Lightweight J2EE Architecture

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Lightweight J2EEArchitecture
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Introduction

• eSage Group
• Consulting company specializing in agile project
  management system architecture and development
• Mike Porter
• Co-founder and System Architect
• mike_at_esagegroup.com
• Charlie Morss
• System Architect
• charlie_at_esagegroup.com

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Overview

• Review current state of J2EE
• Lightweight Frameworks and what they can do
• Todays Frameworks
• Spring
• Hibernate
• Spring and Hibernate Integration
• Demos along the way
• Review

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Current J2EE State

• J2EE has done a great deal to standardize our
  industry
• These J2EE services are tremendously successful
  with wide adoption
• JDBC
• Servlet/JSP/WAR
• JNDI
• JMS
• Useful EJB Services
• Declarative transactions support
• Persistence
• Security
• Distributed component model
• Instance pooling and caching

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Genesis of EJB

• 1998 Distributed Computing was the big buzz-word
• Sun made EJBs remote to compete with technologies
  like CORBA
• The specification was intrusive
• And we have been dealing with these decisions
  ever since
• Lets take a look at the Sun Best practices.

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Uhh we have a problem here
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EJB Issues

• Intrusive Noisy
• Must be an EJBObject
• Must run within the container
• Rapid iterative code/debug/test cycles difficult
• If the Sun Pet Store is the best, were in
  trouble
• Too many different patterns
• Performs poorly
• Reliance on Entity Beans
• Too many different files needed to do simple
  things

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Treating the Symptoms

• Tools exist to make EJB development easier
• XDoclet
• IDE Wizards
• Cactus
• Work-a-rounds
• Data Transfer Objects (DTOs)
• Service Locator

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The Way Ahead

• Development teams need a better frameworks that
  supports these ideas
• Implementing business requirements first
• Simplicity
• Productivity
• Testability
• Object Orientation
• Lightweight Frameworks can get us there

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What are Lightweight Frameworks?

• Non-intrusive
• No container requirements
• Simplify Application Development
• Remove re-occurring pattern code
• Productivity friendly
• Unit test friendly
• Very Pluggable
• Usually Open Source

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Leading Lightweight Frameworks

• Spring, Pico, Hivemind
• Hibernate, IBatis, Castor
• WebWork
• Quartz
• Sitemesh
• JBoss is NOT a lightweight framework

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Spring
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Spring is in the Air

• Spring is a glue framework that ties many
  frameworks together in a consistent way
• Inversion of Control Framework (Dependency
  Injection)
• Dont call us well call you
• Service Injection rather than Service Lookup
• Encourages programming to Interfaces
• Reduces coupling between components
• Supports Testing
• Configuration
• Supports externalizing the configuration
• And more

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Spring Modules

• Core IoC container
• Application context module
• AOP module
• JDBC abstraction and DAO module
• Object/relational mapping integration module
• Web module
• MVC module
• Quartz, Email, WebServices Integration and more.

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Why use IoC?
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IoC Example

• Review Attached Spring DataSource IoC Example

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IoC Types

• Three basic types
• Type I
• Interface Injection
• Your service or component implement a specific
  interface
• Much like EJBs
• Type II
• Method Injection
• Dependent objects are provided to the object by
  methods
• Based on JavaBeans constructs
• Ordering of method calls may not be achievable
• Type III
• Constructor Injection
• Dependent objects are provided to the object by
  constructors
• Large constructor argument lists

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AOP Introduction

• AOP Aspect Oriented Programming
• Separates concerns of an object into their own
  aspects
• Helps to remove infrastructure code from the
  application
• AOP can remove replicated code that is scattered
  across an entire system
• Used to apply cross-cutting concerns uniformly to
  objects.
• Logging
• Security
• Transaction Management

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AOP Crosscutting

• Without AOP

• With AOP

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AOP Definitions

• Aspect - An application wide concern that is
  often duplicated in many classes, that could be
  implemented before, after, or upon failure across
  a group of methods.
• JointPoint - A join of methods across which an
  aspect can be implemented.
• Spring allows method interception. This means
  when a method is called the framework can attach
  functionality.
• Pointcut - Description of the collection of
  methods for which advice is to be applied
• Introduction - Adding methods or properties to a
  class with advice.
• AOP Proxies - Surrogate object that invokes
  advice and advises the invoked class

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AOP Example

• Spring AOP Code Example

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Spring Tips and Tricks

• Start with just the IoC and build from there
• Be careful with the autowire changes in
  Interfaces and refactoring can change autowire
  rules
• AOP supports proxying of classes via interface
  and via CGLib
• Interfaces are recommended to reduce coupling
• CGLib is available to support legacy code or 3rd
  party code
• Methods marked as final can not be advised
• Dynamic Pointcuts (ControlFlowPointcuts) can be
  slow so try to avoid them
• Avoid applying Advise to fine grained objects
• Use autoproxing when you want system wide advice

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Break Time?
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Hibernate
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Why ORM?

