SpringFramework Interview Questions

 

 

What is Spring ?
Spring is an open source framework created to address the complexity of enterprise application development. One of the chief advantages of the Spring framework is its layered architecture, which allows you to be selective about which of its components you use while also providing a cohesive framework for J2EE application development.

 

 

 

what is Factory Bean ??

 

factory-bean in spring facilitates to create bean by factory class. Factory class will have non- static methods to return the object of bean. Factory class must have a static method to return the instance of class itself. Below the example to understand factory-bean.

spring-config.xml

<bean id="serviceFactory" class="com.concretepage.ServiceFactory" factory-method="createInstance">

</bean>   

 

<bean id="userService" factory-bean="serviceFactory" factory-method="createUserService"> </bean>

 

<bean id="loginService" factory-bean ="serviceFactory" factory-method="createLoginService"></bean>

 

Static Methods in Spring ?

 

  • A static method is nothing more than a singleton method
  • core point of the IoC container is to manage your singletons.
  • You must redesign to use instance methods and fields.
  • The only way static methods get into the picture is as factory methods,

 

Event Handling in Spring


  • Core of Spring is the ApplicationContext, which manages complete life cycle of the beans.
  • The ApplicationContext publishes certain types of events when loading the beans.
  • ContextStartedEvent is published when the context is started
  • ContextStoppedEvent is published when the context is stopped.
  • Event handling in the ApplicationContext is provided through the ApplicationEvent class and ApplicationListener interface.
  • When a bean implements the ApplicationListener, then every time an ApplicationEvent gets published to the ApplicationContext, that bean is notified.

 

Spring provides the following standard Built-in events:

   
  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.
  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.
  ContextStoppedEvent
This event is published when the ApplicationContext is stopped using the stop() method on the ConfigurableApplicationContext interface. You can do required housekeep work after receiving this event.
  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.
  RequestHandledEvent
This is a web-specific event telling all beans that an HTTP request has been serviced.

 

Spring's event handling is single-threaded so if an event is published, until and unless all the receivers get the message, the processes are blocked and the flow will not continue. Hence, care should be taken when designing your application if event handling is to be used.

Listening to Context Events:

  • To listen a context event, a bean should implement the ApplicationListener interface which has just one method onApplicationEvent().
  • So let us write an example to see how the events propagates and how you can put your code to do required task based on certain events.

 

Let us have working Eclipse IDE in place and follow the following steps to create a Spring application:

 

Step Description           View Code Example
1 Create a project with a name SpringExample and create a package com.tutorialspoint under the src folder in the created project.
2 Add required Spring libraries using Add External JARs option as explained in the Spring Hello World Example chapter.
3 Create Java classes HelloWorld, CStartEventHandler, CStopEventHandler and MainApp under the com.tutorialspoint package.
4 Create Beans configuration file Beans.xml under the src folder.
5 The final step is to create the content of all the Java files and Bean Configuration file and run the application as explained below.

 

Once you are done with creating source and bean configuration files, let us run the application. If everything is fine with your application, this will print the following message:

ContextStartedEvent Received
Your Message : Hello World!
ContextStoppedEvent Received

If you like, you can publish your own custom events and later you can capture the same to take any action against those custom events. If you are interested in writing your own custom events,

you can check Custom Events in Spring

 

What is IOC (or Dependency Injection)?

The basic concept of the Inversion of Control pattern (also known as dependency injection) is 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 (in the case of the Spring framework, the IOC container) is then responsible for hooking it all up.

 

What are the different types of IOC (dependency injection) ?

There are three types of dependency injection:

  • Constructor Injection (e.g. Pico container, Spring etc): Dependencies are provided as constructor parameters.
  • Setter Injection (e.g. Spring): Dependencies are assigned through JavaBeans properties (ex: setter methods).
  • Interface Injection (e.g. Avalon): Injection is done through an interface.

 

What are the benefits of IOC (Dependency Injection)?

