Java Spring Interview Questions and Answers

Java Spring Interview Questions And Answers

1. What is Spring?

Ans. Spring is an open-source development framework for Enterprise Java. The core features of the Spring Framework can be used in developing any Java application, but there are extensions for building web applications on top of the Java EE platform. Spring framework targets to make Java EE development easier to use and promote good programming practice by enabling a POJO-based programming model.

2. What are the benefits of the Spring Framework?

Ans.

• Lightweight: Spring is lightweight when it comes to size and transparency. The basic version of the spring framework is around 2MB.
• Inversion of control (IOC): Loose coupling is achieved in Spring, with the Inversion of Control technique. The objects give their dependencies instead of creating or looking for dependent objects.
• Aspect-oriented (AOP): Spring supports Aspect-oriented programming and separates application business logic from system services.
• Container: Spring contains and manages the life cycle and configuration of application objects.
• MVC Framework: Spring’s web framework is a well-designed web MVC framework, which provides a great alternative to web frameworks.
• Transaction Management: Spring provides a consistent transaction management interface that can scale down to a local transaction and scale up to global transactions (JTA).
• Exception Handling: Spring provides a convenient API to translate technology-specific exceptions (thrown by JDBC, Hibernate, or JDO) into consistent, unchecked exceptions.

3. Which are the Spring framework modules?

Ans. The basic modules of the Spring framework are :

• Core module
• Bean module
• Context module
• Expression Language module
• JDBC module
• ORM module
• OXM module
• Java Messaging Service(JMS) module
• Transaction module
• Web module
• Web-Servlet module
• Web-Struts module
• Web-Portlet module

4. Explain the Core Container (Application context) module?

Ans. This is the basic Spring module, which provides the fundamental functionality of the Spring framework. BeanFactory is the heart of any spring-based application. Spring framework was built on the top of this module, which makes the Spring container.

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5. BeanFactory – BeanFactory implementation example?

Ans. A BeanFactory is an implementation of the factory pattern that applies Inversion of Control to separate the application’s configuration and dependencies from the actual application code.

The most commonly used BeanFactory implementation is the xmlBeanFactory class.

6. XMLBeanFactory?

Ans. The most useful one is org.springframework.beans.factory.xml.xmlBeanFactory, which loads its beans based on the definitions contained in an XML file. This container reads the configuration metadata from an XML file and uses it to create a fully configured system or application.

7. Explain the AOP module?

Ans. The AOP module is used for developing aspects for our Spring-enabled application. Much of the support has been provided by the AOP Alliance in order to ensure the interoperability between Spring and other AOP frameworks. This module also introduces metadata programming to Spring.

8. Explain the JDBC abstraction and DAO module?

Ans. With the JDBC abstraction and DAO module, we can be sure that we keep up the database code clean and simple, and prevent problems that result from a failure to close database resources. It provides a layer of meaningful exceptions on top of the error messages given by several database servers. It also makes use of Spring’s AOP module to provide transaction management services for objects in a Spring application.

9. Explain the object/relational mapping integration module?

Ans. Spring also supports for use of an object/relational mapping (ORM) tool over straight JDBC by providing the ORM module. Spring provides support to tie into several popular ORM frameworks, including Hibernate, JDO, and iBATIS SQL Maps. Spring’s transaction management supports each of these ORM frameworks as well as JDBC.

10. Explain the web module?

Ans. The Spring web module is built on the application context module, providing a context that is appropriate for web-based applications. This module also contains support for several web-oriented tasks such as transparently handling multipart requests for file uploads and programmatic binding of request parameters to your business objects. It also contains integration support with Jakarta Struts.

11. Explain the Spring MVC module?

Ans. MVC framework is provided by Spring for building web applications. Spring can easily be integrated with other MVC frameworks, but Spring’s MVC framework is a better choice since it uses IoC to provide for a clean separation of controller logic from business objects. With Spring MVC you can declaratively bind request parameters to your business objects.

12. Spring configuration file?

Ans. Spring configuration file is an XML file. This file contains the class information and describes how these classes are configured and introduced to each other.

13. What is Spring IoC container?

Ans. The Spring IoC is responsible for creating the objects, managing them (with dependency injection (DI)), wiring them together, configuring them, as also managing their complete lifecycle.

