Hybernat and structs, spring classes in mumbai

Spring Tutorial
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by

Introduction to the Spring
Framework

• Java Architect for MATRIX Resources in
Atlanta
• 8 years of software development experience
• Sun Certified Java Programmer
• Sun Certified Web Component Developer

Overview
• Application Layering Architecture
• Spring in the Middle Tier
• Spring Inversion of Control + AOP
• Wiring objects together
• Spring Database Components
• Demo

Application Layering
• A clear separation of application component responsibility.
– Presentation layer
• Concentrates on request/response actions
• Handles UI rendering from a model.
• Contains formatting logic and non-business related validation logic.
• Handles exceptions thrown from other layers
– Persistence layer
• Used to communicate with a persistence store such as a relational
database.
• Provides a query language
• Possible O/R mapping capabilities
• JDBC, Hibernate, iBATIS, JDO, Entity Beans, etc.
– Domain layer
• Contains business objects that are used across above layers.
• Contain complex relationships between other domain objects
• May be rich in business logic
• May have ORM mappings
• Domain objects should only have dependencies on other domain
objects

What about a Service Layer?
• Where do we position loosely-coupled business logic?
• What is service logic?
• How should container level services be implemented?
• How do we support transactions in a POJO based application?
• How do we communicate from our presentation layer to our persistence layer?
• How do we get to services that contain business logic?
• How should our business objects communicate with our persistence layer?
• How do we get objects retrieved from our persistence layer to our UI layer?

Application Layering (cont)
– Service layer
• Gateway to expose business logic to the
outside world
• Manages ‘container level services’ such as
transactions, security, data access logic, and
manipulates domain objects
• Not well defined in many applications today or
tightly coupled in an inappropriate layer.

More Application Layering
Combinations
• Presentation/Business/Persistence
• Struts+Spring+Hibernate
• Struts + Spring + EJB
• JavaServer Faces + Spring + iBATIS
• Spring + Spring + JDO
• Flex + Spring + Hibernate
• Struts + Spring + JDBC
• You decide…

EJB (<=2.x) in the Service Layer
• Sun’s traditional solution to middle tier business logic
• Specification that did not always work as projected in
real applications.
• EJBs are less portable than POJO based
architectures.
• Inconsistencies by vendors make EJBs break the
“write once, run anywhere” rule.
• Fosters over-engineering in most cases
• Entity Beans – very limiting compared to alternatives
such as Hibernate.
• Performance with POJOs are much faster then EJBs.
• EJBs run in a heavy container
• Your code becomes coupled to EJB API.
• We need to redefine what J2EE means…

Spring Mission Statement
• J2EE should be easier to use
• OO design is more important than any
implementation technology, such as
J2EE.
• Testability is essential, and a framework
such as Spring should help make your
code easier to test.
• Spring should not compete with good
existing solutions, but should foster
integration.

Spring
• A lightweight framework that addresses each tier in a
Web application.
– Presentation layer – An MVC framework that is most similar
to Struts but is more powerful and easy to use.
– Business layer – Lightweight IoC container and AOP support
(including built in aspects)
– Persistence layer – DAO template support for popular ORMs
and JDBC
• Simplifies persistence frameworks and JDBC
• Complimentary: Not a replacement for a persistence framework
• Helps organize your middle tier and handle typical
J2EE plumbing problems.
• Reduces code and speeds up development
• Current Version is 1.0.2

Spring (continued)
• Do I have to use all components of Spring?
• Spring is a non-invasive and portable framework that allows you
to introduce as much or as little as you want to your application.
• Promotes decoupling and reusability
• POJO Based
• Allows developers to focus more on reused business logic and
less on plumbing problems.
• Reduces or alleviates code littering, ad hoc singletons, factories,
service locators and multiple configuration files.
• Removes common code issues like leaking connections and
more.
• Built in aspects such as transaction management
• Most business objects in Spring apps do not depend on the
Spring framework.

Why Did I choose Spring?
• Introduced to Spring by way of Hibernate
• Originally wanted Spring to provide a way to simplify
DAO objects and provide declarative transaction
support to our non-EJB applications.
• Needed a solution to loosely couple business logic in
a POJO fashion.
• Wanted to build portable applications that provided
clearer separation of presentation, business, and
persistence logic.
• Easily integrated with our existing frameworks
• Great documentation and community support

Simplify your code with Spring
• Enables you to stop polluting code
• No more custom singleton objects
– Beans are defined in a centralized configuration file
• No more custom factory object to build and/or locate other
objects
• DAO simplification
– Consistent CRUD
– Data access templates
– No more copy-paste try/catch/finally blocks
– No more passing Connection objects between methods
– No more leaked connections
• POJO Based
• Refactoring experience with Spring
• Caution Spring is addictive!

