporter = new SchemaExport(cfg.getHibernateConfiguration());
        exporter.setFormat(true);
        exporter.setDelimiter(";");
        exporter.setOutputFile(outputFileName);

        exporter.execute(true, false, false, true);
    }
   
    private static boolean beanValidationInClasspath() {
        try {
            Class.forName("javax.validation.constraints.NotNull");
            return true;
        } catch (ClassNotFoundException e) {
            return false;
        }
    }
   
    // This integration is usually performed by BeanValidationIntegrator.
    // Unfortunately, that integration will only be activated upon
    // initialization of the ServiceRegistry, which initializes
    // DatasourceConnectionProviderImpl, which looks up the datasource,
    // which requires a JNDI context ...
    // We therefore reimplement the relevant parts of BeanValidatorIntegrator.
    // Since that must occur after secondPassCompile(), which is invoked by
    // Configuration.generateSchemaCreationScript, which is invoked by
    // SchemaExport, some fancy subclassing is needed to invoke the integration
    // at the right time.
   
    private static void injectBeanValidationConstraintToDdlTranslator(Ejb3Configuration jpaCfg, final Class<? extends Dialect> dialectClass) {
        try {
            Field cfgField = Ejb3Configuration.class.getDeclaredField("cfg");
            cfgField.setAccessible(true);
            cfgField.set(jpaCfg, new Configuration() {
                @Override
                protected void secondPassCompile() throws MappingException {
                    super.secondPassCompile();
                   
                    try {
                        // thank you, hibernate folks, for making this useful class package private ...
                        Method applyDDL = Class.forName("org.hibernate.cfg.beanvalidation.TypeSafeActivator") //
                                .getMethod("applyDDL", Collection.class, Properties.class, Dialect.class);
                        applyDDL.setAccessible(true);
                        applyDDL.invoke(null, classes.values(), getProperties(), dialectClass.newInstance());
                    } catch (Exception e) {
                        throw new RuntimeException(e);
                    }
                   
                }
            });
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
}

    @NotNull(message = "{comment_notNull}")
    @Size(max = 1000, message = "{comment_max}")
    @Column(nullable = false)
    public String getComment() {
        return comment;
    }

comment varchar2(1000 char) not null

comment varchar2(255 char) not null

@Columns(length=1000)

comment long not null