14. What are the benefits of IOC?

Ans. IOC or dependency injection minimizes the amount of code in an application. It makes it easy to test applications since no singletons or JNDI lookup mechanisms are required in unit tests. Loose coupling is promoted with minimal effort and the least intrusive mechanism. IOC containers support eager instantiation and lazy loading of services.

15. What are the common implementations of the ApplicationContext?

Ans. The FileSystemXmlApplicationContext container loads the definitions of the beans from an XML file. The full path of the XML bean configuration file must be provided to the constructor. The ClassPathXmlApplicationContext container also loads the definitions of the beans from an XML file. Here, you need to set CLASSPATH properly because this container will look bean configuration XML file in CLASSPATH. The WebXmlApplicationContext: container loads the XML file with definitions of all beans from within a web application.

16. What is the difference between Bean Factory and ApplicationContext?

Ans. Application contexts provide a means for resolving text messages, a generic way to load file resources (such as images), they can publish events to beans that are registered as listeners. In addition, operations on the container or beans in the container, which have to be handled in a programmatic fashion with a bean factory, can be handled declaratively in an application context. The application context implements Messagesource, an interface used to obtain localized messages, with the actual implementation being pluggable.

17. What does a Spring application look like?

Ans.

• An interface that defines the functions.
• The implementation that contains properties, its setter and getter methods, functions etc.,
• Spring AOP
• The Spring configuration XML file.
• A client program that uses the function

18. What is Dependency Injection in Spring?

Ans. Dependency Injection, an aspect of Inversion of Control (IoC), is a general concept, and it can be expressed in many different ways.This concept says that you do not create your objects but describe how they should be created. You don’t directly connect your components and services together in code but describe which services are needed by which components in a configuration file. A container (the IOC container) is then responsible for hooking it all up.

19. What are the different types of IoC (dependency injection)?

Ans.

• Constructor-based dependency injection: Constructor-based DI is accomplished when the container invokes a class constructor with a number of arguments, each representing a dependency on other classes.
• Setter-based dependency injection: Setter-based DI is accomplished by the container calling setter methods on your beans after invoking a no-argument constructor or no-argument static factory method to instantiate your bean.

20. Which DI would you suggest Constructor-based or setter-based DI?

Ans. You can use both Constructor-based and Setter-based Dependency Injection. The best solution is using constructor arguments for mandatory dependencies and setters for optional dependencies.

21. What does a Spring Bean definition contain?

Ans. A Spring Bean definition contains all configuration metadata which is needed for the container to know how to create a bean, its lifecycle details and its dependencies.

22. How do you provide configuration metadata to the Spring Container?

Ans. There are three important methods to provide configuration metadata to the Spring Container:

• XML based configuration file.
• Annotation-based configuration
• Java-based configuration

23. How do you define the scope of a bean?

Ans. When defining an in Spring, we can also declare a scope for the bean. It can be defined through the scope attribute in the bean definition. For example, when Spring has to produce a new bean instance each time one is needed, the bean’s scope attribute to be a prototype. On the other hand, when the same instance of a bean must be returned by Spring every time it is needed, the the bean scope attribute must be set to a singleton.

24. Explain the bean scopes supported by Spring?

Ans. There are five scoped provided by the Spring Framework supports the following five scopes:

• In singleton scope, Spring scopes the bean definition to a single instance per - Spring IoC container.
• In prototype scope, a single bean definition has any number of object instances.
• Request scope, a bean is defined to an HTTP request. This scope is valid only in a web-aware Spring ApplicationContext.
• In session scope, a bean definition is scoped to an HTTP session. This scope is also valid only in a web-aware Spring ApplicationContext.
• In global-session scope, a bean definition is scoped to a global HTTP session. This is also a case used in a web-aware Spring ApplicationContext.

The default scope of a Spring Bean is Singleton.

25. Which are the important beans lifecycle methods? Can you override them?

Ans. Two important bean lifecycle methods. The first one is set up which is called when the bean is loaded into the container. The second method is the teardown method which is called when the bean is unloaded from the container. The bean tag has two important attributes (init-method and destroy-method) with which you can define your own custom initialization and destroy methods. There are also the corresponding annotations(@PostConstruct and @PreDestroy).

