1) What is Spring?
Answer:
Spring is a lightweight inversion of control and aspect-oriented
container framework.
2) Explain Spring?
Answer:
- 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?
Answer:
- 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?
Answer:
5) What is the Core container module?
Answer:
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?
Answer:
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?
Answer:
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 Spring and other AOP frameworks.
This module also introduces metadata programming to Spring.
Using Spring’s metadata support, we will be able to addannotations to
our source code that instruct Spring on where
and how to apply aspects.
8) What is JDBC abstraction and DAO module?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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 declaratively 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?
Answer:
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?
Answer:
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.
14) What is Spring configuration file?
Answer:
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?
Answer:
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?
Answer:
BeanFactory has many implementations in Spring. But
one of the most useful one isorg.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. TheInputStream will provide the XML to the
factory. For example, the following code snippet uses a java.io.FileInputStream to
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?
Answer:
- ClassPathXmlApplicationContext
– This context loads a context
definition from an XML file located in theclass 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?
Answer:
- 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 aninstance 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, theirpostProcessAfterInitialization() methods will be
called.
19) What is bean wiring?
Answer:
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?
Answer:
<?xml version="1.0"
encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD
BEAN//EN"
"http://www.springframework.org/dtd/spring-beans.dtd">
<beans>
<bean id="foo"
class="com.act.Foo"/>
<bean id="bar"
class="com.act.Bar"/>
</beans>
In the bean tag the id attribute specifies the
bean name and the class attribute specifies the fully
qualified classname.
21) What are singleton beans and how can you
create prototype beans?
Answer:
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.
<beans>
<bean
id="bar" class="com.act.Foo" singleton=”false”/>
</beans>
22) What are the important beans lifecycle
methods?
Answer:
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?
Answer:
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>
24) What are Inner Beans?
Answer:
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?
Answer:
There are two types of bean injections.
- By
setter
- By
constructor
26) What is Auto wiring?
Answer:
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>
27) What are different types of Autowire types?
Answer:
There are four different types by which autowiring
can be done.
- byName
- byType
- constructor
- autodetect
28) What are the different types of events
related to Listeners?
Answer:
There are a lot of events related to ApplicationContext of
spring framework. All the events are subclasses oforg.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.
29) What is an Aspect?
Answer:
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 yourapplication using AOP.
30) What is a Jointpoint?
Answer:
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.
31) What is an Advice?
Answer:
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.
32) What is a Pointcut?
Answer:
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.
33) What is an Introduction in AOP?
Answer:
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.
34) What is a Target?
Answer:
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.
35) What is a Proxy?
Answer:
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.
36) What is meant by Weaving?
Answer:
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.
37) What are the different points where weaving
can be applied?
Answer:
- Compile
Time
- Classload
Time
- Runtime
38) What are the different advice types in
spring?
Answer:
- 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
39) What are the different types of
AutoProxying?
Answer:
- BeanNameAutoProxyCreator
- DefaultAdvisorAutoProxyCreator
- Metadata
autoproxying
40) What is the Exception class related to all
the exceptions that are thrown in spring applications?
Answer:
DataAccessException - org.springframework.dao.DataAccessException
41) What kind of exceptions those spring DAO
classes throw?
Answer:
The spring’s DAO class does not throw any
technology related exceptions such as SQLException. They throw exceptions which
are subclasses of DataAccessException.
42) What is DataAccessException?
Answer:
DataAccessException is a RuntimeException. This
is an Unchecked Exception. The user is not forced to handle these kinds of
exceptions.
43) How can you configure a bean to get
DataSource from JNDI?
Answer:
<bean id="dataSource"
class="org.springframework.jndi.JndiObjectFactoryBean">
<property name="jndiName">
<value>java:comp/env/jdbc/myDatasource</value>
</property>
</bean>
44) How can you create a DataSource connection
pool?
Answer:
<bean id="dataSource"
class="org.apache.commons.dbcp.BasicDataSource">
<property
name="driver">
<value>${db.driver}</value>
</property>
<property name="url">
<value>${db.url}</value>
</property>
<property name="username">
<value>${db.username}</value>
</property>
<property name="password">
<value>${db.password}</value>
</property>
</bean>
45) How JDBC can be used more efficiently in
spring framework?
Answer:
JDBC can be used more efficiently with the help
of a template class provided by spring framework called asJdbcTemplate.
46) How JdbcTemplate can be used?
Answer:
With use of Spring JDBC framework the burden of
resource management and error handling is reduced a lot. So it leaves
developers to write the statements and queries to get the data to and from the
database.
JdbcTemplate template = new JdbcTemplate(myDataSource);
A simple DAO class looks like this.
public class StudentDaoJdbc implements StudentDao {
private JdbcTemplate
jdbcTemplate;
public void setJdbcTemplate(JdbcTemplate
jdbcTemplate) {
this.jdbcTemplate = jdbcTemplate;
}
more..
}
The configuration is shown below.
<bean id="jdbcTemplate"
class="org.springframework.jdbc.core.JdbcTemplate">
<property
name="dataSource">
<ref
bean="dataSource"/>
</property>
</bean>
<bean id="studentDao" class="StudentDaoJdbc">
<property
name="jdbcTemplate">
<ref
bean="jdbcTemplate"/>
</property>
</bean>
<bean id="courseDao"
class="CourseDaoJdbc">
<property
name="jdbcTemplate">
<ref
bean="jdbcTemplate"/>
</property>
</bean>
47) How do you write data to backend in spring
using JdbcTemplate?
Answer:
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.
48) Explain about PreparedStatementCreator?
Answer:
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 interfaceSqlProvider is also implemented which
has a method called getSql() which is used to provide sql
strings to JdbcTemplate.
49) Explain about BatchPreparedStatementSetter?
Answer:
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.
50) Explain about RowCallbackHandler and why it
is used?
Answer:
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 isRowCallbackHandler. There is a
method processRow() which needs to be implemented so that it
is applicable for each and everyrow.
void processRow(java.sql.ResultSet rs);
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