Spring / Spring interview questions
1. Explain Spring Framework.
Spring is an open source framework that provides comprehensive infrastructure support for developing Java applications . It provides libraries of classes which make it easier to develop tasks such as transaction management, database integration, and web applications and create the help to address...
2. What are the advantages of using Spring Framework?
Spring is a light weight container in comparison to J2EE containers. Spring has layered architecture which means you require to work on the layer you wanted to enhance and leave the rest of the layers to Spring framework. Spring helps creating loosely coupled applications by using DI (Dependency ...
3. What are the different modules in Spring framework?
Below are the modules of the Spring framework. Core Container module. Application context module. AOP (Aspect Oriented Programming). JDBC abstraction and DAO module. ORM integration module (Object/Relational). Web module. Servlet module. Struts module. MVC framework module. Expression Language mo...
4. Explain lifecycle of a bean in Spring framework.
When a bean is instantiated, it may be required to perform some initialization to get it into a usable state. Similarly, when the bean is no longer required and is removed from the container, some cleanup may be required. Spring bean factory is responsible for managing the life cycle of a Spring ...
5. What is the difference between singleton and prototype bean?
Both refers to the scope of a beans which defines their existence on the application. Singleton single object instance per Spring IOC container. Prototype Spring IoC container creates new bean instance of the object every time a request for that specific bean is made.
6. What are the types of Dependency Injection Spring supports?
There are 2 kinds of Dependency Injection Spring supports. Setter Injection: Setter-based DI accomplished by calling setter methods on the beans after invoking a no-argument constructor or no-argument static factory method to instantiate your bean. Constructor Injection: Constructor-based DI that...
7. What is Bean Factory in Spring?
Bean Factory is like a factory class that contains collections of beans. The Bean Factory holds bean definition of multiple beans within itself and then instantiates the bean when asked by client. Bean Factory is an actual representation of the Spring IOC container that is responsible for contain...
8. How do I decide between when to use prototype scope and singleton-scoped bean?
Use the prototype scope for all beans that are stateful and the singleton scope for stateless beans.
9. Different types of IOC.
There are two types of dependency Injection: Constructor Injection Dependencies are provided as a constructor parameter. Setter Injection Dependencies are assigned through setter method. Interface Injection Injection is done through an interface and not supported in spring framework.
10. Difference between BeanFactory and ApplicationContext in spring.
With ApplicationContext more than one config files are possible while only one config file or .xml file is possible with BeanFactory. ApplicationContext support internationalization messages, application life-cycle events, validation and many enterprise services like JNDI access, EJB integration ...
11. Type of transaction Management in spring.
Spring supports two types of transaction management: a. Programmatic transaction management b. Declarative transaction management.
12. When do you use programmatic and declarative transaction management?
Programmatic transaction management can be considered for applications with less volume transaction operations and declarative transaction management is preferred for application involving large scale transactions.
13. What is Bean Wiring?
Bean wiring means creating associations between application components i.e. beans within the spring container.
14. Types of IoC containers.
There are 2 types of IoC containers: Bean Factory container: Simplest container providing basic support for DI. The BeanFactory is usually preferred where the resources are limited like mobile devices or applet based applications. Spring ApplicationContext Container: This container adds more ente...
15. Explain Aspect oriented Programming.
Enterprise applications have some common cross-cutting concerns that will be applied to the different types of objects and application modules such as logging, transaction management, data validation and authentication. In object-oriented Programming, modularity of application is achieved by clas...
16. Explain different modes of bean autowiring in Spring Framework.
There are 5 auto wiring modes in spring framework. no: autowiring is OFF. You have to explicitly set the dependencies using tags in bean definitions; default option for bean wiring in spring framework. byName: This option enables the dependency injection identified by bean names. When autowiring ...
17. How do I enable annotation based auto wiring in Spring Framework?
To enable annotation based wiring, @Autowired, org.springframework.beans .factory.annotation. AutowiredAnnotation BeanPostProcessor need to be registered and it could be achieved in 2 ways. Include
18. What is Dependency Injection in Spring framework?
Dependency Injection is an aspect of Inversion of Control (IoC) and a general concept expressed in many different ways. As this concept suggests you do not create your objects but describe how it should be created . You don't directly associate your components and services together in code but de...
19. Which DI should I prefer, Constructor-based or setter-based in spring?
Use constructor-based DI for dependencies that are required (mandatory) and setters for dependencies that are optional.
20. What is Spring annotation?
The spring annotation is a library that facilitates the use of annotations to configure your application using spring framework. Example spring annotations include @Required, @Autowired etc.
21. Spring: What are Lazily-instantiated beans?
Spring instantiate all the beans at startup by default. But sometimes, some beans are not required to be initialized during startup, rather we want them to be initialized in later stages of the application on demand. For such beans, we include lazy-init="true" while configuring beans.
