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 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 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 public class Cabin { private int id; private String name; private int deckLevel;

@Column(name=“ID”) public int getId() { return id; } public void setId(int pk) { this.id = pk; }

Remaining public String getName() { return name; } public void setName(String str) { this.name = str; 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 ProcPayBean com.relaxalot.ProcPayRemote com.relaxalot.ProcPayLocal com.relaxalot.ProcPayBean Stateless

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 java:/TitanDB

EJB Development and Support Services Bean/Container Interaction

EJB Container Implementation Component interfaces allow external or co- located 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

bean remote interface EJB object EJB Architecture EJB Container remote interface EJB object proxy Client

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 Filesystem LDAP Service Provider LDAP Directory RMI Service Provider 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 usr bin tom Context Subcontext Binding

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 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 DataSource for Relaxalot Database theDataSource javax.sql.DataSource Container java:/DefaultDS edu.weber.ProcessPaymentBean dataSource

ENC Example (Annotation) – Describing the Resource public class ProcessPaymentBean implements ProcessPaymentRemote 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 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