Spring Interview Questions with Answers

This page lists the most asked and important Spring framework interview questions that we may face in our next job interview.

1. What is Spring Framework? What are it’s Main Modules?

Spring is probably the most used Java framework for developing simple web applications to enterprise-class cloud applications and microservices. Spring provides comprehensive infrastructure support for developing applications with complex requirements and designs.

Spring framework handles the infrastructure part (using dependency injection), so we can focus on the application’s core functionality. Spring framework contains formalized design patterns as first-class objects that we can integrate into our application(s) without worrying too much about how they work in the backend.

The Spring Framework is divided into modules. Applications can choose which modules they need based on what functionality they require.

Spring modules are grouped into Core Container, Data Access/Integration, WebMVC, AOP (Aspect Oriented Programming), Instrumentation, Messaging, Testing and, others as shown in the following diagram.

spring modules
Spring Framework Modules

2. What are the Advantages of Spring Framework?

Following is a partial list of benefits of using Spring Framework.

  • With Dependency Injection (DI) pattern, application dependencies are explicitely declared and maintained.
  • IoC containers tend to be lightweight, especially when compared to EJB containers. This is beneficial for developing and deploying Spring applications on computers with limited memory and CPU resources.
  • Spring does not reinvent the wheel, instead, it truly makes use of some of the existing technologies like several ORM frameworks, logging frameworks, JMS and, other view technologies.
  • Spring is organized in a modular fashion and even though the number of packages and classes are substantial, we have to worry about only those dependencies we need and we can gnore the rest.
  • Testing a Spring application is simple because the environment-dependent code is managed by the framework. Further, by using java beans style POJOs, it becomes easier to use dependency injection for injecting test data.
  • Spring’s web framework is a well-designed web MVC framework, which provides a great alternative to web frameworks such as Struts or other over engineered or less popular web frameworks.
  • Spring provides a consistent transaction management interface that can scale down to a local transaction (using a single database, for example) and scale up to global transactions (using JTA, for example).

3. What is Inversion of Control (IoC) and Dependency Injection (DI)?

In software engineering, inversion of control (IoC) is a programming technique in which object coupling is bound at run time by an assembler object and is typically not known at compile time using static analysis.

In traditional programming, the business logic flow is determined by objects statically assigned to one another.

With inversion of control, the application flow depends on the object graph instantiated by the assembler and is made possible by object interactions defined through abstractions. The binding process is achieved through “dependency injection“.

Inversion of control is a design paradigm to give more control to the targeted components of the application, the ones that are actually doing the work.

Dependency injection is a pattern used to create instances of objects that other objects rely on without knowing at compile time which class will be used to provide that functionality.

Inversion of control relies on dependency injection because a mechanism is needed to activate the components providing the specific functionality. Otherwise, how will the framework know which components to create if it is no longer in control?

In Spring, dependency injection may happen in the following ways:

  • Constructor injection
  • Setter injection
  • Fields Injection

4. Explain Inversion of Control in Spring Framework?

In the spring framework, inversion of control refers to the framework’s ability to create, destroy, and manage the beans’ lifecycle.

The ApplicationContext (internally, it uses BeanFactory) is in the center of inversion of control in Spring.

To assemble beans, the spring bean factory uses configuration metadata, which can be in the form of XML configuration or annotations.

5. Difference between BeanFactory and ApplicationContext?

A BeanFactory is like a factory class that contains a collection of beans. The BeanFactory holds bean definitions within itself and then instantiates a bean whenever asked for by clients.

BeanFactory is able to create associations between collaborating beans as they are instantiated. BeanFactory also takes part in the life cycle of the beans, making calls to custom initialization and destruction methods.

At a high level, an application context is the same as a bean factory. Both load bean definitions, wire beans together, and dispense beans upon request. But the application context also provides:

  1. A means for resolving text messages, including support for internationalization.
  2. A generic way to load file resources.
  3. Events to beans that are registered as listeners.

The three commonly used implementations of ApplicationContext are:

  • ClassPathXmlApplicationContext: loads context definition from an XML file located in the classpath, treating context definitions as classpath resources. The application context is loaded from the application’s classpath by using the code.
ApplicationContext context = new ClassPathXmlApplicationContext(“bean.xml”);
  • FileSystemXmlApplicationContext: loads context definition from an XML file in the filesystem. The application context is loaded from the file system by using the code.
ApplicationContext context = new FileSystemXmlApplicationContext(“bean.xml”);
  • XmlWebApplicationContext: loads context definition from an XML file contained within a web application.

