Date of First Response: 2009-09-10 01:34:39
securitylevel_name: Public

The attached file should generate everyting into a subdirectory ./movie and compile and execute.

You'll have to modify the classpath, though.

Regards
-W


# Shell this file to create subdir movie with *.java, Movie.drl, database.xml
#
# you'll have to modify the classpath setting - see below
#

mkdir movie || true

cat <<'TheEnd' >movie/Main.java
package movie;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.OutputStream;
import java.util.Collection;

import javax.xml.bind.JAXBContext;

import org.drools.KnowledgeBase;
import org.drools.KnowledgeBaseFactory;
import org.drools.builder.KnowledgeBuilder;
import org.drools.builder.KnowledgeBuilderError;
import org.drools.builder.KnowledgeBuilderFactory;
import org.drools.builder.ResourceType;
import org.drools.definition.KnowledgePackage;
import org.drools.io.ResourceFactory;
import org.drools.runtime.StatefulKnowledgeSession;

import javax.xml.bind.Unmarshaller;

public class Main {

       private StatefulKnowledgeSession session;

       public Main(){
       }

       public void init() throws Exception {

       KnowledgeBase kBase = KnowledgeBaseFactory.newKnowledgeBase();
       KnowledgeBuilder kBuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();
       kBuilder.add( ResourceFactory.newFileResource( "movie/Movie.drl" ),
                     ResourceType.DRL );
       if( kBuilder.hasErrors() ){
               for( KnowledgeBuilderError err: kBuilder.getErrors() ){
                       System.out.println( err.toString() );
               }
               throw new IllegalStateException( "DRL errors" );
       }

       kBase.addKnowledgePackages( kBuilder.getKnowledgePackages() );

               File xml = new File( "database.xml" );
               JAXBContext jc = JAXBContext.newInstance( Database.class );
               Unmarshaller u = jc.createUnmarshaller();
               InputStream inputStream = new FileInputStream( xml );
               Database db = (Database)u.unmarshal( inputStream );
               inputStream.close();

       session = kBase.newStatefulKnowledgeSession();

               for( Movie m: db.getMovie() ){
                       session.insert( m );
               }
               for( Actor a: db.getActor() ){
                       session.insert( a );
               }
               for( Role r: db.getRole() ){
                       session.insert( r );
               }
               session.fireAllRules();
       }

       public static void main( String[] args ) throws Exception {
               Main rf = new Main();
               rf.init();
       }

}
TheEnd

cat <<'TheEnd' >movie/Role.java
package movie;

import javax.xml.bind.annotation.XmlAttribute;

public class Role implements Item {

       private String actor;
       private String movie;

       public Role(){
       }

       @XmlAttribute
       public String getActor() {
               return actor;
       }

       public void setActor(String actor) {
               this.actor = actor;
       }

       @XmlAttribute
       public String getMovie() {
               return movie;
       }

       public void setMovie(String movie) {
               this.movie = movie;
       }

       @Override
       public String toString(){
               return actor + " plays in " + movie;
       }

}
TheEnd

cat <<'TheEnd' >movie/Movie.java
package movie;

import java.util.HashSet;
import java.util.Set;
import javax.xml.bind.annotation.XmlAttribute;

public class Movie implements Item {
       private String title;
       private Set<Actor> cast;

       public Movie(){
       }

       @XmlAttribute
       public String getTitle() {
               return title;
       }
       public void setTitle(String title) {
               this.title = title;
       }

       public Set<Actor> getCast(){
               if( cast == null ) cast = new HashSet<Actor>();
               return cast;
       }

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

       @Override
       public boolean equals( Object o ){
               if( ! (o instanceof Movie ) ) return false;
               return this.title.equals( ((Movie)o).getTitle() );
       }

       @Override
       public String toString(){
               StringBuilder sb = new StringBuilder();
               sb.append( title ).append( "\n" );
               for( Actor a: getCast() ){
                       sb.append( "  " ).append( a.getName() ).append( "\n" );
               }
               return sb.toString();
       }
}
TheEnd

cat <<'TheEnd' >movie/Item.java
package movie;

/**
 * Marker interface for WMEs
 * @author Wolfgang Laun
 */
public interface Item {
}
TheEnd

cat <<'TheEnd' >movie/Database.java
package movie;

import java.util.ArrayList;
import java.util.List;

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlType;

@XmlRootElement
@XmlType(propOrder={"movie", "actor" , "role" })
public class Database {

       private List<Movie> movie;
       private List<Actor> actor;
       private List<Role> role;

       public Database(){
       }

       @XmlElement
       public List<Movie> getMovie() {
               if( movie == null ) movie = new ArrayList<Movie>();
               return movie;
       }

       @XmlElement
       public List<Actor> getActor() {
               if( actor == null ) actor = new ArrayList<Actor>();
               return actor;
       }

       @XmlElement
       public List<Role> getRole() {
               if( role == null ) role = new ArrayList<Role>();
               return role;
       }

