Spring:

Spring is a lightweight inversion of control and aspect-oriented container framework.

Advantages:

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.

Spring framework modules:

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

Structure of Spring framework:

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.

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.

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 Spring and 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 Spring on where and how to apply aspects.

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.

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.

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.

MVC Framework:

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.

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.

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.

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.

simple spring application:

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.

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.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");

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.

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, their postProcessAfterInitialization() methods will be called.

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.

Adding bean in spring application:

<?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 class name.

Singleton beans and 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.

<beans>

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

</beans>

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.

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>

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.

Types of bean injections:

There are two types of bean injections.

1. By setter 2. By constructor 3. Method Injection (Interface Injection, rarely used)

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>

Different types of Autowiring:

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

o byName o byType

o constructor

o autodetect

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.

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.

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.

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.

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.

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.

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.

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.

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.

Different points where weaving can be applied:

Compile Time Classload Time

Runtime

Advice types:

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

Different types of AutoProxying:

BeanNameAutoProxyCreator DefaultAdvisorAutoProxyCreator

Metadata autoproxying

Exception class related to all the exceptions that are thrown in spring applications:

DataAccessException - org.springframework.dao.DataAccessException

Exceptions thrown by spring DAO classes:

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

DataAccessException:

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

Configuring 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>

DataSource connection pool creation:

<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>

How JDBC can be used more efficiently in spring framework?

JDBC can be used more efficiently with the help of a template class provided by spring framework called as JdbcTemplate.

How JdbcTemplate can be used?

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>

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.

void processRow(java.sql.ResultSet rs);

Hibernate:

Hibernate is a powerful, high performance object/relational persistence and query service. This lets the users to develop persistent classes following object-oriented principles such as association, inheritance, polymorphism, composition, and collections.

ORM:

ORM stands for Object/Relational mapping. It is the programmed and translucent perseverance of objects in a Java application in to the tables of a relational database using the metadata that describes the mapping between the objects and the database. It works by transforming the data from one representation to another.

What does an ORM solution comprises of?

It should have an API for performing basic CRUD (Create, Read, Update, Delete) operations on objects of persistent classes

Should have a language or an API for specifying queries that refer to the classes and the properties of classes

An ability for specifying mapping metadata

It should have a technique for ORM implementation to interact with transactional objects to perform dirty checking, lazy association fetching, and other optimization functions

Different levels of ORM quality:

There are four levels defined for ORM quality.

i. Pure relational ii. Light object mapping

iii. Medium object mapping

iv. Full object mapping

What is a pure relational ORM?

The entire application, including the user interface, is designed around the relational model and SQL-based relational operations.

What is a meant by light object mapping?

The entities are represented as classes that are mapped manually to the relational tables. The code is hidden from the business logic using specific design patterns. This approach is successful for applications with a less number of entities, or applications with common, metadata-driven data models. This approach is most known to all.

What is a meant by medium object mapping?

The application is designed around an object model. The SQL code is generated at build time. And the associations between objects are supported by the persistence mechanism, and queries are specified using an object-oriented expression language. This is best suited for medium-sized applications with some complex transactions. Used when the mapping exceeds 25 different database products at a time.

What is meant by full object mapping?

Full object mapping supports sophisticated object modeling: composition, inheritance, polymorphism and persistence. The persistence layer implements transparent persistence; persistent classes do not inherit any special base class or have to implement a special interface. Efficient fetching strategies and caching strategies are implemented transparently to the application.

Benefits of ORM and Hibernate:

There are many benefits from these. Out of which the following are the most important one.

i. Productivity – Hibernate reduces the burden of developer by providing much of the functionality and let the developer to concentrate on business logic.

ii. Maintainability – As hibernate provides most of the functionality, the LOC for the application will be reduced and it is easy to maintain. By automated object/relational persistence it even reduces the LOC.

iii. Performance – Hand-coded persistence provided greater performance than automated one. But this is not true all the times. But in hibernate, it provides more optimization that works all the

time there by increasing the performance. If it is automated persistence then it still increases the performance.

iv. Vendor independence – Irrespective of the different types of databases that are there, hibernate provides a much easier way to develop a cross platform application.

