Spring: Using @Configuration to dynamically return a Bean [closed]

Question

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Closed 8 years ago.

Suppose you need to dynamically (at runtime) get an instance of a subtype of a given type.

How would you accomplish that using Spring IoC?

Answer 1

You can also use @Profile to achieve similar functionality in a more declarative way.

@Configuration
@Profile("default")
public class TypeAConfig {
    @Bean
    public Type getType() {
        return new TypeA();
    }
}

@Configuration
@Profile("otherProfile")
public class TypeBConfig() {
    @Bean
    public Type getType() {
        return new TypeB();
    }
}

@Configuration
public class SysConfig {
    @Autowired
    Type type;       

    @Bean Type getType() {
        return type;
    }
}

You can then control which implementation to use by specifying the profiles that Spring should activate, e.g. with the spring.profiles.active system property. More information in the JavaDoc for Profile

Answer 2

I've found the following is an easy way to do it.

@Component
public class SystemPreferences {
  public boolean useA() {...}
}

interface Type {....}

public class TypeA implements Type {
   @Autowired
   Other xyz;
}

public class TypeB implements Type {...}

@Configuration
public class SysConfig {
  @Autowired
  SystemPreferences sysPrefs;

  @Bean
  public Type getType() {
    if (sysPrefs.useA()) {
      //Even though we are using *new*, Spring will autowire A's xyz instance variable
      return new TypeA();
    } else {
      return new TypeB();
    }
  }
}