Java Data Objects Write Once Persist Everywhere

1
Java Data ObjectsWrite Once - Persist
Everywhere!

• Robin M. Roos
• Principal Consultant
• Ogilvie Partners
• www.OgilviePartners.com

2
Introduction

• Robin Roos (Robin_at_OgilviePartners.com)
• Using Java since 1997
• Sun certified
• Programmer, Developer, Architect, WCD
• Java instructor architecture consultant
• Member of JDO Expert Group (JSR12)
• Training course JDO Book

3
Background

• JDO Specification...
• Transparent Persistence for Java Objects
• Café June 1999
• Participant Review May 2000
• Public Review July 2000
• 1st Proposed Final Draft May 2001
• Standardized March 2002

4
Acknowledgements

• Java
• is a Trade Mark of Sun Microsystems
• JDOQL
• The Query examples are taken from the JDO
  Specification
• JDO
• would not have happened without the efforts of
  the JDO Expert Group

5
Agenda

• Part 1 JDO - Write Once, Persist Anywhere
• 1. Overview
• 2. JDO Architecture
• 3. JDO Instance Lifecycle
• 4. Persistent Object Model
• 5. Primary Interfaces and Classes
• 6. Queries with JDOQL

6
WARNING

• This presentation contains Java and XML

7
Persistence Overview

• Object-Relational Mapping
• Most Java application objects need to be
  persisted
• Object/Relational impedance mismatch
• Until now, JDBC programming used to map between
  rows/columns and object properties
• JDBC must be crafted by an SQL expert
• Resulting objects restricted to Relational
  persistence

8
UML for JDBC Example
9
JDBC Pros and Cons

• Advantages
• Application works with any JDBC-compliant
  database
• Can adapt to existing Customer table structure

• Disadvantages
• Only JDBC-compliant (Relational) databases
• Must write persistence infrastructure taking
  resource away from application logic.
• Need SQL expertise
• SQL not always portable

10
Java Data Objects

• Specification for Transparent Persistence
• Abstract API for persistence services
• Influenced by ODMG and Forté for Java
• Supported by many vendors
• Program to the standard API
• Select a compliant implementation based on
  quality of service

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Elementary JDO (1/4)

• Some domain classes capable of persistence
• Write as ordinary classes and compile them.
• Describe their persistence needs in XML
• Enhance by hand or using the enhancer tool
• Provided by your JDO vendor
• Might generates DDL file for relational tables
• Create the tables using the DDL file as required

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Elementary JDO (2/4)

• Some applications read/write Persistent objects
• Lookup or otherwise obtain a factory
• Use PersistenceManagerFactory instance to obtain
  a PersistenceManager instance
• Invoke methods on the PersistenceManager
• makePersistent() to store a new object
• getExtent() to read lists of objects

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Elementary JDO (3/4)

• Developer does not
• use SQL
• know or worry about table structure
• map objects/attributes to tables/columns
• write infrastructure code

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Elementary JDO (4/4)

• Application is independent of
• JDO Vendor
• OpenFusion JDO from Prism Technologies today
• Xxx JDO from Xxx Corporation tomorrow
• Storage technology
• RDBMS today, ODBMS tomorrow, low-footprint
  storage engine next week.

15
UML for JDO Example
16
Persistence Descriptor (XML)

• Customer.jdo

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Understanding the JDO Example

• Bootstrap the JDO Implementation
• Get a PersistenceManagerFactory
• Get a PersistenceManager
• Create and Persist a new Customer
• Read and display all persistent Customers
• Close Resources

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jdo.properties

• jdo.properties is not part of the JDO standard
• it is used by the helper class JDOBootstrap
• javax.jdo.PersistenceManagerFactoryClasscom.prism
  t.j2ee.jdo.PersistenceManagerFactoryImpl
• javax.jdo.option.ConnectionUserNamesa
• javax.jdo.option.ConnectionPassword
• javax.jdo.option.ConnectionURLjdbchsqldbhsql//
  localhost
• javax.jdo.option.ConnectionDriverNameorg.hsqldb.j
  dbcDriver

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Bootstrap JDO Implementation

• JDOBootstrap bootstrap new JDOBootstrap()
• PersistenceManagerFactory pmf
• pmf bootstrap.getPersistenceManagerFactory()
• pm pmf.getPersistenceManager()

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Create a new Customer

• Customer c new Customer()
• c.setCustomerNumber(args0)
• c.setName(args1)
• c.setAddress(args2)
• try
• c.setCreditLimit(Double.parseDouble(args3))
• catch (NumberFormatException nfe)
• c.setCreditLimit(0)

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Persist the new Customer

• Transaction t pm.currentTransaction()
• t.begin()
• pm.makePersistent(c)
• t.commit()

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Read and display all Customers

• t.begin()
• Extent ext pm.getExtent(Customer.class, true)
• Iterator i ext.iterator()
• System.out.println(Listing all Customers)
• while (i.hasNext())
• System.out.println(i.next())
• System.out.println(Done.)

