JDO PRESENTASI

8/6/2019 JDO PRESENTASI

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Java Data Objects (JDO)

Overview and Future

Michael Vorburger, Vertical*i

Java User Group SwitzerlandZurich, 31.03.05


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Agenda

Object Persistence

O/R Mapping (ORM)

History

JDO Introduction

JDO API

JDOQL

JDO 2.0 (JSR 243)

JDO Implementations(Vendors & OSS)

Using JDO in EJB 2.1

Using JDO in Web Apps

Using JDO and/or JDBC

EJB 3.0 (JSR 220)

Future


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About Speaker

Personal interest in persistence space

Culprit for an in-house ORM layer

Somehow picked up JDO in 2001

Core Java Data Objects co-author

For past ca. 3 years user of JDO


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About

Audience

How many of you would consider

themselves moderately familiar with

JDO, or another similar persistence

framework, anyway?

How many of you have read the JDO2.0 and EJB 3.0 Persistence Specs?


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Object Persistence Concepts Graph of data objects (Domain Model)

API: persist(), Persistence by Reachability

Transactions

Query!

Internal: Memory Management, Caching, etc.


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O/R Mapping (ORM)Impedance Mismatch of OOP & RBDMS:

Classes vs. Tables, Inheritance mapping strategies

Relationships: Single 1-1 or 1-M, Multiple M-N, Linkwith attributes DBA mixed data and relationship,Inverses/Bi-directionality, Lists, Maps

Identity Management, Uniqueness

Class Attribute vs. Column Type Mappings

More in Core JDO Book Chapter2, but: Solutions for

mismatches exist; see also your ORM Vendor Doc!


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History Few things fall from the sky

object persistence in general

and JDO in particular buildupon a long history

Have you heard of any of

these names before?

CORBA POS

Persistent Object

Service Project Forest of Sun

Labs (OPJ, PJama)

ODMG API

Gemstone, O2,

TopLink (15y+)

(EJB 2.1 Entity Beans)


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JDO Introduction JDO is an interface-based API for selection and

transformation of transactional persistent storagedata into native Java programming language

objects Transparent Object Persistence!

Various implements for this API exist: Most as ORMfor your favourite RDB; some for standalone or

built-in OODBMS.

JDO 1.0 (JSR 12) in 2003

JDO 2.0 (JSR 243) Extension, accepted 1m ago


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JDOA

PI: PMF & PM PersistenceManagerFactory pmf =

JDOHelper.getPersistenceManagerFactory(Properties p);

javax.jdo.PersistenceManager pm =pmf.getPersistenceManager();

pm.makePersistent(customer);

customer = pm.getObjectById(oid,true);


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JDO Metadata & Enhancement JDO XML metadata describes which classes can be

persisted (), with relevant options(, )

JDO implementation run-time needs to interact withpersistence instances for lifecycle notification, load,store/flush. Generally, this is achieved by running abuild-time tool, a JDO [byte code] enhancer. (It addsthe PersistenceCapable interface from SPI API topersistent classes. This is no longer strictly for JDOcompliance,see BinaryCompatibility.)

Subject of hot debates strange, think AOP etc.


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JDOA

PI: Transactions Non-Managed

javax.jdo.Transaction jtx =pm.currentTransaction();

jtx.begin(); /* Do Stuff */ jtx.commit();

Managed (usually in J2EE container) JTAAPI

javax.transaction.UserTransaction ut;

ut = {lookup somewhere, e.g. JNDI};ut = ejbContext.getUserTransaction()

ut.begin(); /* Do Stuff */ ut.commit();

Declarative EJB container managed transactions

Core JDO Book Chapter 11


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JDOA

PI: Query and JDOQL Query q = pm.newQuery(Customer.class,

"customerName.startsWith('Tintin') &&lastOrder.price > 100");

Collection results = (Collection)q.execute();Iterator it = results.iterator();while (it.hasNext()) {

Customer cust = (Customer)it.next());

Parameters: q.declareParameters(String variable")and q.execute(variable) etc. etc. many manymore query facilities!


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JDO Queries: More of v1.0 JDOQL Filter can contain almost all Java

language operators, and some methods such asCollection.isEmpty() & contains(),

String.startsWith() & endsWith()[But not arbitrary other domain model methods!]

Ordering

Free Variables

Compiled Queries

Namespaces (packages)

Navigation (dots) in Filters, Ordering, etc.


