Spring Power to the POJO Introductie tot het Spring Framework

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Spring Power to the POJOIntroductie tot het
Spring Framework

• Aino Andriessen Lucas Jellema
• KC Web Java, donderdag 30 juni 2005

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Agenda

• Introductie Spring History, Background
• Hoe kom je aan nieuwe objecten
• BeanFactory en Inversion of Control Dependency
  Injection
• Hoe laat je bestaande objecten naar je pijpen
  dansen?
• Aspect Oriented Programming (AOP)
• Business Tier Architectuur
• Test Driven Development
• Spring Persistence Spring DAO
• Spring Remoting
• Losse eindjes, conclusies, discussie
• Workshop

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Where weve come from

• EJB as we know it
• Resembles the original JavaBeans specification in
  name only.
• Heavyweight
• Requires application server
• Difficult to unit-test
• Intrusive (must implement EJB interfaces)
• Complex
• Home/Remote/Local/LocalHome interfaces
• Deployment descriptors
• Non-intuitive

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The future of EJB

• Spilling the beans
• EJB 3.0 will embrace simplicity
• Based on POJO/POJI (? Well, maybe)
• Employ dependency injection instead of LDAP
• Declarative services (transactions, security)
  will be aspects
• Entity beans will be POJOs, persisted via
  Hibernate-like framework

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The future is NOW!

• Spring is a lightweight container framework
• Build applications based on POJO/POJI.
• Wire beans together using dependency injection.
• Declaratively apply transactions and security
  using aspect.
• Integrates cleanly with Hibernate for
  persistence.
• EJB 3.0Spring Hibernate Metadata

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Spring History

• J2EE Design and Development by Rod Johnson,
  2002
• Introducing the i21 framework
• First release of Spring Spring 2004
• Spring 1.2.1 June 2005
• Open Source
• Interface21 small company with most core
  committers
• Contributions from Oracle and otherparties
• Spawned many sub-projects

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Power to the POJO
AOP
Consistent Service Abstractions (Template Pattern)
IoC (Dependency Injection)
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Springs modules
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Whats more

• Remoting support via RMI, JAX-RPC, and
  Hessian/Burlap
• Metadata (ala, JSR-175 or Commons Attributes)
• Persistence via TopLink, Hibernate, JDO, or
  iBatis support
• E-mail support
• EJB support
• JMX Support (Spring 1.1)
• JMS support
• Spring Rich Client Platform (Spring 1.1)
• Spring .Net

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Spring is HOT!
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Many books available

• J2EE without EJB
• The starting point
• Spring Live
• Pro Spring
• Spring in Action
• Professional Spring Development
• To be released, july 2005

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Core SpringInversion of Control Dependency
Injection
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Coupling

• Highly coupled code is
• Hard to test
• Hard to maintain
• Exhibits whack-a-mole style bugs
• Uncoupled code is
• Code that doesnt do anything
• Coupling is somewhat necessary
• but should be controlled

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Dependency Injection

• The Hollywood Principle Dont call me, Ill
  call you.
• Collaborators arent asked fortheyre received.
• Also known as Dependency Injection, thanks to
  Martin Fowler.

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Benefits of IoC

• Objects are more cohesive because they are no
  longer responsible for obtaining their own
  collaborators.
• When used with interfaces, code is very loosely
  coupled.

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Elements of a Spring app

• Beans
• Not EJBs. Actually, not necessarily JavaBeans.
  Just POJOs
• Bean wiring
• Typically an XML file.
• A bootstrap class
• A class with a main() method.
• A servlet.
• The bootstrap class uses a BeanFactory (or IoC
  Container) to retrieve POJOs
• That have been wired and dependency injected

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IoC Container in ActionApplication Class needs
POJOs
POJO 2
IoC Container
POJO 1
POJO 3
xml
pojo 1
pojo 2
getBean(POJO1)
pojo 3
Application
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Wiring beans in XML

• Root elements is ltbeansgt
• Contains one or more ltbeangt elements
• id (or name) attribute to identify bean
• class attribute to specify class

The beans ID
ltbeansgt ltbean idfoo classcom.habuma.f
oobar.Foogt lt!-- Properties defined here --gt
lt/beangt lt/beansgt
The beans fully- qualified classname
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Wiring a property

• Use ltpropertygt element
• name attribute specifies name of property

ltbeansgt ltbean idfoo classcom.habuma.f
oobar.Foogt ltproperty namebargt lt!--
Property value goes here --gt lt/propertygt
lt/beangt lt/beansgt
Maps to a setBar() call
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Property values

