How to achieve a dynamic dependency injection in spring? - spring

Question

We have a scenario where the dependency should be determinded at runtime. An example shows the detail below:
public class OrderProcessor {
// The Validator should be determinded based on the version of the service.
private Validator orderProcessValidator;
public Confirmation process(Order order) {
if(orderProcessValidator.validate(order)) {
// Business logic
}
}
}
Is possible to inject Validator dynamically with Spring IOC, or can only be solved through the factory pattern?

Answer 1

It is still a bit unclear for me your scenario, but I am assuming you have two actual Order classes in your project. Maybe one is in com.foo.api1 package and the other is in com.foo.api2 package. Or one Order is called Order1 and the other is called Order2. The idea is that I'm assuming you have two different classes for the two 'api versions' of Order.
You can achieve what you need by using Spring AOP:
#Aspect
#Component
public class MyAspect {
#Autowired
private Validator1 validator1;
#Autowired
private Validator2 validator2;
#Pointcut("execution(* com.foo.bar.OrderProcessor.process(..))")
private void myPointcut() {}
#Around("myPointcut() && args(order)")
public Object myAroundAdvice(ProceedingJoinPoint pjp, Object order) throws Throwable {
if (order instanceof Order1) {
validator1.validate((Order1) order);
} else
if (order instanceof Order2) {
validator2.validate((Order2) order);
}
Object retVal = pjp.proceed();
return retVal;
}
}
#Component
public class OrderProcessor {
public void process(Object order) {
System.out.println("processing order");
}
}
#Component
public class Validator1 {
public void validate(Order1 order) {
System.out.println("validating inside validator 1");
}
}
#Component
public class Validator2 {
public void validate(Order2 order) {
System.out.println("validating inside validator 2");
}
}
So, basically, you are defining an aspect that should intercept calls to your OrderProcessor class and, depending on what parameter it receives, it calls one validator or the other.