24 Autowired Interview Questions and Answers

Introduction:

Welcome to our comprehensive guide on Autowired interview questions and answers. Whether you are an experienced professional or a fresher looking to dive into the world of Spring Framework, this compilation covers common questions that might come your way during an Autowired interview.

As Autowired is a crucial concept in Spring, mastering the related interview questions can make a significant difference in your success. In this guide, we'll explore various questions that range from basic to advanced, ensuring you're well-prepared for any level of Autowired inquiry.

Role and Responsibility of Autowired in Spring:

Autowired is a powerful feature in the Spring Framework that automatically injects dependencies into a bean. It simplifies the process of bean wiring and promotes loose coupling. Understanding the role and responsibility of Autowired is essential for efficient dependency injection, contributing to the overall flexibility and maintainability of a Spring-based application.

Common Interview Question Answers Section:

1. What is Autowiring in Spring?

Autowiring in Spring is a technique that allows the Spring IoC (Inversion of Control) container to automatically inject dependencies into a Spring bean. It eliminates the need for explicit bean configuration in the Spring configuration file, promoting a more concise and maintainable codebase.

How to answer: Explain that Autowiring helps in achieving loose coupling by automatically connecting Spring beans based on their types. Mention the different Autowiring modes: no autowiring, autowiring by type, autowiring by name, and autowiring by constructor.

Example Answer: "Autowiring in Spring is a feature that allows the container to automatically inject dependencies into a bean. It promotes loose coupling and reduces the need for explicit configuration. There are different Autowiring modes, such as by type, by name, constructor autowiring, and no autowiring."

2. How does Autowiring by Type work?

Autowiring by type is one of the Autowiring modes in Spring, where the container searches for a bean of the same data type as the property being autowired and injects it.

How to answer: Explain that when Autowiring by type is used, Spring looks for a bean of the same data type as the property to be autowired. If a matching bean is found, it is injected into the property.

Example Answer: "Autowiring by type in Spring involves the container searching for a bean with the same data type as the property being autowired. For example, if we have a property of type 'DataSource,' Spring will look for a bean of type 'DataSource' and inject it into the property."

3. Explain the difference between Autowiring by Name and Autowiring by Type.

Autowiring by Name and Autowiring by Type are two different Autowiring modes in Spring. Autowiring by Name relies on matching the property name to the bean name, while Autowiring by Type matches based on the property data type.

How to answer: Highlight the key difference between Autowiring by Name and Autowiring by Type - one relies on property names, and the other relies on data types.

Example Answer: "Autowiring by Name in Spring looks for a bean with a name matching the property name. On the other hand, Autowiring by Type searches for a bean with the same data type as the property being autowired. So, Autowiring by Name is based on bean names, and Autowiring by Type is based on data types."

4. What are the different modes of Autowiring in Spring?

Spring supports several Autowiring modes to inject dependencies automatically. These include Autowiring by Type, Autowiring by Name, Constructor Autowiring, and Autowiring by Qualifier.

How to answer: Briefly explain each Autowiring mode and its purpose. Mention that Autowiring by Qualifier is used to specify the bean to be injected when multiple beans of the same type exist.

Example Answer: "Spring provides various Autowiring modes, including Autowiring by Type, Autowiring by Name, Constructor Autowiring, and Autowiring by Qualifier. Autowiring by Qualifier is particularly useful when dealing with multiple beans of the same type, allowing us to specify the exact bean to be injected."

5. Explain the @Autowired annotation in Spring.

The @Autowired annotation in Spring is used to automatically inject dependencies. It can be applied to fields, methods, and constructors, indicating that Spring should automatically provide the necessary dependencies.

How to answer: Emphasize that @Autowired simplifies the process of injecting dependencies and is a key component of achieving Inversion of Control (IoC) in Spring.

Example Answer: "The @Autowired annotation in Spring is a powerful tool for dependency injection. It can be applied to fields, methods, and constructors, signifying that Spring should handle the injection of dependencies automatically. This annotation is instrumental in achieving Inversion of Control (IoC) by allowing the Spring container to manage the creation and injection of beans."

6. When would you use Constructor Autowiring?

Constructor Autowiring in Spring involves automatic injection of dependencies through the constructor of a class. It's a preferred method in many cases for achieving better immutability and ensuring that the required dependencies are available when an instance is created.

How to answer: Explain that Constructor Autowiring is useful for cases where all required dependencies are essential for the proper functioning of the bean, promoting a clearer and more straightforward instantiation process.

Example Answer: "Constructor Autowiring is beneficial when all required dependencies are crucial for the proper functioning of the bean. By injecting dependencies through the constructor, we ensure that the bean is instantiated with all necessary dependencies, promoting better immutability and clarity in the code."

7. How can you handle multiple beans of the same type with Autowiring?

Handling multiple beans of the same type can be done using the @Qualifier annotation in conjunction with Autowiring. @Qualifier allows you to specify the bean name that should be injected when there are multiple beans of the same type.

How to answer: Emphasize the use of @Qualifier to disambiguate when there are multiple beans of the same type, ensuring that the correct bean is injected.

