'Spring framework interview questions' or 'Spring interview questions' is covered in this topic. Spring is the facto enterprise server and integration tool in Investment banks. This IOC based development and hosting service become very popular for java based service development. We should be clear on basic concept and usage of spring for any java based interview. The Spring Framework is an open source application framework and Inversion of control container for the Java platform. This framework reduce the cost and burden of application server and provided more flexibility to developers.
The Spring Framework comprises several modules that provide a range of services:
- Inversion of Control container: configuration of application components and lifecycle management of Java objects, done mainly via Dependency Injection
- Aspect-oriented programming: enables implementation of cross-cutting routines
- Data access: working with relational database management systems on the Java platform using JDBC and object-relational mapping tools and with NoSQL databases
- Transaction management: unifies several transaction management APIs and coordinates transactions for Java objects
- Model-view-controller: an HTTP- and servlet-based framework providing hooks for extension and customization for web applications and RESTful web services.
- Remote Access framework: configurative RPC-style export and import of Java objects over networks supporting RMI, CORBA and HTTP-based protocols including web services (SOAP)
- Convention-over-configuration: a rapid application development solution for Spring-based enterprise applications is offered in the Spring Roo module
- Batch processing: a framework for high-volume processing featuring reusable functions including logging/tracing, transaction management, job processing statistics, job restart, skip, and resource management
- Authentication and authorization: configurable security processes that support a range of standards, protocols, tools and practices via the Spring Security sub-project (formerly Acegi Security System for Spring).
- Remote Management: configurative exposure and management of Java objects for local or remote configuration via JMX
- Messaging: configurative registration of message listener objects for transparent message-consumption from message queues via JMS, improvement of message sending over standard JMS APIs
- Testing: support classes for writing unit tests and integration tests.
Spring Interview Questions
1) What is Spring Framework?
Spring is a lightweight inversion of control and aspect-oriented container framework. Spring Framework’s contribution towards java community is immense and spring community is the largest and most innovative community by size. They have numerous projects under their portfolio and have their own spring dm server for running spring applications. This community is acquired by VMWare, a leading cloud compting company for enabling the java application in the cloud by using spring stacks. If you are looking to read more about the spring framework and its products, please read in their official site Spring Source.
2) Explain Spring?
- Lightweight : Spring is lightweight when it comes to size and transparency. The basic version of spring framework is around 1MB. And the processing overhead is also very negligible.
- Inversion of control (IoC) : Loose coupling is achieved in spring using the technique Inversion of Control. The objects give their dependencies instead of creating or looking for dependent objects.
- Aspect oriented (AOP) : Spring supports Aspect oriented programming and enables cohesive development by separating application business logic from system services.
- Container : Spring contains and manages the life cycle and configuration of application objects.
- Framework : Spring provides most of the intra functionality leaving rest of the coding to the developer.
3) What are the different modules in Spring framework?
The Core container module
- Application context module
- AOP module (Aspect Oriented Programming)
- JDBC abstraction and DAO module
- O/R mapping integration module (Object/Relational)
- Web module
- MVC framework module
4) What is the structure of Spring framework?
DAO
ORM
AOP
JEE
CORE
WEB
5) What is the Core container module?
This module is provides the fundamental functionality of the spring framework. In this module BeanFactory is the heart of any spring-based application. The entire framework was built on the top of this module. This module makes the Spring container.
6) What is Application context module?
The Application context module makes spring a framework. This module extends the concept of BeanFactory, providing support for internationalization (I18N) messages, application lifecycle events, and validation. This module also supplies many enterprise services such JNDI access, EJB integration, remoting, and scheduling. It also provides support to other framework.
7) What is AOP module?
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 Springand other AOP frameworks. This module also introduces metadata programming to Spring. Using Spring’s metadata support, we will be able to add annotations to our source code that instruct Springon where and how to apply aspects.
8) What is JDBC abstraction and DAO module?
