Buyers and Sellers

Seller Agent

A seller registers its service (selling whiskey) with the local DF agent, then adds a seller behavior.

public class Seller extends Agent {

protected void setup() {

DFAgentDescription dfd = new DFAgentDescription();
dfd.setName(getAID());

ServiceDescription service = new ServiceDescription();
service.setType( "whiskey" );
service.setName( getLocalName() );

try {
DFAgentDescription list[] = DFService.search( this, dfd );
if ( list.length > 0 ) DFService.deregister(this);
dfd.addServices(service);
DFService.register(this, dfd);
} catch (FIPAException fe) {
System.err.println(fe.getMessage());
}
addBehaviour(new SellerBehavior(this));
}
}

Seller Behavior

Selling whiskey is a cyclic behavior. It blocks until it receives an appropriate message, then creates an appropriate reply and sends it after some delay:

class SellerBehavior extends CyclicBehaviour {
MessageTemplate template =
MessageTemplate.MatchPerformative( ACLMessage.QUERY_REF );
ACLMessage reply;
Random generator = new Random();
public SellerBehavior(Agent a) { super(a); }

public void action() {
int price = generator.nextInt(500); // price per bottle
int delay = generator.nextInt(100); // respond after delay

ACLMessage msg = myAgent.receive(template);

if (msg != null) {
reply = msg.createReply();
reply.setPerformative( ACLMessage.INFORM );
reply.setContent("" + price);

System.out.print(myAgent.getLocalName());
System.out.print(" will offer $" + price + " to ");
System.out.print(msg.getSender().getLocalName());
System.out.println(" in " + delay + " ms");

myAgent.addBehaviour(
new DelayBehaviour(myAgent, delay) {
public void handleElapsedTimeout() {
myAgent.send(reply);
}
});
} // if
block();
} // action
}

Buyer Agent

A buyer finds out which agents sell whiskey. It adds each one to the receivers list for a request for whiskey. It creates a sequential behavior consisting of a parallel behavior followed by a one shot behavior that prints the lowest bid. The parallel behavior consists of a buyer behavior for each seller:

public class Buyer extends Agent {
int bestPrice = 9999999;
ACLMessage bestOffer = null;
protected void setup() {

AID[] providers = DFUtils.searchDF(this, "whiskey");
if (providers != null) {

SequentialBehaviour seq = new SequentialBehaviour();
ParallelBehaviour par =
new ParallelBehaviour( ParallelBehaviour.WHEN_ALL );

ACLMessage msg = new ACLMessage(ACLMessage.QUERY_REF);
String id = "whiskey request";
msg.setConversationId(id);
msg.setContent( "how much?" );

for(int i = 0; i < providers.length; i++) {
msg.addReceiver(providers[i]);
MessageTemplate template = MessageTemplate.and(
MessageTemplate.MatchPerformative(ACLMessage.INFORM),
MessageTemplate.MatchConversationId(id));
par.addSubBehaviour(
new BuyerBehavior(this, 2000, template));
send(msg);
} // for

seq.addSubBehaviour( par );
addBehaviour( seq );

seq.addSubBehaviour(
new OneShotBehaviour() {
public void action() {
if (bestOffer != null)
System.out.println("Best Price $" + bestPrice );
else
System.out.println("Got no quotes");
}
);
send(msg);
} // if
} // setup
} // Buyer

Buyer Behavior

class BuyerBehavior extends MyReceiver {

public BuyerBehavior(
Agent a, int delay, MessageTemplate template ) {
super(a, delay, template);
}

public void handle( ACLMessage msg) {
if (msg == null) return;
int offer = Integer.parseInt( msg.getContent());
System.out.println("Buyer considering an offer for $" + offer);
if (offer < ((Buyer)myAgent).bestPrice) {
((Buyer)myAgent).bestPrice = offer;
((Buyer)myAgent).bestOffer = msg;
}
}
}

Output

s1 will offer $227 to b1 in 66 ms
s3 will offer $173 to b1 in 86 ms
s2 will offer $75 to b1 in 65 ms
s1 will offer $323 to b1 in 29 ms
s3 will offer $105 to b1 in 44 ms
s2 will offer $114 to b1 in 18 ms
Buyer considering an offer for $114
Buyer considering an offer for $323
Buyer considering an offer for $105
Best Price $105