BAEL-4057: Hibernate Hi/Lo algorithm example (#9802)

* BAEL-4057: Hibernate Hi/Lo algorithm example

* BAEL-4057: fixed code indentation

persistence-modules/hibernate5/src/main/java/com/baeldung/hibernate/hilo/RestaurantOrder.java

@@ -0,0 +1,34 @@
+package com.baeldung.hibernate.hilo;
+
+import org.hibernate.annotations.GenericGenerator;
+import org.hibernate.annotations.Parameter;
+
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.GenerationType;
+import javax.persistence.Id;
+
+@Entity
+public class RestaurantOrder {
+    @Id
+    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "hilo_sequence_generator")
+    @GenericGenerator(
+      name = "hilo_sequence_generator",
+      strategy = "sequence",
+      parameters = {
+        @Parameter(name = "sequence_name", value = "hilo_seqeunce"),
+        @Parameter(name = "initial_value", value = "1"),
+        @Parameter(name = "increment_size", value = "3"),
+        @Parameter(name = "optimizer", value = "hilo")
+      }
+    )
+    private Long id;
+
+    public long getId() {
+        return id;
+    }
+
+    public void setId(long id) {
+        this.id = id;
+    }
+}

persistence-modules/hibernate5/src/test/java/com/baeldung/hibernate/hilo/HibernateHiloUnitTest.java

@@ -0,0 +1,99 @@
+package com.baeldung.hibernate.hilo;
+
+import org.apache.log4j.BasicConfigurator;
+import org.apache.log4j.Level;
+import org.apache.log4j.LogManager;
+import org.hibernate.HibernateException;
+import org.hibernate.Session;
+import org.hibernate.SessionFactory;
+import org.hibernate.Transaction;
+import org.hibernate.boot.Metadata;
+import org.hibernate.boot.MetadataSources;
+import org.hibernate.boot.SessionFactoryBuilder;
+import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
+import org.hibernate.service.ServiceRegistry;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.net.URL;
+import java.util.Properties;
+
+import static org.junit.Assert.fail;
+
+public class HibernateHiloUnitTest {
+    private Session session;
+
+    @Before
+    public void init() {
+        try {
+            configureLogger();
+
+            ServiceRegistry serviceRegistry = configureServiceRegistry();
+            SessionFactory factory = getSessionFactoryBuilder(serviceRegistry).build();
+            session = factory.openSession();
+        } catch (HibernateException | IOException e) {
+            fail("Failed to initiate Hibernate Session [Exception:" + e.toString() + "]");
+        }
+    }
+
+    private void configureLogger() {
+        BasicConfigurator.configure();
+        LogManager.getLogger("org.hibernate").setLevel(Level.ERROR);
+        LogManager.getLogger("org.hibernate.id.enhanced.SequenceStructure").setLevel(Level.DEBUG);
+        LogManager.getLogger("org.hibernate.event.internal.AbstractSaveEventListener").setLevel(Level.DEBUG);
+        LogManager.getLogger("org.hibernate.SQL").setLevel(Level.DEBUG);
+    }
+
+
+    private static SessionFactoryBuilder getSessionFactoryBuilder(ServiceRegistry serviceRegistry) {
+        MetadataSources metadataSources = new MetadataSources(serviceRegistry);
+        metadataSources.addAnnotatedClass(RestaurantOrder.class);
+        Metadata metadata = metadataSources.buildMetadata();
+
+        return metadata.getSessionFactoryBuilder();
+    }
+
+    private static ServiceRegistry configureServiceRegistry() throws IOException {
+        Properties properties = getProperties();
+
+        return new StandardServiceRegistryBuilder().applySettings(properties)
+          .build();
+    }
+
+    private static Properties getProperties() throws IOException {
+        Properties properties = new Properties();
+        URL propertiesURL = getPropertiesURL();
+
+        try (FileInputStream inputStream = new FileInputStream(propertiesURL.getFile())) {
+            properties.load(inputStream);
+        }
+
+        return properties;
+    }
+
+    private static URL getPropertiesURL() {
+        return Thread.currentThread()
+          .getContextClassLoader()
+          .getResource("hibernate-hilo.properties");
+    }
+
+    @Test
+    public void givenHiLoAlgorithm_when9EntitiesArePersisted_Then3callsToDBForNextValueShouldBeMade() {
+        Transaction transaction = session.beginTransaction();
+
+        for (int i = 0; i < 9; i++) {
+            session.persist(new RestaurantOrder());
+            session.flush();
+        }
+
+        transaction.commit();
+    }
+
+    @After
+    public void cleanup() {
+        session.close();
+    }
+}

persistence-modules/hibernate5/src/test/resources/hibernate-hilo.properties

@@ -0,0 +1,10 @@
+hibernate.connection.driver_class=org.h2.Driver
+hibernate.connection.url=jdbc:h2:mem:hilo_db;DB_CLOSE_DELAY=-1
+hibernate.connection.username=sa
+hibernate.dialect=org.hibernate.dialect.H2Dialect
+hibernate.show_sql=true
+hibernate.hbm2ddl.auto=create-drop
+hibernate.c3p0.min_size=5
+hibernate.c3p0.max_size=20
+hibernate.c3p0.acquire_increment=5
+hibernate.c3p0.timeout=1800