6. In How Many ways, We can Configure Spring into our Applications?

we can configure Spring into our applications in 3 ways:

  • XML based configuration
  • Annotation-based configuration
  • Java-based configuration

We will read about these configurations in the next section.

7. What is XML Configuration for Spring?

In Spring framework, the required dependencies and the services are specified in external configuration files, which are typically in an XML format. These XML configuration files usually start with <beans> tag and contain a lot of bean definitions AND application-specific configuration options.

The main goal of Spring XML Configuration is to have all the Spring components configured by using XML files.
It means that there will not be present any other type of Spring Configuration (like annotations or configuration via Java classes).

A Spring XML Configuration uses Spring namespaces to make available the sets of XML tags used in the configuration; the main Spring namespaces are context, beans, JDBC, TX, AOP, MVC, etc.

<beans>
    <bean name="viewResolver" class="org.springframework.web.servlet.view.BeanNameViewResolver"/>
    <bean name="jsonTemplate" class="org.springframework.web.servlet.view.json.MappingJackson2JsonView"/>
    <bean id="restTemplate" class="org.springframework.web.client.RestTemplate"/>
</beans>

8. What is Java-based Configuration in Spring?

The central artifacts in Spring’s java-configuration support are @Configuration annotated classes and @Bean annotated methods.

The @Bean annotation is used to indicate that a method instantiates, configures and initializes a new object to be managed by the Spring IoC container. @Bean annotation plays the same role as the <bean/> element.

Annotating a class with @Configuration indicates that its primary purpose is as a source of bean definitions. Furthermore, @Configuration classes allow inter-bean dependencies to be defined by simply calling other @Bean methods in the same class. The most straightforward possible @Configuration class would read as follows:

@Configuration
public class AppConfig
{
    @Bean
    public MyService myService() {
        return new MyServiceImpl();
    }
}

The equivalent XML configuration for the above java-config would be:

<beans>
    <bean id="myService" class="com.howtodoinjava.services.MyServiceImpl"/>
</beans>

To instantiate such config, you will need the help of AnnotationConfigApplicationContext class.

public static void main(String[] args) {
    ApplicationContext ctx = new AnnotationConfigApplicationContext(AppConfig.class);
    MyService myService = ctx.getBean(MyService.class);
    myService.doStuff();
}

To enable component scanning, annotate your @Configuration class as follows:

@Configuration
@ComponentScan(basePackages = "com.howtodoinjava")
public class AppConfig  {
    ...
}

In the example above, the com.acme package will be scanned, looking for any @Component annotated classes and those classes will be registered as Spring bean definitions within the container.

If you are using the above configuration in a web application then you will be using AnnotationConfigWebApplicationContext class. This implementation may be used when configuring the Spring ContextLoaderListener servlet listener, Spring MVC DispatcherServlet etc.

<web-app>
    <!-- Configure ContextLoaderListener to use AnnotationConfigWebApplicationContext instead of the default XmlWebApplicationContext -->
    <context-param>
        <param-name>contextClass</param-name>
        <param-value>
            org.springframework.web.context.support.AnnotationConfigWebApplicationContext
        </param-value>
    </context-param>
 
    <!-- Configuration locations must consist of one or more comma- or space-delimited fully-qualified @Configuration classes. Fully-qualified packages may also be specified for component-scanning -->
    <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>com.howtodoinjava.AppConfig</param-value>
    </context-param>
 
    <!-- Bootstrap the root application context as usual using ContextLoaderListener -->
    <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>
 
    <!-- Declare a Spring MVC DispatcherServlet as usual -->
    <servlet>
        <servlet-name>dispatcher</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <!-- Configure DispatcherServlet to use AnnotationConfigWebApplicationContext instead of the default XmlWebApplicationContext -->
        <init-param>
            <param-name>contextClass</param-name>
            <param-value>
                org.springframework.web.context.support.AnnotationConfigWebApplicationContext
            </param-value>
        </init-param>
        <!-- Again, config locations must consist of one or more comma- or space-delimited and fully-qualified @Configuration classes -->
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>com.howtodoinjava.web.MvcConfig</param-value>
        </init-param>
    </servlet>
 