Benefits of IOC (Dependency Injection) are as follows:

  • Minimizes the amount of code in your application. With IOC containers you do not care about how services are created and how you get references to the ones you need. You can also easily add additional services by adding a new constructor or a setter method with little or no extra configuration.
  • Make your application more testable by not requiring any singletons or JNDI lookup mechanisms in your unit test cases. IOC containers make unit testing and switching implementations very easy by manually allowing you to inject your own objects into the object under test.
  • Loose coupling is promoted with minimal effort and least intrusive mechanism. The factory design pattern is more intrusive because components or services need to be requested explicitly whereas in IOC the dependency is injected into requesting piece of code. Also some containers promote the design to interfaces not to implementations design concept by encouraging managed objects to implement a well-defined service interface of your own.
  • IOC containers support eager instantiation and lazy loading of services. Containers also provide support for instantiation of managed objects, cyclical dependencies, life cycles management, and dependency resolution between managed objects etc.

What are the advantages of Spring framework?

  • Spring has layered architecture. Use what you need and leave you don't need now.
  • Spring Enables POJO Programming. There is no behind the scene magic here. POJO programming enables continuous integration and testability.
  • Dependency Injection and Inversion of Control Simplifies JDBC
  • Open source and no vendor lock-in.

 

 What are features of 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.
  • MVC Framework:Spring comes with MVC web application framework, built on core Spring functionality. This framework is highly configurable via strategy interfaces, and accommodates multiple view technologies like JSP, Velocity, Tiles, iText, and POI. But other frameworks can be easily used instead of Spring MVC Framework.
  • Transaction Management:Spring framework provides a generic abstraction layer for transaction management. This allowing the developer to add the pluggable transaction managers, and making it easy to demarcate transactions without dealing with low-level issues. Spring's transaction support is not tied to J2EE environments and it can be also used in container less environments.
  • JDBC Exception Handling: The JDBC abstraction layer of the Spring offers a meaningful exception hierarchy, which simplifies the error handling strategy. Integration with Hibernate, JDO, and iBATIS: Spring provides best Integration services with Hibernate, JDO and iBATIS

 

 

 

How many modules are there in Spring? What are they? 
Spring comprises of seven modules. They are..

  • The core container:
    The core container provides the essential functionality of the Spring framework. A primary component of the core container is the
    BeanFactory, an implementation of the Factory pattern. The BeanFactory applies the Inversion of Control (IOC) pattern to separate an application's configuration and dependency specification from the actual application code.
  • Spring context:
    The Spring context is a configuration file that provides context information to the Spring framework. The Spring context includes enterprise services such as JNDI, EJB, e-mail, internalization, validation, and scheduling functionality.
  • Spring AOP:
    The Spring AOP module integrates aspect-oriented programming functionality directly into the Spring framework, through its configuration management feature. As a result you can easily AOP-enable any object managed by the Spring framework. The Spring AOP module provides transaction management services for objects in any Spring-based application. With Spring AOP you can incorporate declarative transaction management into your applications without relying on EJB components.
  • Spring DAO:
    The Spring JDBC DAO abstraction layer offers a meaningful exception hierarchy for managing the exception handling and error messages thrown by different database vendors. The exception hierarchy simplifies error handling and greatly reduces the amount of exception code you need to write, such as opening and closing connections. Spring DAO's JDBC-oriented exceptions comply to its generic DAO exception hierarchy.
  • Spring ORM:
    The Spring framework plugs into several ORM frameworks to provide its Object Relational tool, including JDO, Hibernate, and iBatis SQL Maps. All of these comply to Spring's generic transaction and DAO exception hierarchies.
  • Spring Web module:
    The Web context module builds on top of the application context module, providing contexts for Web-based applications. As a result, the Spring framework supports integration with Jakarta Struts. The Web module also eases the tasks of handling multi-part requests and binding request parameters to domain objects.
  • Spring MVC framework:
    The Model-View-Controller (MVC) framework is a full-featured MVC implementation for building Web applications. The MVC framework is highly configurable via strategy interfaces and accommodates numerous view technologies including JSP, Velocity, Tiles, iText, and POI.