Using this module we can keep up the database code clean and simple, and prevent problems that result from a failure to close database resources. A new layer of meaningful exceptions on top of the error messages given by several database servers is bought in this module. In addition, this module uses Spring’s AOP module to provide transaction management services for objects in a Spring application.
9) What are object/relational mapping integration module?
Spring also supports for using of an object/relational mapping (ORM) tool over straight JDBC by providing the ORM module. Spring provide 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) What is web module?
This 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) What is web module?
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 for a clean separation of controller logic from business objects. It also allows you to decoratively bind request parameters to your business objects. It also can take advantage of any of Spring’s other services, such as I18N messaging and validation.
12) What is a BeanFactory?
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.
13) What is AOP Alliance?
AOP Alliance is an open-source project whose goal is to promote adoption of AOP and interoperability among different AOP implementations by defining a common set of interfaces and components. We can use Spring AOP module or we can integrate services with AspectJ. We can only advice method join points using Spring AOP.
Spring AOP works on concept of proxies using JDK dynamic proxies or CGLIB.
Spring AOP works on concept of proxies using JDK dynamic proxies or CGLIB.
14) What is Spring configuration file?
Spring configuration file is an XML file. This file contains the classes information and describes how these classes are configured and introduced to each other.
15) What does a simple spring application contain?
These applications are like any Java application. They are made up of several classes, each performing a specific purpose within the application. But these classes are configured and introduced to each other through an XML file. This XML file describes how to configure the classes, known as the Spring configuration file.
16) What is XMLBeanFactory?
BeanFactory has many implementations in Spring. But one of the most useful one is org.springframework.beans.factory.xml.XmlBeanFactory, which loads its beans based on the definitions contained in an XML file. To create an XmlBeanFactory, pass a java.io.InputStream to the constructor. The InputStream will provide the XML to the factory. For example, the following code snippet uses a java.io.FileInputStreamto provide a bean definition XML file to XmlBeanFactory.
| BeanFactory factory = new XmlBeanFactory( new FileInputStream("beans.xml")); |
To retrieve the bean from a BeanFactory, call the getBean() method by passing the name of the bean you want to retrieve.
MyBean myBean = (MyBean) factory.getBean("myBean"); |
17) What are important ApplicationContext implementations in spring framework?
- ClassPathXmlApplicationContext – This context loads a context definition from an XML file located in the class path, treating context definition files as class path resources.
- FileSystemXmlApplicationContext – This context loads a context definition from an XML file in the filesystem.
- XmlWebApplicationContext – This context loads the context definitions from an XML file contained within a web application.
18) Explain Bean lifecycle in Spring framework?
The spring container finds the bean’s definition from the XML file and instantiates the bean.
- Using the dependency injection, spring populates all of the properties as specified in the bean definition.
- If the bean implements the BeanNameAware interface, the factory calls setBeanName() passing the bean’s ID.
- If the bean implements the BeanFactoryAware interface, the factory calls setBeanFactory(), passing an instance of itself.
- If there are any BeanPostProcessors associated with the bean, their post- ProcessBeforeInitialization() methods will be called.
- If an init-method is specified for the bean, it will be called.
- Finally, if there are any BeanPostProcessors associated with the bean, their postProcessAfterInitialization() methods will be called.
19) What is bean wiring?
Combining together beans within the Spring container is known as bean wiring or wiring. When wiring beans, you should tell the container what beans are needed and how the container should use dependency injection to tie them together.
20) How do add a bean in spring application?
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd"> <bean name="/helloWorld" class="test.HelloWorldController"> |
In the bean tag the id attribute specifies the bean name and the class attribute specifies the fully qualified class name.
21) What are singleton beans and how can you create prototype beans?
Beans defined in spring framework are singleton beans. There is an attribute in bean tag named ‘singleton’ if specified true then bean becomes singleton and if set to false then the bean becomes a prototype bean. By default it is set to true. So, all the beans in spring framework are by default singleton beans.
< bean |
22) What are the important beans lifecycle methods?
