Spring Questions

Q) Why do we need DTD or XSD declaration tags in the spring XML configuration file?

A)  Either we need to declare DTD at the top level or XSD inside beans root tag

·         DTD and XSD are used to validate our XML file.

·         Inside IOC we have SAX parser which parsers XML file.  SAX parser will read and parsers XML file.

·         To parser the XML file it should be in the well-formed XML file (means having close and end tag) so DTD or XSD is used to check the XML file in the well-formed file and check the valid file which is nothing but tags without a declaration.

Q) What is the use of container in Spring?

A) The container in spring is responsible for reading the XML file and creating the instances(objects)  of the respective beans in the XML file. The container is responsible for bean life.

Q) How many containers we have in IOC?

A)   In IOC, we have mainly two containers

·         Core Container (Bean Factory)

·         J2ee container (Application Context)

Q)  what is the difference between BeanFactory(Core Container) and ApplicationContext(J2EE container) ?

A) Application Context build on the top of BeanFactoryContainer

·         Bean Factory will create the object for the first user request. That means it won’t create an object at the time of loading. By default, bean scope is a singleton.

·         Application Context container will create object while loading itself if the beans scopes is a singleton.

·          if we change the bean’s scope in Application Context to prototype. It will not create the objects for the POJO class while loading the XML file.

·         If bean scope is equal to the porotype Application context behaves like Bean factory. It will create each object for each request.

·         BeanFactory will create an instance(objects) whenever call get bean method but ApplicationContext creates instance while loading the XML file into the container.

·         By default, the scope of the bean singleton. If the scope of the bean is singleton the Bean Factory Container will create an object for the POJO class on-demand that mean when we call the bean method (get bean) but in case of application context container if the scope is singleton application context container will create the objects for the POJO class at the time of loading the XML file.

·         If the scope of the bean is prototype than both containers creates the objects, the one demand only and different objects for each user.

·         If we have 10 beans in my XML documents than bean factory container will create one object when we called get bean method and that one object will have used for the remaining 9 beans. so remaining 9 beans have to wait for first one complete so it will take a lot of time to give a response to all user at a time but in case of application context if I have 10 beans it will create 10 objects at the time of loading the XML so if it uses the response to 10 users same time so there is no time delay when the scope of the of a bean is a singleton.

·         When the bean scope is a prototype in the Application Context Container it will create the instance when a user requested get bean method. In this scenario both containers Bean Factory and Application Context behaves same

·         In containers when we called get bean method in IOC container by using class. for name container creates an object. when class is public  

Q) What is a POJO class?

A)  POJO Plain Old Java Object. Basically, a class with attributes and its getters and setters.


Q) Autowired Annotation in spring?
A)  Autowired annotation can be implemented in web applications. We can not implement Autowired in standalone application because to access objects inside the static method we need an instance of the class when you use autowired  instance is created after loading application context or configuration file.