Transcript Using Enterprise Beans Server Side Services

EJB Development and
Support Services
EJB Development and
Support Services
Topics to be Covered:
• EJB Design
• Bean/Container Interaction
• Java Naming and Directory Interface (JNDI)
• Using Enterprise Beans
• Server Side Services
EJB Development and
Support Services
EJB Design
Class and Interface Review
• javax.ejb package
– Core of the EJB API
• Remote interface
– Defines bean’s remote business methods
• Local interface
– Defines bean’s local business methods
• Endpoint interface
– Defines SOAP-accessible business methods
• Message interface
– Defines methods for asynchronous messages
• Bean class
– Implementation of business and lifecycle methods
Remote Interface
• Defines business methods
import javax.ejb.Remote;
@Remote
public interface CalculatorRemote {
public int add(int x, int y);
public int subtract(int x, int y);
}
Bean Class
• Actual implementation of business methods
import javax.ejb.*;
@Stateless
public class CalculatorBean
implements CalculatorRemote {
public int add(int x, int y) {
return x + y;
}
public int subtract(int x, int y) {
return x – y;
}
}
Entity
• Java Persistence API
import javax.persistence.*;
@Entity
@Table(name=“CABIN”)
public class Cabin {
private int id;
private String name;
private int deckLevel;
Primary Key
@Id
@GeneratedValue
@Column(name=“ID”)
public int getId() { return id; }
public void setId(int pk) { this.id = pk; }
Remaining Fields
@Column(name=“NAME”)
public String getName() { return name; }
public void setName(String str)
{ this.name = str; }
@Column(name=“DECK_LEVEL”)
public int getDeckLevel() { return deckLevel; }
public void setDeckLevel(int level)
{ this.deckLevel = level; }
}
Primary Keys
• Pointer that locates an enterprise bean
• Defined by the bean developer
• Must map to one of the following types:
– Any Java primitive type (including wrappers)
– java.lang.String
– Primary-key class composed of primitives
and/or Strings
Primary Key Class
•
•
•
•
Composed of primitives and/or strings
Must be serializable
Must have a public no-arg constructor
Must implement the equals() and
hashCode() methods
Deployment Descriptors
• Specifies how to apply primary services
– security
– transactions
– naming
• Specifies persistence unit and associated
database
• Describe runtime attributes of server-side
component
EJB Packaging
• JAR Files used for packaging
– Applets
– Applications
– JavaBeans
– Web Application
– Enterprise JavaBeans
• Bean classes
• Component interfaces
• Supporting Classes
• Appropriate Deployment Descriptors
Example Deployment Descriptor
<?xml version="1.0"?>
<ejb-jar>
<enterprise-beans>
<session>
<ejb-name>ProcPayBean</ejb-name>
<remote>com.relaxalot.ProcPayRemote</remote>
<local>com.relaxalot.ProcPayLocal</local>
<ejb-class>com.relaxalot.ProcPayBean</ejb-class>
<session-type>Stateless</session-type>
</session>
</enterprise-beans>
</ejb-jar>
XML and/or Annotations
• Defaults make XML deployment descriptors
optional
– Default transaction property REQUIRED
– Default security semantics UNCHECKED
• Annotations provide further information
– Metadata placed directly in the bean class
file
– Deployment descriptors can override
annotations
Example persistence.xml
<persistence>
<persistence-unit name=“titan”>
<jta-data-source>java:/TitanDB</jta-data-source>
</persistence-unit>
</persistence>
EJB Development and
Support Services
Bean/Container
Interaction
EJB Container Implementation
• Component interfaces allow external or colocated clients to interact with session bean
class
• Component interfaces interact with instances
of the session bean class
• Proxy Stub
– Interacts with client, sends message to EJB
Container
• EJB Object
– Implements remote interface
– Wraps enterprise bean instance
– Generated by the container
EJB Architecture
Client
EJB Container
remote EJB object
interface
proxy
remote EJB object
interface
bean
EJB Container
• Intermediary between bean and server
• Interaction defined by SessionBean interface,
and JMS-MessageDrivenBean onMessage()
method
• javax.ejb.EJBContext interface
implemented by the container.