There are two important bean lifecycle methods. The first one is setup which is called when the bean is loaded in to the container. The second method is the teardown method which is called when the bean is unloaded from the container.
23) How can you override beans default lifecycle methods?
The bean tag has two more important attributes with which you can define your own custom initialization and destroy methods. Here I have shown a small demonstration. Two new methods fooSetup and fooTeardown are to be added to your Foo class.
init-method="fooSetup" destroy="fooTeardown">; |
24) What are Inner Beans?
When wiring beans, if a bean element is embedded to a property tag directly, then that bean is said to the Inner Bean. The drawback of this bean is that it cannot be reused anywhere else.
25) What are the different types of bean injections?
There are two types of bean injections.
- By setter
- By constructor
Spring Core Modules:
Inversion of Control container (dependency injection)
Central to the Spring Framework is its Inversion of control container, which provides a consistent means of configuring and managing Java objects using reflection. The container is responsible for managing object lifecycles: creating objects, calling initialization methods, and configuring objects by wiring them together.
Objects created by the container are also called Managed Objects or Beans. Typically, the container is configured by loading XML files containing Bean definitions which provide the information required to create the beans.
Objects can be obtained by means of Dependency lookup or Dependency injection. Dependency lookup is a pattern where a caller asks the container object for an object with a specific name or of a specific type. Dependency injection is a pattern where the container passes objects by name to other objects, via either constructors, properties, or factory methods.
In many cases one need not use the container when using other parts of the Spring Framework, although using it will likely make an application easier to configure and customize. The Spring container provides a consistent mechanism to configure applications and integrates with almost all Java environments, from small-scale applications to large enterprise applications.
The container can be turned into a partially compliant EJB3 container by means of the Pitchfork project. Some[who?] criticize the Spring Framework for not complying with standards.However, SpringSource doesn't see EJB3 compliance as a major goal, and claims that the Spring Framework and the container allow for more powerful programming models.
Aspect-oriented programming framework
The Spring Framework has its own AOP framework which modularizes cross-cutting concerns in aspects. The motivation for creating a separate AOP framework comes from the belief that it would be possible to provide basic AOP features without too much complexity in either design, implementation, or configuration. The Spring AOP framework also takes full advantage of the Spring Container.
The Spring AOP framework is interception based, and is configured at run time. This removes the need for a compilation step or load-time weaving. On the other hand, interception only allows for public method-execution on existing objects at a join point.
Compared to the AspectJ framework, Spring AOP is less powerful but also less complicated. Spring 1.2 includes support to configure AspectJ aspects in the container. Spring 2.0 added more integration with AspectJ; for example, the pointcut language is reused and can be mixed with Spring AOP-based aspects. Further, Spring 2.0 added a Spring Aspects library which uses AspectJ to offer common Spring features such as declarative transaction management and dependency injection via AspectJ compile-time or load-time weaving. SpringSource also uses AspectJ for AOP in other Spring projects such as Spring Roo and Spring Insight, with Spring Security also offering an AspectJ-based aspect library.
Spring AOP has been designed to make it able to work with cross-cutting concerns inside the Spring Framework. Any object which is created and configured by the container can be enriched using Spring AOP.
The Spring Framework uses Spring AOP internally for transaction management, security, remote access, and JMX.
Since version 2.0 of the framework, Spring provides two approaches to the AOP configuration:
schema-based approach and @AspectJ-based annotation style.
The Spring team decided not to introduce new AOP-related terminology; therefore, in the Spring reference documentation and API, terms such as aspect, join point, advice, pointcut, introduction, target object (advised object), AOP proxy, and weaving all have the same meanings as in most other AOP frameworks (particularly AspectJ).
Data access framework
Spring's data access framework addresses common difficulties developers face when working with databases in applications. Support is provided for all popular data access frameworks in Java: JDBC, iBatis / MyBatis, Hibernate, JDO, JPA, Oracle TopLink, Apache OJB, and Apache Cayenne, among others.