26. What are inner beans in Spring?

Ans. When a bean is only used as a property of another bean it can be declared as an inner bean. Spring’s XML-based configuration metadata provides the use of element inside the or elements of a bean definition, in order to define the so-called inner bean. Inner beans are always anonymous and they are always scoped as prototypes.

27. How can you inject a Java Collection in Spring?

Ans. Spring offers the following types of collection configuration elements:

• The type is used for injecting a list of values, in the case that duplicates are allowed.
• The type is used for wiring a set of values but without any duplicates.
• The
• The type can be used to inject a collection of name-value pairs where the name and value are both Strings.

28. What is the bean wiring?

Ans. Wiring, or else bean wiring is the case when beans are combined together within the Spring container. When wiring beans, the Spring container needs to know what beans are needed and how the container should use dependency injection to tie them together.

29. What is bean auto wiring?

Ans. The Spring container is able to autowire relationships between collaborating beans. This means that it is possible to automatically let Spring resolve collaborators (other beans) for a bean by inspecting the contents of the BeanFactory without using and elements.

30. Explain different modes of auto wiring?

Ans. The autowiring functionality has five modes which can be used to instruct Spring container to use autowiring for dependency injection:

• no: This is default setting. Explicit bean reference should be used for wiring.
• byName: When autowiring byName, the Spring container looks at the properties of the beans on which autowire attribute is set to byName in the XML configuration file. It then tries to match and wire its properties with the beans defined by the same names in the configuration file.
• byType: When autowiring by datatype, the Spring container looks at the properties of the beans on which autowire attribute is set to byType in the XML configuration file. It then tries to match and wire a property if its type matches with exactly one of the beans name in configuration file. If more than one such beans exist, a fatal exception is thrown.
• constructor: This mode is similar to byType, but type applies to constructor arguments. If there is not exactly one bean of the constructor argument type in the container, a fatal error is raised.
• autodetect: Spring first tries to wire using autowire by constructor, if it does not work, Spring tries to autowire by byType.

31. Are there limitations with autowiring?

Ans. Limitations of autowiring are:

• Overriding: You can still specify dependencies using and settings that will always override autowiring.
• Primitive data types: You cannot autowire simple properties such as primitives, Strings, and Classes.
• Confusing nature: Autowiring is less exact than explicit wiring, so if possible prefer using explicit wiring.

32. Can you inject null and empty string values in Spring?

Ans. Yes, you can.

33. What is Spring Java-Based Configuration? Give some annotation example.

Ans. Java-based configuration option enables you to write most of your Spring configuration without XML but with the help of few Java-based annotations. An example is a @Configuration annotation, which indicates that the class can be used by the Spring IoC container as a source of bean definitions. Another example is the@Beanannotated method that will return an object that should be registered as a bean in the Spring application context.

34. What is Annotation-based container configuration?

Ans. An alternative to XML setups is provided by annotation-based configuration which relies on the bytecode metadata for wiring up components instead of angle-bracket declarations. Instead of using XML to describe a bean wiring, the developer moves the configuration into the component class itself by using annotations on the relevant class, method, or field declaration.

35. How do you turn on annotation wiring?

Ans. Annotation wiring is not turned on in the Spring container by default. In order to use annotation-based wiring, we must enable it in our Spring configuration file by configuring element.

36. @Required annotation?

Ans. This annotation simply indicates that the affected bean property must be populated at configuration time, through an explicit property value in a bean definition or through autowiring. The container throws BeanInitializationException if the affected bean property has not been populated.

37. @Autowired annotation?

Ans. The @Autowired annotation provides more fine-grained control over where and how autowiring should be accomplished. It can be used to autowire bean on the setter method just like @Required annotation, on the constructor, on a property or pn methods with arbitrary names and/or multiple arguments.

38. @Qualifier annotation?

Ans. When there are more than one beans of the same type and only one is needed to be wired with a property, the @Qualifier annotation is used along with @Autowired annotation to remove the confusion by specifying which exact bean will be wired.

