Java Data Object is an API (Application program interface) ,used by java programing language to interact with the database. It is very effective with both relational and object oriented databases. JDO allows the programmer to access the database using java instead of using specific database languages such as SQL. JDO allows the programmer to persist java objects.
The JDO is not an alternative to JDBC ,programmer can make use of each of its capabilities . JDBC offer direct control over underlying database thorough queries while JDO offers better convenience to programmer offering database independent way to handle the datasource.
Advantages of JDO
  • Portability
    • Application developed using JDO will run in any implementation of JDO with out any need of recompiling, since it is the meta data describe the behavior of JDO instead of java source code
  • Ease of use
    • JDO allows the programmer to concentrate on their document object mode without being worried about object persistence ,which is handled by JDO itself.
  • Database portability
    • The JDO application is independent on underlying database. So JDO will work with different database from different vendors.
  • Performance
    • JDO can optimize the database access, results improved performance in database operations without any burden to the programmer.
  • Performance
    • JDO can be integrated with EJB. This feature allows the programmer to use both these API together.
  • Container agnostic
    • Since JDO is very lightweight it doesn’t need any particular container . So the JDO applications can be implemented like normal desktop (jsp,servlet etc) application.
    JDO Programming Model
    JDO Programming Model has the following aspects
  • PersistenceManager
    • The PersistenceManager handles the access,transactions and queries about underlying data source. It acts as interface between the application and the data source.
  • Transaction
    • Transaction defines a atomic unit of work for data management,which satisfies ACID properties.
  • Query
    • The JDO query language known as JDOQL is used to query the persistent object with the given criteria. This language is independent of query language of underlying data source, which makes it suitable for any type of database .
  • PersistenceCapable classes
    • The JDO query language known as JDOQL is used to query the persistent object with the given criteria. This language is independent of query language of underlying data source, which makes it suitable for any type of database .
  • Persistence-aware classes
    • These classes process persistance-capable classes.
  • Normal classes
    • These are normal classes used in the application
    Working
    The JDO has three phases
    1.Design -creating an ordinary class

    public class me
    {

    String myname;

    public String getMyname() { return myname; }

    public void setMyname(String myname) { this.myname = myname; }

    }

    2.Preparation -make the ordinary class persistent using JDO enhancer.
  • Create a package.jdo file for writing meta data information for the class. This file is placed with class file.

    <?xml version="1.0" encoding="UTF-8"?>

    <!DOCTYPE jdo SYSTEM “jdo.dtd”>

    <jdo>

    <package name=”pack.pack”>

    <class name=”me” identity-type=”application” objectidclass=”EmployeeKey”>

    <field name=”name” primary-key=”true”>

    </field>

    </class>

    </package>

    </jdo>

  • To get PersistenceManager from PersistenceManagerFactory with given implementation

    • Properties proper = new Properties();

    proper.put(…);//give implementation

    // get a PersistenceManagerFactory

    PersistenceManagerFactory pmft = JDOHelper.getPersistenceManagerFactory(proper);

    PersistenceManager pm = pmf.getPersistenceManager();

  • Set ManagedConnectionFactoryImpl to PersistenceManager
  • persist me by pm.makePersistent(new me(“me”));
    • 3. Run time – implements persistence
    JDO offer interface definition to manipulate stored data and convert them to native objects. It is easy to learn, use and implement, providing a standard for object persistence. There are many open source implementation available for JDO.