May 19, 2017

Srikaanth Kumar

Spring MVC Framework Interview Questions Answers

These are the Frequently asked  Spring framework Interview Questions and Answers:

1) What is spring framework? Why Java programmer should use Spring framework?

Very common Spring interview question, Spring is a framework which helps Java programmer in development. Spring provides dependency Injection and IOC container, Spring MVC flow and several useful API for Java programmer.

2) What is default scope of bean in Spring framework ?

The default scope of a Spring bean is Singleton scope.

3) Does Spring singleton beans are thread-safe ?

No, Spring singleton beans are not thread-safe. Singleton doesn't mean bean would be thread-safe.

4) What is dependency Injection?

Dependency Injection is one of the design pattern, which allows injecting dependency on Object, instead of object resolving the dependency.

5) What is the front controller class of Spring MVC?

A front controller is defined as “a controller which handles all requests for a Web Application.” DispatcherServlet (actually a servlet) is the front controller in Spring MVC that intercepts every request and then dispatches/forwards requests to an appropriate controller.

When a web request is sent to a Spring MVC application, dispatcher servlet first receives the request. Then it organizes the different components configured in Spring’s web application context (e.g. actual request handler controller and view resolvers) or annotations present in the controller itself, all needed to handle the request.

6) Difference between <context:annotation-config> vs <context:component-scan>?

1) First big difference between both tags is that <context:annotation-config> is used to activate applied annotations in already registered beans in application context. Note that it simply does not matter whether bean was registered by which mechanism e.g. using <context:component-scan> or it was defined in application-context.xml file itself.

2) Second difference is driven from first difference itself. It registers the beans defined in config file into context + it also scans the annotations inside beans and activate them. So <context:component-scan> does what <context:annotation-config> does, but additionally it scan the packages and register the beans in application context.

7) Difference between @Component, @Controller, @Repository & @Service annotations?

1) The @Component annotation marks a java class as a bean so the component-scanning mechanism of spring can pick it up and pull it into the application context. To use this annotation, apply it over class as below:

public class EmployeeDAOImpl implements EmployeeDAO {
2) The @Repository annotation is a specialization of the @Component annotation with similar use and functionality. In addition to importing the DAOs into the DI container, it also makes the unchecked exceptions (thrown from DAO methods) eligible for translation into Spring DataAccessException.

3) The @Service annotation is also a specialization of the component annotation. It doesn’t currently provide any additional behavior over the @Component annotation, but it’s a good idea to use @Service over @Component in service-layer classes because it specifies intent better.

4) @Controller annotation marks a class as a Spring Web MVC controller. It too is a @Component specialization, so beans marked with it are automatically imported into the DI container. When you add the @Controller annotation to a class, you can use another annotation i.e. @RequestMapping; to map URLs to instance methods of a class.

8) What is view Resolver pattern ? how it work in Spring MVC?

Spring Framework Interview Question Answers | Spring MVC FAQView Resolver pattern is a J2EE pattern which allows a web application to dynamically choose it's view technology e.g. HTML, JSP, Tapestry, JSF, XSLT or any other view technology. In this pattern, View resolver holds mapping of different views, controller return name of the view, which is then passed to View Resolver for selecting an appropriate view. Spring MVC framework supplies inbuilt view resolver for selecting views.

9) What is Spring Security ?

Spring security is a project under spring framework umbrella, which provides support for security requirements of enterprise Java projects. Spring Security formerly known as aegis security provides out of box support for creating login screen, remember me cookie support, securing URL, authentication provider to authenticate the user from the database, LDAP and in memory, concurrent active session management support and much more. In order to use Spring security in a Spring MVC based project, you need to include spring-security.jar and configure it in application-Context-security.XML file, you can name it whatever you want, but make sure to supply this to ContextLoaderListener, which is responsible for creating Spring context and initializing dispatcher servlet.

10) How do you control concurrent Session on Java web application using Spring Security?

You can use Spring Security to control a number of active session in Java web application. Spring security framework provides this feature out of the box and when enabled , a user can only have one active session at a time.

11) What types of dependency injection is supported by Spring Framework? When do you use Setter and Constructor Injection, pros and cons?

There are 2 types of dependency injection supported by Spring, constructor based injection, and setter-based injection. Both types have their own advantages and disadvantages, you should use Constructor injection when object's dependencies are not optional and they must be initialized with their dependencies. Also use constructor injection if the order of initialization or dependency matters because in Setter based injection you cannot impose any order. Use setter injection when dependencies are optional.

12) How do Spring resolves view returned by ModelAndView class ?

Some Spring MVC questions are tricky e.g. Struts and Spring integration and can be only answered by experienced Java program with 2 to 4-year experience in Spring MVC framework.

13) What are different implementations of View interface you have used in Spring MVC?

ULBased View e.g. JSP , JSTLView,

14) How to escape HTML special characters using Spring MVC?

