Why is My Autowired Bean Null in the Constructor?

Autowiring Beans in Constructors: Understanding Null References

When working with Spring-managed POJOs, it is common to inject dependencies using the @Autowired annotation. However, some developers encounter a puzzling issue where the autowired bean is null when accessed in a constructor. This article aims to clarify this behavior and provide a solution.

As mentioned in the provided answer, autowiring typically occurs after object construction. This means that any references to autowired beans within the constructor will likely be null. To address this, it is recommended to move the initialization code from the constructor to a separate method annotated with @PostConstruct.

The following modified code snippet illustrates this approach:

@Component
public class DocumentManager implements IDocumentManager {

  @Autowired
  private IApplicationProperties applicationProperties;

  // Move initialization code to a PostConstruct method
  @PostConstruct
  public void init() {
    startOOServer();
  }

  private void startOOServer() {
    if (applicationProperties != null) {
      // Rest of the initialization code here
    }
  }

  // ... Rest of the class remains the same
}

By annotating the init method with @PostConstruct, Spring will automatically invoke it after the bean has been constructed but before it is fully initialized. This ensures that the applicationProperties bean is available for use within the initialization logic.

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