Spring IoC + AOP
• IoC container
– Setter based and constructor based dependency injection
– Portable across application servers
– Promotes good use of OO practices such as programming
to interfaces.
– Beans managed by an IoC container are reusable and
decoupled from business logic
• AOP
– Spring uses Dynamic AOP Proxy objects to provide cross-cutting
services
– Reusable components
– Aopalliance support today
– Integrates with the IoC container
– AspectJ support in Spring 1.1

Inversion of Control
• Dependency injection
– Beans define their dependencies through constructor
arguments or properties
– The container provides the injection at runtime
• “Don’t talk to strangers”
• Also known as the Hollywood principle – “don’t call
me I will call you”
• Decouples object creators and locators from
application logic
• Easy to maintain and reuse
• Testing is easier

Non-IoC / Dependency Injection

Non-IoC Service Object
public class OrderServiceImpl implements
IOrderService {
public Order saveOrder(Order order) throws
OrderException{
try{
// 1. Create a Session/Connection object
// 2. Start a transaction
// 3. Lookup and invoke one of the methods in a
// DAO and pass the Session/Connection object.
// 4. Commit transaction
}catch(Exception e){
// handle e, rollback transaction,
//cleanup, // throw e
}finally{
//Release resources and handle more exceptions
}
}

IoC Service Object
public class OrderSpringService
implements IOrderService {
IOrderDAO orderDAO;
public Order saveOrder(Order order)
throws OrderException{
// perform some business logic…
return orderDAO.saveNewOrder(order);
}
public void setOrderDAO(IOrderDAO
orderDAO) {
this.orderDAO = orderDAO;
}
• Program to interfaces for your bean dependencies!

Spring Bean Definition
• The bean class is the actual implementation of the bean being
described by the BeanFactory.
• Bean examples – DAO, DataSource, Transaction Manager,
Persistence Managers, Service objects, etc
• Spring config contains implementation classes while your code
should program to interfaces.
• Bean behaviors include:
– Singleton or prototype
– Autowiring
– Initialization and destruction methods
• init-method
• destroy-method
• Beans can be configured to have property values set.
– Can read simple values, collections, maps, references to other
beans, etc.

Simple Spring Bean Example
• <bean id=“orderBean” class=“example.OrderBean”
init-method=“init”>
<property
name=“minimumAmountToProcess”>10</property>
<property name=“orderDAO”>
<ref bean=“orderDAOBean”/>
</property>
</bean>
• public class OrderBean implements IOrderBean{
…
public void
setMinimumAmountToProcess(double d){
this. minimumAmountToProcess = d;
}
public void setOrderDAO(IOrderDAO odao){
this.orderDAO = odao;
}
}

Spring BeanFactory
• BeanFactory is core to the Spring framework
– Lightweight container that loads bean definitions and
manages your beans.
– Configured declaratively using an XML file, or files, that
determine how beans can be referenced and wired together.
– Knows how to serve and manage a singleton or prototype
defined bean
– Responsible for lifecycle methods.
– Injects dependencies into defined beans when served
• Avoids the use of singletons and factories

Spring ApplicationContext
• A Spring ApplicationContext allows you to get access
to the objects that are configured in a BeanFactory in
a framework manner.
• ApplicationContext extends BeanFactory
– Adds services such as international messaging capabilities.
– Add the ability to load file resources in a generic fashion.
• Several ways to configure a context:
– XMLWebApplicationContext – Configuration for a web
application.
– ClassPathXMLApplicationContext – standalone XML
application context
– FileSystemXmlApplicationContext
• Allows you to avoid writing Service Locators

Configuring an XMLWebApplicationContext
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>
/WEB-INF/applicationContext.xml
</param-value>
</context-param>
<listener>
<listener-class>
org.springframework.web.context.ContextLoader
Listener
</listener-class>
</listener>

Configuring an XMLWebApplicationContext
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>
/WEB-INF/applicationContext.xml
</param-value>
</context-param>
<servlet>
<servlet-name>context</servlet-name>
<servlet-class>
org.springframework.web.context.ContextLoader
Servlet
</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>