• Bean uses EJBContext interface to
communicate with EJB environment
• JNDI namespace
EJB Development and
Support Services
Java Naming and
Directory Interface
(JNDI)
Naming and Directory Services
• Naming Service
– Associates names with Objects
– Provides facility to find an object based on a
name
– Examples: DNS, File System
• Directory Object
– Contains attributes
– Like a record in a database
• Directory Service
– Provides directory object operations for
manipulating attributes
JNDI Architecture
JNDI Application
Filesystem
Service
Provider
LDAP
Service
Provider
RMI
Service
Provider
Filesystem
LDAP Directory
RMI Registry
JNDI API Benefits
• Standard Java Extension
– javax.naming
– javax.naming.directory
• Unified system for resource access
• Insulates application from naming and
directory service protocols
• Extensible
• Composite or federated namespaces
Naming Concepts
• Binding
– Association of a name with an object
• Context
– Set of bindings
• Subcontext
– Binding one context within another
Context
Subcontext
Binding
usr
bin
tom
Context & InitialContext
• javax.naming.Context interface
– Collection of bindings
– Operations apply only to bindings, not to
Context itself
• javax.naming.InitialContext class
– Implements the Context interface
– Starting point for exploring a namespace
– Requires an initial context factory
com.sun.jndi.fscontext.RefFSContextFactory
InitialContext Properties
• InitialContext constructor takes a set of
properties
Properties props = new Properties();
props.put(Context.INITIAL_CONTEXT_FACTORY,
“com.sun.jndi.fscontext.RefFSContextFactory”);
props.put(Context.PROVIDER_URL,”file:///”);
Context initialContext = new
InitialContext(props);
Looking Up Objects
• lookup() method
• Specify the name of the child
• Type of returned object determined by service
provider
• Container with children should implement
javax.naming.Context
Object obj =
initialContext.lookup(name);
Listing Objects
• list() method
• Returns a list of names of an object’s children
as an instance of
javax.naming.NamingEnumeration
• NamingEnumeration contains a collection of
javax.naming.NameClassPair objects
• Browsing is a combination of list() and
lookup() calls
NamingEnumberation kids =
initialContext.list(name);
Binding Objects
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•
•
•
bind() method
Creates a Binding object
Use rebind() if name already exists
Use unbind() to remove a binding
File newfile =
File(“c:\temp\newfile”);
tempContext.bind(“newfile”, newfile);
JNDI and JDBC
• JDBC 2.0 DataSource
– Provides Database connections
– Information to create connections are stored
as properties
– Registered with a directory service
Context ctx = new InitialContext();
DataSource ds = (DataSource)
ctx.lookup(“jdbc/EmployeeDB”);
Connection con = ds.getConnection();
con.close();
JNDI and EJB
• JNDI used to locate a specific EJB Home
Context ctx = new InitialContext();
Object ref = ctx.lookup(“TravelAgntBean”);
TravelAgntRemote dao = (TravelAgntRemote)
PortableRemoteObject.narrow(ref,
TravelAgntRemote.class);
dao.makeReservation();
JNDI Environment Naming Context
• Part of Bean-Container Contract
• Common naming context
– java:comp/env
• Declare resources using XML deployment
descriptor or Annotation
– EJBs
– JDBC DataSource
– Java Message Service
– Environment Properties
Context ctx = new InitialContext();
ENC Example (Deployment Descriptor) –
Describing the Resource
<resource-ref>
<description>DataSource for Relaxalot
Database</description>
<res-ref-name>theDataSource</res-ref-name>
<res-type>javax.sql.DataSource</res-type>
<res-auth>Container</res-auth>
<mapped-name>java:/DefaultDS</mapped-name>
<injection-target>
<injection-target-class>
edu.weber.ProcessPaymentBean
</injection-target-class>
<injection-target-name>dataSource
</injection-target-name>
<injection-target>
</resource-ref>
ENC Example (Annotation) – Describing the
Resource
public class ProcessPaymentBean implements
ProcessPaymentRemote
{
...