    <!-- map all requests for /app/* to the dispatcher servlet -->
    <servlet-mapping>
        <servlet-name>dispatcher</servlet-name>
        <url-pattern>/app/*</url-pattern>
    </servlet-mapping>
</web-app>

9. What is Annotation-based Configuration?

Starting from Spring 2.5, it became possible to configure the dependency injection using annotations. So instead of using XML to describe a bean wiring, we can move the bean configuration into the component class itself by using annotations on the relevant class, method, or field declaration.

Annotation injection is performed before XML injection, thus the XML configuration will override the annotation configuration when we wire the beans through both approaches.

Annotation wiring is not turned on in the Spring container by default. So, before we can use annotation-based wiring, we must enable it in our Spring configuration file. So consider having the following configuration file if you want to use any annotation in your Spring application.

<beans>
 
   <context:annotation-config/>

   <!-- bean definitions go here -->
 
</beans>

Once <context:annotation-config/> is configured, you can start annotating your code to indicate that Spring should automatically wire values into properties, methods, and constructors.

A few essential annotations which you will be using in this type of configuration are :

  1. @Required : The @Required annotation applies to bean property setter methods.
  2. @Autowired : The @Autowired annotation can apply to bean property setter methods, non-setter methods, constructor and properties.
  3. @Qualifier : The @Qualifier annotation along with @Autowired can be used to remove the confusion by specifiying which exact bean will be wired.
  4. JSR-250 Annotations : Spring supports JSR-250 based annotations which include @Resource, @PostConstruct and @PreDestroy annotations.

10. Explain Spring Bean Lifecycle?

The life cycle of a Spring bean is easy to understand. When a bean is instantiated, it may be required to perform some initialization to get it into a usable state. Similarly, spring context may require some cleanup when the bean is no longer needed and is removed from the container.

Spring bean factory is responsible for managing the life cycle of beans created through spring containers. The life cycle of beans consist of call back methods which can be categorized broadly into two groups:

  1. Post initialization call back methods
  2. Pre destruction call back methods

Spring framework provides the following four ways for controlling life cycle events of bean:

  • InitializingBean and DisposableBean callback interfaces
  • Other Aware interfaces for specific behavior
  • Custom init() and destroy() methods in bean configuration file
  • @PostConstruct and @PreDestroy annotations

For example, customInit() and customDestroy() methods are examples of the life cycle methods.

<beans>
    <bean id="demoBean" class="com.howtodoinjava.task.DemoBean" 
        init-method="customInit" destroy-method="customDestroy"></bean>
</beans>

11. What are Different Spring Bean Scopes?

We can create the beans in the spring container in six bean scopes. All the scope names are self-explanatory, but let us make them clear so there will be no doubt.

  1. Singleton (default): This bean scope is default and it enforces the container to have only one instance per spring container irrespective of how much time you request for its instance. This singleton behavior is maintained by bean factory itself.
  2. Prototype: This bean scope just reverses the behavior of singleton scope and produces a new instance each and every time a bean is requested.
  3. Request: With this bean scope, a new bean instance will be created for each web request made by client. As soon as request completes, bean will be out of scope and garbage collected.
  4. Session: Just like request scope, this ensures one instance of bean per user session. As soon as user ends its session, bean is out of scope.
  5. Application: global-session is something which is connected to Portlet applications. When your application works in Portlet container it is built of some amount of portlets. Each portlet has its own session, but if your want to store variables global for all portlets in your application than you should store them in global-session. This scope doesn’t have any special effect different from session scope in Servlet based applications.
  6. Websocket: enables two-way communication between a client and a remote host. Web socket provides a single TCP connection for traffic in both directions. This is specially useful for multi-user applications with simultaneous editing and multi-user games.

12. What are Inner Beans in Spring?

In Spring framework, whenever a bean is used for only one particular property, it’s advised to declare it as an inner bean. And the inner bean is supported both in setter injection ‘property‘ and constructor injection ‘constructor-arg‘.

