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