Why Does Autowiring Fail in Spring Boot Constructors?

Constructor Autowiring in Spring Boot

When working with Spring Boot, injecting dependencies into bean constructors using autowiring can sometimes result in null values. This is because autowiring occurs after bean construction.

In the given code snippet, the @Autowired applicationProperties bean is null when referenced in the DocumentManager constructor, but not when referenced in the convert method. The issue is that autowiring happens after the constructor is executed.

Solution: Post-Construction Initialization

To resolve this problem, use the @PostConstruct annotation on a method in the bean class where the dependency should be initialized. This method will be called after bean construction and can be used to perform necessary initialization logic.

Here's how the DocumentManager class can be modified to use the @PostConstruct annotation:

@Component
public class DocumentManager implements IDocumentManager {

  private Log logger = LogFactory.getLog(this.getClass());
  private OfficeManager officeManager = null;
  private ConverterService converterService = null;

  @Autowired
  private IApplicationProperties applicationProperties;

  // Remove initialization code from constructor
  public DocumentManager() {
  }

  @PostConstruct
  public void initialize() {
    startOOServer();
  }

  ...

In this revised code, the initialization logic has been moved to the initialize method, which is annotated with @PostConstruct. This ensures that the applicationProperties bean is available when the method is called after bean construction.

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