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Close Resources

• // close the iterator
• ext.close(i)
• // commit transaction
• t.commit()
• // close the PersistenceManager
• pm.close()

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JDO Pros and Cons

• Advantages
• Application works with any compliant JDO
  implementation
• RDBMS, OODBMS or lightweight alternative
• Dont write persistence infrastructure just
  application logic
• No SQL dependency

• Disadvantages
• Mapping to existing relational schema is
  described in a vendor-specific manner.

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JDO Instance

• Java language instance of a class which
• usually part of business domain object model
• implements application functionality
• can represent data from a persistent store
• Implement the PersistenceCapable interface
• explicitly via class developer
• implicitly via class Enhancer

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JDO Implementation

• Set of classes implementing JDO Interfaces
• implementations are expected to be appropriate
  for one particular storage medium
• a generic JDBC-compliant RDBMS, or a particular
  RDBMS (optimised at expense of SQL portability)
• a particular ODBMS
• a lightweight medium such as binary files
• Applications using JDO portable across different
  JDO Vendors implementations

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Enhancer

• Byte-Code Enhancer
• Modifies .class files to facilitate field access
  by JDO infrastructure
• methods/attributes do not have to be public
• Result implements PersistenceCapable and provides
  concrete method implementations
• Full binary compatibility

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Transparent Persistence (1/2)
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Transparent Persistence (2/2)

• Persistence by Reachability
• very rarely need to use makePersistent()
• Automatic change tracking
• Automatic synchronization of dirty Instances on
  commit
• no need to save() changes to persistent
  instances

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JDO Environments

• JDO usage is envisaged in 2 environments
• Non-managed Environment
• usage independent of J2EE Application Servers
• all the benefits of transparent persistence
• Managed Environment
• Entity, Session, MessageDriven Beans,
  Servlets/JSP
• Additional transparency for components use of
  infrastructure (transactions, security,
  connections)

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Transactional/Persistent

• JDO Instances may be
• Transient or Persistent
• Transactional or Nontransactional

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JDO Identity Mechanisms (1/2)

• Application (Primary Key) Identity
• values in the instance determine its identity
• Data Store Identity
• independent of any instance values
• Non-durable JDO Identity
• uniqueness is guaranteed in the JVM but is not
  supported in the data store.

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Specifying JDO Identity

• . . .
• . . .
• . . .

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Specifying Application Identity

• identity-typeapplication
• objectid-classop.PersonKey

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Inheritance

• JDO supports Inheritance

nameProduct persistence-capable-superclass
AbstractItem /
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Collection Example

• transient Collection orders
• orders new HashSet()
• nameorders
• persistence-modifier persistent

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Required Lifecycle States

• Transient
• Persistent-New
• Persistent-New-Deleted
• Hollow
• Persistent-Clean
• Persistent-Dirty
• Persistent-Deleted

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Required State Transitions
39
JDO Exception Hierarchy
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Primary Interfaces

• JDOHelper
• PersistenceManagerFactory
• PersistenceManager
• Extent
• Transaction
• Query
• (PersistenceCapable)

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Getting to the First Object

• Application may access a closure of instances
  navigated to from one instance
• 3 ways to get the first instance
• PersistenceManager.getObjectById()
• must be able to construct the Object ID
• PersistenceManager.getExtent()
• must navigate extent of all persistent instances
• JDOQL

42
JDO Query Language

• JDO removes SQL-dependencies for manipulating
  persistent data
• JDOQL is a data store-independent Java-like query
  language
• Java developers no longer require SQL for queries
  either
• Efficient architecture (no instantiation)
• Future migration to ODBMS is seamless

43
Query Structure

• Candidate class
• Candidate collection or extent
• Java-like Syntax for
• Variable declarations
• Parameter declarations
• Filter expression
• Import declarations
• Ordering declarations

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Supported Operators
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Query Execution

• Parameters passed to execute methods are for this
  execution only
• Specify parameters in sequence of declaration
• execute()
• execute(Object p1)
• execute(Object p1, Object p2)
• execute(Object p1, Object p2, Object p3)
• executeWithArray(Object a)
• executeWithMap(Map m)

46
Query Examples

• 5 examples follow using the classes described
  below

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Query Example 1

• Basic query
• Select all Order instances where the orderValue
  is greater than the constant 250.

