Why is your Spring @Autowired field coming up null even though everything looks right? It’s a common headache, and often trickier than it seems. Whether it’s a missing annotation, a bean registration issue, or something deeper in the configuration, there are several reasons Spring dependency injection might not be working as expected.
In this blog, we will discuss the reasons why the Spring @Autowired field is null.
Table of Contents:
What is @Autowired in Spring?
@Autowired is an annotation used in Spring for automatically injecting dependencies in a class. It can be applied to fields, constructors, and setter methods so that the Spring container automatically links the appropriate beans.
@Autowired can be injected in fields, constructors, and setter methods. When an @Autowired is used on a field, Spring scans the application for a matching bean and injects it directly, removing the need for a manual instantiation. However, field injection is not used because it makes unit testing difficult and increases the coupling between the two classes. A better approach than this is to inject a dependency in a constructor, which makes the class immutable and easier to test. It avoids the NullPointerException.
Another way to inject dependencies is through setter injection, where the dependency is set using a setter method. This is useful when the dependency is optional or can be changed after object creation.
Setting @Autowired(required = false) makes the dependency injection optional and allows the application to run even if the bean is not available. This is useful in Spring’s Dependency Injection (DI) mechanism and simplifies bean management.
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Dependency Injection with Spring
Dependency Injection (DI) is a pattern in Spring where the dependencies of the object, like services or components, are provided to it, rather than creating the object internally.
DI allows you to define how the objects are created and how they should interact or communicate with each other. It promotes loose coupling and makes the code more modular and easier to maintain.
The simple example you can think of is that, think of building a house, instead of constructing the whole furniture in your house, you will hire a carpenter to do all the work.
Similarly, in Spring DI, instead of manually creating dependencies like objects or services within a class, Spring will ask someone else for the creation and management of these dependencies to its container. This process is like asking the Spring container to handle the construction of the required furniture (dependencies) for your class.
How Does Spring Implement Dependency Injection?
Instead of creating the objects manually using the new keyword by the user. Spring is responsible for defining your classes and telling them which ones should be managed. This is done by the use of annotations like @Component, @Service, @Repository, or by declaring them in a configuration class using @Bean.
When the application starts, Spring creates the ApplicationContext, which is a container that manages the beans (objects). After that, Spring scans all the code to find all the classes that are annotated as Spring components. These classes are registered as beans in the container.
Reasons Why @Autowired Might Be Null
There are many reasons why an @Autowired field may be null. Some of them are:
1. Component Not Scanned by Spring
Spring scans for the beans only in the packages that are specified in @ComponentScan. If your class is outside this package, then Spring will not realize it as a bean.
2. Missing the @Component, @Service, @Repository and @Controller annotations
For any class to be eligible for dependency injection in Spring, it has to be first registered as a bean in the Spring Application Context. However, Spring will do it automatically if you annotate the class with:
- @Controller: It is used for web controllers that handle incoming HTTP requests.
It decides “what to show” to the user.
- @Component: It is a general-purpose annotation to tell Spring to “manage this class”. It is used when no specific role applies.
- @Service: It is used for classes that contain business logic, like calculations or processing. It handles the “what to do” part.
- @Repository: It is used for classes that talk to the database. It handles “how to get/save data”.
3. Using the new keyword to instantiate the class
Using the new keyword creates a new object manually, which is not managed by Spring, due to which Spring will not be able to inject the dependencies into it.
Example:
MyService myService = new MyService(); // Not managed by Spring
4. Field injection in a Non-Spring class
The dependency is injected only in Spring-managed beans. If a class is not managed by Spring (i.e., not a Spring bean), the @Autowired annotation will not work.
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5. Incorrect autowiring of the interfaces
When there are many Spring implementations, the Spring will not be able to decide which one to inject, unless you use annotations like @Qualifier or @Primary.
6. Incorrect Scope for the Bean
If the dependency has a different scope, e.g., a prototype bean has been injected into a singleton bean, it may not behave as expected. The singleton bean will receive only a single instance of the prototype bean at the time of injection, which means a new instance will not be created for each use.