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JDO Queries: More in v2.0

Single-String JDOQL Form

String.matches(), toLowerCase(), toUpperCase(),indexOf() x2, substring() x2, Map.containsKey() &containsValue(), Math.abs() & sqrt().

Paging Query Results with Query.setRange() orrange :start to :end and java.util.List results

User-Defined Result Class, single results, Unique

Projections, Aggregates functions Standardized SQL pass-through


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JDO Implementations[DISCLAIMER]

Open Source JPOX

ObjectWeb Speedo

TJDO

XORM (?) Apache JDO 2.0 RI (?)

Orient (ODBMS, OSS is new)

Commercial JDO ORM Vendors Solarmetric Kodo

Xcalia (formerly Libelis LiDO) .FR

Signsoft intellBO .DE Versant Open Access (formerly JDO Genie)

Others, e.g. Exadel, ObjectFrontier, ObjectMatter, Spadesoft XJDO,

Commercial non-ORM Versant (incl. Poet)

ObjectDB (simple &inexpensive)

Non-JDO ORMs JBoss Hibernate

Oracle Toplink

Castor JDO

OJB (?)


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JDO & EJB2

.1 EJB 2.1 CMP Entity Beans mixed persistence

and remoting, with a complicated API and

development model (container) sorry, butconsider that dead, essentially.

Session and Message-Driven Beans however

certainly have their place. So JDO inside theimplementation logic of those makes a lot of

sense!


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JDO & EJB2

.1 When using JDO inside a RPC-like (SOA)

EJB Session Bean (or RMI, Spring

Remoting.. your-favourite-here) :

Syntax aspects: About how to get, when

to etc. For full code details see Core JDO

book chapter 9 and/or Vendor Doc.

Architectural aspects: How to write your DTOs

(AKA VO) here or do you write them at all?!


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JDO & EJB: DTO (A

KA

VO) Either, traditionally write dedicated

SerializableDTO/VO in addition to PC,

maybe per service/use case. Nothing new;see Core J2EE Patterns etc.

Or, mark domain model PCs asSerializable

(although JDO will neverserialize) and use makeTransient (1.0) or

detachCopy (2.0)


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JDO & EJB: detachCopy New JDO 2.0 state: detached-clean/dirty. API:

Object PersistenceManager.detachCopy(Object pc);

Object PersistenceManager.attachCopy(Object detached,boolean makeTransactional);

Scenario: detach/disconnect, close PM,serialize across tier, modify disconnected,send back. New PM, new Tx, re-attach.

Keeps original identity and version!

Simplifies & makes safer the similar manualmakeTransient() approach from Core JDObook chapter 9.


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JDO in the Web Tier (directly) If your project does not need EJB-like remoting and

physical separation of tiers, directly using JDO inthe Web Tier (Struts, JSF, etc.) can be very nice,

and lead to a simple and efficient developmentmodel!

Recommended Architecture: One shared PMF(application context) and one PM and Tx per

request (context), managed by a Servlet Filter.Better: Enforce Web MVC with Model 2 View,allowing pull view (e.g. JSP) but read-only; allowwrite changes in Controller only.


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EJB 3.0 EJB 3.0 EG decided to abandon EJB 2.1

Entity Beans, and create new and separatePersistence Doc and API:

This will be an ORM not a transparentPersistence API. Some other differences.However, will also be usable in J2SE,outside J2EE container.


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EJB 3.0

Also a POJO-style approach. Many realworld domain models will probably be usablewith both APIs!

Both a similarAPI, conceptually close forpractical purposes, e.g. life cycle aligned.EntityManager.persist(),EntityManager.createQuery(),javax.persistence.Query.getResultList()

Query Languages (JDOQL & EJBQL) differ,but maybe JDO 2.1 and EJB 3.1 allow cross-spec query language? (A la SQL in JDO 2.0)


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Future of Java Persistence

Today, the choice is JDO; why wait? A

proven JCP standard with many

implementations. EJB 3 Final Release supposedly summer

2005 (?). Requires JDK 5. Slow adoption?

Longer Term (2-3 years?) who knows?

Note: All major JDO implementations very

likely also EJB 3 "persistence engines".


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Q & A

Thanks for listening!

To play with running code after this:

http://www.jpox.org great tutorials!

Questions?

Drinks.

Documents

JDO PRESENTASI