Parameter 0 of constructor in required a bean of type that could not be found

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When receiving the error message “Parameter 0 of constructor in [classname] required a bean of type [beanname] that could not be found”, it means that Spring framework was unable to find a bean of the specified type to inject into the constructor of the specified class. This typically occurs when Spring’s dependency injection mechanism is unable to match the required dependency with an available bean.

An example scenario to better understand this error is when you have a class called “UserService” with a constructor that requires a bean of type “UserRepository”. However, Spring is not able to find a bean of type “UserRepository” in its application context.


public class UserService {
    private UserRepository userRepository;
    
    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }
    
    // Other methods...
}

public interface UserRepository {
    // Methods...
}

To resolve this error, you need to make sure that a bean of the required type is available in the Spring application context. There are a few ways to achieve this:

  • Check if you have properly defined the bean in your configuration file (e.g., XML, JavaConfig).
  • If you are using component scan, ensure that the proper packages are being scanned and the component or stereotype annotation (e.g., @Component, @Repository) is present on the class implementing the required interface.
  • If you’re using Spring Boot, make sure that your bean is being auto-detected by Spring Boot’s component scan mechanism.
  • Check if you have multiple beans of the same type and there is an ambiguity. In such cases, you can use the qualifier annotation (@Qualifier) to specify the exact bean to be injected.

For example, assume the following implementation of the UserRepository interface:


@Repository
public class UserRepositoryImpl implements UserRepository {
    // Implementation of methods...
}

In this case, Spring should be able to auto-detect the UserRepositoryImpl as a bean and inject it into the UserService constructor.

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