Feeds

Migrating EJB 2.1 Entity and Session Beans to EJB 3.0

The nuts and bolts

Internet Security Threat Report 2014

Table 1. EJB 3.0 Metadata Annotations

Annotation Description Annotation Elements
@Entity Specifies an entity bean.
@Table Specifies the entity bean table. name, schema
@Id Specifies an identifier property.
@Column Specifies the database table column for a persistent entity bean property. name, primaryKey, nullable, length
@NamedQueries Specifies a group of named queries.
@NamedQuery Specifies a named query or a query associated with a finder method. name, queryString
@OneToMany Specifies a one-to-many CMR relationship. cascade
@OneToOne Specifies a one-to-one CMR relationship. cascade
@ManyToMany Specifies a many-to-many CMR relationship. cascade
@ManyToOne Specifies a many-to-one CMR relationship. cascade

The EJB 3.0 annotation types are defined in the javax.persistence package. The EJB 3.0 entity bean class, corresponding to the EJB 2.1 entity bean class, is annotated with metadata annotation @Entity. The finder method findByJournal in the EJB 2.1 bean class is specified in the EJB 3.0 POJO class with the @NamedQuery annotation. The CMR relationship Catalog-Editions in the EJB 2.1 entity bean is specified in EJB 3.0 entity bean class with the @OneToMany annotation. The @Id annotation specifies the identifier property catalogId. The @Column annotation specifies the database column corresponding to the identifier property catalogId. If a @Column annotation is not specified for a persistent entity bean property, the column name is same as the entity bean property name. Transient entity bean properties are specified with the @Transient annotation. The EJB 3.0 entity bean POJO class, corresponding to the EJB 2.1 entity bean is listed in Listing 8.

Listing 8. CatalogBean.java. EJB 3.0 Entity Bean POJO Class

import javax.persistence.Entity;
import javax.persistence.NamedQuery;
import javax.persistence.Id;
import javax.persistence.Column;
import javax.persistence.OneToMany;

@Entity
@NamedQuery(name="findByJournal",
    queryString="SELECT DISTINCT OBJECT(obj)  FROM Catalog obj WHERE obj.journal = ?1")

public class CatalogBean{
    public CatalogBean() {}
    public CatalogBean(String catalogId) {
        this.catalogId=catalogId;
    }

    private String catalogId;
    private String journal;
    private String publisher;

    @Id
    @Column(name="CatalogId", primaryKey="true")
    public  String getCatalogId() {return catalogId;}
    public  void setCatalogId() {this.catalogId=catalogId;}

    public  void setJournal(String journal) {this.journal=journal;}
    public String getJournal() {return journal;}

    public  void setPublisher(String publisher) {this.publisher=publisher;}
    public  String getPublisher() {return publisher;}

    private java.util.Collection<Edition> editions;

    @OneToMany
    public  void setEditions(java.util.Collection editions) {
        this.editions=editions;
    }

    public  java.util.Collection getEditions() {return editions;}
}

An EJB 2.1 entity bean is created with the create() method in the entity bean home/local home interface. A client for an EJB 2.1 entity bean obtains a reference for the entity bean with JNDI lookup. An example code snippet to create an instance of the example EJB 2.1 entity bean is:

InitialContext ctx=new InitialContext();
Object objref=ctx.lookup("CatalogLocalHome");
CatalogLocalHome catalogLocalHome=(CatalogLocalHome)objref;

//Create an instance of Entity bean
CatalogLocal catalogLocal=(CatalogLocal)catalogLocalHome.create(catalogId);

The example client class for the EJB 2.1 entity bean class is available in the resources zip file . CatalogLocalHome is the JNDI name of the CatalogBean entity bean.

To access the getter/setter methods of an entity bean, the remote/local object in EJB 2.1 is obtained with the finder methods:

CatalogLocal catalogLocal =
    (CatalogLocal) catalogLocalHome.findByPrimaryKey(catalogId);

A entity bean instance is removed with the remove() method:

catalogLocal.remove();

The example client class for the EJB 2.1 entity bean class is available in the resources zip file.

An EJB 3.0 entity bean class does not include the local/remote and home/local home interfaces. In EJB 3.0, persistence and lookup is provided by the EntityMangerclass.

Some of the methods in the javax.persistence.EntityManager class are listed in Table 2.

Choosing a cloud hosting partner with confidence

More from The Register

next story
Netscape Navigator - the browser that started it all - turns 20
It was 20 years ago today, Marc Andreeesen taught the band to play
Sway: Microsoft's new Office app doesn't have an Undo function
Content aggregation, meet the workplace ... oh
Sign off my IT project or I’ll PHONE your MUM
Honestly, it’s a piece of piss
Return of the Jedi – Apache reclaims web server crown
.london, .hamburg and .公司 - that's .com in Chinese - storm the web server charts
NetWare sales revive in China thanks to that man Snowden
If it ain't Microsoft, it's in fashion behind the Great Firewall
Chrome 38's new HTML tag support makes fatties FIT and SKINNIER
First browser to protect networks' bandwith using official spec
Admins! Never mind POODLE, there're NEW OpenSSL bugs to splat
Four new patches for open-source crypto libraries
prev story

Whitepapers

Forging a new future with identity relationship management
Learn about ForgeRock's next generation IRM platform and how it is designed to empower CEOS's and enterprises to engage with consumers.
Why cloud backup?
Combining the latest advancements in disk-based backup with secure, integrated, cloud technologies offer organizations fast and assured recovery of their critical enterprise data.
Win a year’s supply of chocolate
There is no techie angle to this competition so we're not going to pretend there is, but everyone loves chocolate so who cares.
High Performance for All
While HPC is not new, it has traditionally been seen as a specialist area – is it now geared up to meet more mainstream requirements?
Intelligent flash storage arrays
Tegile Intelligent Storage Arrays with IntelliFlash helps IT boost storage utilization and effciency while delivering unmatched storage savings and performance.