 

 

What is Bean Factory ?

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

  • BeanFactory is able to create associations between collaborating objects as they are instantiated. This removes the burden of configuration from bean itself and the beans client.
  • BeanFactory also takes part in the life cycle of a bean, making calls to custom initialization and destruction methods.

 

What is Application Context?

A bean factory is fine to simple applications, but to take advantage of the full power of the Spring framework, you may want to move up to Springs more advanced container, the application context. On the surface, an application context is same as a bean factory.Both load bean definitions, wire beans together, and dispense beans upon request. But it also provides:

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

 

What is the difference between Bean Factory and Application Context ?  

On the surface, an application context is same as a bean factory. application context offers much more..

  • Application contexts provide a means for resolving text messages, including support for i18n of those messages.
  • Application contexts provide a generic way to load file resources, such as images.
  • Application contexts can publish events to beans that are registered as listeners.
  • Certain 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.
  • ResourceLoader support: Spring’s Resource interface us a flexible generic abstraction for handling low-level resources. An application context itself is a ResourceLoader, Hence provides an application with access to deployment-specific Resource instances.
  • MessageSource support: The application context implements MessageSource, an interface used to obtain localized messages, with the actual implementation being pluggable

 

What are the common implementations of the Application Context ?
The three commonly used implementation of 'Application Context' are

  • ClassPathXmlApplicationContext : It 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 : It 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 : It loads context definition from an XML file contained within a web application.

 

What is the typical Bean life cycle in Spring Bean Factory Container ?

   Bean life cycle in Spring Bean Factory Container is as follows:

  • 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.

 

What do you mean by Bean wiring ?

The act of creating associations b/w application components (beans) within the Spring container is reffered to as Bean wiring.

 

 

What do you mean by Auto Wiring?

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 your bean by inspecting the contents of the BeanFactory. The autowiring functionality has five modes.

  • no
  • byName
  • byType
  • constructor
  • autodirect

 

How to integrate your Struts application with Spring?  
To integrate your Struts application with Spring, we have two options:

  • Configure Spring to manage your Actions as beans, using the ContextLoaderPlugin, and set their dependencies in a Spring context file.
  • Subclass Spring's ActionSupport classes and grab your Spring-managed beans explicitly using a getWebApplicationContext() method.

 

What are the ways to access Hibernate using Spring ?

There are two approaches to Spring’s Hibernate integration:

  • Inversion of Control with a HibernateTemplate and Callback
  • Extending HibernateDaoSupport and Applying an AOP Interceptor

 

What are Bean scopes in Spring Framework ?

 The Spring Framework supports exactly five scopes (of which three are available only if you are using a web-aware ApplicationContext). The scopes supported are listed below:

Scope

Description

singleton

Scopes a single bean definition to a single object instance per Spring IoC container.

prototype

Scopes a single bean definition to any number of object instances.

request

Scopes a single bean definition to the lifecycle of a single HTTP request; that is each and every HTTP request will have its own instance of a bean created off the back of a single bean definition. Only valid in the context of a web-aware Spring ApplicationContext.

session

Scopes a single bean definition to the lifecycle of a HTTP Session. Only valid in the context of a web-aware Spring ApplicationContext.

global session

Scopes a single bean definition to the lifecycle of a global HTTP Session. Typically only valid when used in a portlet context. Only valid in the context of a web-aware Spring ApplicationContext.

 

 

What is AOP? 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. The core construct of AOP is the aspect, which encapsulates behaviors affecting multiple classes into reusable modules.

 

How the AOP used in Spring?

AOP is used in the Spring Framework: To provide declarative enterprise services, especially as a replacement for EJB declarative services. The most important such service is declarative transaction management, which builds on the Spring Framework's transaction abstraction.To allow users to implement custom aspects, complementing their use of OOP with AOP.

