CODEWITHSUNDEEP
springannotationsdesign-patternsfactory
user1421204
user1421204

Reputation: 41

Implement factory design pattern with spring annotaion

I have a factory class that should return me an instance of classA or classB. These classes implement interface XYZ:

   interface xyz;
   getInstance()

   @service 
   classA implements xyz{
      public void checkStatus(){
      }
   }

   @service  classB implements xyz{
      public void checkStatus(){
      }
   }

Factory class:

   @component
   class ABCFactory{
       @Autowire classA A;
       public static getInstance(str a){
           return classA;
       }
   }

Client code:

   Class A a = ABCFactory.getInstance("A");
   a.checkStatus();

I get null pointer exception -- probably a is returned as null?

What is the best approach to implement the factory pattern with spring annotation and autowired bean?

Upvotes: 1

Views: 1923

Answers (2)

Tomasz Nurkiewicz
Tomasz Nurkiewicz

Reputation: 340743

static is the root of all evil. How did you managed to access classA here?

@Component
class ABCFactory{
   @Autowire classA A;
   public static getInstance(str a){
       return classA;
   }
}

A field is not static while getInstance() method is - your code won't compile.

Furthermore, dependency injection works on instances, not on static classes. Thus you should get rid of static:

@Component
class ABCFactory {
   @Autowire classA A;
   public xyz getInstance(str a){
       return A;
   }
}

and inject ABCFactory where you need it (e.g. in other services or controllers):

@Autowired
private ABCFactory factory;

BTW your design looks supicious in Spring environment, what do you want to achieve?

Upvotes: 0

GaryF
GaryF

Reputation: 24350

It's difficult to say with any certainty why your auto-wiring isn't taking place without seeing your Spring config. My first guess is that you don't have component scanning switched on:

<context:component-scan base-package="org.example"/>

Adding something like that to your spring config file (with the correct package) will tell Spring to scan the package structure for fields that need to be auto-wired, and services that can be used for auto-wiring.

Upvotes: 1

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