How does hibernate code looks like:

Session session = getSessionFactory().openSession();Transaction tx = session.beginTransaction();MyPersistanceClass mpc = new MyPersistanceClass ("Sample App");session.save(mpc);tx.commit();session.close();

The Session and Transaction are the interfaces provided by hibernate. There are many other interfaces besides this.

What is a hibernate xml mapping document and how does it look like?

In order to make most of the things work in hibernate, usually the information is provided in an xml document. This document is called as xml mapping document. The document defines, among other things, how properties of the user defined persistence classes’ map to the columns of the relative tables in database.

<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>   <class name="sample.MyPersistanceClass" table="MyPersitaceTable">      <id name="id" column="MyPerId">         <generator class="increment"/>      </id>      <property name="text" column="Persistance_message"/>      <many-to-one name="nxtPer" cascade="all" column="NxtPerId"/>   </class></hibernate-mapping>

Everything should be included under <hibernate-mapping> tag. This is the main tag for an xml mapping document.

Hibernate overview:

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Core interfaces of hibernate framework:

There are many benefits from these. Out of which the following are the most important one.

i. Session Interface – This is the primary interface used by hibernate applications. The instances of this interface are lightweight and are inexpensive to create and destroy. Hibernate sessions are not thread safe.

ii. SessionFactory Interface – This is a factory that delivers the session objects to hibernate application. Generally there will be a single SessionFactory for the whole application and it will be shared among all the application threads.

iii. Configuration Interface – This interface is used to configure and bootstrap hibernate. The instance of this interface is used by the application in order to specify the location of hibernate specific mapping documents.

iv. Transaction Interface – This is an optional interface but the above three interfaces are mandatory in each and every application. This interface abstracts the code from any kind of transaction implementations such as JDBC transaction, JTA transaction.

v. Query and Criteria Interface – This interface allows the user to perform queries and also control the flow of the query execution.

Callback interfaces:

These interfaces are used in the application to receive a notification when some object events occur. Like when an object is loaded, saved or deleted. There is no need to implement callbacks in hibernate applications, but they’re useful for implementing certain kinds of generic functionality.

Extension interfaces:

When the built-in functionalities provided by hibernate is not sufficient enough, it provides a way so that user can include other interfaces and implement those interfaces for user desire functionality. These interfaces are called as Extension interfaces.

Extension interfaces in hibernate:

There are many extension interfaces provided by hibernate.

ProxyFactory interface - used to create proxies ConnectionProvider interface – used for JDBC connection

management

TransactionFactory interface – Used for transaction management

Transaction interface – Used for transaction management

TransactionManagementLookup interface – Used in transaction management.

Cahce interface – provides caching techniques and strategies

CacheProvider interface – same as Cache interface

ClassPersister interface – provides ORM strategies

IdentifierGenerator interface – used for primary key generation

Dialect abstract class – provides SQL support

Different environments to configure hibernate:

There are mainly two types of environments in which the configuration of hibernate application differs.

i. Managed environment – In this kind of environment everything from database connections, transaction boundaries, security levels and all are defined. An example of this kind of environment is environment provided by application servers such as JBoss, Weblogic and WebSphere.

ii. Non-managed environment – This kind of environment provides a basic configuration template. Tomcat is one of the best examples that provide this kind of environment.

What is the file extension you use for hibernate mapping file?

The name of the file should be like this : filename.hbm.xmlThe filename varies here. The extension of these files should be “.hbm.xml”.This is just a convention and it’s not mandatory. But this is the best practice to follow this extension.