 

What do you mean by Aspect ?
A modularization of a concern that cuts across multiple objects. Transaction management is a good example of a crosscutting concern in J2EE applications. In Spring AOP, aspects are implemented using regular classes (the schema-based approach) or regular classes annotated with the @Aspect annotation (@AspectJ style).

 

What do you mean by JointPoint?
A point during the execution of a program, such as the execution of a method or the handling of an exception. In Spring AOP, a join point always represents a method execution.

 

What do you mean by Advice?
Action taken by an aspect at a particular join point. Different types of advice include "around," "before" and "after" advice. Many AOP frameworks, including Spring, model an advice as an interceptor, maintaining a chain of interceptors "around" the join point.

 

What are the types of Advice?

  • Before advice: Advice that executes before a join point, but which does not have the ability to prevent execution flow proceeding to the join point (unless it throws an exception).
  • After returning advice: Advice to be executed after a join point completes normally: for example, if a method returns without throwing an exception.
  • After throwing advice: Advice to be executed if a method exits by throwing an exception.
  • After (finally) advice: Advice to be executed regardless of the means by which a join point exits (normal or exceptional return).
  • Around advice: Advice that surrounds a join point such as a method invocation. This is the most powerful kind of advice. Around advice can perform custom behavior before and after the method invocation. It is also responsible for choosing whether to proceed to the join point or to shortcut the advised method execution by returning its own return value or throwing an exception

 

What are the types of the transaction management Spring supports ?

   Spring Framework supports:

  • Programmatic transaction management.
  • Declarative transaction management.

 

What are the benefits of the Spring Framework transaction management ?

Spring Framework provides abstraction for transaction management that delivers the following benefits:

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

 

Why most users of the Spring Framework choose declarative transaction management ?

   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.

 

Explain the similarities and differences between EJB and the Spring Framework's declarative transaction management ?

The basic approach is similar: it is possible to specify transaction behavior (or lack of it) down to individual method level. It is possible to make a setRollbackOnly() call within a transaction context if necessary. The differences are:

  • Unlike EJB CMT, which is tied to JTA, the Spring Framework's declarative transaction management works in any environment. It can work with JDBC, JDO, Hibernate or other transactions under the covers, with configuration changes only.
  • The Spring Framework enables declarative transaction management to be applied to any class, not merely special classes such as EJBs.
  • The Spring Framework offers declarative rollback rules: this is a feature with no EJB equivalent. Both programmatic and declarative support for rollback rules is provided.
  • The Spring Framework gives you an opportunity to customize transactional behavior, using AOP. With EJB CMT, you have no way to influence the container's transaction management other than setRollbackOnly().
  • The Spring Framework does not support propagation of transaction contexts across remote calls, as do high-end application servers.

 

When to use programmatic and declarative transaction management ?

Programmatic transaction management is usually a good idea only if you have a small number of transactional operations. On the other hand, if your application has numerous transactional operations, declarative transaction management is usually worthwhile. It keeps transaction management out of business logic, and is not difficult to configure.

 

Explain about the Spring DAO support ?

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 one to switch between the persistence technologies fairly easily and it also allows one to code without worrying about catching exceptions that are specific to each technology.

 

What are the exceptions thrown by the Spring DAO classes ?

Spring DAO classes throw exceptions which are subclasses of DataAccessException(org.springframework.dao.DataAccessException).Spring provides a convenient translation from technology-specific exceptions like SQLException to its own exception class hierarchy with the DataAccessException as the root exception. These exceptions wrap the original exception.

 

What is SQLExceptionTranslator ?

SQLExceptionTranslator, is an interface to be implemented by classes that can translate between SQLExceptions and Spring's own data-access-strategy-agnostic org.springframework.dao.DataAccessException.

 

What is Spring's JdbcTemplate ?Spring's JdbcTemplate is central class to interact with a database through JDBC. JdbcTemplate 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.

What are the differences between EJB and Spring ? Spring and EJB feature comparison.

