My First JPA Application - 2

In the previous post I created  the project structure for my JPA application. Now to look deeper into the code. I decided to build a simple Pet-Owner relation. One owner can have multiple pets. The java classes for the same is as below:
The java classes are as below:

@Entity()
@Table(name = "OWNER",schema="firstOne")
public class Owner {

    private Long id; // This is used by hibernate as the Identifier
    private String name;
    private String userId; // This can represent a user uniquely (and cannot be
                            // changed)
    private Set<Pet> pets; // Every owner has a collection of pets ( One To Many
                            // Relation)

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    public Long getId() {
        return id;
    }

    @Column(name = "NAME")
    public String getName() {
        return name;
    }

    @Column(name = "USER_ID", insertable = true, updatable = false, 
                 length = 20, nullable = false, unique = true)
    public String getUserId() {
        return userId;
    }

    @OneToMany(cascade = { CascadeType.PERSIST, CascadeType.MERGE }, 
                 mappedBy = "owner", fetch = FetchType.LAZY, 
                 targetEntity = Pet.class)
    public Set<Pet> getPets() {
        return pets;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setUserId(String userId) {
        this.userId = userId;
    }

    public void setPets(Set<Pet> pets) {
        this.pets = pets;
    }

    public void addPet(Pet pet) {
        if (null == pet) {
            throw new IllegalArgumentException("Null Pet not supported !!");
        }
        pet.setOwner(this);
        if (null == this.pets) {
            this.pets = new HashSet<Pet>();
        }
        this.getPets().add(pet);
    }

    @Override
    public String toString() {
        return "(Owner : [userId: " + this.getUserId() 
                + " ],[name: " + this.getName() + " ], [age:  " + this.getId() + "])";
    }

    @Override
    public boolean equals(Object obj) {
        // The equals method here does not depend on the Db Identifier
        boolean equal = false;
        if (obj instanceof Owner) {
            Owner otherOwner = (Owner) obj;
            equal = this.getUserId().equals(otherOwner.getUserId());
        }
        return equal;
    }

    @Override
    public int hashCode() {
        return this.getUserId().hashCode();
    }

}

Pet.java:

@Entity(name = "Pet")
@Table(name = "PET", schema="firstOne",uniqueConstraints = { 
               @UniqueConstraint(columnNames = { "TAG_ID" }) })
public class Pet {
    private Long id; // the Db identifier
    private String name;
    private int age;
    private String tagId; // a unique identifier (that can be changed)
    private Owner owner; // a reference to the owning record

    public void setId(Long id) {
        this.id = id;
    }

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    public Long getId() {
        return id;
    }

    @Column(name = "NAME", length = 12, nullable = false, 
             insertable = true, unique = false, updatable = true)
    public String getName() {
        return name;
    }

    @Column(name = "TAG_ID")
    public String getTagId() {
        return tagId;
    }

    @Column(name = "AGE")
    public int getAge() {
        return age;
    }

    @ManyToOne(fetch = FetchType.LAZY, optional = false, 
             targetEntity = Owner.class)
    @JoinColumn(name="OWNER_ID")
    public Owner getOwner() {
        return owner;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public void setTagId(String tagId) {
        this.tagId = tagId;
    }

    public void setOwner(Owner owner) {
        this.owner = owner;
    }

    @Override
    public String toString() {
        // avoided any reference to Owner here as that could result in extra
        // queries
        return "(Pet : [name: " + this.getName() 
                 + "[tagId: " + this.getTagId() + " ], [id:  " + this.getId() + "])";
    }

    @Override
    public boolean equals(Object obj) {
        // The equals method here does not depend on the DB Identifier
        boolean equal = false;
        if (obj instanceof Pet) {
            Pet otherPet = (Pet) obj;
            equal = this.getTagId().equals(otherPet.getTagId());
        }
        return equal;
    }

    @Override
    public int hashCode() {
        return this.getTagId().hashCode();
    }

}

As can be seen, the code uses annotations to provide information about the tables. All the annotations are JPA's standard set. I haven't used any Hibernate extensions.
The next step is to setup the configuration information:
Unlike hibernate, JPA has a very fixed way of providing the configuration information. The configuration start-point is a file "persistence.xml". This file needs to be placed in the META-INF folder on the classpath.

<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/persistence 
        http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd"
    version="1.0">
    <persistence-unit name="firstOne">
        <properties>
            <property name="hibernate.ejb.cfgfile" value="/META-INF/hibernate.cfg.xml" />
        </properties>
    </persistence-unit>
</persistence>

In this we redirect the persistence unit to hibernate.cfg.xml for more detailed settings:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
            "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
            "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <property name="connection.driver_class">org.postgresql.Driver</property>
        <property name="dialect">org.hibernate.dialect.PostgreSQLDialect</property>
        <property name="hibernate.connection.username">postgres</property>
        <property name="hibernate.connection.password">root</property>
        <property name="hibernate.connection.url">jdbc:postgresql://localhost:5432/pets</property>
        <property name="hibernate.hbm2ddl.auto">create</property>
        <property name="hibernate.generate_statistics">false</property>
        <property name="show_sql">true</property>
        <property name="format_sql">true</property>
        <property name="hibernate.cache.use_structured_entries">false</property>
        <property name="hibernate.cache.use_second_level_cache">false</property>

        <mapping class="com.basic.Owner" />
        <mapping class="com.basic.Pet" />

    </session-factory>
</hibernate-configuration>

As can be seen all the database settings are in provider specific format i.e. Hibernate style. This completes the code setup. Now to run the code.