For example, let’s say we one Customer class having reference of Person class. In our application, we will be creating only one instance of Person class, and using it inside Customer.

public class Customer
{
	private Person person;

	//Setters and Getters
}
public class Person
{
	private String name;
	private String address;
	private int age;

	//Setters and Getters
}

Now inner bean declaration will look like this:

<bean id="CustomerBean" class="com.howtodoinjava.common.Customer">
    <property name="person">
        <!-- This is inner bean -->
        <bean class="com.howtodoinjava.common.Person">
            <property name="name" value="adminis"></property>
            <property name="address" value="India"></property>
            <property name="age" value="34"></property>
        </bean>
    </property>
</bean>

13. Are Singleton Beans Thread-safe?

Spring framework does not do anything under the hood concerning the multi-threaded behavior of a singleton bean. It is the developer’s responsibility to deal with the singleton bean’s concurrency issues and thread safety.

While practically, most spring beans have no mutable state (e.g., Service and DAO classes), and as such are trivially thread-safe. But if your bean has a mutable state (e.g., View Model Objects), so you need to ensure thread safety.

The easiest and obvious solution for this problem is to change the scope of mutable beans from “singleton” to “prototype“.

14. How to Inject a Collection in Spring? Give an example?

Spring offers four types of collection configuration elements which are as follows:

  • <list> : This helps in wiring ie injecting a list of values, allowing duplicates.
  • <set> : This helps in wiring a set of values but without any duplicates.
  • <map> : This can be used to inject a collection of name-value pairs where name and value can be of any type.
  • <props> : This can be used to inject a collection of name-value pairs where the name and value are both Strings.

Let’s see an example of each type.

<beans>
 
   <!-- Definition for javaCollection -->
   <bean id="javaCollection" class="com.howtodoinjava.JavaCollection">
 
      <!-- java.util.List -->
      <property name="customList">
        <list>
           <value>INDIA</value>
           <value>Pakistan</value>
           <value>USA</value>
           <value>UK</value>
        </list>
      </property>
 
     <!-- java.util.Set -->
     <property name="customSet">
        <set>
           <value>INDIA</value>
           <value>Pakistan</value>
           <value>USA</value>
           <value>UK</value>
        </set>
      </property>
 
     <!-- java.util.Map -->
     <property name="customMap">
         
        <map>
           <entry key="1" value="INDIA"/>
           <entry key="2" value="Pakistan"/>
           <entry key="3" value="USA"/>
           <entry key="4" value="UK"/>
        </map>
 
      </property>
       
      <!-- java.util.Properties -->
    <property name="customProperies">
        <props>
            <prop key="admin">admin@nospam.com</prop>
            <prop key="support">support@nospam.com</prop>
        </props>
    </property>
 
   </bean>
 
</beans>

15. How to Inject java.util.Properties into a Bean?

The first way is to use <props> tag as below.

<bean id="adminUser" class="com.howtodoinjava.common.Customer">
  
    <!-- java.util.Properties -->
    <property name="emails">
        <props>
            <prop key="admin">admin@nospam.com</prop>
            <prop key="support">support@nospam.com</prop>
        </props>
    </property>
 
</bean>

You can use the “util:” namespace as well to create properties bean from a properties file and use bean reference for setter injection.

<util:properties id="emails" location="classpath:com/foo/emails.properties" />

16. Explain Spring Bean Autowiring?

In the spring framework, setting bean dependencies in configuration files is a good practice, but the spring container can also autowire relationships between collaborating beans.

This means that it is possible to automatically let Spring resolve collaborators (other beans) for your bean by inspecting the contents of the BeanFactory.

Autowiring is specified per bean and can thus be enabled for some beans, while others will not be autowired.

The following excerpt from the XML configuration file shows a bean being autowired by name.

<bean id="employeeDAO" 
        class="com.howtodoinjava.EmployeeDAOImpl" autowire="byName" />

Apart from the autowiring modes provided in the bean configuration file, autowiring can be specified in bean classes using @Autowired annotation. To use @Autowired annotation in bean classes, you must first enable the annotation in the spring application using the below configuration.

<context:annotation-config />

The same can be achieved using AutowiredAnnotationBeanPostProcessor bean definition in the configuration file.

<bean class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor"/>

Now, when annotation configuration has been enabled, you can autowire bean dependencies using @Autowired, the way you like.