Feature

EJB

Spring

Transaction management

  • Must use a JTA transaction manager.
  • Supports transactions that span remote method calls.
  • Supports multiple transaction environments through its PlatformTransactionManager interface, including JTA, Hibernate, JDO, and JDBC.
  • Does not natively support distributed transactions—it must be used with a JTA transaction manager.

Declarative transaction support

  • Can define transactions declaratively through the deployment descriptor.
  • Can define transaction behavior per method or per class by using the wildcard character *.
  • Cannot declaratively define rollback behavior—this must be done programmatically.
  • Can define transactions declaratively through the Spring configuration file or through class metadata.
  • Can define which methods to apply transaction behavior explicitly or by using regular expressions.
  • Can declaratively define rollback behavior per method and per exception type.

Persistence

Supports programmatic bean-managed persistence and declarative container managed persistence.

Provides a framework for integrating with several persistence technologies, including JDBC, Hibernate, JDO, and iBATIS.

Declarative security

  • Supports declarative security through users and roles. The management and implementation of users and roles is container specific.
  • Declarative security is configured in the deployment descriptor.
  • No security implementation out-of-the box.
  • Acegi, an open source security framework built on top of Spring, provides declarative security through the Spring configuration file or class metadata.

Distributed computing

Provides container-managed remote method calls.

Provides proxying for remote calls via RMI, JAX-RPC, and web services.

 

 

<beans>
 <bean id="bar" class="com.act.Foo" singleton=”false”/>
</beans>

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.

 

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.

<beans>
 <bean id="bar" class="com.act.Foo" init-method=”fooSetup” destroy=”fooTeardown”/>
</beans>

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.

What are the different types of bean injections?

There are two types of bean injections.

  1. By setter
  2. By constructor

 

What is Auto wiring?

You can wire the beans as you wish. But spring framework also does this work for you. It can auto wire the related beans together. All you have to do is just set the autowire attribute of bean tag to an autowire type.            

<beans>
 <bean id="bar" class="com.act.Foo" Autowire=”autowire type”/>
</beans>

What are different types of Autowire types?

There are four different types by which autowiring can be done.

  • byName
  • byType
  • constructor
  • autodetect

What are the different types of events related to Listeners?

There are a lot of events related to ApplicationContext of spring framework. All the events are subclasses of org.springframework.context.Application-Event. They are

  • ContextClosedEvent – This is fired when the context is closed.
  • ContextRefreshedEvent – This is fired when the context is initialized or refreshed.
  • RequestHandledEvent – This is fired when the web context handles any request.

 What is an Aspect?

An aspect is the cross-cutting functionality that you are implementing. It is the aspect of your application you are modularizing. An example of an aspect is logging. Logging is something that is required throughout an application. However, because applications tend to be broken down into layers based on functionality, reusing a logging module through inheritance does not make sense. However, you can create a logging aspect and apply it throughout your application using AOP.

 

What is a Jointpoint?

A joinpoint is a point in the execution of the application where an aspect can be plugged in. This point could be a method being called, an exception being thrown, or even a field being modified. These are the points where your aspect’s code can be inserted into the normal flow of your application to add new behavior.

 

What is an Advice?

Advice is the implementation of an aspect. It is something like telling your application of a new behavior. Generally, and advice is inserted into an application at joinpoints.

 

What is a Pointcut?

A pointcut is something that defines at what joinpoints an advice should be applied. Advices can be applied at any joinpoint that is supported by the AOP framework. These Pointcuts allow you to specify where the advice can be applied.

 

What is an Introduction in AOP?

An introduction allows the user to add new methods or attributes to an existing class. This can then be introduced to an existing class without having to change the structure of the class, but give them the new behavior and state.

 

What is a Target?

A target is the class that is being advised. The class can be a third party class or your own class to which you want to add your own custom behavior. By using the concepts of AOP, the target class is free to center on its major concern, unaware to any advice that is being applied.

What is a Proxy?

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.

 

What is meant by Weaving?

The process of applying aspects to a target object to create a new proxy object is called as Weaving. The aspects are woven into the target object at the specified joinpoints.

 

What are the different points where weaving can be applied?