• Strings and numbers
• Null
• Lists and arrays

ltproperty namebargtltvaluegt42lt/valuegtlt/propertygt
ltproperty namebargtltvaluegtHellolt/valuegtlt/propert
ygt
ltproperty namebargtltnull/gtlt/propertygt
ltproperty namebargt ltlistgt
ltvaluegtABClt/valuegt ltvaluegt123lt/valuegt
lt/listgt lt/propertygt
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Property values

• Sets
• Maps

ltproperty namebargt ltsetgt
ltvaluegtABClt/valuegt ltvaluegt123lt/valuegt
lt/setgt lt/propertygt
ltproperty namebargt ltmapgt ltentry
keykey1gtltvaluegtABClt/valuegtlt/entrygt ltentry
keykey2gtltvaluegt123lt/valuegtlt/entrygt
lt/setgt lt/propertygt
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Property values

• Property sets
• Other beans

ltproperty namebargt ltpropsgt ltprop
keyprop1gtABClt/propgt ltprop
keyprop2gt123lt/propgt lt/setgt lt/propertygt
ltproperty namebargt ltref beanbar/gt lt/proper
tygt
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Auto-wiring

• You can auto-wire
• byName Property names are matched to bean
  names
• byType Property names are matched to bean
  types
• constructor Pico-like constructor wiring. Like
  byType except using constructor.
• autodetect Uses reflection to decide whether
  to use byType or constructor

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Auto-wiring
ltbean idfoo classcom.habuma.foobar.Foo
autowirebyName/gt
ltbean idfoo classcom.habuma.foobar.Foo
autowirebyNamegt ltproperty
namebargtltvaluegtbarlt/valuegtlt/propertygt lt/beangt
ltbeans default-autowirebyTypegt lt!-- Bean
definitions go here --gt lt/beansgt
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BeanFactory vs. ApplicationContext

• A BeanFactory is the Spring container.
• Loads beans and wires beans together.
• Dispenses beans as requested.
• XmlBeanFactory is the most commonly used.
• An ApplicationContext is a BeanFactory, but adds
  framework features such as
• I18N messages
• Event notification

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IoC Examples
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Example of a IoC based programming
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The knight before
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The knight after
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Core SpringAspect Oriented Programming

• AOP a programming technique that promotes
  separation of concerns within a software system
• Recurring often infrastructural concerns can
  easily be duplicatedin many objects
• Security
• Transaction Management
• Logging
• Profiling
• AOP suggestsseparation
• Concerns are appliedat compile or run-time

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AOP in a nutshell

• Aspect A modularization of a cross-cutting
  concern. Implemented in Spring as Advisors or
  interceptors
• Joinpoint Point during the execution of
  execution.
• Advice Action taken at a particular joinpoint.
• Pointcut A set of joinpoints specifying where
  advice should be applied.
• Advisor Fully represents an aspect, including
  both advice and a pointcut.
• Introduction Adding methods or fields to an
  advised class.
• Weaving Assembling aspects into advised objects.

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Without AOP
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With AOP
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Implementing AOP

• Compile time modify the source code during
  compilation
• Requires a customized Java Compiler
• For example AspectJ Spring does not do compile
  time AOP
• Run time byte injection
• Change the class when loaded, generating a
  subclass that contains the aspects
• Uses CGLib library
• Run time using the JDK 1.3 Dynamic Proxy
• Instead of getting an object instance, the
  application receives a proxy object
• The proxy implements the same interface
• And maybe something else as well
• Besides, it can intercept and wrap method calls

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IoC Container hides AOP implementation from POJO
consumer
Aspect A invoke()
Proxy
Pojo1Impl
xml
target
Aspect B before()
targetpojo1Impl
IoC Container
implements

• pojo1 proxy
• Target
• interceptorNames
• gt AspectA, AspectB

implements
POJO 1(interface)
getBean(POJO1)
Application
AspectA
AspectB
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Different types of Advice

• Before advice
• Calls to advised methods are intercepted before
  the method is called.
• After returning advice
• Calls to advised methods are intercepted after a
  successful return.
• After throws advice
• Calls to advised methods are intercepted after an
  exception is thrown.
• Around advice/interception
• Calls to advised methods are intercepted. Call
  must be explicitly made to target method.
• Introduction advice
• Allows a class (or rather its proxy) to implement
  additional interfaces
• Calls to methods are interceptedeven when the
  target bean doesnt have the method!
• Actually, just a special case of around advice