@Autowired
public EmployeeDAOImpl ( EmployeeManager manager ) {
    this.manager = manager;
}

17. Explain Different Autowiring Modes?

There are five auto wiring modes in the spring framework. Let us discuss them one by one.

  1. no: This option is default for spring framework and it means that autowiring is OFF. You have to explicitly set the dependencies using tags in bean definitions.
  2. byName: This option enables the dependency injection based on bean names. When autowiring a property in bean, property name is used for searching a matching bean definition in configuration file.
    If such bean is found, it is injected in property. If no such bean is found, a error is raised.
  3. byType: This option enables the dependency injection based on bean types. When autowiring a property in bean, property’s class type is used for searching a matching bean definition in configuration file.
    If such bean is found, it is injected in property. If no such bean is found, a error is raised.
  4. constructor: Autowiring by constructor is similar to byType, but applies to constructor arguments. In autowire enabled bean, it will look for class type of constructor arguments, and then do a autowire by type on all constructor arguments.
    Please note that if there isn’t exactly one bean of the constructor argument type in the container, a fatal error is raised.
  5. autodetect (deprecated in Spring 3): Autowiring by autodetect uses either of two modes i.e. constructor or byType modes. First it will try to look for valid constructor with arguments, If found the constructor mode is chosen.
    If there is no constructor defined in bean, or explicit default no-args constructor is present, the autowire byType mode is chosen.

18. How to Turn On Annotation based Autowiring?

To enable @Autowired, you have to register AutowiredAnnotationBeanPostProcessor, and you can do it in two ways.

1. Include <context:annotation-config > in bean configuration file.

<beans>
    <context:annotation-config />
</beans>

2. Include AutowiredAnnotationBeanPostProcessor directly in bean configuration file.

<beans>
    <bean class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor"/>
</beans>

19. Explain @Required Annotation with Example?

There may be hundreds or thousands of beans declared in the IoC container in a production-scale application, and the dependencies between them are often very complicated.

One of the shortcomings of setter injection is that it’s very hard to check if all required properties have been set or not. To overcome this problem, you can set “dependency-check” attribute of <bean> and set one of four attributes, i.e., none, simple, objects or all (none is the default option).

In real life application, you will not be interested in checking all the bean properties configured in your context files. Instead, you would like to check if certain properties have been set or not in some specific beans only.

Spring’s dependency checking feature using “dependency-check” attribute will not help you in this case. To solve this problem, you can use @Required annotation.

To Use the @Required annotation over setter method of bean property in the class file as below:

public class EmployeeFactoryBean extends AbstractFactoryBean&amp;lt;Object&amp;gt;
{
    private String designation;

    public String getDesignation() {
        return designation;
    }

    @Required
    public void setDesignation(String designation) {
        this.designation = designation;
    }

    //more code here
}

RequiredAnnotationBeanPostProcessor is a spring bean post-processor that checks if all the bean properties with the @Required annotation have been set. To enable this bean post-processor for property checking, you must register it in the Spring IoC container.

<bean class="org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor" />

If any properties with @Required have not been set, a BeanInitializationException will be thrown by this bean post-processor.

20. Explain @Autowired Annotation with Example?

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

For example, we can use @Autowired annotation on setter methods to get rid of the <property> element in the XML configuration file. When Spring finds an @Autowired annotation used with setter methods, it tries to perform byType autowiring on the method.

We can apply @Autowired to constructors as well. A constructor @Autowired annotation indicates that the constructor should be autowired when creating the bean, even if no <constructor-arg> elements are used while configuring the bean in the XML file.

public class TextEditor {
   private SpellChecker spellChecker;

   @Autowired
   public TextEditor(SpellChecker spellChecker){
      System.out.println("Inside TextEditor constructor." );
      this.spellChecker = spellChecker;
   }

   public void spellCheck(){
      spellChecker.checkSpelling();
   }
}

And its configuration without constructor arguments.

<beans>
 
   <context:annotation-config/>
 
   <!-- Definition for textEditor bean without constructor-arg -->
   <bean id="textEditor" class="com.howtodoinjava.TextEditor">
   </bean>
 
   <!-- Definition for spellChecker bean -->
   <bean id="spellChecker" class="com.howtodoinjava.SpellChecker">
   </bean>
 
</beans>

21. Explain @Qualifier Annotation with Example?

@Qualifier means, which bean is qualified to be autowired on a field. The qualifier annotation helps disambiguate bean references when Spring would otherwise not be able to do so.