For all of these supported frameworks, Spring provides these features
Resource management - automatically acquiring and releasing database resources
Exception handling - translating data access related exception to a Spring data access hierarchy
Transaction participation - transparent participation in ongoing transactions
Resource unwrapping - retrieving database objects from connection pool wrappers
Abstraction for BLOB and CLOB handling
All these features become available when using Template classes provided by Spring for each supported framework. Critics say these Template classes are intrusive and offer no advantage over using (for example) the Hibernate API directly.[8][not in citation given] In response, the Spring developers have made it possible to use the Hibernate and JPA APIs directly. This however requires transparent transaction management, as application code no longer assumes the responsibility to obtain and close database resources, and does not support exception translation.
Together with Spring's transaction management, its data access framework offers a flexible abstraction for working with data access frameworks. The Spring Framework doesn't offer a common data access API; instead, the full power of the supported APIs is kept intact. The Spring Framework is the only framework available in Java which offers managed data access environments outside of an application server or container.[citation needed]
While using Spring for transaction management with Hibernate, the following beans may have to be configured
- DataSource like com.mchange.v2.c3p0.ComboPooledDataSource or org.apache.commons.dbcp.BasicDataSource
- SessionFactory like org.springframework.orm.hibernate3.LocalSessionFactoryBean with a DataSource attribute
- HibernateProperties like org.springframework.beans.factory.config.PropertiesFactoryBean
- TransactionManager like org.springframework.orm.hibernate3.HibernateTransactionManager with a SessionFactory attribute
Other configurations
- AOP configuration of cutting points using
- Transaction semantics of AOP advice using
Transaction management framework
Spring's transaction management framework brings an abstraction mechanism to the Java platform. Its abstraction is capable of:
- Working with local and global transactions (local transaction does not require an application server)
- Working with nested transactions
- Working with transaction savepoints
- Working in almost all environments of the Java platform
In comparison, JTA only supports nested transactions and global transactions, and requires an application server (and in some cases also deployment of applications in an application server).
The Spring Framework ships a PlatformTransactionManager for a number of transaction management strategies:
- Transactions managed on a JDBC Connection
- Transactions managed on Object-relational mapping Units of Work
- Transactions managed via the JTA TransactionManager and UserTransaction
- Transactions managed on other resources, like object databases
Next to this abstraction mechanism the framework also provides two ways of adding transaction management to applications:
Programmatically, by using Spring's TransactionTemplate
Configuratively, by using metadata like XML or Java 5 annotations (@Transactional, etc)
Together with Spring's data access framework — which integrates the transaction management framework — it is possible to set up a transactional system through configuration without having to rely on JTA or EJB. The transactional framework also integrates with messaging and caching engines.
Model-view-controller framework
The Spring Framework features its own MVC web application framework, which wasn't originally planned. The Spring developers decided to write their own web framework as a reaction to what they perceived as the poor design of the (then) popular Jakarta Struts web framework, as well as deficiencies in other available frameworks. In particular, they felt there was insufficient separation between the presentation and request handling layers, and between the request handling layer and the model.
Like Struts, Spring MVC is a request-based framework. The framework defines strategy interfaces for all of the responsibilities which must be handled by a modern request-based framework. The goal of each interface is to be simple and clear so that it's easy for Spring MVC users to write their own implementations if they so choose. MVC paves the way for cleaner front end code. All interfaces are tightly coupled to the Servlet API. This tight coupling to the Servlet API is seen by some as a failure on the part of the Spring developers to offer a high-level abstraction for web-based applications[citation needed]. However, this coupling makes sure that the features of the Servlet API remain available to developers while offering a high abstraction framework to ease working with said API.
The DispatcherServlet class is the front controller of the framework and is responsible for delegating control to the various interfaces during the execution phases of a HTTP request.
The most important interfaces defined by Spring MVC, and their responsibilities, are listed below:
HandlerMapping: selecting objects that handle incoming requests (handlers) based on any attribute or condition internal or external to those requests
HandlerAdapter: execution of objects that handle incoming requests
Controller: comes between Model and View to manage incoming requests and redirect to proper response. It acts as a gate that directs the incoming information. It switches between going into model or view.