  • Compile Time
  • Classload Time
  • Runtime

What are the different advice types in spring?

  • Around : Intercepts the calls to the target method
  • Before : This is called before the target method is invoked
  • After : This is called after the target method is returned
  • Throws : This is called when the target method throws and exception
  • Around : org.aopalliance.intercept.MethodInterceptor
  • Before : org.springframework.aop.BeforeAdvice
  • After : org.springframework.aop.AfterReturningAdvice
  • Throws : org.springframework.aop.ThrowsAdvice
  •  

What is the Exception class related to all the exceptions that are thrown in spring applications?

DataAccessException - org.springframework.dao.DataAccessException

What kind of exceptions those spring DAO classes throw?

The spring’s DAO class does not throw any technology related exceptions such as SQLException. They throw exceptions which are subclasses of DataAccessException.

 

What is DataAccessException?

DataAccessException is a RuntimeException. This is an Unchecked Exception. The user is not forced to handle these kinds of exceptions.

 

How can you configure a bean to get DataSource from JNDI?


 
<bean id="dataSource" class="org.springframework.jndi.JndiObjectFactoryBean">
 <property name="jndiName">
 <value>java:comp/env/jdbc/myDatasource</value>
 </property>
</bean>

How do you write data to backend in spring using JdbcTemplate?

The JdbcTemplate uses several of these callbacks when writing data to the database. The usefulness you will find in each of these interfaces will vary. There are two simple interfaces. One is PreparedStatementCreator and the other interface is BatchPreparedStatementSetter.

 

Explain about PreparedStatementCreator?

PreparedStatementCreator is one of the most common used interfaces for writing data to database. The interface has one method createPreparedStatement().

PreparedStatement createPreparedStatement(Connection conn)
throws SQLException;

When this interface is implemented, we should create and return a PreparedStatement from the Connection argument, and the exception handling is automatically taken care off. When this interface is implemented, another interface SqlProvider is also implemented which has a method called getSql() which is used to provide sql strings to JdbcTemplate.

 

Explain about BatchPreparedStatementSetter?

If the user what to update more than one row at a shot then he can go for BatchPreparedStatementSetter. This interface provides two methods

setValues(PreparedStatement ps, int i) throws SQLException;
int getBatchSize();

The getBatchSize() tells the JdbcTemplate class how many statements to create. And this also determines how many times setValues() will be called.

 

Explain about RowCallbackHandler and why it is used?

In order to navigate through the records we generally go for ResultSet. But spring provides an interface that handles this entire burden and leaves the user to decide what to do with each row. The interface provided by spring is RowCallbackHandler. There is a method processRow() which needs to be implemented so that it is applicable for each and everyrow.

 

What are the different types of IOC (dependency injection) ?

There are three types of dependency injection:

  • Constructor Injection (e.g. Pico container, Spring etc): Dependencies are provided as constructor parameters.
  • Setter Injection (e.g. Spring): Dependencies are assigned through JavaBeans properties (ex: setter methods).
  • Interface Injection (e.g. Avalon): Injection is done through an interface.

The basic concept of the Inversion of Control pattern (also known as dependency injection) is 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 (in the case of the Spring framework, the IOC container) is then responsible for hooking it all up.

 

 

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.

 

 

 

Explain Bean lifecycle in Spring framework?

 

  1. The spring container finds the bean’s definition from the XML file and instantiates the bean.
  2. Using the dependency injection, spring populates all of the properties as specified in the bean definition.
  3. If the bean implements the BeanNameAware interface, the factory calls setBeanName() passing the bean’s ID.
  4. If the bean implements the BeanFactoryAware interface, the factory calls setBeanFactory(), passing an instance of itself.
  5. If there are any BeanPostProcessors associated with the bean, their post- ProcessBeforeInitialization() methods will be called.
  6. If an init-method is specified for the bean, it will be called.
  7. Finally, if there are any BeanPostProcessors associated with the bean, theirpostProcessAfterInitialization() methods will be called.