Locating a Bean with Struts
public abstract class BaseAction extends
ActionSupport {
protected IOrderService
getOrderService() {
return (IOrderService)
getWebApplicationContext()
.getBean("orderService");
}
}
<bean id=“orderService"
class="com.meagle.service.spring.OrderServiceImpl">

AOP
• Complements OO programming
• Core business concerns vs. Crosscutting enterprise concerns
• Components of AOP
– Aspect – unit of modularity for crosscutting concerns
– Join point – well-defined points in the program flow
– Pointcut – join point queries where advice executes
– Advice – the block of code that runs based on the pointcut
definition
– Weaving – can be done at runtime or compile time. Inserts the
advice (crosscutting concerns) into the code (core concerns).
• Aspects can be used as an alternative to existing technologies
such as EJB. Ex: declarative transaction management,
declarative security, profiling, logging, etc.
• Aspects can be added or removed as needed without changing
your code.

Spring AOP
• Framework that builds on the aopalliance interfaces.
• Aspects are coded with pure Java code. You do not
need to learn pointcut query languages that are
available in other AOP implementations.
• Spring aspects can be configured using its own IoC
container.
– Objects obtained from the IoC container can be
transparently advised based on configuration
• Spring AOP has built in aspects such as providing
transaction management, performance monitoring
and more for your beans
• Spring AOP is not as robust as some other
implementations such as AspectJ.
– However, it does support common aspect uses to solve
common problems in enterprise applications

Spring AOP
• Supports the following advices:
– method before
– method after returning
– throws advice
– around advice (uses AOPAlliance MethodInterceptor
directly)
• Spring allows you to chain together interceptors and
advice with precedence.
• Aspects are weaved together at runtime. AspectJ
uses compile time weaving.
• Spring AOP also includes advisors that contain
advice and pointcut filtering.
• ProxyFactoryBean – sources AOP proxies from a
Spring BeanFactory
• IoC + AOP is a great combination that is non-invasive

Spring AOP Around Advice Example
public class PerformanceMonitorDetailInterceptor implements
MethodInterceptor {
protected final Log logger = LogFactory.getLog(getClass());
public Object invoke(MethodInvocation invocation) throws Throwable
{
String name =
invocation.getMethod().getDeclaringClass().getName()
+ "."
+ invocation.getMethod().getName();
StopWatch sw = new StopWatch(name);
sw.start(name);
Object rval = invocation.proceed();
sw.stop();
logger.info(sw.prettyPrint());
return rval;
}
}

Spring AOP Advice (Cont’)
• Advisor references the advice and the pointcut
<bean id="perfMonInterceptor"
class=
"com.meagle.service.interceptor.PerformanceMonitorDetailInterceptor"/>
<bean id="performanceAdvisor"
class="org.springframework.aop.support.RegexpMethodPointcutAdvisor">
<property name="advice">
<ref local="perfMonInterceptor"/>
</property>
<property name="patterns">
<list>
<value>.*find.*</value>
<value>.*save.*</value>
<value>.*update.*</value>
</list>
</property>
</bean>

Wiring Beans Together with
Spring

Wiring your Persistence Layer
<bean id=“mySessionFactory" class=
“org.springframework.orm.hibernate.LocalSessionFactoryBean“>
<property name="mappingResources">
<list>
<value>com/matrix/bo/Order.hbm.xml</value>
<value>com/matrix/bo/OrderLineItem.hbm.xml</value>
</list>
</property>
<property name="hibernateProperties">
<props>
<prop key="hibernate.dialect">
net.sf.hibernate.dialect.DB2Dialect
</prop>
<prop key="hibernate.default_schema">DB2ADMIN</prop>
<prop key="hibernate.show_sql">false</prop>
<prop key="hibernate.proxool.xml">
/WEB-INF/proxool.xml</prop>
<prop key="hibernate.proxool.pool_alias">spring</prop>
</props>
</property>
</bean>

Wiring your Transaction Management
Four transaction managers available
– DataSourceTransactionManager
– HibernateTransactionManager
– JdoTransactionManager
– JtaTransactionManager
<bean id=“myTransactionManager"
class="org
.springframework
.orm
.hibernate
.HibernateTransactionManager">
<property name=“sessionFactory">
<ref local=“mySessionFactory"/>
</property>
</bean>

