In order to query for instances of this business entity, we are going to add a few named queries. We also have to mark the entity as an XML element, so it can be processed by JAXB.

First, let's add the named queries that will support our use case. So, open the Exhibition class and add this block of code after the @Entity decoration:

@NamedQueries({
   @NamedQuery(name=Exhibition.findAll,query="SELECT r FROM Exhibition r"),
   @NamedQuery(name=Exhibition.findById,query="SELECT r FROM Exhibition r WHERE r.id = :id"),
   @NamedQuery(name=Exhibition.findByMovie,query="SELECT r FROM Exhibition r WHEREr.movie.id = :movieId")
   })

Also, add the names of the queries:

public final static String findAll = "Exhibition.findAll";
public final static String findById = "Exhibition.findById";
public final static String findByMovie = "Exhibition.findByMovie";

As we're going to expose this entity through a web service, we need to decorate the class with a JAXB annotation, java.xml.bind.annotation.XmlRootElement, so the engine can process the instance as a JAXB object when generating the web service's response. This must be done only to top-level entities of a request or response— for instance, even though the Movie entity will be a part of our response, we don't need to mark it. Just add the following line after @Table:

@XmlRootElement(name="Exhibition")

This annotation states that this class can be represented as an XML or JSON document through the use of JAXB and its binding providers, such as EclipseLink MOXy, the default JAXB provider of WebLogic Server 12c.

After adding these customizations to the class, your code should look like this:

@Entity
@NamedQueries({
   @NamedQuery(name=Exhibition.findAll,query="SELECT r FROM Exhibition r"),
   @NamedQuery(name=Exhibition.findById,query="SELECT r FROM Exhibition r WHERE r.id = :id"),
   @NamedQuery(name=Exhibition.findByMovie,query="SELECT r FROM Exhibition r WHEREr.movie.id = :movieId")
   })
@XmlRootElement(name="Exhibition")
public class Exhibition implements Serializable {
   public final static String findAll = "Exhibition.findAll";
   public final static String findById = "Exhibition.findById";
   public final static String findByMovie = " Exhibition.findByMovie";
...

We have to do a simple modification to two entities, Movie and Room, in order to prevent a very common issue with JAXB and XML parsing: cyclic references or bidirectional relationships. In standard JAXB this is not supported and one side of the relationship must be marked with @XmlTransient, but some JAXB implementations are also trying to solve this issue with extensions, such as EclipseLink MOXy.

Following the database model, for each Exhibition instance we have references to both Movie and Room via @ManyToOne relationships. And Movie and Room both have a list of all exhibitions pointing back to the Exhibition entity, a @OneToMany relationship. The object graph generated by default for a given Exhibition object and its references would look like this:

The solution for this situation is to mark the field and method you don't want JAXB to parse with the XmlTransient annotation, found in the javax.xml.bind.annotation package. So, in this specific case, we need to modify the Movie and Room classes to instruct JAXB to not go over their list of exhibitions. Update your code by decorating both the variable declaration and their getter methods with @XmlTransient:

@Entity
public class Movie implements Serializable {
...
   @XmlTransient
   @OneToMany(mappedBy="movie")
   private List<Exhibition> exhibitions;
...
   @XmlTransient
   public List<Exhibition> getExhibitions() {
      return this.exhibitions;
   }
    ...

And:

@Entity
public class Room implements Serializable {
    ...
   @XmlTransient
   @OneToMany(mappedBy = "room")
   private List<Exhibition> exhibitions;
    ...
   @XmlTransient
   public List<Exhibition> getExhibitions() {
      return this.exhibitions;
   }
    ...

We also need to execute the same procedure to adjust the relationship between Seat and Room—when marshaling a Seat instance, JAXB must not include the referenced Room instance. To do so, open the Seat class and mark the Room reference with @XMLTransient, also add @XMLRootElement to the class declaration while you are at it:

@Entity
@Table("Seat")
@XmlRootElement(name="Seat")
public class Seat implements Serializable {
    ...
   @XmlTransient    
   @ManyToOne
   @JoinColumn(name = "roomRef")
   private Room room;
    ...
   @XmlTransient
   public Room getRoom() {
      return this.room;
   }
    ...

In order to show a user-friendly exhibition time on the query page, we are going to change the getDate method of the Exhibition class to join the date and time information (available as separate attributes, date and hour) and return the result. Also, the hour is saved in military format, so we need to break it down to hours and minutes before joining it to the date.

Open the source code of Exhibition and change the contents of getDate() from the following code:

public Date getDate() {
   return this.date;
}

To this:

public Date getDate() {
   Calendar cal = Calendar.getInstance();
   cal.setTime(this.date);
   cal.set(Calendar.HOUR_OF_DAY, this.hour / 100);
   cal.set(Calendar.MINUTE, this.hour % 100);
   
   return cal.getTime();
}

After these changes, the entities are good to go, we just need to create the proper descriptors before packaging the project for deployment.