 

 

 

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.

 

What is the difference between Bean Factory and Application Context ?

On the surface, an application context is same as a bean factory. But application context offers...

  • Application contexts provide a means for resolving text messages, including support for i18n of those messages.
  • Application contexts provide a generic way to load file resources, such as images.
  • Application contexts can publish events to beans that are registered as listeners.
  • Certain 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.
  • ResourceLoader support: Spring’s Resource interface us a flexible generic abstraction for handling low-level resources. An application context itself is a ResourceLoader, Hence provides an application with access to deployment-specific Resource instances.
  • MessageSource support: The application context implements MessageSource, an interface used to obtain localized messages, with the actual implementation being pluggable

Declarative Transaction management , applying @Transactional annotation to the methods that require transaction management and enable the <tx:annotation-driven> element in ur configration file.

Transaction Attributes

Propagation – tells how a transaction should be propagated when a transactional method is called by other method, the method may continue to run within the existing transaction or it may start a new transaction and run within its own new transaction.

REQUIRED – if there is an existing transaction is in progress , the current method should run within this transaction . Otherwise , it should start a new transaction and run within its new transaction.

REQUIRES_NEW – The current method must start a new transaction and run within this new transaction , if there is an existing transaction in progress , is should be suspended

SUPPORTS – If there is an existing transaction in progress, the method can run within existing transaction , otherwise it is not necessary to run within a transaction

NOT_SUPPORTED – The current methode should not run within a transaction , if there is an existing transaction in progress , it must be aborted.

MANDATORY – The current method must run within a transaction , if there is no existing transaction in progress an exception will be thrown

NEVER – The current method should never run within a transaction , if there is an existing transaction in progress an exception will be thrown.

Isolation Level – specifies how a transaction should be isolated from other transactions when multiple transactions are operating concurrently on the same dataset.

Concurrent Transactions cause 3 type of problems

1 – Dirty Read   : two transactions T1 and T2, T1 reads a field updated by T2 but not yet been commited,
later if T2   rollback , the field read by T1 will be invalid.

2 – non-Repeatable Read : two transactions T1 and T2, T1 reads a field and then T2 updates the field,
if T1 reads the same field again the value will be different.

3- Phantom Read :   2 transactions T1 and T2 , T1 reads some rows from the table, then T2 inserts new rows into the table.later if T1 reads the same table again there will be additional rows.

Transactions should be completely isolated from each other to avoid all above problems but will cause performance issues bcz transactions have to run in serial order, transactions can run in lower isolation levels to improve performance.

ISOLATION-LEVELS

DEFAULT: is READ_COMMITED

READ_UNCOMMITTED = Allows transaction to read un commited changes by other transactions. Dirty read, non-repeatable read, phantom all 3 problems may accur.

READ_COMMITTED = allows a transaction to read only those changes that have been committed by other transactions , dirty read will be avoided , but non-repeatable-read and phantom read problems still occur.

REPEATABLE_READ = ensures that a transaction can read same values from a field multiple times. For the duration of this transaction , updates by other transactions to this field are not allowed , dirty read and non-repeatable-read problems can be avoided but phantom read problem still occur

SERIALIZABLE = ensures that a transaction can read same rows from a table multiple times. For the durations of this transaction , inserts , updates and deletes by other transactions to this table are not allowed. All the concurrency problems will be avoided but performance will be low.

 

RollBack Rule – specifies which kind of exceptions should cause a rollback and which kinds should not, default rule is to rollback on run time exceptions(un-checked exceptions) and do not rollback for checked exceptions

@Transactional( isolation = Isolation.REPEATABLE_READ,
                           ROLLBACKFOR = IOEXCEPTION.CLASS,
                           NOROLLBACKFOR = ARITHMETICeXCEPTION.CLASS)

 

Transaction Time-Out – specifies how long a transaction can survive before it is forced to rollback

@Transactional( isolation = Isolation.REPEATABLE_READ,
                          TIMEOUT = 30,
                             READONLY = TRUE)