@Resource(mappedName=“java:/DefaultDS”)
DataSource dataSource
ENC Example – Use the Resource
public class ProcessPaymentBean implements
ProcessPayment Remote
{
...
private boolean process()
{
Connection con = dataSource.getConnection();
...
con.close();
}
EJB Development and
Support Services
Using Enterpise Beans
Entities
• Model data and behavior
– Provide interface to data
– Business rules that directly affect data
– Relationships with other entities
//
//
//
//
Use javax.persistence.PersistenceContext
annotation to get access to entities
using an EntityManager service that
references a persistence unit
@PersistenceContext(unitName=“titan”)
private EntityManager manager;
...
public void createCabin(Cabin cabin) {
manager.persist(cabin);
}
Session Beans
• Model processes and tasks
– Functions of the business
• Inappropriate for client application or
entity beans
• Provide business logic
• Control workflow
// Lookup session bean
TravelAgent tAgent = (TravelAgent)...
// Create a reservation
tAgent.setCustomer(customer);
tAgent.setRoomID(roomID);
tAgent.setHotelID(hotelID);
Ticket ticket =
tAgent.bookReserve(creditCard, price);
Session Beans
• Stateful
– Maintain conversational state
• State kept in memory
• Dedicated to a single client
• Stateless
– No conversational state
• Method calls are independent
– Provide higher performance
• A few stateless beans can service many
clients
EJB Development and
Support Services
Server Side
Services
Resource Management
• Instance Pooling
– Clients do not directly access EJB’s
– Number of instances can be efficiently
managed and minimized
– Reuse existing beans for different client
requests
• Activation Mechanism
– Used for stateful session beans
– Passivation
• Serialize bean’s state to storage
– Activation
• Restore a stateful bean instance’s state
Concurrency
• Multiple clients accessing the same bean at the
same time
• Not supported by session beans
• Entities represent shared data
– Java Persistence spec: persistence
container protects shared data by making a
copy of the entity bean on a per-transaction
basis
– Defense against stale reads or simultaneous
updates is vendor specific
– EJB prohibits synchronized keyword
– EJB prohibits beans from creating threads
Transactions
• Set of tasks executed together
– Atomic
• Reservation and Payment must both be
successful
• Manage automatically
– Declare transactional attribute
• Manage explicitly
– Use
javax.transaction.UserTransaction
object
Persistence
• Applies to Entities
– Java Persistence specification
• Plain Old Java objects (POJO)
• Can be created outside the scope of the
EJB container
• Attached/Detached
• Entity Manager
– Object-to-relational persistence
• Map entity state to relational database
tables and columns
Distributed Object Interoperability
• Location Transparency
– CORBA IIOP
– Support mandated in EJB 3.0
• RMI/IIOP
• SOAP via JAX-RPC API
• Programming model used by Java EJB Client
– Other protocols and clients can be supported by
servers
• CORBA clients written in C++, Smalltalk, Ada
using EJB-to-CORBA mapping
• SOAP clients written in Visual Basic.NET, C#, Perl
using EJB-to-SOAP mapping
Asynchronous Enterprise Messaging
• Message-driven Beans (MDBs)
• Route messages from JMS clients to JMS-MDB
• Reliable delivery
– Attempt redelivery on failure
• Persisted messages
• Transactional
• EJBs can send messages
EJB Development and
Support Services
Topics to be Covered:
• EJB Design
• Bean/Container Interaction
• Java Naming and Directory Interface (JNDI)
• Using Enterprise Beans
• Server Side Services