Wiring a Service Object
<bean id=“orderService" class="org.springframework.transaction.
interceptor.TransactionProxyFactoryBean">
<property name="transactionManager">
<ref local=“myTransactionManager"/>
</property>
<property name="target"><ref local=“orderTarget"/></property>
<property name="transactionAttributes">
<props>
<prop key="find*">
PROPAGATION_REQUIRED,readOnly,-OrderException
</prop>
<prop key="save*">
PROPAGATION_REQUIRED,-OrderMinimumAmountException
</prop>
<prop key="update*">
PROPAGATION_REQUIRED,-OrderException
</prop>
</props>
</property>
</bean>

Defining a Target to Proxy
public class OrderServiceSpringImpl
implements IOrderService {
private IOrderDAO orderDAO;
// service methods…
public void setOrderDAO(IOrderDAO
orderDAO) {
this.orderDAO = orderDAO;
}
}

Wiring a Service Object (cont’)
<bean id=“orderTarget"
class="com.meagle.service.spring.OrderServiceSp
ringImpl">
<property name=“orderDAO">
<ref local=“orderDAO"/>
</property>
</bean>
<bean id=“orderDAO"
class="com.meagle.dao.hibernate.OrderHibernateD
AO">
<property name="sessionFactory">
<ref local=“mySessionFactory"/>
</property>
</bean>

Consistent Abstract Classes for DAO Support
• Extend your DAO classes with the proper xxxDAOSupport class
that matches your persistence mechanism.
• JdbcDaoSupport
– Super class for JDBC data access objects.
– Requires a DataSource to be set, providing a JdbcTemplate based
on it to subclasses.
• HibernateDaoSupport
– Super class for Hibernate data access objects.
– Requires a SessionFactory to be set, providing a
HibernateTemplate based on it to subclasses.
• JdoDaoSupport
– Super class for JDO data access objects.
– Requires a PersistenceManagerFactory to be set, providing a
JdoTemplate based on it to subclasses.
• SqlMapDaoSupport
– Supper class for iBATIS SqlMap data access object.
– Requires a DataSource to be set, providing a SqlMapTemplate

Spring DAO Templates
• Built in code templates that support JDBC, Hibernate, JDO, and
iBatis SQL Maps
• Simplifies data access coding by reducing redundant code and
helps avoid common errors.
• Alleviates opening and closing connections in your DAO code.
• No more ThreadLocal or passing Connection/Session objects.
• Transaction management is handled by a wired bean
• You are dropped into the template with the resources you need
for data access – Session, PreparedStatement, etc.
• Code only needs to be implemented in callback methods.
– doInXXX(Object)
• Optional separate JDBC framework

Ex: Code without a template
public class OrderHibernateDAO implements IOrderDAO {
public Order saveOrder(Order order) throws
OrderException{
Session s = null;
Transaction tx = null;
try{
s = ... // get a new Session object
tx = s.beginTransaction();
s.save(order);
tx.commit();
} catch (HibernateException he){
// log, rollback, and convert to OrderException
} catch (SQLException sqle){
// log, rollback, and convert to OrderException
} finally {
s.close(); // needs a try/catch block
}
return order;
}

Ex: Spring DAO Template Example
public class OrderHibernateDAO extends HibernateDaoSupport
implements IOrderDAO {
...
public Order saveOrder(final Order order) {
return (Order) getHibernateTemplate().execute(new
HibernateCallback() {
public Object doInHibernate(Session session)
throws HibernateException, SQLException {
session.save(order);
return order;
}
});
}
...
}

Ex 2: Spring DAO Template Example
public class OrderHibernateDAO extends
HibernateDaoSupport
implements IOrderDAO {
...
public List findOrdersByCustomerId(int id) {
return getHibernateTemplate()
.findByNamedQuery(“OrdersByCustomerID”,
new Integer(id));
}
public Order findOrderById(int orderId ) {
return (Order) getHibernateTemplate().load(
Order. class,
new Integer(orderId));
}
...
}

Consistent Exception Handling
• Spring has it’s own exception handling hierarchy for DAO logic.
• No more copy and pasting redundant exception logic!
• Exceptions from JDBC, or a supported ORM, are wrapped up
into an appropriate, and consistent, DataAccessException and
thrown.
• This allows you to decouple exceptions in your business logic.
• These exceptions are treated as unchecked exceptions that you
can handle in your business tier if needed. No need to try/catch
in your DAO.
• Define your own exception translation by subclassing classes
such as SQLErrorCodeSQLExceptionTranslator