22. Difference between the setter and constructor injection in Spring.
Setter injection is flexible than constructor injection because you must remember the type and order of constructor parameter. Also, constructor injection is generally used to inject the mandatory dependency, while setter can be used to inject optional dependency.
23. Difference between Dependency Injection and Factory Pattern.
Using factory your code is still actually responsible for creating objects. By DI you delegate that responsibility to another class or a framework, which is separate from your code. Use of dependency injection results in loosely coupled design but the use of factory pattern create a tight couplin...
24. What is the default scope of Spring bean?
Singleton is the default scope.
25. Mention the steps to create a Web application using Spring.
Download Spring and its dependency jars from Spring site. You may also configure spring dependency using Gradle or maven. Create application context XML to define beans and dependencies. Integrate application context xml with web.xml. Deploy and run the application.
26. How do you create bean for class with constructor having arguments?
Using constructor-arg property, we can pass reference to another bean or a value to constructor arguments. index attribute may be used to specify order of arguments.
27. How does Spring achieve loose coupling?
Spring uses runtime polymorphism and encourages association (HAS-A relationship) rather than inheritance.
28. Can we use a final class as spring bean?
It depends actually. When spring creates a JDK dynamic proxy, the final class will work. When Spring create a CGLIB proxy and your class has at least one public method, then the class cannot be final. String class is a final class that is widely used as spring bean.
29. When Spring creates a CGLIB proxy?
Spring will create a CGLIB proxy if one of the following statements is true. aop:config has proxy-target-classes set to true. Any other namespace configurations (for example, transaction-management) also have proxy-target-classes set to true. Your class does not implement an interface.
30. When Spring creates a JDK dynamic proxy?
Refer the previous question and answer. If all of the statements are not true, spring will create JDK dynamic proxy.
31. Is Spring DTD/XSD mandatory for XML validation? Where I can find the Spring DTD?
Yes, DTD or XSD is mandatory for Spring bean xml documents. spring-beans.jar file has the dtd (document type definition) file spring-beans.dtd under the package org.springframework.beans.factory.xml.
32. The main difference between JDK dynamic proxy and CGLib.
JDK Dynamic proxy can only proxy by interface while CGLIB (and javassist) can create a proxy by subclassing. In JDK dynamic proxy, your target class need to implement an interface, which is then implemented by the proxy class. In CGLIB the proxy becomes a subclass of the target class so there is ...
33. How do I Inject value into static variables in Spring bean?
Spring does not allow injecting to public static non-final fields. So the workaround will be changing to private modifier. Another workaround will be to create a non static setter to assign the injected value for the static variable. @Value ( "${my.name}" ) public void setName(String privateName)...
34. Can we inject a eum to spring bean?
Yes.
35. Is spring prototype bean threadsafe?
No. Prototype beans are stateful however if it is managed by multiple threads, then steps must be taken to ensure it is thread safe.
36. Is request scoped spring beans threadsafe?
Yes. Each request will get its own bean so thread safety is guaranteed.
37. What is the preferred bean scope for DAO, Service and Controller?
Singleton scope is preferred. DAO, service and controllers do not have to maintain its state.
38. Difference between Java bean and spring bean.
JavaBeans are Java classes which adhere to certain coding conventions. Java bean classes will, have public default (no argument) constructors, have accessor (getter and setter) methods. implement java.io.Serializable. Spring bean is basically an object managed by Spring. It is an object that is i...
39. Mention an alternate DI framework like Spring.
Google Guice framework.
40. How to deploy a Spring Boot project to the Application Server (non-embedded)?
Generate the WAR artifact from the Spring boot project by executing the Maven/Gradle build process. Deploy the generated WAR into any server that has a web-container. For example, if you are using TOMCAT server, copy the WAR to the webapp folder under the tomcat folder. Tomcat auto-detects any ch...
41. What does the word "Actuator" in spring boot refer to?
As per the Spring-boot reference documentation, an actuator is a manufacturing term that refers to a mechanical device for moving or controlling something. Actuators can generate a large amount of motion from a small change.
42. How do I instantiate Spring bean by passing constructor-args programmatically?
You can use the ApplicationContext.getBean(String name, Object ... params) method, which allows for specifying explicit constructor arguments / factory method arguments, overriding the specified default arguments (if any) in the bean definition. For example, the Employee object needs 2 constructo...
43. What is the purpose of @ControllerAdvice Annotation?
@ControllerAdvice annotation manages the exceptions in Spring Boot Application.It is an interceptor of exceptions thrown by methods annotated with @RequestMapping. @ControllerAdvice is a specialization of the @Component annotation that allows to handle exceptions across the entire application in ...
