[BAEL-694] Hibernate immutable annotation (eugenp#1302)

* Add project for hibernate immutable article
Add Event entity
Add hibernate configuration file
Add hibernateutil for configuration
Add test to match snippets from article

* Create README.md

* Update README.md

hibernate-immutable/README.md

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+Article
+- [Guide to @Immutable Annotation in Hibernate](http://inprogress.baeldung.com/?p=35824&preview=true)

hibernate-immutable/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>com.baeldung</groupId>
+    <artifactId>hibernate-immutable</artifactId>
+    <version>1.0-SNAPSHOT</version>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.hibernate</groupId>
+            <artifactId>hibernate-core</artifactId>
+            <version>4.3.10.Final</version>
+        </dependency>
+        <dependency>
+            <groupId>org.hsqldb</groupId>
+            <artifactId>hsqldb</artifactId>
+            <version>2.2.9</version>
+        </dependency>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>4.11</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+</project>

hibernate-immutable/src/main/java/com/baeldung/entities/Event.java

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+package com.baeldung.entities;
+
+import org.hibernate.annotations.*;
+import org.hibernate.annotations.CascadeType;
+
+import javax.persistence.*;
+import javax.persistence.Entity;
+import javax.persistence.Table;
+import java.util.Set;
+
+@Entity
+@Immutable
+@Table(name = "events")
+public class Event {
+    @Id
+    @Column(name = "event_id")
+    @GeneratedValue(generator = "increment")
+    @GenericGenerator(name = "increment", strategy = "increment")
+    private Long id;
+
+    @Column(name = "title")
+    private String title;
+
+    @ElementCollection
+    @Immutable
+    private Set<String> guestList;
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getTitle() {
+        return title;
+    }
+
+    public void setTitle(String title) {
+        this.title = title;
+    }
+
+    @Cascade({CascadeType.SAVE_UPDATE, CascadeType.DELETE})
+    public Set<String> getGuestList() {
+        return guestList;
+    }
+
+    public void setGuestList(Set<String> guestList) {
+        this.guestList = guestList;
+    }
+}

hibernate-immutable/src/main/java/com/baeldung/util/HibernateUtil.java

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+package com.baeldung.util;
+
+import org.hibernate.SessionFactory;
+import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
+import org.hibernate.cfg.Configuration;
+import org.hibernate.service.ServiceRegistry;
+
+public class HibernateUtil {
+    private static final SessionFactory sessionFactory = buildSessionFactory();
+
+    private static SessionFactory buildSessionFactory() {
+        try {
+            // Create a session factory from hibernate.cfg.xml
+            Configuration configuration = new Configuration();
+            configuration.configure("hibernate.cfg.xml");
+            ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder()
+                    .applySettings(configuration.getProperties())
+                    .build();
+            return configuration.buildSessionFactory(serviceRegistry);
+        } catch (Throwable ex) {
+            System.out.println("Initial SessionFactory creation failed." + ex);
+            throw new ExceptionInInitializerError(ex);
+        }
+    }
+
+    public static SessionFactory getSessionFactory() {
+        return sessionFactory;
+    }
+}

hibernate-immutable/src/main/resources/hibernate.cfg.xml

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+<?xml version='1.0' encoding='utf-8'?>
+<!DOCTYPE hibernate-configuration PUBLIC
+        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
+        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
+
+<hibernate-configuration>
+
+    <session-factory>
+
+        <!-- Database connection settings -->
+        <property name="connection.driver_class">org.hsqldb.jdbcDriver</property>
+        <property name="connection.url">jdbc:hsqldb:hsql://localhost/xdb</property>
+        <property name="connection.username">sa</property>
+        <property name="connection.password"></property>
+
+        <!-- JDBC connection pool (use the built-in) -->
+        <property name="connection.pool_size">1</property>
+
+        <!-- SQL dialect -->
+        <property name="dialect">org.hibernate.dialect.HSQLDialect</property>
+
+        <!-- Enable Hibernate's automatic session context management -->
+        <property name="current_session_context_class">thread</property>
+
+        <!-- Disable the second-level cache  -->
+        <property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>
+
+        <!-- Echo all executed SQL to stdout -->
+        <property name="show_sql">true</property>
+
+        <!-- Drop and re-create the database schema on startup -->
+        <property name="hbm2ddl.auto">update</property>
+
+        <mapping class="com.baeldung.entities.Event"/>
+
+    </session-factory>
+
+</hibernate-configuration>

hibernate-immutable/src/test/java/EventTest.java

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+import com.baeldung.entities.Event;
+import com.baeldung.util.HibernateUtil;
+import org.hibernate.HibernateException;
+import org.hibernate.Session;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+
+import javax.persistence.Table;
+
+public class EventTest {
+
+    private Session session;
+    @Rule
+    public final ExpectedException exception = ExpectedException.none();
+
+    @Before
+    public void setup() {
+        session = HibernateUtil.getSessionFactory().getCurrentSession();
+        session.beginTransaction();
+    }
+
+    @After
+    public void teardown() {
+        HibernateUtil.getSessionFactory().close();
+    }
+
+    @Test
+    public void addEvent() {
+        Event event = new Event();
+        event.setTitle("Public Event");
+        session.save(event);
+        session.getTransaction().commit();
+    }
+
+    @Test
+    public void updateEvent() {
+        Event event = (Event) session.createQuery(
+                "FROM Event WHERE title='My Event'").list().get(0);
+        event.setTitle("Public Event");
+        session.saveOrUpdate(event);
+        session.getTransaction().commit();
+    }
+
+    @Test
+    public void deleteEvent() {
+        Event event = (Event) session.createQuery(
+                "FROM Event WHERE title='My Event'").list().get(0);
+        session.delete(event);
+        session.getTransaction().commit();
+    }
+
+    @Test
+    public void addGuest() {
+        Event event = (Event) session.createQuery(
+                "FROM Event WHERE title='Public Event'").list().get(0);
+        String newGuest = "Sara";
+        event.getGuestList().add(newGuest);
+
+        exception.expect(HibernateException.class);
+        session.save(event);
+        session.getTransaction().commit();
+    }
+
+    @Test
+    public void deleteCascade() {
+        Event event = (Event) session.createQuery(
+                "FROM Event WHERE title='Public Event'").list().get(0);
+        String guest = event.getGuestList().iterator().next();
+        event.getGuestList().remove(guest);
+
+        exception.expect(HibernateException.class);
+        session.saveOrUpdate(event);
+        session.getTransaction().commit();
+    }
+}