BAEL-2043: An Intro to Hibernate Entity Lifecycle (#4960)

* "An Intro to Hibernate Entity Lifecycle"

"An Intro to Hibernate Entity Lifecycle"
by Rudi

* Revision from Predrag's feedback

* Another revision from Predrag's feedback

* Another feedback.

hibernate5/src/main/java/com/baeldung/hibernate/lifecycle/DirtyDataInspector.java

@@ -0,0 +1,26 @@
+package com.baeldung.hibernate.lifecycle;
+
+import org.hibernate.EmptyInterceptor;
+import org.hibernate.type.Type;
+
+import java.io.Serializable;
+import java.util.ArrayList;
+import java.util.List;
+
+public class DirtyDataInspector extends EmptyInterceptor {
+    private static final ArrayList<FootballPlayer> dirtyEntities = new ArrayList<>();
+
+    @Override
+    public boolean onFlushDirty(Object entity, Serializable id, Object[] currentState, Object[] previousState, String[] propertyNames, Type[] types) {
+        dirtyEntities.add((FootballPlayer) entity);
+        return true;
+    }
+
+    public static List<FootballPlayer> getDirtyEntities() {
+        return dirtyEntities;
+    }
+
+    public static void clearDirtyEntitites() {
+        dirtyEntities.clear();
+    }
+}

hibernate5/src/main/java/com/baeldung/hibernate/lifecycle/FootballPlayer.java

@@ -0,0 +1,35 @@
+package com.baeldung.hibernate.lifecycle;
+
+import javax.persistence.*;
+
+@Entity
+@Table(name = "Football_Player")
+public class FootballPlayer {
+    @Id
+    @GeneratedValue
+    private long id;
+
+    @Column
+    private String name;
+
+    public long getId() {
+        return id;
+    }
+
+    public void setId(long id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    @Override
+    public String toString() {
+        return "FootballPlayer{" + "id=" + id + ", name='" + name + '\'' + '}';
+    }
+}

hibernate5/src/main/java/com/baeldung/hibernate/lifecycle/HibernateLifecycleUtil.java

@@ -0,0 +1,96 @@
+package com.baeldung.hibernate.lifecycle;
+
+import org.h2.tools.RunScript;
+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.engine.spi.EntityEntry;
+import org.hibernate.engine.spi.SessionImplementor;
+import org.hibernate.service.ServiceRegistry;
+
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.net.URL;
+import java.sql.Connection;
+import java.sql.DriverManager;
+import java.sql.ResultSet;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+import java.util.Properties;
+import java.util.stream.Collectors;
+
+public class HibernateLifecycleUtil {
+    private static SessionFactory sessionFactory;
+    private static Connection connection;
+
+    public static void init() throws Exception {
+        Properties hbConfigProp = getHibernateProperties();
+        Class.forName(hbConfigProp.getProperty("hibernate.connection.driver_class"));
+        connection = DriverManager.getConnection(hbConfigProp.getProperty("hibernate.connection.url"), hbConfigProp.getProperty("hibernate.connection.username"), hbConfigProp.getProperty("hibernate.connection.password"));
+
+        try (InputStream h2InitStream = Thread.currentThread().getContextClassLoader().getResourceAsStream("lifecycle-init.sql");
+            InputStreamReader h2InitReader = new InputStreamReader(h2InitStream)) {
+            RunScript.execute(connection, h2InitReader);
+        }
+
+        ServiceRegistry serviceRegistry = configureServiceRegistry();
+        sessionFactory = getSessionFactoryBuilder(serviceRegistry).applyInterceptor(new DirtyDataInspector()).build();
+    }
+
+    public static void tearDown() throws Exception {
+        sessionFactory.close();
+        connection.close();
+    }
+
+    public static SessionFactory getSessionFactory() {
+        return sessionFactory;
+    }
+
+    private static SessionFactoryBuilder getSessionFactoryBuilder(ServiceRegistry serviceRegistry) {
+        MetadataSources metadataSources = new MetadataSources(serviceRegistry);
+        metadataSources.addAnnotatedClass(FootballPlayer.class);
+
+        Metadata metadata = metadataSources.buildMetadata();
+        return metadata.getSessionFactoryBuilder();
+
+    }
+
+    private static ServiceRegistry configureServiceRegistry() throws IOException {
+        Properties properties = getHibernateProperties();
+        return new StandardServiceRegistryBuilder().applySettings(properties).build();
+    }
+
+    private static Properties getHibernateProperties() throws IOException {
+        Properties properties = new Properties();
+        URL propertiesURL = Thread.currentThread().getContextClassLoader().getResource("hibernate-lifecycle.properties");
+        try (FileInputStream inputStream = new FileInputStream(propertiesURL.getFile())) {
+            properties.load(inputStream);
+        }
+        return properties;
+    }
+
+    public static List<EntityEntry> getManagedEntities(Session session) {
+        Map.Entry<Object, EntityEntry>[] entries = ((SessionImplementor) session).getPersistenceContext().reentrantSafeEntityEntries();
+        return Arrays.stream(entries).map(e -> e.getValue()).collect(Collectors.toList());
+    }
+
+    public static Transaction startTransaction(Session s) {
+        Transaction tx = s.getTransaction();
+        tx.begin();
+        return tx;
+    }
+
+    public static int queryCount(String query) throws Exception {
+        try (ResultSet rs = connection.createStatement().executeQuery(query)) {
+            rs.next();
+            return rs.getInt(1);
+        }
+    }
+}