View: responsible for returning a response to the client. Some requests may go straight to view without going to the model part; others may go through all three.
ViewResolver: selecting a View based on a logical name for the view (use is not strictly required)
HandlerInterceptor: interception of incoming requests comparable but not equal to Servlet filters (use is optional and not controlled by DispatcherServlet).
LocaleResolver: resolving and optionally saving of the locale of an individual user
MultipartResolver: facilitate working with file uploads by wrapping incoming requests
Each strategy interface above has an important responsibility in the overall framework. The abstractions offered by these interfaces are powerful, so to allow for a set of variations in their implementations, Spring MVC ships with implementations of all these interfaces and together offers a feature set on top of the Servlet API. However, developers and vendors are free to write other implementations. Spring MVC uses the Java java.util.Map interface as a data-oriented abstraction for the Model where keys are expected to be string values.
The ease of testing the implementations of these interfaces seems one important advantage of the high level of abstraction offered by Spring MVC. DispatcherServlet is tightly coupled to the Spring Inversion of Control container for configuring the web layers of applications. However, web applications can use other parts of the Spring Framework—including the container—and choose not to use Spring MVC.
Remote access framework
Spring's Remote Access framework is an abstraction for working with various RPC-based technologies available on the Java platform both for client connectivity and exporting objects on servers. The most important feature offered by this framework is to ease configuration and usage of these technologies as much as possible by combining Inversion of Control and AOP.
The framework also provides fault-recovery (automatic reconnection after connection failure) and some optimizations for client-side use of EJB remote stateless session beans.
Spring provides support for these protocols and products out of the box:
HTTP-based protocols
- Hessian: binary serialization protocol, open-sourced and maintained by CORBA-based protocols
- RMI (1): method invocations using RMI infrastructure yet specific to Spring
- RMI (2): method invocations using RMI interfaces complying with regular RMI usage
- RMI-IIOP (CORBA): method invocations using RMI-IIOP/CORBA
Enterprise JavaBean client integration
- Local EJB stateless session bean connectivity: connecting to local stateless session beans
- Remote EJB stateless session bean connectivity: connecting to remote stateless session beans
SOAP
- Integration with the Apache Axis web services framework
Apache CXF provides integration with the Spring Framework for RPC-style exporting of object on the server side.
Both client and server setup for all RPC-style protocols and products supported by the Spring Remote access framework (except for the Apache Axis support) is configured in the Spring Core container.
There is alternative open-source implementation (Cluster4Spring) of a remoting subsystem included into Spring Framework which is intended to support various schemes of remoting (1-1, 1-many, dynamic services discovering).
Convention-over-configuration rapid application development
Spring Roo is Spring's Convention-over-configuration solution for rapidly building applications in Java. It currently supports Spring Framework, Spring Security and Spring Web Flow, with remaining Spring projects scheduled to be added in due course. Roo differs from other rapid application development frameworks by focusing on:
- Java platform productivity (as opposed to other languages)
- Usability (particularly via the shell features and usage patterns)
- Runtime avoidance (with associated deployment advantages)
- Lock-in avoidance (Roo can be removed within a few minutes from any application)
- Extensibility (via add-ons)
Batch framework
Spring Batch is a framework for batch processing that provides reusable functions that are essential in processing large volumes of records, including:
- Logging/tracing
- Transaction management
- Job processing statistics
- Job restart
- Skip
- Resource management
It also provides more advanced technical services and features that will enable extremely high-volume and high performance batch jobs through optimizations and partitioning techniques.
Integration framework
Spring Integration is a framework for Enterprise application integration that provides reusable functions that are essential in messaging, or event-driven architectures.
routers
transformers
adapters to integrate with other technologies and systems (HTTP, AMQP, JMS, XMPP, SMTP, IMAP, FTP (as well as FTPS/SFTP), file systems, etc.)
filters
service activators
management and auditing
Other Java Interview Topics
3) XML PArsing