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Query Example 1 - Code

• Extent extOrder pm.getExtent(Order.class,
  true)
• String filter orderValue 250
• Query q pm.newQuery(extOrder, filter)
• Collection results (Collection) q.execute()

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Query Example 2

• Basic query with ordering
• This query selects all Order instances where the
  orderValue is greater than the constant 250, and
  returns a Collection ordered according to
  orderDate descending

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Query Example 2 - Code

• Extent extOrder pm.getExtent(Order.class,
  true)
• String filter orderValue 250
• Query q pm.newQuery(extEmployee, filter)
• q.setOrdering(orderDate descending)
• Collection results (Collection) q.execute()

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Query Example 3

• Parameter passing
• This query selects all Order Instances where the
  orderValue is greater than the value passed as a
  parameter.

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Query Example 3 - Code

• Extent extOrder pm.getExtent(Order.class,
  true)
• String filter orderValue val
• Query q pm.newQuery(extOrder, filter)
• q.setOrdering(orderDate descending)
• q.declareParameters(Double val)
• Collection results
• results (Collection) q.execute(new Double(250))

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Query Example 4

• Navigation through single-valued field
• This query selects all Order instances from the
  candidate collection where the value of the
  address field in the corresponding Customer
  instance equals the value passed in as a
  parameter.

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Query Example 4 - Code

• Extent extOrder pm.getExtent(Order.class,
  true)
• String filter customer.address addr
• Query q pm.newQuery(extOrder, filter)
• q.declareParameters(String addr)
• Collection emps (Collection) q.execute(London)
  

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Query Example 5

• Navigation through multi-valued field
• This query selects all Customer instances where
  the orders collection contains at least one Order
  instance having an orderValue greater than the
  value passed in as a parameter.

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Query Example 5 - Code

• String filter, vars, param
• Class custCls Customer.class
• Extent extCustomer pm.getExtent(custCls, true)
• vars Order o
• filter orders.contains(o) o.orderValue
  val
• param Float val
• Query q pm.newQuery(extCustomer, filter)
• q.declareParameters(param)
• q.declareVariables(vars)
• Double searchVal new Double(250)
• Collection result (Collection)
  q.execute(searchVal)

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But Can I Use JDO Today
?
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Commercial Implementations

• enJin by Versant Software
• FastObjects by Poet Software
• FrontierSuite by ObjectFrontier
• IntelliBO by Signsoft GmbH
• JDO Genie by Hemisphere Technologies
• JRelay by Object Industries GmbH
• Kodo JDO by Solarmetric
• LiDO by LIBeLIS
• OpenFusion JDO by Prism Technologies
• Orient by Orient Technologies

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Managing Complexity
Just one of many diagrams that comprise a
non-trivial object model, designed in Together
6.0 and persisted with JDO as part of a recent
Ogilvie Partners client engagement
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Conclusion

• JDO
• provides significant development time savings
• is easier than JDBC and can be faster!
• prepared batched statements
• is more reliable than JDBC
• particularly for complex domain object models
• integrates fully with all J2EE components
• Vendors will still let you use SQL if you prefer!

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Ogilvie Partners JDO Training

• 2-day labs-based vendor-independent

• Public Training
• UK
• Milton Keynes
• Edinburgh
• USA
• New York
• Washington
• Others

• Dedicated Training
• Available world-wide

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Ogilvie Partners Consultancy

• Consultancy
• JDO applicability to your projects
• JDO Implementation selection
• Architecture design
• Domain object modelling
• Mentoring
• Meeting JDO-based learning objectives whilst
  working with developers on their project work

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Ogilvie Partners The JDO Book

• Java Data Objects
• Written by Robin Roos
• Published by Addison-Wesley Publishers Ltd
• ISBN 013066839, Available from August 2002
• Foreword by Craig Russell, JDO Spec Lead
• Pre-order at Amazon.co.uk now
• Complete coverage of JDO, many examples
• including J2EE and JDOQL
• prerequisite knowledge of the Java language

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Online JDO-Related Forums

• JavaDataObjects at Yahoo!Groups
• www.groups.yahoo.com/group/JavaDataObjects
• JDOcentral
• www.JDOcentral.com
• Lots more information on our website
• www.OgilviePartners.com
• Contact me
• Robin_at_OgilviePartners.com

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www.OgilviePartners.com
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Rewriting the J2EE Blueprints

• Integrating JDO with J2EE Architectures and
  Components

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Client-Server Architecture

• Before JDO
• Today

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RMI Server Architecture
Before JDO Today
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J2EE Blueprint - Original
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J2EE Blueprint - Session Façade
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J2EE Blueprint - Real World
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JDO in the J2EE Architecture
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Reassuring Entity Bean Lovers
JDO as delegate for BMP
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