I am trying to autowire a bean inside of a Singleton class, I know that it always a best idea to avoid manual autowiring, but this class is being used in so many places so I do not want to change the caller of this class.
Runner.java
@Component
public class RunnerClass {
@Autowired
public ConfigService configService;
}
ConfigService.java
@Service
public class ConfigService {
private ConfigServiceDAO = ConfigServiceDAO.getInstance();
}
ConfigServiceDAO.java
public class ConfigServiceDAO {
//Bean I want to autowire here....
@Autowired
ConfigServiceDAOBuilder DAOBuilder
public static ConfigServiceDAO getInstance() {
return SingletonHolder.INSTANCE;
}
private static class SingletonHolder {
public static final ConfigServiceDAO INSTANCE = new ConfigServiceDAO();
private SingletonHolder() {}
}
}
DAOBuilder inside ConfigServiceDAO is always null, which makes sense because my understanding is when the class is instantiated manually, spring injection doesn't happen. What could be the solution here if I want to keep ConfigServiceDAO as non spring component?
====EDIT==== I know it is possible to make ConfigServiceDAO as a spring component and autowire all dependencies. But a lot of classes from different packages already call ConfigServiceDAO.getInstance().someMethod() So I guess the the right question is, what would be the best way to autowire a spring component to the class that is instantiated manually.
I don't know your use case but you cannot use @Autowired annotation outside a Spring bean. However if you really need to access a Spring bean from a non Spring piece of code you can do it like below. However this is a very non Spring way of designing your dependencies.
import org.springframework.context.ApplicationContext;
public enum ApplicationContextHolder {
INSTANCE;
private ApplicationContext applicationContext;
public ApplicationContext getApplicationContext() {
return applicationContext;
}
public void setApplicationContext(ApplicationContext applicationContext) {
this.applicationContext = applicationContext;
}
}
Then you have a configuration class:
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Configuration;
import javax.annotation.PostConstruct;
@Configuration
public class SomeConfig {
@Autowired
private ApplicationContext applicationContext;
@PostConstruct
public void init() {
ApplicationContextHolder.INSTANCE.setApplicationContext(applicationContext);
}
}
Then in your DAO class you get a reference to the builder bean you are interested. Something like this:
public class ConfigServiceDAO {
public static ConfigServiceDAO getInstance() {
return SingletonHolder.INSTANCE;
}
private static class SingletonHolder {
public static final ConfigServiceDAO INSTANCE =
ApplicationContextHolder.INSTANCE.getApplicationContext().getBean(ConfigServiceDAOBuilder.class).buildConfigServiceDAO()
private SingletonHolder() {}
}
}
Again this is a very non Spring way of doing things.
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