Decoupling is one of the prominent mantras in software engineering.
Chain of responsibility helps to decouple sender of a request and receiver of the request with some trade-offs.
Chain of responsibility is a design pattern where a sender sends a request to a chain of objects, where the objects in the chain decide themselves who to honor the request. If an object in the chain decides not to serve the request, it forwards the request to the next object in the chain.
In a chain of objects, the responsibility of deciding who to serve the request is left to the objects participating in the chains.
รจIt is similar to ‘passing the question in a quiz scenario’. When the quiz master asks a question to a person, if he doesn’t knows the answer, he passes the question to next person and so on. When one person answers the question, the passing flow stops. Sometimes, the passing might reach the last person and still nobody gives the answer.
Currency.java
public class Currency {
private intamount;
public Currency(intamt){
this.amount = amt;
}
public intgetAmount(){
return this.amount;
}
}
DispenseChain.java
public interface DispenseChain {
voidsetNextChain(DispenseChain nextChain);
void dispense(Currency cur);
}
Rupees1000Dispenser.java
public class Rupees1000Dispenser implements DispenseChain {
private DispenseChain chain;
@Override
public voidsetNextChain(DispenseChain nextChain) {
this.chain=nextChain;
}
@Override
public voiddispense(Currency cur) {
if(cur.getAmount() >= 1000){
int num = cur.getAmount()/1000;
int remainder = cur.getAmount() % 1000;
System.out.println("Dispensing "+num+" Rs. 1000 note");
if(remainder !=0) this.chain.dispense(newCurrency(remainder));
} else {
this.chain.dispense(cur);
}
}
}
Rupees500Dispenser.java
public class Rupees500Dispenser implements DispenseChain{
private DispenseChain chain;
@Override
public voidsetNextChain(DispenseChain nextChain) {
this.chain=nextChain;
}
@Override
public voiddispense(Currency cur) {
if(cur.getAmount() >= 500){
int num = cur.getAmount()/500;
int remainder = cur.getAmount() % 500;
System.out.println("Dispensing "+num+" Rs. 500 note");
if(remainder !=0) this.chain.dispense(newCurrency(remainder));
} else {
this.chain.dispense(cur);
}
}
}
Rupees100Dispenser.java
public class Rupees100Dispenser implements DispenseChain {
private DispenseChain chain;
@Override
public voidsetNextChain(DispenseChain nextChain) {
this.chain=nextChain;
}
@Override
public voiddispense(Currency cur) {
if(cur.getAmount() >= 100) {
int num = cur.getAmount()/100;
int remainder = cur.getAmount() % 100;
System.out.println("Dispensing "+num+" Rs. 100 note");
if(remainder !=0) this.chain.dispense(newCurrency(remainder));
} else {
this.chain.dispense(cur);
}
}
}
ATMDispenseChain.java
public classATMDispenseChain {
privateDispenseChain chainStart;
publicATMDispenseChain() {
// initialize the chain
this.chainStart = new Rupees1000Dispenser();
DispenseChain chain500 = new Rupees500Dispenser();
DispenseChain chain100 = new Rupees100Dispenser();
// set the chain of responsibility
chainStart.setNextChain(chain500);
chain500.setNextChain(chain100);
}
publicDispenseChain getChainStart() {
return chainStart;
}
}
TestChainPattern.java
importjava.util.Scanner;
public classTestChainPattern {
public static voidmain(String[] args) {
ATMDispenseChain atmDispenser = new ATMDispenseChain();
int amount = 0;
System.out.println("Enter amount to dispense");
Scanner input = new Scanner(System.in);
amount = input.nextInt();
if (amount % 100 != 0) {
System.out.println("Amount should be in multiple of 100s.");
return;
}
// process the request
atmDispenser.getChainStart().dispense(new Currency(amount));
input.close();
}
}
Chain of Responsibility Pattern Examples
ATM dispense machine.
Struts interceptor.
Usage of Chain of Responsibility Pattern in JDK
java.util.logging.Logger#log()
javax.servlet.Filter#doFilter()