• Productivity
• Shield developers from messy SQL
• Maintainability
• Fewer lines of typically redundant code
• Performant
• Good ORM Solutions can perform better
  alternatives
• Program to the Business Domain rather than to the
  Data Model
• Domain Objects with encapsulated behavior
• Support for Natural Object Navigation

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What is Hibernate

• A high performing ORM framework
• Community driven distilled over years
• Persistent Classes are POJOs
• Easier to write and refactor
• Can be serialized
• Can execute outside a container (TEST TEST TEST)
• Hibernate 3 is the model for EJB3
• The core to JBoss EJB3

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Why Use Hibernate

• Reduces code
• SQL Mapping Localized
• Easy programming model (POJO)
• Performant
• Advanced Cache Strategy
• Transparent Write-Behind
• Optimized SQL-Never updates clean data
• Lazy and Eager Association fetching strategies
• Supports Vendor Abstraction and Independence
• Container and DB

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Hibernate Features

• Supports fine grained object mapping. IE A
  Customer can be composed of Address Objects
• True Polymorphic Associations and Mapping
• Three types of Inheritance Mapping Strategies
• Rich relationship types one-to-one, one-to-many,
  many-to-many, etc
• Detached Objects No more DTOs
• Full JTA Support
• Excellent Spring Integration

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Querying in Hibernate

• HQL - Hibernate Query Language
• SQL-esque but Object Oriented
• Understands inheritance, polymorphism,
  association
• Criteria API
• Build a set of objects which represent your query
• Also supports query by example
• Both support limit queries
• setFirstResults() and setMaxResults() methods
  exist on Criteria and Query (HQL)

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Hibernate Examples

• Review Attached Hibernate Example

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Hibernate Tips

• Turn on SQL logging
• hibernate.show_sql true
• Set lazytrue for most collections (default value
  is true)
• Eager Fetching of a query does not result in a
  distinct list
• return new HashSet(originalResults)
• Cache your entities, and make sure to apply the
  cache settings to their association mappings as
  well (set, map, bag, list)
• Be aware of Cascade Deletes
• We have only had limited success with this
  feature
• Understand the First Level Cache
• Read Hibernate in Action

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Hibernate Tips Cont

• Implement the equals() and hashCode() methods
• Use the natural key, not the object Id
• Alternatively use a GUID initialized at object
  creation
• Must be used in conjunction with the ltversiongt
  unsaved-value attribute
• ltversion name"version" column"VERSION"
  unsaved-valuenull" /gt

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Spring Hibernate Integration
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Spring Hibernate Integration

• HibernateTemplate
• Many convenience methods
• Use is restricted to unchecked exceptions
• Uses anonymous inner class callbacks
• Hibernate AOP
• Any exception types can be thrown within the data
  access code
• DAO must extend HibernateDAOSupport
• Very clean DAO methods

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Spring Transactions

• Clear application layering supporting most data
  access and transaction technologies
• Not bound to a container
• Transactions can either be managed
  programmatically or declarative using AOP
• TransactionTemplate
• Allows execution of transactional code without
  the need to re-implement transaction workflows
  (Exception Handling)
• Triggers a rollback if the callback throws a
  runtime exception or if it sets the transaction
  to rollback-only
• TransactionInterceptor
• Business object does not need to be transaction
  aware (similar to EJB)
• Check and unchecked exceptions supported
• Default rollback behavior is to rollback on
  runtime exceptions but this can be configured

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Spring Hibernate Integration Examples

• Spring Hibernate Code Example

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Questions???

• Questions and Comments?

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References

• Jason Careiras Blog
• www.jroller.com/page/jcarreira/20041215
• Hibernate in Action
• Gavin King and Christian Bauer
• J2EE Development without EJB
• Rod Johnson
• Spring in Action
• Craig Walls and Ryan Breidenbach