Enterprise JavaBeans EJB Container Services. EJB container Enterprise JavaBeans are deployed in an EJB container within the application server EJB container.

Enterprise JavaBeans

EJB Container Services

EJB container• Enterprise JavaBeans are deployed in an EJB

container within the application server

• EJB container manages the execution of enterprise beans for Java EE applications

• EJB benefit - container is charged with the task of making system services available to EJB components

J2EE Components and Container

http://java.sun.com/blueprints/guidelines/designing_enterprise_applications/platform_technologies/component/index.html

EJB container servicesContainer-provided services:

• Persistence• Transactions• Security• JNDI• Distribution

• Concurrency• Multi-threading• Component pooling• Component life cycle• Timer service• Interceptors

Persistence

Java Persistence APIJava Persistence API

@Entity

public class Account {

@Id

private int id;

. . .

}

@Entity

public class Customer {

@Id private int id;

private String name;

@OneToMany

private List<Account>accounts;

. . .

}

Transactions• A transaction is a group of activities performed as

a single unit

• Transaction demarcation types:• Container-managed

• Declarative, default

• Bean-managed• User transaction API

• Annotation @TransactionManagement• Is applied to bean class• Values: CONTAINER or BEAN

Example: Container-managed@TransactionAttribute(MANDATORY)@Statelesspublic class ShopBean implements Shop {

public void setPrice(int prodId, int price){...}

@TransactionAttribute(REQUIRED)public int getPrice(int prodId){...}

}

Transaction Attribute Definitions

http://java.sys-con.com/read/325149.htm

Example: Bean-managed@TransactionManagement(BEAN)@Statelesspublic class ShopBean implements Shop {

@Resource UserTransaction tx;@PersistenceContext EntityManager productMgr;

public void setPrice(int prodId, int price){tx.begin();productMgr.find(Product.class,

prodId).setPrice(price);tx.commit();

}}

Security• Security is very important in the enterprise

environment• Authentication• Authorization

• Security annotations• @DeclareRoles • @DenyAll • @PermitAll • @RolesAllowed • @RunAs

Example: Security@Stateless@DeclareRoles({“javaee"}) public class HelloEJB implements Hello {

@PermitAllpublic String hello1(String msg) {

return "1: Hello, " + msg;}

@RolesAllowed("javaee")public String hello2(String msg) {

return "2: Hello, " + msg;}

@DenyAllpublic String hello3(String msg) {

return "3: Hello, " + msg;}

}

Example: Security@Stateless

@DeclareRoles({"A", "B"})

public class HelloEJB implements Hello {

@Resource private SessionContext sc;

public String hello(String msg) {

if (sc.isCallerInRole("A") && !sc.isCallerInRole("B")){

...

} else {

...

}

}

}

JNDI• JNDI = Java Naming and Directory Interface

• API that provides naming and directory functionality to applications

• store and retrieve named Java objects of any type• associate attributes with objects and search for

objects using their attributes

• A naming service helps organize an enterprise application by acting as a central registry for components

Naming and Directory services

• JNDI is independent of any specific directory service implementation

• LDAP, DNS, NIS, RMI, CORBA

http://www.javaworld.com/javaworld/jw-02-2000/jw-02-howto.html

http://www.javaworld.com/javaworld/jw-01-2000/jw-01-howto.html

JNDI functions• void bind(String stringName, Object object)

• Binds a name to an object

• Object lookup(String stringName)

• Returns the specified object

import javax.naming.Context;import javax.naming.InitialContext;

Context ctx = new InitialContext();

Calculator calculatorRemote =

(Calculator).lookup("CalculatorBean/remote");

JNDI architecture

http://java.sun.com/products/jndi/tutorial/getStarted/overview/index.html

Bean pooling• To reduce memory consumption and processing,

containers pool resources and manage the lifecycles of all the beans very carefully

• When a bean is not being used, a container will place it in a pool to be reused by another client

• The container copies data into or out of these pooled instances as necessary

• The best thing - client application is completely unaware of the resource management activities

Bean pooling benefits• Reduces the resource requirements for a single server

• pooled beans are context switched as required

• Dynamic growth pool can be expanded/contracted as demand requires

• Pooled objects are instantiated on startup instead of every time

• may be expensive to instantiate

• Fine-grained control of resources able to set max/min beans

Bean lifecycle management• Two strategies to perform lifecycle management:

• instance pooling• passivation/activation

• Passivation is a technique to temporarily serialize a bean and store it to some persistent store

• Containers free up resources by passivating a bean and then re-activating it when resources are available

Stateless Session bean lifecycle

Source: Sun J2EE tutorial

Stateful Session bean lifecycle

Source: Sun J2EE tutorial

References• Transactions

http://java.sys-con.com/read/325149.htm

• Securityhttp://java.sun.com/developer/technicalArticles/J2EE/security_annotation/

• JNDIhttp://www.java2s.com/Article/Java/J2EE/JNDI.htm