}
TheEnd

cat <<'TheEnd' >movie/Actor.java
package movie;

import java.util.ArrayList;
import java.util.List;
import javax.xml.bind.annotation.XmlAttribute;

public class Actor implements Item {

       private String name;
       private List<Movie> movies;

       public Actor(){
       }

       @XmlAttribute
       public String getName() {
               return name;
       }
       public void setName(String name) {
               this.name = name;
       }

       public List<Movie> getMovies(){
               if( movies == null ) movies = new ArrayList<Movie>();
               return movies;
       }

       @Override
       public String toString(){
               StringBuilder sb = new StringBuilder();
               sb.append( name ).append( "\n" );
               for( Movie m: getMovies() ){
                       sb.append( "  " ).append( m.getTitle() ).append( "\n" );
               }
               return sb.toString();
       }

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

       @Override
       public boolean equals( Object o ){
               if( ! (o instanceof Actor ) ) return false;
               return this.name.equals( ((Actor)o).getName() );
       }
}
TheEnd

cat <<'TheEnd' >movie/Movie.drl
package movie;

/***
 - List<?> as fact field type
 - Set<?> as fact field type
 - Match WMEs with elements from field with List<?> type: from
 - inline eval() for determining membership in Collection()
 - Write rules for a set of WME types using a "marker" interface.

*/

#
# Fill the Movies' cast lists with data from Role.
#
rule fillCast
   salience 100
   when
       $r : Role( $actor : actor, $movie : movie )
       $a : Actor( name == $actor )
       $m : Movie( title == $movie )
   then
       modify( $m ){
           getCast().add( $a );
       }
       retract( $r );
end

#
# Fill the Actors' list of movies with data from a Movie's cast list
#
rule fillMovies
   salience 90
   when
       $m : Movie( $cast : cast )
       $a : Actor() from $cast
   then
       System.out.println( "movie " + $m.getTitle() + " actor " + $a.getName() );
       modify( $a ){
           getMovies().add( $m );
       }
end

#
# Find a movie where HB and LB are in together
#
rule findHBLB
   when
       $hb : Actor( name == "Humphrey Bogart" )
       $lb : Actor( name == "Lauren Bacall" )
       $m : Movie( $title : title, $cast : cast, eval( $cast.contains( $hb ) && $cast.contains( $lb ) ) )
   then
       System.out.println( "HB & LB together in " + $title );
end

#
# Display any WME
#
rule showItem
   salience -100
   when
       $i : Item()
   then
       System.out.println( $i.toString() );
end
TheEnd

cat <<'TheEnd' >database.xml
<?xml version="1.0" encoding="UTF-8"?>
<database>
<movie title="Casablanca"/>
<movie title="Key Largo"/>
<movie title="To Have and Have Not"/>
<movie title="The African Queen"/>
<actor name="Humphrey Bogart"/>
<actor name="Katherine Hepburn"/>
<actor name="Ingrid Bergman"/>
<actor name="Lauren Bacall"/>
<role actor="Humphrey Bogart" movie="Casablanca"/>
<role actor="Ingrid Bergman"  movie="Casablanca"/>
<role actor="Humphrey Bogart" movie="The African Queen"/>
<role actor="Humphrey Bogart" movie="Key Largo"/>
<role actor="Humphrey Bogart" movie="To Have and Have Not"/>
<role actor="Lauren Bacall" movie="To Have and Have Not"/>
<role actor="Lauren Bacall" movie="Key Largo"/>
<role actor="Katherine Hepburn" movie="The African Queen"/>
</database>
TheEnd

export CLASSPATH=.:/extra/Drools-5.0.1.SNAPSHOT/drools-core.jar:/extra/Drools-5.0.1.SNAPSHOT/drools-api.jar:/extra/Drools-5.0.1.SNAPSHOT/drools-compiler.jar:/extra/Drools-5.0.1.SNAPSHOT/drools-ant.jar:/extra/Drools-5.0.1.SNAPSHOT/antlr-runtime.jar:/usr/local/eclipse/plugins/org.eclipse.jdt.core_3.4.4.v_894_R34x.jar:/extra/Drools-5.0.0.CR1/bin/lib/mvel2-2.0.8pre1.jar

javac movie/*.java

java movie/Main

cat <<'TheEnd'

#
# This is what I get:
#

movie Casablanca actor Ingrid Bergman
Exception in thread "main" org.drools.runtime.rule.ConsequenceException: java.lang.NullPointerException
       at org.drools.runtime.rule.impl.DefaultConsequenceExceptionHandler.handleException(DefaultConsequenceExceptionHandler.java:23)
       at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:943)
       at org.drools.common.DefaultAgenda.fireNextItem(DefaultAgenda.java:885)
       at org.drools.common.DefaultAgenda.fireAllRules(DefaultAgenda.java:1086)
       at org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:682)
       at org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:649)
       at org.drools.impl.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:183)
       at movie.Main.init(Main.java:65)
       at movie.Main.main(Main.java:70)
Caused by: java.lang.NullPointerException
       at org.drools.base.DefaultKnowledgeHelper.modifyRetract(DefaultKnowledgeHelper.java:190)
       at movie.Rule_fillMovies_0.consequence(Rule_fillMovies_0.java:8)
       at movie.Rule_fillMovies_0ConsequenceInvoker.evaluate(Rule_fillMovies_0ConsequenceInvoker.java:28)
       at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:934)
       ... 7 more
TheEnd