There are some methods in Spring tag library, can't remember now.

15) What does the ViewResolver class?

ViewResolver is an interface to be implemented by objects that can resolve views by name. There are plenty of ways using which you can resolve view names. These ways are supported by various in-built implementations of this interface. Most commonly used implementation is InternalResourceViewResolver class. It defines prefix and suffix properties to resolve the view component.

<bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
    <property name="prefix" value="/WEB-INF/views/" />
    <property name="suffix" value=".jsp" />
So with above view resolver configuration, if controller method return “login” string, then the “/WEB-INF/views/login.jsp” file will be searched and rendered.

16) What is a MultipartResolver and when its used?

Spring comes with MultipartResolver to handle file upload in web application. There are two concrete implementations included in Spring:

CommonsMultipartResolver for Jakarta Commons FileUpload
StandardServletMultipartResolver for Servlet 3.0 Part API
To define an implementation, create a bean with the id “multipartResolver” in a DispatcherServlet’s application context. Such a resolver gets applied to all requests handled by that DispatcherServlet.

If a DispatcherServlet detects a multipart request, it will resolve it via the configured MultipartResolver and pass on a wrapped HttpServletRequest. Controllers can then cast their given request to the MultipartHttpServletRequest interface, which permits access to any MultipartFiles.

17) How does Spring MVC provide validation support?

Spring supports validations primarily into two ways.

Using JSR-303 Annotations and any reference implementation e.g. Hibernate Validator
Using custom implementation of org.springframework.validation.Validator interface.

18) What is Spring MVC Interceptor and how to use it?

As you know about servlet filters that they can pre-handle and post-handle every web request they serve — before and after it’s handled by that servlet. In the similar way, you can use HandlerInterceptor interface in your spring mvc application to pre-handle and post-handle web requests that are handled by Spring MVC controllers. These handlers are mostly used to manipulate the model attributes returned/submitted they are passed to the views/controllers.

A handler interceptor can be registered for particular URL mappings, so it only intercepts requests mapped to certain URLs. Each handler interceptor must implement the HandlerInterceptor interface, which contains three callback methods for you to implement: preHandle(), postHandle() and afterCompletion().

Problem with HandlerInterceptor interface is that your new class will have to implement all three methods irrespective of whether it is needed or not. To avoid overriding, you can use HandlerInterceptorAdapter class. This class implements HandlerInterceptor and provide default blank implementations.

19) What is Spring Security?

Spring security framework focuses on providing both authentication and authorization in java applications. It also takes care of most of the common security vulnerabilities such as CSRF attack.

It’s very beneficial and easy to use Spring security in web applications, through the use of annotations such as @EnableWebSecurity. You should go through following posts to learn how to use Spring Security framework.

20) Name some of the design patterns used in Spring Framework?

Spring Framework is using a lot of design patterns, some of the common ones are:
  1. Singleton Pattern: Creating beans with default scope.
  2. Factory Pattern: Bean Factory classes
  3. Prototype Pattern: Bean scopes
  4. Adapter Pattern: Spring Web and Spring MVC
  5. Proxy Pattern: Spring Aspect Oriented Programming support
  6. Template Method Pattern: JdbcTemplate, HibernateTemplate etc
  7. Front Controller: Spring MVC DispatcherServlet
  8. Data Access Object: Spring DAO support
  9. Dependency Injection and Aspect Oriented Programming.
21) Can we send an Object as the response of Controller handler method?

Yes we can, using @ResponseBody annotation. This is how we send JSON or XML based response in restful web services.

22) How to upload file in Spring MVC Application?

Spring provides built-in support for uploading files through MultipartResolver interface implementations. It’s very easy to use and requires only configuration changes to get it working. Obviously we would need to write controller handler method to handle the incoming file and process it.

23) How to validate form data in Spring Web MVC Framework?

Spring supports JSR-303 annotation based validations as well as provide Validator interface that we can implement to create our own custom validator. For using JSR-303 based validation, we need to annotate bean variables with the required validations.

For custom validator implementation, we need to configure it in the controller class.

24) What is Spring MVC Interceptor and how to use it?

Spring MVC Interceptors are like Servlet Filters and allow us to intercept client request and process it. We can intercept client request at three places – preHandle, postHandle and afterCompletion.

We can create spring interceptor by implementing HandlerInterceptor interface or by extending abstract class HandlerInterceptorAdapter.

We need to configure interceptors in the spring bean configuration file. We can define an interceptor to intercept all the client requests or we can configure it for specific URI mapping too.

25) What is Spring JdbcTemplate class and how to use it?

Spring Framework provides excellent integration with JDBC API and provides JdbcTemplate utility class that we can use to avoid bolier-plate code from our database operations logic such as Opening/Closing Connection, ResultSet, PreparedStatement etc.

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