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Creating Advise

• Create a class that implements one or more of the
  Spring AOP interfaces
• MethodInterceptor
• BeforeAdvice
• AfterReturningAdvice
• ThrowsAdvice
• Implement the interface method
• before (Method method, Object args)
• afterReturning(Object returnValue, Method method,
  Object args)
• invoke(MethodInvocation invocation)

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Defining Pointcuts in Spring(specify where to
apply which Advice)

• Programmatically
• No BeanFactory required
• Can be used independently of the rest of Spring
• Declaratively
• In the bean container configuration file
  (applicationContext.xml)

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Applications of AOP by Spring itselfalways in
conjunction with IoC/DI

• Remoting Support
• Proxy references a remote object
• Transaction Management
• Service method is wrapped in around advice that
  opens and closes the transaction
• Security
• JMX
• Proxy implements the MBean interfaces for its
  target object
• Mock Testing
• Tested objects are injected with Mock objects
  that are dynamically created (made up)

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AOP through Proxy
Proxy
EmployeeImpl
Employee
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Future of AOP according to Rod Johnson

• Programming Aspects and composing an Application
  from Aspects will become widely accepted
• Various orthogonal concerns can be dealt with in
  parallel
• Maintaining a single cross application concern
  is done by maintaining a single aspect
• Tool and Runtime support for AOP will further
  increase
• Development of IBM WebSphere WSAD is heavily
  done in an AOP fashion

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Springs recommended Application Guidelines and
Architecture

• Program against interfaces
• For example Service Interface, DAO Interfaces
• Typically no interfaces for Domain Classes
• No configuration plumbing in your classes
• Have configuration details injected
• Domain Classes are used through all tiers
• No Struts ActionForms to wrap domain classes
• Controllers use Business Service methods to
  create or manipulate Domain Objects
• Practice Test driven development

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Springs recommended architecture
Presentation Tier
View Components Generate HTML or PDF
Remote Service Exporters Using SOAP, RMI, JAX-RPC
etc.
Web Tier Actions (Controllers)
Business Tier
Business Services Layer Interfaces and Container
Managed Implementations
Data Tier
DAO Interface Layer Interfaces, independent of
implementing DAO Technology
Persistent DomainObjects
DAO Implementation layer Retrieves, saves
entities using ORM tool or JDBC
O/R Mapping Layer
JDBC
JDBC
RDBMS
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Spring and Test Driven Development

• Agile Software Engineering methods, such as XP
• First design and develop a test based on
  interfaces
• Before implementing the interfaces
• Before starting to resolve a bug
• Automated Unit Testing for every class in the
  application
• At every stage of development, the test can be
  rerun!
• Unit Testing usually based on JUnit
• Great integration in Eclipse and JDeveloper
  10.1.3 (10.1.2 is somewhat sparse)

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Spring and Test Driven Development

• Challenges include
• Container Dependencies (HttpServlet object)
• Dependencies on external objects (not a unit
  test)
• Especially objects that are hard to configure,
  e.g. DAO Impl
• Dependencies on objects that have not yet been
  implemented

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Spring support for Test Driven Development

• When all objects (Service and DAO Impl) are
  Spring Beans
• They get dependency injected by the container
• During a test, instead of injecting them with
  real objects
• We can inject them with Mock Objects, that will
  return the values we specify when called
• The real objects do not need to exist
• even when they do exist, using mock objects
  ensures we are performing a true UNIT test

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Unit Testing HrmServiceImpl using Mock objects
Unit Test
MockEmployeeDAOImpl
HrmServiceTest (JUnit TestCase)
Business Tier
HrmServiceImpl
Data Tier
EmployeeDAO Interfaces, independent of
implementing DAO Technology
Persistent DomainObjects
EmployeeDAOImpl (does not yet exist)
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Properly implementing those Mock DAO objects

• (Aino)

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Spring and Web ApplicationsStruts and other
Controller Frameworks

• Struts support
• Auto-Load WebContext ( BeanFactory) in session
• Make Action Classes Spring aware and have them
  reference the WebContext
• Proxy Action Classes and Dependency Inject them
• Register Actions as Spring Beans
• Similar support for
• WebWork
• Tapestry

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Spring and Web ApplicationsJava Server Faces

• Java Server Faces
• JSF has managed-beans
• Very similar to Spring Beans
• Though no support for AOP
• And do you want low level, persistency related
  configuration details in the faces-config.xml
• JSF-Spring project offers a JSF variable resolver
• It takes bean references in faces-config.xml and
  tries to resolve them in Spring context files

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Spring and Web ApplicationsSpring MVC Controller
Framework