Spring and Testing
• Easier test driven development (TDD)
• Integration testing
– Can use a standalone Spring configuration
with mock objects for testing.
– Consider XMLApplicationContext or
FileSystemApplicationContext.
• Unit testing
– Allows you to test outside the container
without using the Spring container.
• Easy to test POJOs

Struts Support
• ContextLoaderPlugin - Struts 1.1 PlugIn that
loads a Spring application context for the
Struts ActionServlet. This context will
automatically refer to the root
WebApplicationContext (loaded by
ContextLoaderListener/Servlet) as parent.
• ActionSupport and DispatchActionSupport
are pre-built convenience classes that
provide easy access to the context. These
classes alleviate the need to build custom
service locators.

Even More Spring Components
• JavaMail helpers
• Scheduling support via Quartz
• Convenience implementation classes for
– Remoting support – JAXRPC, RMI, Hessian, and Burlap
• EJB support for easier access.
• Acegi Security System for Spring
• http://acegisecurity.sourceforge.net/
• Very good framework!
• Eclipse Plugin – Spring IDE for Eclipse
• Coming soon
– JMS implementation classes
– JMX support

Future Trends and Predictions
• Traditional J2EE development with EJB will become more
POJO based with EJB 3.0
• Lightweight IoC container support will become more popular
• Future versions of J2EE will resemble frameworks like Spring
and Hibernate for business logic and persistence logic
respectively.
– EJB 3.0 ~ (Spring + Hibernate)
• AOP is gaining momentum as an alternative to providing
enterprise services
• Annotations will be helpful for applying AOP advice – J2SE 1.5
• IoC + AOP is a great non-invasive combination.
• Spring is already available today!
• If you are considering EJB 3.0 - Spring will make an easier
migration path

Demo
• Shows an end-to-end implementation using
Struts, Spring, and Hibernate.
• Demonstrates declarative transaction
management with POJOs using Spring
Aspect.
• Demonstrates working with a custom
Spring aspect for performance monitoring.
• DAO replacement Hibernate << >> JDBC
• Look at some code.

Resources
• Spring – www.springframework.org
• J2EE without EJB – Rod Johnson/ Jurgen
Hoeller
• Better, Faster, Lighter Java – Bruce Tate
• Wiring your Web Application with Open
Source Java
http://www.onjava.com/pub/a/onjava/2004/04/
07/wiringwebapps.html

Real World EJB Usage
• Stateless Session Beans (SLSBs)
– One of the easiest beans to program, but still want to
program with POJOs.
– Local interfaces alleviate remote interface performance
issues.
– Used as facades to other objects
– Allows developers to provide declarative transaction
management.
• Message Driven Beans (MDBs)
– Easy to program
– Provides asynchronous messaging
• Distributed Transaction Management
• RMI Remoting
• How do we get the benefits of EJB without using an
EJB container?

• More Architectural decisions…
– How do we achieve independent layers of code that can
provide clear separation, loose coupling, and allow
communication with each other?
– How can we design an architecture that can allow layer
replacement without affecting existing layers?
– What technologies, and frameworks, should be implemented
in each layer?
– How will we implement security?
– Will the application be flexible to technology changes?
– How will the application handle enterprise level services
such as transactions, security, logging, resource pooling,
profiling, etc?

More about the Service Layer
• Often tightly coupled with other layers
– Struts is not where you place business logic and persistence logic!
• The missing link IMHO in most applications today.
• EJB – SLSB, SFSB provide the common J2EE business layer
enterprise solutions for transactions within a container. What
about POJO?
• Hand code transaction logic with JTA
• Frameworks – Spring, Picocontainer, HiveMind, etc.
• Lighterweight containers use
– IoC/Dependency Injection
– AOP

• Where do we code business logic?
– Domain objects
• Heavy domain model / thin service layer approach
• Business logic is embedded in domain objects
• Takes advantage of OO programming
• Behavior rich domain model
– Service Layer
• Thin domain model / heavy service layer approach
• Wraps procedural business logic over domain objects
• Anti-pattern according to Fowler – ‘Anemic Domain
Model’
• Provides a separation of business logic concerns from
the domain model
• Treats the domain model as ORM objects

ClassPathXMLApplicationContext
• Usually used with a standalone application to
obtain a context
– Ex: Swing application
• Useful when performing integration testing
– In-container testing.
– Define a separate application context XML file that
contains mappings to your mock objects.

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