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To handle the three objects we have coded three Java-classes:
As you may recall from the last article these classes are simple
beans where the "many"-relations are implemented using
Collections. To simplify adding and removing an element to a
Collection we've coded add- and remove-methods. When Castor adds
or removes elements to the Collections it will use these methods
and also the set-methods. To see what's going on inside the
classes I've added some System.out lines in the code. If
you prefer using a logging utility like Log4J or the Logging API
in JDK1.4 feel free to do so.
The Media class now looks like
this:
package hansen.playground;
import java.util.*;
public class Media {
private int id;
private String type;
private Collection movies = new ArrayList();
public Media() {}
public Media(int id, String type) {
this.id = id; this.type = type;}
public int getId() { return id; }
public void setId(int id) { this.id = id; }
public String getType() { return type; }
public void setType(String type) { this.type = type; }
public Collection getMovies() { return movies; }
public void setMovies(Collection movies) {
System.out.println(
"***Media.setMovies: "
+ movies.size()
+ " movies to media "
+ this);
this.movies = movies;
}
public void addMovie(Movie movie) {
System.out.println(
"***Media.addMovie: "
+ movie
+ " to media "
+ this);
movies.add(movie);
}
public void removeMovie(Movie movie) {
System.out.println(
"***Media.removeMovie: "
+ movie
+ " from media "
+ this);
movies.remove(movie);
}
public String toString() {
return "\"" + this.type + "\"";
}
}
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- Listing 1: The Media class -
Note that all output from the add-, set-, and remove-methods are prefixed
with "***", so they're easy to spot. Our first exercise is to run
the ReadActor program from the last article. It lists the movies where
Keanu Reeves acts.
The output looks like this:
***Media.addMovie: "The Matrix" to media "DVD"
***Movie.addActor: "Keanu Reeves" to movie "The Matrix"
***Actor.addMovie: "The Matrix" to actor "Laurence Fishburne"
***Movie.addActor: "Laurence Fishburne" to movie "The Matrix"
***Actor.addMovie: "The Matrix" to actor "Keanu Reeves"
***Media.addMovie: "Chain Reaction" to media "VHS"
***Movie.addActor: "Keanu Reeves" to movie "Chain Reaction"
***Actor.addMovie: "Chain Reaction" to actor "Keanu Reeves"
Movies starring Keanu Reeves
Movie: The Matrix
Media: DVD
Actor: Keanu Reeves
Actor: Laurence Fishburne
Movie: Chain Reaction
Media: VHS
Actor: Keanu Reeves
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- Listing 2: Output
from ReadActor -
Since the record with Keanu Reeves has relations to all the
other entities in the database Castor will fetch all data from
the database and create 6 beans: 2 media-, 2 actor-, and 2
movie-beans. One interesting observation is Castor uses the add-
methods to insert data in the Collections. What if we haven't
coded add-methods? Let's temporarily remove the addMovie
method in class Media, and run the program again:
***Media.setMovies: 1 movies to media "DVD"
***Movie.addActor: "Keanu Reeves" to movie "The Matrix"
***Actor.addMovie: "The Matrix" to actor "Laurence Fishburne"
***Movie.addActor: "Laurence Fishburne" to movie "The Matrix"
***Actor.addMovie: "The Matrix" to actor "Keanu Reeves"
***Media.setMovies: 1 movies to media "VHS"
***Movie.addActor: "Keanu Reeves" to movie "Chain Reaction"
***Actor.addMovie: "Chain Reaction" to actor "Keanu Reeves"
. . .
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- Listing 3: Output from
ReadActorforcing Castor to use set-methods -
As you can see Castor switches over to using the setMovies method,
which must be present in the class to be a bean. If you're interested in
changing this priority you may define the field for the Movies
Collection like this in the mapping.xml
file:
<field name="movies" type="hansen.playground.Movie"
collection="collection"
set-method="setMovies"
get-method="getMovies">
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