• Positioned to replace Struts
• Better, more intuitive, modern architecture
• Full benefits from IoC and AOP
• Works with (these are all Spring Beans)
• Controllers that process the request, update
  and prepare the Model they also return a result,
  a symbolic indication of the ModelView to proceed
  to
• ViewResolvers that decide which View to let
  render
• ViewBeans thatwrap View Componentssuch as
  JSP, Velocity Template, FreeMarker page

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Spring MVC Controller FrameworkSupport for
various View technologies

• JSP using the Spring tag-library (very small,
  primarily use JSTL)
• FreeMarker
• Velocity
• Tiles
• File Download
• Excel using Apache POI
• PDF using iText
• XSL-T
• JasperReports

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Spring RemoteSupport for distributed applications

• Springs number one concept concerning remote,
  distributed objects (take from Martin Fowler)
• Do NOT distribute!!!
• However, in certain circumstances you probably
  have to
• Cross organizational boundaries
• Rich Clients
• Remote process accessing back-end server

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Springs Remote Façade Philosphy

• Remote access
• for example supporting remote clients over RMI or
  publishing a WebService
• should be regarded as an alternative presentation
  layer
• no different from an standard Browser oriented
  HTML interface
• On well-defined middle tier service interfaces
• that are blissfully unaware that they are exposed
  and consumed remotely
• Remoting infrastructure for example Data
  Transfer Objects should be added on top of the
  well defined, OO, fully POJO based service

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Spring support for remoting

• Spring will
• Declaratively expose Service interfaces for
  remote clients
• Declaratively expose remote Service interfaces
  for local clients
• Support for these protocols
• RMI
• Cauchos Hessian and Burlap
• Springs own HttpInvoker
• EJB
• SOAP (based on JAX-RPC, using AXIS or XFire)

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Exposing Service to remote clients
ClientCode
Proxy for Service (generated by BeanFactory)
Service Interface
Spring Exporter
Service Implementation
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Spring Exporters

• Declaratively set up in the configuration file
• Using a specific protocol
• Spring Service Exporter
• defines an End Point where the Service can be
  invoked
• typically linked to a port
• translates incoming remote calls to local calls
• unmarshalling parameter values
• marshalling return values and exceptions
• Spring Exporter often works with Spring Remote
  Client

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Details from Server and Client side
BeanConfiguration files

• Server Side HttpInvoker Protocol Exporter
• Client Side HttpInvoker Protocol proxy creator

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Extra Features

• JMX proxy Spring Beans to register them as
  MBeans
• JMS
• Email
• JNDI
• Scheduling (Quartz)
• Transaction Management

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Spring and the Oracle Java Technology Stack

• Spring DAO has TopLink support
• Since Spring 2005, contributed by Oracle
• Spring based POJO business service can be
  registered with ADF Binding Framework
• Ideally we can have the registration mechanism
  honor the ApplicationContext origin of the
  Service Object
• Spring DAO for ADF BC seems pointless
• Spring MVC on ADF BC Business Service could be
  done
• though a lot of the natural benefits are lost
• UIX could be used with Spring MVC as View
  technology
• Spring Remoting can be used to publish and
  consume
• Somewhat overlapping with JDeveloper WebServices
  support
• Spring AOP could be applied to ADF BC objects
• If we can find the right hook

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Spring and AMIS

• Spring concepts
• Programming against Interfaces
• Strong Domain Model
• DAO Interfaces
• Service methods to bundle Use Case DAO
  interactions
• Test Driven Development
• Spring DAO and Persistence when we are dealing
  with Hibernate, JDBC and maybe TopLink
• Spring Remoting, especially when WebService
  support in JDeveloper falls short
• For example with RMI or EJB (if we have to)
• Spring IoC and Dependency Injection
• Very interesting concepts
• Gradually introduce within Business Service

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Spring and AMIS

• Spring AOP
• AOP has many applications
• Especially for POJO provided by Spring
  BeanFactory
• Lets keep a very open mind for using (Spring)
  AOP
• Spring toolbox
• Scheduling
• Email
• JMX
• JMS
• PDF, Excel, JasperReports

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Sub Projects and initiatives around Spring

• Spring Security
• Spring IDE (for Eclipse)
• Spring Rich Client
• Spring Modules Spring WebFlow
• Spring BeanDoc
• Spring .NET by Rod Johnson et. al.
• Focus on C
• JSF-Spring
• XDoclet Spring Bean Configuration generator
• Aurora MVC Framework
• More support for Persistency OO/R Frameworks
• EJB 3.0