See below example, it will autowired a “person” bean into customer’s person property.

public class Customer
{
	@Autowired
	private Person person;
}

And we have two bean definitions for Person class.

<bean id="customer" class="com.howtodoinjava.common.Customer" />
 
<bean id="personA" class="com.howtodoinjava.common.Person" >
    <property name="name" value="lokesh" />
</bean>
 
<bean id="personB" class="com.howtodoinjava.common.Person" >
    <property name="name" value="alex" />
</bean>

Will Spring know which person bean should autowired? NO. When you run the above example, it hits the below exception :

Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException:
	No unique bean of type [com.howtodoinjava.common.Person] is defined:
		expected single matching bean but found 2: [personA, personB]

To fix the above problem, you need @Qualifier to tell Spring about which bean should autowired.

public class Customer
{
	@Autowired
	@Qualifier(&amp;quot;personA&amp;quot;)
	private Person person;
}

22. Difference between Constructor Injection and Setter Injection?

Please find below the noticeable differences:

  1. In Setter Injection, partial injection of dependencies can possible, means if we have 3 dependencies like int, string, long, then its not necessary to inject all values if we use setter injection. If you will not inject then it will takes default values for those primitives.
    In constructor injection, partial injection of dependencies is not possible, because for calling constructor we must pass all the arguments right, if not so we may get error.
  2. Setter Injection will overrides the constructor injection value, provided if we write setter and constructor injection for the same property.
    But, constructor injection cannot overrides the setter injected values. It’s obvious because constructors are called to first to create the instance.
  3. Using setter injection you can not guarantee that certain dependency is injected or not, which means you may have an object with incomplete dependency.
    On other hand constructor Injection does not allow you to construct object, until your dependencies are ready.
  4. In constructor injection, if Object A and B are dependent each other i.e A is depends on B and vice-versa, Spring throws ObjectCurrentlyInCreationException while creating objects of A and B because A object cannot be created until B is created and vice-versa.
    So spring can resolve circular dependencies through setter-injection because Objects are constructed before setter methods invoked.

23. What are the Different Types of Events in Spring?

Spring’s ApplicationContext provides the functionality to support events and listeners in code. We can create beans that listen for events that are published through our ApplicationContext.

Event handling in the ApplicationContext is provided through the ApplicationEvent class and ApplicationListener interface. So if a bean implements the ApplicationListener, then every time an ApplicationEvent gets published to the ApplicationContext, that bean is notified.

public class AllApplicationEventListener implements ApplicationListener <ApplicationEvent>
{
    @Override
    public void onApplicationEvent(ApplicationEvent applicationEvent)
	{
        //process event
    }
}

Spring provides the following five standard events:

  1. ContextRefreshedEvent : This event is published when the ApplicationContext is either initialized or refreshed. This can also be raised using the refresh() method on the ConfigurableApplicationContext interface.
  2. ContextStartedEvent : This event is published when the ApplicationContext is started using the start() method on the ConfigurableApplicationContext interface. You can poll your database or you can re/start any stopped application after receiving this event.
  3. ContextStoppedEvent : This event is published when the ApplicationContext is stopped using the stop() method on the ConfigurableApplicationContext interface. You can do required house keeping work after receiving this event.
  4. ContextClosedEvent : This event is published when the ApplicationContext is closed using the close() method on the ConfigurableApplicationContext interface. A closed context reaches its end of life; it cannot be refreshed or restarted.
  5. RequestHandledEvent : This is a web-specific event telling all beans that an HTTP request has been serviced.

Apart from the above, you can create your own custom events by extending ApplicationEvent class. e.g.

public class CustomApplicationEvent extends ApplicationEvent
{
	public CustomApplicationEvent ( Object source, final String msg )
	{
		super(source);
		System.out.println("Created a Custom event");
	}
}

To listen to this event, create a listener like this:

public class CustomEventListener implements ApplicationListener <CustomApplicationEvent>
{
	@Override
    public void onApplicationEvent(CustomApplicationEvent applicationEvent) {
		//handle event
	}
}

And to publish this event, you will need the help of the applicationContext instance.

