EJB Overview Celsina Bignoli

Distributed Business Applications Server DB Client DB Server DB

Distributed Systems – Issues Remote method invocation Load balancing Transparent fail-over Back-end integration Transactions Clustering Dynamic redeployment Clean shutdown

Distributed Systems – Issues(2) Logging an auditing System management Threading Message-oriented middleware Object life cycle Resource pooling Security Caching

Middleware Each issue correspond to a service that needs to be addressed in serious server- side computing (middleware) A company can build its own middleware –Complicated to build and maintain –Requires expert-level knowledge –Completely orthogonal to most companies’ core business A company can buy an application server –They implement the middleware layer –Allow developer to focus on the code specific to the vertical industry

Component Architecture Agreement or set of interfaces between application servers and components Allows any component to run within any application server without changing code or even recompiling it

Enterprise JavaBeans (EJB) Standard for building server-side components in Java Defines a contract between components and applications servers, agreed upon by the industry Focus on vertical, rapid business development rather than middleware development Designed to support portability, scalability and reusability across any vendor’s middleware services

EJB as Business Tier Enterprise Beans are server-side components –Perform complex computations to code business logic –Access databases –Access other systems –Must run in a fault-tolerant, transactional, multi-user, secure environment Enterprise Beans are NOT presentation components Sit BEHIND the presentation layer (and do the hard work)

EJB Ecosystem Supply Tools Construct Enterprise Beans Tool Provider ( Eclipse JDeveloper NetBeans Sun’s Java Studio ) Build Application Bean Provider Application Assembler Supply EJB Container Deploy System Deployer System Administrator EJB Container/ Server Provider ( BEA WebLogic jBoss, WebSphere, … )

J2EE Architecture Browser Application Client ServletJSP Page Web Container Enterprise Bean Enterprise Bean EJB Container J2EE Server Database

J2EE Technologies Enterprise JavaBeans (EJB) Java API for XML RPC (JAX-RPC) Java Remote Method Invocation (RMI-IIOP) Java Naming and Directory Service (JNDI) Java Database Connectivity (JDBC) Java Transaction Service (JTS)

J2EE Technologies Java Messaging System (JMS) Java Servlets JavaServer Pages (JSP) Java IDL (CORBA) JavaMail Java API for XML Parsing (JASP) Java Authentication and Authorization Service (JAAS)