39. How can JDBC be used more efficiently in the Spring framework?

Ans. When using the Spring JDBC framework the burden of resource management and error handling is reduced. So developers only need to write the statements and queries to get the data to and from the database. JDBC can be used more efficiently with the help of a template class provided by Spring framework, which is the JdbcTemplate.

40. JdbcTemplate?

Ans. JdbcTemplate class provides many convenience methods for doing things such as converting database data into primitives or objects, executing prepared and callable statements, and providing custom database error handling.

41. Spring DAO support?

Ans. The Data Access Object (DAO) support in Spring is aimed at making it easy to work with data access technologies like JDBC, Hibernate or JDO in a consistent way. This allows us to switch between the persistence technologies fairly easily and to code without worrying about catching exceptions that are specific to each technology.

42. ORM’s Spring support?

Ans. Spring supports the following ORM’s:

• Hibernate
• iBatis
• JPA (Java Persistence API)
• TopLink
• JDO (Java Data Objects)
• OJB

43. How can we integrate Spring and Hibernate using HibernateDaoSupport?

Ans. Use Spring’s SessionFactory called LocalSessionFactory. The integration process is of 3 steps:

• Configure the Hibernate SessionFactory
•  Extend a DAO Implementation fromHibernateDaoSupport
• Wire in Transaction Support with AOP

44. Types of transaction management Spring support?

Ans. Spring supports two types of transaction management:

• Programmatic transaction management: This means that you have managed the transaction with the help of programming. That gives you extreme flexibility, but it is difficult to maintain.
• Declarative transaction management: This means you separate transaction management from the business code. You only use annotations or XML based configuration to manage the transactions.

45. What are the benefits of the Spring Framework’s transaction management?

Ans. 

• It provides a consistent programming model across different transaction APIs such as JTA, JDBC, Hibernate, JPA, and JDO.
• It provides a simpler API for programmatic transaction management than a number of complex transaction APIs such as JTA.
• It supports declarative transaction management.
• It integrates very well with Spring’s various data access abstractions.

46. Which Transaction management type is more preferable?

Ans. Most users of the Spring Framework choose declarative transaction management because it is the option with the least impact on application code, and hence is most consistent with the ideals of a non-invasive lightweight container. Declarative transaction management is preferable over programmatic transaction management though it is less flexible than programmatic transaction management, which allows you to control transactions through your code.

47. Explain AOP?

Ans. Aspect-oriented programming, or AOP, is a programming technique that allows programmers to modularize crosscutting concerns or behavior that cuts across the typical divisions of responsibility, such as logging and transaction management.

48. Explain Aspect?

Ans. The core construct of AOP is the aspect, which encapsulates behaviors affecting multiple classes into reusable modules. It is a module that has a set of APIs providing cross-cutting requirements. For example, a logging module would be called the AOP aspect for logging. An application can have any number of aspects depending on the requirement. In Spring AOP, aspects are implemented using regular classes annotated with the @Aspect annotation (@AspectJ style).

49. What is the difference between concern and crosscutting concerns in Spring AOP?

Ans. The Concern is the behavior we want to have in a module of an application. A Concern may be defined as the functionality we want to implement. The cross-cutting concern is a concern that is applicable throughout the application and it affects the entire application. For example, logging, security, and data transfer are the concerns which are needed in almost every module of an application, hence they are cross-cutting concerns.

50. What is Join point?

Ans. The join point represents a point in an application where we can plug-in an AOP aspect. It is the actual place in the application where an action will be taken using Spring AOP framework.

51. What is Advice?

Ans. The advice is the actual action that will be taken either before or after the method execution. This is actual piece of code that is invoked during the program execution by the Spring AOP framework.

Spring aspects can work with five kinds of advice:

• before:Run advice before the a method execution.
• after:Run advice after the a method execution regardless of its outcome.
• after-returning:Run advice after a method execution only if the method completes successfully.
• after-throwing:Run advice after the a method execution only if method exits by throwing an exception.
• around:Run advice before and after the advised method is invoked.

52. What is Pointcut?

Ans. The pointcut is a set of one or more joinpoints where an advice should be executed. You can specify pointcuts using expressions or patterns.

53. What is the Introduction?

Ans. An Introduction allows us to add new methods or attributes to existing classes.