CustomApplicationEvent customEvent 
        = new CustomApplicationEvent( applicationContext, "Test message");
applicationContext.publishEvent ( customEvent )

24. Difference between FileSystemResource and ClassPathResource?

In FileSystemResource you need to give the path of spring-config.xml (Spring Configuration) file relative to your project or the absolute location of the file.

In ClassPathResource spring looks for the file using ClassPath so spring-config.xml should be included in classpath. If spring-config.xml is in “src” so we can give just its name because src is in the classpath path by default.

In one sentence, ClassPathResource looks in the classpath and FileSystemResource looks in the file system.

25. Name few Design Patterns used in Spring Framework?

There are loads of different design patterns used, but there are a few obvious ones:

  • Proxy – used heavily in AOP, and remoting.
  • Singleton – beans defined in spring config files are singletons by default.
  • Template method – used extensively to deal with boilerplate repeated code e.g. RestTemplate, JmsTemplate, JpaTemplate.
  • Front controller – Spring provides DispatcherServlet to ensure an incoming request gets dispatched to your controllers.
  • View Helper – Spring has a number of custom JSP tags, and velocity macros, to assist in separating code from presentation in views.
  • Dependency injection – Center to the whole BeanFactory / ApplicationContext concepts.
  • Factory patternBeanFactory for creating instance of an object.

Would you mind sharing the latest spring interview questions that you may have faced somewhere in any interview?

Happy Learning !!

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17 thoughts on “Spring Interview Questions with Answers”

  1. How to restrict bean creation up to 10 beans i.e after creating 10 beans if we try to create 11th bean in spring it is not allowed to do it so?

    Reply
  2. I wanted to get a clarification about different types of configuration in Spring. As you have mentioned that there are three types of configuration i.e XML based, Annotation Based and Java Based.
    I wanted to know, when java based configuration is also using annotation of spring framework only then how it is different from annotation based configuration and why it is called java based configuration ?

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    • In java based configuration, you completely drop the XML and whole config exist only in java files.
      I annotation based, you partially move configuration through annotations but starting point is XML file where you mention “context:annotation-config”.

      Reply
  3. In “What is Spring Java-Based Configuration?” question

    you have configured AnnotationConfigWebApplicationContext in two places , one in and other in DispatcherServlet‘s tags.

    Here my question is – if we are configuring it would be applicable to all Servlets i suppose, then again why are we configuring it in DispacterServlet?

    Please answer me for this, correct me if my question was wrong.

    Thanks,
    Mahendra

    Reply
  4. Hi Lokesh ,

    Great Job thanks for help and post interview questions.

    I want to ask to you recently I attend a interview and he asked me what is the alternate of spring framework ? I just answer him because Spring replace EJB so the alternate of it is same .

    So please correct me if I am wrong and suggest a good answer for same

    Thanks
    Sumeet Saini

    Reply
    • This question is more of opinion based, so any answer may be correct or incorrect. It all depends on what interviewer is able to connect to.

      In my view, there is no single alternative for spring framework – because spring itself is collection of lots of independent modules – and each module can be replaced by some other third party framework easily. So if you want to replace spring, you will end up using lots of framework rather than any single library.

      Refer: https://github.com/Vedenin/useful-java-links

      Reply
  5. Hi Lokesh,

    I think in above post there should be a small corection in fourth section of Difference between constructor injection and setter injection? Instead of (In setter injection, if Object A and B are dependent each other i.e A is depends on B and vice-versa), It should be In constructor injection.
    Please put your thoughts on this.

    Thanks
    Praveen

    Reply
  6. Hi Lokesh,

    Really nice article.
    Can u please share tutorials related to new technologies like spring boot,Jboss architechture.

    Thanks for article.

    Reply
  7. Hi Lokesh,
    I am struggling to download bulk of Jar’s that is used for Spring MVC via annotation or XML. Can anyone please let me know with the list of Jars or URL .

    Reply
  8. hi Pankaj,
    Thanks for your tutorials it has helped me a lot .when can we expect the AOP tutorials along with Interview question and answers.

    Regards,
    Sanjeev Pathak

    Reply

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HowToDoInJava

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