Strategy within Spring boot
Make your StrategyFactory another Spring bean, and inject all the strategies in the factory:
@Component
public class StrategyFactory {
private final List<Strategy> strategies;
@Autowired
public StrategyFactory(List<Strategy> strategies) {
this.strategies = strategies;
}
public Strategy getStrategy(String strategyName) {
// iterate through the strategies to find the right one, and return it.
}
}
I usually use an enum rather than a String to identify the stratehy, and I make each Strategy return the enum value that it handles, so the iteration can be as simple as
return strategies.stream().filter(strategy -> strategy.getType() == type).findAny().orElseThrow(
() -> new IllegalStateException("No strategy found for type " + type));
Of course, you can also store the strategies in a Map inside the constructor, to make the lookup O(1).
All the previous answers are using a pretty straight forward usage of spring DI. However it's also possible to use ServiceLocatorFactoryBean in order to create a factory without having to specify any bean in the factory. First define a interface for your factory:
public interface MyFactory {
Strategy get(String type);
}
// Could be an abstract class
public interface Strategy {
void doStuff();
}
Then in your application:
@Configuration
public class AppConfiguration {
@Autowired
private BeanFactory beanFactory;
public ServiceLocatorFactoryBean myFactoryLocator() {
final ServiceLocatorFactoryBean locator = new ServiceLocatorFactoryBean();
locator.setServiceLocatorInterface(MyFactory.class);
locator.setBeanFactory(beanFactory);
return locator;
}
@Bean
public MyFactory myFactory() {
final ServiceLocatorFactoryBean locator = myFactoryLocator();
locator.afterPropertiesSet();
return (MyFactory) locator.getObject();
}
}
Now you can define bean (using annotation @Service, @Component or @Bean) that implements/extends and they are automatically registered into the MyFactory bean and can be created with:
myFactory.get("beanName");
The best part is you can register the Strategy bean as lazy and with different scopes.
I would suggest you to make your StrategyFactory
a bean and inject into it a Map<String, Strategy>
. Spring fill it with the name of the strategy bean as a key and a value will be a strategy itself. Then all you'll need to do is to call get
on that Map
.
Here is an example:
@SpringBootApplication
public class So44761709Application {
public static void main(String[] args) {
SpringApplication.run(So44761709Application.class, args);
}
public interface Strategy { }
@Component
public static class DependencyA {}
@Component
public static class DependencyB {}
@Component("StrategyA")
public static class StrategyA implements Strategy {
private DependencyA depA;
private DependencyB depB;
@Autowired
public StrategyA(DependencyA depA, DependencyB depB) {
this.depA = depA;
this.depB = depB;
}
}
@Component("StrategyB")
public class StrategyB implements Strategy {
private DependencyA depA;
private DependencyB depB;
@Autowired
public StrategyB(DependencyA depA, DependencyB depB) {
this.depA = depA;
this.depB = depB;
}
}
@Component
public class StrategyFactory {
@Autowired
private Map<String, Strategy> strategies;
public Strategy getStrategy(String strategyName) {
return strategies.get(strategyName);
}
}
@Bean
CommandLineRunner run(StrategyFactory strategyFactory) {
return args -> {
System.out.println(strategyFactory.getStrategy("StrategyB").getClass().getSimpleName());
System.out.println(strategyFactory.getStrategy("StrategyA").getClass().getSimpleName());
};
}
}
Prints:
StrategyB
StrategyA