54. What is the Target object?

Ans. A target object is an object being advised by one or more aspects. It will always be a proxy object. It is also referred to as the advised object.

55. What is a Proxy?

Ans. A proxy is an object that is created after applying advice to a target object. When you think of client objects the target object and the proxy object are the same.

56. What are the different types of AutoProxying?

Ans. 

BeanNameAutoProxyCreator

- DefaultAdvisorAutoProxyCreator

- Metadata autoproxying

57. What is Weaving? What are the different points where weaving can be applied?

Ans. Weaving is the process of linking aspects with other application types or objects to create an advised object. Weaving can be done at compile time, at load time, or at runtime.

58. Explain XML Schema-based aspect implementation?

Ans. In this implementation case, aspects are implemented using regular classes along with XML based configuration.

59. Explain annotation-based (@AspectJ based) aspect implementation

Ans. This implementation case (@AspectJ based implementation) refers to a style of declaring aspects as regular Java classes annotated with Java 5 annotations.

60. What is Spring MVC framework?

Ans. Spring comes with a full-featured MVC framework for building web applications. Although Spring can easily be integrated with other MVC frameworks, such as Struts, Spring’s MVC framework uses IoC to provide a clean separation of controller logic from business objects. It also allows to declaratively bind request parameters to business objects.

61. What is DispatcherServlet?

Ans. The Spring Web MVC framework is designed around a DispatcherServlet that handles all the HTTP requests and responses.

62. Explain WebApplicationContext?

Ans. The WebApplicationContext is an extension of the plain ApplicationContext that has some extra features necessary for web applications. It differs from a normal ApplicationContextin that it is capable of resolving themes, and that it knows which servlet it is associated with.

63. What is Controller in Spring MVC framework?

Ans. Controllers provide access to the application behavior that you typically define through a service interface. Controllers interpret user input and transform it into a model that is represented to the user by the view. Spring implements a controller in a very abstract way, which enables you to create a wide variety of controllers.

64. @Controller annotation?

Ans. The @Controller annotation indicates that a particular class serves the role of a controller. Spring does not require you to extend any controller base class or reference the Servlet API.

65. @RequestMapping annotation?

Ans. @RequestMapping annotation is used to map a URL to either an entire class or a particular handler method.

Spring Boot Interview Questions

1. what is spring boot

Ans. Spring boot is a module which used to simplify the use of the spring framework in Java development. It utilised to build stand-alone spring based applications which can simply run. So, it radically eliminates a lot of dependencies and configurations.

2. List the features of spring boot?

Ans. It allows avoiding complex configuration of XML which is there in spring  

It carries an embedded Tomcat server.

It is effortless to maintain and creation of REST end-points

Deployment is effortless

Its architecture based on microservice.

3. Explain the evolution of spring boot?

Ans. Spring boot appeared into presence in  October 2012, a user made a request asking spring framework and bootstrapping so that Jira can quickly start, and hence at the beginning of 2013 spring boot is made

In 2014 April spring boot version 1.0 is created.

On June 2014, version 1.1 created.

Version 1.2  came into existence in march 2015

In Dec 2016 version 1.3  is released

Version 1.4 came into existence in January of 2017

Spring boot version 1.5 created in 2017 February

4. Differentiate between Spring and Springboot?

Ans. 

Spring	Springboot
A framework of Web application which based on Java	A module which belongs to spring
Spring is complicated than spring boot	Springboot is easy when compared to spring
Takes an unopinionated aspect	Takes an opinionated aspect of a platform
Gives libraries and tools to build optimised web applications	It used to create a spring application which can simply execute

5. What are the benefits of using spring boot?

Ans. It is simpler to understand and to develop spring applications.

Productivity increased

Reduces the time of development

6. What are the goals of spring boot?

Ans. To run the application individually and to decrease the development time.

To easily develop a production-ready spring application.

To avoid complicated XML configuration.

Offer a simpler way to start an application.

