1. By Ru Shen Department of Computer Science UAlbany, 2008
Spring Framework
By Ru Shen
Department of Computer Science
UAlbany, 2008

2. Outline of the presentation
History of Spring
The framework
What is it good for?
Spring Inversion of Control
Spring Aspect Oriented Programming
My experience with Spring AOP
Installing Spring
References
Small assignment

3. A little bit of history Who Rod Johnson (Sydney University) When
Spring was started in Feb 2003.
What
Spring is an open source framework for building enterprise Java applications.

4. Overview of Spring framework
Picture excerpted from Manning – Spring in Action by Craig Walls and Ryan Breidenbach

5. Overview of Spring framework continued
The core container is the fundamental layer of the framework that provides Inversion of Control functionality.
Application context module extends the core modules by supplying many enterprise services such as JNDI access, remote access, multi-language support and scheduling.
AOP module provides rich support for aspect-oriented programming.

6. Overview of framework contintued
JDBC layer simplifies the process of database connection.
ORM module provides compatibility to existing framework such as Hibernate, JDO and TopLink.
Web module provides a context for web-based applications.
Spring comes with a full-featured MVC framework for building web applications.

7. What is Spring good for?
Allows you to build applications with Plain Old Java Objects (POJOs) containing only the business logic. vs EJB
The famous “Inversion of Control”.
Compatible with various ORM technology, such as TopLink and Hibernate.
Provides a testing framework that you can perform unit testing on.
Supports Aspect Oriented Programming.
Supports Model-View-Controller framework.

8. Spring IoC IoC stands for Inversion of Control
Hollywood Principle: “Don’t call me, I’ll call you.”
In a nutshell … inversion of control is about: the responsibility of coordinating collaboration between dependent objects is transferred away from the objects themselves. – Spring in Action

9. Traditional approach
In order to use object B, object A has to instantiate from Class B.
In order to use object C, object B has to instantiate from Class C.
Object A
Object B
Class B
Object C
Class C

10. Problem with traditional approach
Classes are tightly coupled
Hard to test: A← B, B← C
Hard to reuse
Hard to understand: cannot see the main flow
Hard to maintain: fixing one bug may result creating more new bugs
Utilizing interface will not solve the problem

11. Revised approach changes … <beans> <bean id=A class=A>
<property name=b>
<ref bean=B>
</property>
</bean>
<bean id=B class=B>
<property name=c>
<ref bean=C>
<bean id=C class=C/>
</beans>
Class A{
private BGroup b; …
Public void setBGroup(BGroup b){
this.b = b; }
Interface BGroup
Class B{
private CGroup c; …
Public void setCGroup(CGroup c){
this.c = c; }
Class B’
Class B’’
Interface CGroup
Class C
Class C’
Class C’’

12. Components of Spring IoC
IoC is practiced using Dependency Injection
Two forms of DI: Setter Injection and Constructor Injection
Code are decoupled with interface
Spring IoC Container is the platform
Bean factory produce beans
Configuration file defines beans and the main flow

13. Demonstrate Spring IoC
Bean factory is created with a single line of code
Beans are obtained from the bean factory
Picture excerpted from Manning – Spring in Action by Craig Walls and Ryan Breidenbach

14. Demonstrate Spring IoC continued
Picture excerpted from Manning – Spring in Action by Craig Walls and Ryan Breidenbach

15. Demonstrate Spring IoC continued
Things to notice:
Class implements interface
A setter method
Container calls the setter
What’s the impact:
Any class that implements “Knight” can be called at run time
Knight is GIVEN a quest rather than GETTING a quest
Picture excerpted from Manning – Spring in Action by Craig Walls and Ryan Breidenbach

16. Demonstrate Spring IoC continued
An example of Constructor Injection
Picture excerpted from Manning – Spring in Action by Craig Walls and Ryan Breidenbach

17. Summarize Spring IoC Decoupling with interface
Configuration file defines the rules
Objects are given rather than obtained
More options in the configuration file
Inheritance between the beans
Singleton or non-singleton
Abstract beans
The Spring container glues everything together

18. Spring AOP Aspect-Oriented Programming AOP complements OOP
Decompose programs into aspects (concerns)
An aspect crosscuts multiple programs
Common aspects:
Exception handling
Transaction management
Logging
Security checking

19. Aspect-Oriented Programming
Class A
Class B
Class C
Aspect 1 (logging)
Aspect 2 (security check)
Classes handle functional requirements
Use cases
Functions
Aspects handle non-functional requirements
Security
Logging
One aspect usually impacts multiple classes. It’s tedious to implement the aspect in each class.

20. AOP concepts Aspect Join point – A method invocation
Advice – Action to take at a join point
Point cut – A set of join points
Target – Object containing the join point
AOP proxy and advisor – Objects for weaving the above components together

21. Type of Advices in AOP Before advice After advice Around advice
Executed before a joint point.
After advice
Executed after a joint point completes.
Around advice
Most powerful one. Both before and after.
Throws advice
Before throwing an exception
After throwing an exception

22. Weave the components together
Advice
Point cut
Advisor + = +
A method of
Target =
Deploy it to the Spring container!
Proxy

23. My experience with Spring AOP
The purpose: exception handling
Background:
Java Enterprise Application on EJB
Backend Weblogic server
Front end Swing
Uniformed method for exception handling – prompt the formatted error messages to users

24. AOP continued … Vehicle management Driver management
Add vehicle / driver
Remove vehicle / driver
Update vehicle / driver
Search vehicle / driver
Management module
Vehicle management …
Driver management …
Scheduling module
Dispatch module
Report module

25. AOP continued
Without using AOP, each exception has to be handled individually, even though they are handled in the same way.
With AOP, we don’t handle exceptions in individual classes. We just throw them. One advice is sufficient to handle a group of exceptions.

26. AOP continued Spring embedded AOP objects ThrowsAdvice
RegexpMethodPointcutAdvisor
ProxyFactoryBean
MyVehicleProxy
ThrowsAdvice
Pointcut Regular expression pattern
Vehicle management bean
MyAdvice
ProxyFactoryBean
RegexpMethodPointcutAdvisor
MyAdvisor

27. Summarize Spring AOP
Embedded objects to facilitate AOP implementation, runtime
Works for Spring beans only – vehicle management bean has to be deployed in the container
More things to explore with beforeAdvice, afterAdvice and aroundAdvice

28. Install Spring
1. Download Spring framework from
2. Include the downloaded spring.jar in your $CLASSPATH.
Maybe you need to download apache commons logging package: commons-logging-1.1.jar. It is used internally by Spring.
3. Write your first configuration file.
4. Create bean factory by specifying the location of the configuration file.
5. Refer each class through their bean name
6. Start writing your Java classes.

29. Reference Introduction by Rod Johnson on The Server Side
Manning – Spring in Action
Spring reference documentation

30. A small assignment
Using Spring, write a simple program that prints the configuration of different brands of cars. Define Car as an interface. Try printing the configuration of different brands of cars by writing different implementation of Car. Modify the configuration file at runtime to switch between the cars every time and see the output.