Lightweight Development Strategies JavaZone, Olso 2005

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Lightweight Development StrategiesJavaZone, Olso
2005

• Bruce A. Tate
• http//www.springframework.com
• bruce.tate_at_j2life.com

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Agenda

• Introduction
• Process
• POJO programming frameworks
• Inversion of control (not just DI)
• Conclusion

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Progress report

• Introduction
• Process
• POJO programming frameworks
• Inversion of control (not just DI)
• Conclusion

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About Me

• Author 6 books
• Better, Faster, Lighter Java
• Bitter Java, Bitter EJB
• Spring Developer Notebook
• Beyond Java due this Summer
• Independent consultant, author, speaker
• Founder and president of J2Life, LLC
• Customers include FedEx, Great West Life, IHS,
  many others
• Worked for IBM for 13 years
• Database lab
• Object infrastructure lab
• Java consulting

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Motivation

• Java development must get
• Simpler
• More reliable
• More efficient
• Or it will die!

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Java is bloating

• Pressure to add
• With no counterbalance
• Pressure from industry
• Big money creates massive frameworks
• To solve massive problems
• And sells them to the mainstream
• Misuse
• Massive frameworks for simple problems

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How will you respond?

• Do nothing
• Pick a new language or environment
• Pick a new development paradigm
• Let your vendor shield you from complexity
• Simplify
• The subject of this talk

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Progress report

• Introduction
• Process
• POJO programming frameworks
• Inversion of control (not just DI)
• Conclusion

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Which process?

• Pick a couple of principles
• And follow them
• And call it whatever you want to

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Emphasis (in order) on

• Small, smart teams
• Good feedback from customers
• Quality
• Simple requirements management
• Simplicity
• Refactoring
• Automated unit testing

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Agile Development Perception

• Managers often fear agile processes
• Perception is lack of discipline

Agile development (XP, Scrum)
Formal OO development (RUP)

• Like, just wing it, dude!

• Design artifacts
• Early design
• Meticulous requirement

Discipline
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Agile Development

• Agile development is disciplined
• It draws discipline from another source

Agile development (XP, Scrum)
Formal OO development (RUP)

• Automated testing
• Continuous integration
• Refactoring emphasis
• On site customer

• Design artifacts
• Early design
• Meticulous requirement

Discipline
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Principles Getting started

• Dont sell a process sell principles.
• Simplicity
• Continuous refactoring and integration
• Automated tests, code tests first
• Small teams with access to customer

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Progress report

• Introduction
• Process
• POJO programming frameworks
• Inversion of control (not just DI)
• Conclusion

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POJO programming

• Stretching Java!
• Adding services
• Interceptors
• AOP
• Proxies
• Dependency injection
• Loosen coupling
• Multiple configurations of components

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Concepts dependency injection

• Old ways
• Hard wiring
• service new service()
• Limiting relies on tight coupling
• Lookup
• Application.register(service, serviceName)
• client.lookup(serviceName)
• Traditional J2EE way.
• Loosens coupling but does not break it

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Concepts dependency injection

• The parts a service, a consumer, and a container
• Wrap the service in an interface
• Provide a property in the consumer
• Type the services interface
• Let the container manage life cycles
• The container is responsible for setting the
  property in the consumer

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Setter-based injection example

• Load context
• Instantiates beans
• Configures simple properties
• Resolves dependencies

MyDataSource
Configuration File Beans Name
MyDataSource URL host/ProductDatabase
UserID batate Password pass
Name PetStoreDao Datasource
MyDataSource Version 4.7
URL host/ProductDatabase UserID
batate Password pass
PetStoreDao
Version 4.7
Datasource MyDataSource
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What is AOP?

• AOP seeks to get crosscutting concerns
• Away from main-line code
• To develop AOP code
• You build your main-line logic
• You code independent services
• And weave them together with configuration
• Advantages
• Full transparency to services
• Isolated aspects (often pre-defined)
• Disadvantages? Immature

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The core problem
Method body Exceptions
Security
Security
Open transaction
Open transaction
Mainline logic
Method Client
Commit transaction
Roll back
Commit transaction
Roll back
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Active strategies

• AOP
• Code generation
• Example EJB 2.x
• Byte code enhancement/injection
• Run time dynamic proxies
• Hibernate, Spring, Hive Mind, etc
• Compile time byte code injection step
• JDO, AspectJ, obfuscators
• Source level metadata
• Can be both active and passive
• In Java 5 annotations
• In XDoclet tags

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Passive strategies

• Reflection
• Deal with an object via its primitive parts
• Deal with methods, attributes generically
• Combine with other techniques
• Example Hibernate

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Java limitations

• How do you express configuration
• For dependency injection?
• For AOP?
• For reflection (specify methods, sigs, etc)
• In Java or XML?
• Metaprogramming in Java?

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Progress report

• Introduction
• Process
• POJO programming frameworks
• Inversion of control (not just DI)
• Conclusion

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Inversion of control

• Javas customization is outside first
• while(iltlength)
• row customLibrary()
• Certain problems require inside out customization
• Iteration
• JDBC

Custom code
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Typical JDBC
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Example from jPetStore

• Get a list of pet types (Strings)
• JdbcTemplate template new JdbcTemplate(dataSourc
  e)
• final List names new LinkedList()
• template.query("SELECT id,name FROM types ORDER
  BY name",
• new RowCallbackHandler(
  )
• public void
  processRow(ResultSet rs)
• throws
  SQLException
• 
  names.add(rs.getString(1))
• )

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What is a continuation?

• The rest of the program
• A frozen point in time
• A copy of the call stack
• With local variable values
• And current point of execution

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Continuation server

• Back button
• Threading
• Inversion of control

Server
Application
Request
Request
Request
Request
Query
Query
Query
Browser
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A brief demo

• Seaside
• Developed by Avi Bryant
• In a language called Squeak
• A derivative of Smalltalk

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Solution in Java

• Spring WebFlow
• Implement a state machine
• Specify a machine using Web Flow rules
• Nodes are pages or methods
• Transition on events (failure, success, etc)
• Store a state in a dictionary like a continuation
• Rife
• Implements native Java continuations
• Watch class loader, get stack
• Compute offset to current line of code
• Do byte code injection to insert stack
• Skip to current line of code
• Force all instance variables to implement
  Clonable
• Cocoon 2
• Implement Java on Rhino (JavaScript engines)
• Use custom code to implement continuations in
  Rhino

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Language limitations

• Java needs code blocks!
• Closures are important parts of other languages
• They are more useful with dynamic typing
• Continuations are important

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Progress Report

• Introduction
• Philosophies
• Process
• Technologies
• Conclusion

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Predictions

• Spring replaces EJB
• EJB will struggle
• Again
• Theyre late
• Both annotations and AOP will get us into
  trouble, in spots
• Java meta-programming increases
• Moving more people to dynamic languages
• REST will slowly subsume WebServices
• Except maybe SOAP
• One dynamic language explodes (Ruby?)

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Resources

• Quick starts and philosophy books
• Better, Faster, Lighter Java by Tate, Gehtland
• Spring Developer Notebook by Tate, Gehtland
• Make sure you get the reprint
• Hibernate Developer Notebook by Elliot
• References
• Pro Spring
• Hibernate in Action
• REST tutorial http//www.xfront.com/REST.html
• Spring Good article http//www.sys-con.com/story/
  print.cfm?storyid47735
• Lightweight development series on DeveloperWorks