Howto generate prototype objects with in a singleton bean using spring java configurations

Question

Here is what i have right now which works fine. All it does is a market class which returns an array of items objects:

I have class market

class market {

    public ArrayList<Items> createItems(HashMap<String,String> map) {
        ArrayList<Items> array = new ArrayList<Items>();
        for (Map.Entry<String, String> m : map.entrySet()) {
            Item item = new Item();
            item.setName(m.key());
            item.setValue(m.value());
            array.add(item);
        }
        return array;
    }
}

class Item is simple class with getter and setter for name and value

Here is how my config file looks:

@Configuration
public class MarketConfig {

    @Bean
    public Market market() {
        return new Market();
    }
}

How I want to change my code:( REASON: i dont want

Item item = new Item(); 

in then method. I want Spring to inject it into Market)

class market {

    public Item item;
    //getters and setters for item

    public ArrayList<Items> createItems(HashMap<String,String> map) {
        ArrayList<Items> array = new ArrayList<Items>();
        for (Map.Entry<String, String> m : map.entrySet()) {
             item.setName(m.key());
             item.setValue(m.value());
             array.add(item);
        }
        return array;
    }
}

@Configuration
public class MarketConfig {

    @Bean
    @Scope("prototype")
    public Item item() {
        return new Item();
    }

    @Bean
    public Market market() {
        Market bean = new Market();
        bean.setItem(item());
    }
}

I know that prototype scope will give me new bean each time i call item(); Now i want new bean for each iteration in the for loop of createItems method. How can i tell spring to give me.

One way i know is Do

applicationContext context = new AnnotationConfigApplicationContext();
context.getBean(Item.class);

But is there any other way to get my work done. Thanks

Answer 1

Yes, you can create prototype method on demand using look-up method

public abstract class ItemFactory {

    public abstract Item createItem();

}

now in applicationContext.xml just put the following:

<bean id="item" class="x.y.z.Item" scope="prototype" lazy-init="true"/>

and configure factory:

<bean id="itemFactory" class="x.y.z.ItemFactory">
<lookup-method name="createItem" bean="item"/>
</bean>

Now all that you need to do in order to use it is Autowire it inside any bean:

and call yout look-up method:

@Service 
public class MyService{

   @Autowired
   ItemFactory itemFactory;

   public someMethod(){
      Item item = itemFactrory.createItem();
   } 

}

each time you call createItem() you will receive the reference to newly created instance of Item class.

P.S: I see that you are using @Configuration instead of xml you need check if look-up method can be configured inside configuration bean.

Hope it helps.

Update: The trick is simple:

@Configuration
public class BeanConfig {

    @Bean
    @Scope(value="prototype")
    public Item item(){
        return new Item();
    }


    @Bean
    public ItemManager itemManager(){
        return new ItemManager() {

            @Override
            public Item createItem() {
                return item();
            }
        };
    }
}

Answer 2

It can be simplified if you are using Java 8

@Configuration
public class Config {

  @Bean
  @Scope(value = "prototype")
  public Item item() {
      return new Item();
  }

  @Bean
  public Supplier<Item> itemSupplier() {
      return this::item;
  }
}

And after that you can use this supplier in your Market class to create prototype Item beans.

@Component
public class Market {

  private final Supplier<Item> itemSupplier;

  @Autowired
  public Market(Supplier<Item> itemSupplier) {
      this.itemSupplier = itemSupplier;
  }

  private Item createItem() {
      return itemSupplier.get();
  }

}

Quite simple and there is no need in additional factory beans or interfaces.