Example Answer: "To handle multiple beans of the same type, we can use the @Qualifier annotation along with Autowiring. By specifying the bean name with @Qualifier, we inform Spring about the exact bean that should be injected, resolving any ambiguity."

8. Explain the @Qualifier annotation in Spring.

The @Qualifier annotation in Spring is used in conjunction with Autowiring to specify the exact bean that should be injected when multiple beans of the same type exist. It helps resolve ambiguity and ensures the correct bean is selected for injection.

How to answer: Describe that @Qualifier is applied to the bean that is to be injected, providing the name of the target bean as an argument to the annotation.

Example Answer: "In Spring, the @Qualifier annotation is employed to disambiguate when dealing with multiple beans of the same type. By applying @Qualifier to the bean that needs injection, and specifying the bean name as an argument, we guide Spring in selecting the appropriate bean for injection."

9. What is the purpose of @Autowired(required = false)?

The use of @Autowired(required = false) in Spring indicates that the dependency is optional. If a matching bean is found, it will be injected; otherwise, the dependency will be set to null.

How to answer: Clarify that @Autowired(required = false) is handy when a dependency is not essential for the bean's functionality and can be absent without causing issues.

Example Answer: "The @Autowired(required = false) annotation in Spring signals that the associated dependency is optional. If a matching bean is available, it will be injected. However, if no suitable bean is found, the dependency will be set to null. This is useful when a particular dependency is not critical for the bean's functionality."

10. How does Autowiring work with primitive data types?

Autowiring with primitive data types in Spring involves the use of the @Value annotation or the <property name="propertyName" value="propertyValue"/> syntax in XML configuration to inject values directly into properties.

How to answer: Explain that Spring doesn't support Autowiring for primitive data types directly, but @Value or XML configuration can be used for injection.

Example Answer: "Autowiring with primitive data types isn't directly supported in Spring. However, we can use the @Value annotation or XML configuration with <property/> to inject values directly into properties. This allows us to handle primitive data types effectively."

11. What is the purpose of the @Autowired annotation on a setter method?

Applying @Autowired to a setter method in Spring indicates that the dependency should be injected through that setter. It provides an alternative to constructor injection and can be useful in certain scenarios.

How to answer: Explain that using @Autowired on a setter method allows for flexibility in managing dependencies and can be particularly beneficial for scenarios where circular dependencies exist.

Example Answer: "When we use the @Autowired annotation on a setter method in Spring, we're signaling that the associated dependency should be injected through that setter. This provides an alternative to constructor injection and can be advantageous, especially in scenarios where circular dependencies exist."

12. Can you use @Autowired with a Map or List?

Yes, you can use @Autowired with a Map or List in Spring to inject all beans of a certain type into a Map or List, making it convenient for handling multiple dependencies of the same type.

How to answer: Clarify that @Autowired can be applied to a Map or List field, and Spring will inject all beans of the specified type into the Map or List.

Example Answer: "Certainly, @Autowired can be used with a Map or List in Spring. When applied to a field of type Map or List, Spring automatically injects all beans of the specified type into the Map or List, simplifying the handling of multiple dependencies."

13. Explain the use of @Primary annotation in Spring.

The @Primary annotation in Spring is used to give a higher preference to a specific bean when multiple beans of the same type exist. It indicates that this bean should be considered as the primary candidate for injection.

How to answer: Describe that @Primary is applied to the bean definition, signaling that it should be given precedence when Spring needs to choose between multiple beans of the same type.

Example Answer: "In Spring, the @Primary annotation is applied to a bean definition, signifying that it should be given precedence when there are multiple beans of the same type. This allows us to explicitly declare a primary candidate for injection."

14. How does Autowiring handle circular dependencies?

Autowiring in Spring can handle circular dependencies through constructor injection. However, it's essential to be cautious and ensure that at least one of the beans in the circular dependency has its dependencies injected through setters or other methods.

How to answer: Explain that circular dependencies can be managed in Spring by using constructor injection and ensuring that one of the beans has dependencies injected through methods other than the constructor.

Example Answer: "Spring can handle circular dependencies through constructor injection. It's crucial to ensure that at least one of the beans involved in the circular dependency has its dependencies injected through setters or other methods, breaking the circular reference."

15. Explain the difference between @Autowired and @Resource annotations.

The main difference between @Autowired and @Resource annotations lies in their origin. @Autowired is part of the Spring framework, while @Resource is a standard Java EE annotation. Additionally, @Autowired is more flexible and powerful in handling dependencies.

How to answer: Highlight that @Autowired is specific to Spring, provides more features, and is generally preferred for dependency injection within the Spring framework.

Example Answer: "@Autowired is a Spring-specific annotation used for dependency injection, providing advanced features and flexibility. On the other hand, @Resource is a standard Java EE annotation. While both can achieve dependency injection, @Autowired is often preferred within the Spring framework for its richer capabilities."

16. Can you use @Autowired with a non-default constructor?

Yes, you can use @Autowired with a non-default constructor in Spring. When a class defines multiple constructors, @Autowired can be applied to the constructor that should be used for dependency injection.