7. Manual instantiation of the Service class
If you manually make the object of the service class, the @Autowired will not be added to it.
Example:
MyService myService = new MyService();
8. Using @Autowired on Static Fields
Spring does not inject dependencies into static fields because static members belong to the class, not an instance.
Example:
@Autowired
private static MyService myService; // Will not work
9. Using Field Injection with Final Fields
Final fields must be initialized at object creation, while Spring injects dependencies later using reflection.
Example:
@Autowired
private final MyService myService; // Will not work
10. Circular Dependencies
If two beans depend on each other, one might not be fully initialized when the other tries to inject it due to which Spring @Autowired Field can be null.
Best Practices for Using @Autowired
1. Component Not Scanned by Spring
One should ensure that the @Component class is available at the correct location.
Example:
@ComponentScan("com.example.myapp") // Ensure correct package
public class AppConfig { }
2. Missing the @Component, @Service, @Repository and @Controller annotations.
Use the correct annotation for the correct class, i.e., for ServiceClass, use the @Service annotation, for the Repo class use @Repository, and so on.
Example:
@Service // Use @Service for service layer components
public class MyService { }
3. Using the new keyword to instantiate the class
Do not use the new keyword when a dependency can be injected. It can lead to errors.
Example:
@Autowired
private MyService myService; // Let Spring inject it
4. Field injection in a Non-Spring class
Make sure that your Component class has the annotation @Component.
5. Incorrect autowiring of the interfaces.
When you have multiple dependencies, use the @Qualifier annotation so that Spring does not get confused in the various injections. Also, apart from this, you can use the @Primary annotation.
Example:
@Autowired
@Qualifier("creditCardPaymentService")
private PaymentService paymentService;
Or
@Service
@Primary
public class DefaultPaymentService implements PaymentService { }
6. Incorrect Scope for the Bean
Make sure that when the bean is injected in the Spring, it is in its lifecycle stage. Otherwise, it will cause the @Autowired field to be null. When you are using single beans, use the objectFactory method.
7. Manual instantiation of the Service class
Do not create the object of the class yourself, otherwise, it will give a null value to the @Autowired. The process of instantiation should be handled by Spring only.
Example:
@Autowired
private MyService myService;
8. Using @Autowired on Static Fields
You can use the instance field rather than the static fields for the dependency injection.
Example:
@Autowired
private MyService myService;
9. Using Field Injection with Final Fields
Make use of the constructor injection instead of the fields injection. As they can throw the error of the null value in autowired.
Example:
@Service
public class MyComponent {
private final MyService myService;
@Autowired
public MyComponent(MyService myService) { //constructor
this.myService = myService;
}
}
10. Circular Dependencies
You can use the @Lazy annotation when there is a chance of circular dependency.
Example:
@Autowired
@Lazy
private MyService myService;
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Conclusion
An @Autowired field in Spring may be null due to missing annotations, incorrect bean scope, manual instantiation, or circular dependencies. To avoid this, make sure that the Spring injects dependency itself, uses a constructor instead of field injection, and configures component scanning. Simple solutions like using @Component, @Service, @Qualifier, or @Lazy will also prevent common issues and ensure smooth dependency injection.
To know more about this topic, you can refer to our Java Course.
Why is My Spring @Autowired field null? – FAQs
Q1. How to enable autowiring in Spring?
To enable Autowiring in the Spring application, we should use the @Autowired annotation.
Q2. What is the meaning of a null field?
A field with a NULL value is a field with no value.
Q3. Can the Spring bean be null?
A Spring bean can be null in one class but work in another, usually due to scope issues or incorrect instantiation.
Q4. What is @autowired in Spring?
@Autowired is one of the annotations in Spring, which is used for automatic dependency injection, i.e., it allows Spring to automatically inject the dependencies into your classes.
Q5. Why is @autowired not recommended?
@Autowired is useful but not recommended because @Autowired hides what the class needs and makes the code harder to read and test.