Spring Interview Questions Preparation Course

Q.    What is Spring framework?

Spring is development framework for Java programming. It is an open source development framework for Enterprise Java.

The core features of Spring Framework can be used in developing a Java Enterprise application.

It has many extensions and jars for developing web applications on top of Java EE platform.

With Spring we can develop large-scale complex Java applications very easily. It is also based on good design patterns like Dependency Injection, Aspect oriented programming for developing extensible feature rich software.

Q.    What are the modules in Core Container of Spring framework?

Spring framework has a Core Container. Modules in Core Container are:

Core module

Bean module

Context module

Spring Expression Language module

Q.   What are the modules in Data Access/Integration layer of Spring framework?

Modules in Data Access/Integration Layer of Spring framework are:

JDBC module: An abstraction layer to remove tedious JDBC coding.

ORM module Integration layers for Object Relational Mapping

OXM module: An abstraction layer to support Object XML mapping.

Java Messaging Service (JMS) module: Module for producing and consuming messages.

Transactions module: Transaction Management for POJO classes

Q.    What are the modules in Web layer of Spring framework?

Modules in Web Layer of Spring framework are:

• Web module: This provides basic web-oriented integration features.
• Servlet module: Support for Servlet Listeners.
• WebSocket module: Support for Web Socket style messaging.
• Portlet module: MVC implementation for Portlet environment.

Q.    What is the main use of Core Container module in Spring framework?

As the name suggests, Spring Core Container is the core of Spring framework. It gives the basic functionality of the Spring. All the parts of Spring Framework are built on top of Core Container.

Its main use is to provide Dependency Injection (DI) and Inversion of control (IOC) features.

Q.   What kind of testing can be done in Spring Test Module?

Spring Test Module provides support for Unit testing as well as Integration testing of Spring components. It allows using JUnit or TestNG testing frameworks. It also gives ability to mock objects to use the test code.

Q.    What are the uses of AOP module in Spring framework?

AOP module is also known as Aspect Oriented Programming module. Its uses are:

Development of aspects in a Spring based application

Provides interoperability between Spring and other AOP frameworks

Supports metadata programming to Spring

Q.    What are the benefits of JDBC abstraction layer module in Spring framework?

Spring provides JDBC abstraction layer module. Main benefits of this module are:

• Helps in keeping the database code clean and simple.
• Prevents problems that result from a failure to close database resources.
• Provides a layer of useful exceptions on top of the error messages given by different database servers.
• Based on Spring’s AOP module
• Provides transaction management services for objects in a Spring application

Q.    What are the main uses of Spring MVC module?

Spring-webmvc module is also known as Web-servlet module. It is based on Web Model View Controller pattern.

Main uses of this module are:

• Integration of Spring with other MVC frameworks
• Supports IoC to provide clean separation of controller logic from business objects
• Provides clean separation between domain model code and web forms 
• Allows developers to declaratively bind request parameters to business objects

Q.    What is the main benefit of Inversion of Control (IOC) principle?

Inversion of Control (IOC) principle is the base of Spring framework. It supports dependency injection in an application. With Dependency Injection, a programmer has to write minimal code. It also makes easier to test an application.

Most important benefit is that it leads to loose coupling within objects. With loose coupling it is easier to change the application with new requirements.

Q.   Does IOC containers support Eager Instantiation or Lazy loading of beans?

IOC Container in Spring supports both the approaches. Eager instantiation as well as lazy loading of beans.

Q.    What are the benefits of ApplicationContext in Spring?

ApplicationContext in Spring provides following benefits:

• Bean factory methods: These are used to access application components
• Load File Resources: It helps in loading file resources in a generic fashion
• Publish Events: It enables publishing events to registered listeners
• Internationalization Support: Ability to resolve messages to support internationalization
• Parent Context: Ability to inherit from a parent context

Q.    How will you implement ApplicationContext in Spring framework?

ApplicationContext in Spring can be implemented in one of the following three ways:

FileSystemXmlApplicationContext: If we want to load the definitions of beans from an XML file then FileSystemXmlApplicationContext is used. The full path of XML bean configuration file is provided to the constructor.

ClassPathXmlApplicationContext: To loads the definitions of beans from an XML file in the CLASSPATH, we use ClassPathXmlApplicationContext. It is used for application context embedded in jars.

WebXmlApplicationContext: To provide configuration for a web application WebXmlApplicationContext is used. While the application is running, it is read only. But it can be reloaded if underlying application supports it.

Q.    What are the main components of a typical Spring based application?

In a Spring based application, main components are:

1. Spring configuration XML file: This is used to configure Spring application
2. API Interfaces: Definition of API interfaces for functions provided by application
3. Implementation: Application code with implementation of APIs
4. Aspects: Spring Aspects implemented by application
5. Client: Application at client side that is used for accessing functions

Q.    What are the disadvantages of Dependency Injection (DI)?

Dependency Injection (DI) pattern has following disadvantages:

• Most of the time Dependency Injection forces developers to use an injection framework like Spring. This causes dependency on a framework.
• With Dependency Injection, clients are dependent on the configuration data. This becomes extra task for developers when the application does not need so many custom configuration values.
• Code is difficult to trace and read in Dependency Injection. DI separates behavior from construction of objects.
• Dependency injection increases complexity in the linkages between classes. It may become harder to manage such complexity outside the implementation of a class.