Creating a SessionFactory:

Configuration cfg = new Configuration();cfg.addResource("myinstance/MyConfig.hbm.xml");cfg.setProperties( System.getProperties() );SessionFactory sessions = cfg.buildSessionFactory();

First, we need to create an instance of Configuration and use that instance to refer to the location of the configuration file. After configuring this instance is used to create the SessionFactory by calling the method buildSessionFactory().

Method chaining:

Method chaining is a programming technique that is supported by many hibernate interfaces. This is less readable when compared to actual java code. And it is not mandatory to use this format. Look how a SessionFactory is created when we use method chaining.

SessionFactory sessions = new Configuration()    .addResource("myinstance/MyConfig.hbm.xml")    .setProperties( System.getProperties() )    .buildSessionFactory();

What does hibernate.properties file consist of:

This is a property file that should be placed in application class path. So when the Configuration object is created, hibernate is first initialized. At this moment the application will automatically detect and read this hibernate.properties file.

hibernate.connection.datasource =java:/comp/env/jdbc/AuctionDBhibernate.transaction.factory_class =         net.sf.hibernate.transaction.JTATransactionFactoryhibernate.transaction.manager_lookup_class =         net.sf.hibernate.transaction.JBossTransactionManagerLookuphibernate.dialect = net.sf.hibernate.dialect.PostgreSQLDialect

Where should SessionFactory be placed so that it can be easily accessed:

As far as it is compared to J2EE environment, if the SessionFactory is placed in JNDI then it can be easily accessed and shared between different threads and various components that are hibernate aware. You can set the SessionFactory to a JNDI by configuring a property hibernate.session_factory_name in the hibernate.properties file.

POJOs:

POJO stands for plain old java objects. These are just basic JavaBeans that have defined setter and getter methods for all the properties that are there in that bean. Besides they can also have some business logic related to that property. Hibernate applications works efficiently with POJOs rather then simple java classes.

What is object/relational mapping metadata:

ORM tools require a metadata format for the application to specify the mapping between classes and tables, properties and columns, associations and foreign keys, Java types and SQL types. This information is called the object/relational mapping metadata. It defines the transformation between the different data type systems and relationship representations.

HQL:

HQL stands for Hibernate Query Language. Hibernate allows the user to express queries in its own portable SQL extension and this is called as HQL. It also allows the user to express in native SQL.

Different types of property and class mappings:

Typical and most common property mapping

<property name="description" column="DESCRIPTION" type="string"/>

Or<property name="description" type="string">    <column name="DESCRIPTION"/></property>

Derived properties

<property name="averageBidAmount" formula="( select AVG(b.AMOUNT) from BID b where b.ITEM_ID = ITEM_ID )" type="big_decimal"/>

Typical and most common property mapping

<property name="description" column="DESCRIPTION" type="string"/>

Controlling inserts and updates

<property name="name" column="NAME" type="string"       insert="false" update="false"/>

Attribute Oriented Programming:

XDoclet has brought the concept of attribute-oriented programming to Java. Until JDK 1.5, the java language had no support for annotations; now XDoclet uses the Javadoc tag format (@attribute) to specify class-, field-, or method-level metadata attributes. These attributes are used to generate hibernate mapping file automatically when the application is built. This kind of programming that works on attributes is called as Attribute Oriented Programming.

Different methods of identifying an object:

There are three methods by which an object can be identified.

i. Object identity –Objects are identical if they reside in the same memory location in the JVM. This can be checked by using the = = operator.

ii. Object equality – Objects are equal if they have the same value, as defined by the equals( ) method. Classes that don’t explicitly override this method inherit the implementation defined by java.lang.Object, which compares object identity.

iii. Database identity – Objects stored in a relational database are identical if they represent the same row or, equivalently, share the same table and primary key value.

Different approaches to represent an inheritance hierarchy:

i. Table per concrete class. ii. Table per class hierarchy.

iii. Table per subclass.

Managed associations and hibernate associations:

Associations that are related to container management persistence are called managed associations. These are bi-directional associations. Coming to hibernate associations, these are unidirectional.