How to answer: Explain that @Autowired supports both default and non-default constructors, allowing flexibility in choosing the appropriate constructor for dependency injection.

Example Answer: "Certainly, @Autowired can be used with a non-default constructor in Spring. When a class has multiple constructors, we can apply @Autowired to the constructor that should be used for dependency injection, providing flexibility in choosing the appropriate constructor."

17. How can you avoid circular dependencies in Spring?

To avoid circular dependencies in Spring, it's recommended to use constructor injection for dependencies. Additionally, ensure that at least one of the beans involved in the circular dependency has its dependencies injected through methods other than the constructor.

How to answer: Emphasize the use of constructor injection and the importance of breaking the circular reference by injecting dependencies through setters or other methods.

Example Answer: "To avoid circular dependencies in Spring, it's advisable to use constructor injection for dependencies. It's also essential to ensure that at least one of the beans in the circular dependency has its dependencies injected through setters or other methods, effectively breaking the circular reference."

18. What is the purpose of the @Lazy annotation with @Autowired?

The @Lazy annotation with @Autowired is used to delay the initialization of a bean until it's explicitly requested. This can be beneficial in scenarios where the bean's creation is resource-intensive, and you want to defer it until it's actually needed.

How to answer: Explain that @Lazy is applied to the dependency to defer its initialization until it's accessed for the first time.

Example Answer: "When we use the @Lazy annotation with @Autowired, we are indicating that the initialization of the bean should be delayed until it's explicitly requested. This is particularly useful when dealing with resource-intensive beans, as it allows us to defer their creation until they are actually needed."

19. How can you inject a property value using @Value annotation?

The @Value annotation in Spring is used to inject values into properties, either directly through Java configuration or via the XML configuration file. It's commonly used for injecting property values from external configuration sources.

How to answer: Describe that @Value can be applied to fields, methods, and constructors, allowing the injection of property values directly into the annotated elements.

Example Answer: "With the @Value annotation in Spring, we can inject property values directly into fields, methods, or constructors. This is often used for injecting values from external configuration sources, providing a flexible way to configure bean properties."

20. Explain the use of @Autowired with Java Configuration (JavaConfig).

When using Java Configuration (JavaConfig) in Spring, the @Autowired annotation can be applied to methods within a configuration class. This allows dependencies to be automatically injected, similar to the way it works with XML-based configuration.

How to answer: Highlight that @Autowired can be used in Java Configuration by applying it to methods that declare dependencies, simplifying the configuration process.

Example Answer: "In Java Configuration (JavaConfig) in Spring, we can use the @Autowired annotation by applying it to methods within a configuration class. This allows dependencies to be automatically injected, providing a cleaner and more concise way to configure beans compared to XML-based configuration."

21. How does Autowiring work with a parent-child context relationship in Spring?

In a parent-child context relationship in Spring, Autowiring works by allowing beans defined in the child context to access beans defined in the parent context. The child context inherits beans from the parent, and Autowiring can be used seamlessly between them.

How to answer: Explain that Autowiring operates smoothly in a parent-child context relationship, enabling dependencies to be resolved across both contexts.

Example Answer: "Autowiring in Spring works seamlessly with a parent-child context relationship. Beans defined in the child context can access and autowire dependencies from the parent context. This relationship allows for a hierarchical structure of contexts, promoting modular and organized application design."

22. When is it appropriate to use the @Autowired annotation on properties?

The @Autowired annotation on properties in Spring is appropriate when you prefer field injection. It's a concise way to inject dependencies directly into class properties without the need for explicit getters or setters.

How to answer: Explain that @Autowired on properties is suitable when you want to use field injection, especially in scenarios where you don't require additional logic in the getters or setters.

Example Answer: "Using @Autowired on properties is appropriate when we prefer field injection. It offers a concise way to inject dependencies directly into class properties without the need for explicit getters or setters. This is particularly useful in scenarios where we don't require additional logic in the accessors."

23. How can you specify the order of bean initialization in Spring using @Order?

The @Order annotation in Spring is used to specify the order in which beans should be initialized when there are multiple beans of the same type. A lower order value indicates an earlier initialization.

How to answer: Describe that @Order is applied to the beans, and the order value determines the sequence of initialization, with lower values being initialized first.

Example Answer: "To specify the order of bean initialization in Spring, we use the @Order annotation. This annotation is applied to the beans, and the order value assigned determines the sequence of initialization. Beans with lower order values will be initialized first."

24. How does Autowiring handle ambiguous dependencies, and how can you resolve them?

Autowired in Spring may encounter ambiguity when there are multiple beans of the same type. To resolve this, you can use the @Qualifier annotation on the injection point to specify the exact bean name to be injected.

How to answer: Explain that when Autowiring encounters ambiguity, @Qualifier can be used to specify the bean name and resolve the ambiguity.

Example Answer: "In cases where Autowiring encounters ambiguous dependencies, we can use the @Qualifier annotation. By applying @Qualifier to the injection point and specifying the bean name as its value, we can resolve the ambiguity and inform Spring about the exact bean to be injected."