Q.    What are the different ways to provide configuration metadata to a Spring Container?

Spring supports three ways to provide configuration metadata to Spring Container:

1. XML based configuration: We can specify configuration data in an XML file.
2. Annotation-based configuration: We can use Annotations to specify configuration. This was introduced in Spring 2.5.
3. Java-based configuration: This is introduced from Spring 3.0. We can embed annotations like @Bean, @Import, @Configuration in Java code to specify configuration metadata.

Q.    How will you define the scope of a bean in Spring?

In configuration xml, we can specify the scope of bean in its definition. This is used by container to decide the scope of bean in Spring.

E.g. <bean id="userService" class="com.um.UserService" scope="prototype"/>

This is an example of userService bean with prototype scope.

Q.   Is it safe to assume that a Singleton bean is thread safe in Spring Framework?

No, Spring framework does not guarantee anything related to multi-threaded behavior of a singleton bean. Developer is responsible for dealing with concurrency issues and maintaining thread safety of a singleton bean.

Q.    What is Bean wiring in Spring?

A Spring container is responsible for injecting dependencies between beans. This process of connecting beans is called wiring.

Developer mentions in configuration file, the dependencies between beans. And Spring container reads these dependencies and wires the beans on creation.

Q.    What are the cases in which Autowiring may not work in Spring framework?

Autowiring is a great feature in Spring. It can be used in most of the cases. But there are certain scenarios in which Autowiring may not work.

Explicit wiring: Since Autowiring is done by Spring, developer does not have full control on specifying the exact class to be used. It is preferable to use Explicit wiring in case of full control over wiring.

Primitive Data types: Autowiring does not allow wiring of properties that are based on primitive data types like- int, float etc.

Q.   Is it allowed to inject null or empty String values in Spring?

Yes, Spring allows injecting null or empty String values.

Q.   What are the benefits of using Spring DAO?

Some of the benefits of using Spring DAO are:

It makes it easier to work on different data access methods like- JDBC, Hibernate etc.

It provides a consistent and common way to deal with different data access methods.

Spring DAO makes it easier to switch between different data persistence frameworks.

No need for catching framework specific exceptions.

Q.   What are the different ways to use Hibernate in Spring?

Spring provides two ways to use Hibernate:

We can extend HibernateDAOSupport and apply an AOP  interceptor node to use Hibernate.

We can also use HibernateTemplate and Callback to access Hibernate. This is based on Inversion of Control.

Q.    What types of Object Relational Mapping (ORM) are supported by Spring?

Spring supports following Object Relational Mapping (ORM) frameworks:

• Hibernate
• Java Persistence API (JPA)
• TopLink
• Java Data Objects (JDO)
• Apache Object Relational Bridge (ORB)

Q.   How will you integrate Spring and Hibernate by using HibernateDaoSupport?

We can use following steps for integrating Spring and Hibernate:

1. Add dependencies for Spring and Hibernate in pom.xml
2. Implement DAO from HibernateDaoSupport
3. Use Hibernate functions via getHibernateTemplate() method

Q.    What is a Joinpoint in Spring AOP?

In Spring AOP, Joinpoint refers to a candidate point in application where we can plug in an Aspect.

Joinpoint can be a method or an exception or a field getting modified.

This is the place where the code of an Aspect is inserted to add new behavior in the existing execution flow.

Q.   What is an Advice in Spring AOP?

An Advice in Spring AOP, is an object containing the actual action that an Aspect introduces.

An Advice is the code of cross cutting concern that gets executed.

There are multiple types of Advice in Spring AOP.

Q.    What are the different types of Advice in Spring AOP?

Spring AOP provides five kinds of Advice:

1. Before Advice: This type of advice runs just before a method executes. We can use @Before annotation for this.
2. After (finally) Advice: This type of advice runs just after a method executes. Even if the method fails, this advice will run. We can use @After annotation here.
3. After Returning Advice: This type of advice runs after a method executes successfully. @AfterReturning annotation can be used here.
4. After Throwing Advice: This type of advice runs after a method executes and throws an exception. The annotation to be used is @AfterThrowing.
5. Around Advice: This type of advice runs before and after the method is invoked. We use @Around annotation for this.

Q.    What is a Proxy in Spring AOP?

In Spring AOP, a Proxy is an object created by the AOP framework to implement Aspect contracts. It is generally a JDK dynamic proxy or CGLIB proxy.

Q.   What are the different types of AutoProxy creators in Spring?

Spring AOP provides following standard types of Autoproxy creators:

1. BeanNameAutoProxyCreator: This is a BeanPostProcessor that creates AOP proxies for beans automatically by matching names.
2. DefaultAdvisorAutoProxyCreator: This creator is more powerful that other Proxy Creators. This also applies eligible advisors automatically to bean in the current context.
3. AbstractAdvisorAutoProxyCreator: This is the parent class of DefaultAdvisorAutoProxyCreator. We can create our own auto-proxy creators by extending this class.