7. List the starters of spring boot?

Ans. Spring boot started Actuator dependency

Spring boot started Security dependency

Spring boot started Web dependency

Spring boot starter Thyme leaf dependency

Spring boot starter Test dependency

8. Write a spring boot example program using @SpringBootApplication?

Ans. 

package com.howtodoinjava.exp;

import org.springframework.boot.SpringApplication;

import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication 

public class SpringBootexpApplication {

 public static void main(String[] args) {

  SpringApplication.run(SpringBootexpApplication.class, args);

 }

}

9. Explain the process of setting up a spring boot?

Ans. From Oracle official site setup Java JDK

Download and setup Spring tool suit

New spring started project can be started by

Tick on File -> New -> Spring starter project

Fill the required details and include dependency and finish

Customise the application properties

Now the main file can be run as Java application.

10. How to encrypt a password in spring boot?

Ans. Spring boot is a Java-based framework to generate microservices in order to create enterprise-level applications. 

You frequently come over creating projects where you ought to connect to databases similar to MongoDB, etc. and save the actual password of DB connection inside that config file from spring boot project (application.yml or application.properties). Furthermore, tokens or passwords wanted for Authorisation to create another API call are additionally stored in a similar way.

You can truly avoid adding the original password inside the config file and utilise ‘jasypt-spring-boot‘, a java library.

11. Why is spring boot used for microservices?

Ans. Spring Boot lets creating production-ready applications immediately and gives non-functional characteristics: Embedded servers that are simple to deploy by some containers. It assists in observing the different components. It helps in configuring these components externally.

12. List the sources of external configuration in spring boot?

Ans. There are three main sources for external configuration in spring boot they are:

Application properties

Command-line properties

Profile-specific properties

13. What are the requirements for a spring boot system?

Ans.

Spring boot version of 2.1.7 requires

Java 8+

The framework of 5.1.9+ of spring

Precise build support

Maven 3.3+

Gardel 4.4+

Support of servlet container

Servlet version 4.0 - Tomcat 9.0

Servlet version 3.1 - jetty 9.4

Servlet version 4.0 - undertow 2.0

14. How can we enable HTTP/2 support in spring boot?

Ans. By using server.http/2.enabled=true we can enable the support of HTTP/2 in spring boot

15. Explain what is microservice in spring boot?

Ans. Microservice is a structure that permits software developers to develop services and deploy them independently; every service running possesses its own process, and this gains the lightweight model to maintain business applications. 

16. List the advantages of microservice?

Ans. Microservice can develop easily

It has effortless scalability

Configuration is minimum

Production time is very less.

17. What is the spring boot actuator starter?

Ans. An actuator is used to monitor and manage applications. An actuator is a tool that contains HTTP end-points while the application is driven to production, you can decide to manage and monitor your application utilizing HTTP end-points. 

18. What is thyme leaf starter?

Ans. It is a server-side Java template locomotive for a web application. Its principal goal is to bring easy natural templates to your web application.

It can be combined with Spring Framework also perfect for HTML5 Java web applications.

19. Explain about spring boot dependency management?

Ans. Spring Boot dependency management is mainly used to manage dependencies and configuration automatically without you designating the version about that dependencies.

20. How can we build a custom end-point in spring boot Actuator?

Ans. A custom end-point in spring boot 2.x can be created by using @enddpoint annotation, and Spring Boot also reveals end-points were utilising @WebEndpointor, @WebEndpointExtension above HTTP with the guidance of Spring MVC, Jersey, etc.

21. How to deploy different servers with spring boot?

Ans. Follow the mention steps to deploy servers with spring boot.

Generating WAR from the project

Then, we can deploy this WAR file into your favorite server.

22. Mention the disadvantage of using spring boot?

Ans. One of the main disadvantages of using spring boot is it is a bit overwhelming for new developers and time-consuming.

23. How to create non-web applications in spring boot?

Ans. By removing the web dependencies from the classpath along with changing the way, we can create non-web applications.

24. Differentiate between Getmapping and Requestmapping?

Ans. The @Getmapping is a shortcut for @Requestmapping. These methods promote consumption. The consume choices are:

consumes= ‘plain/text’

consumes= {‘text/plain’, ‘*/application}

25. What is a component scan in spring boot?

Ans. Spring Boot application scans whole beans plus package declarations when the application starts. You need to combine the @ComponentScan annotation for your class file to examine your components included in your project.