Distributed System Using Java 2 Enterprise Edition (J2EE)IntroductionJ2EE SuiteJ2EE Suite (contd.)Distributed Multi-tiered ApplicationsJ2EE-based ApplicationJ2EE Technology ArchitectureEnterprise Application Model (2007)Enterprise model (J2EE) todayJ2EE clientsWeb-tier ComponentsBusiness-tier ComponentsEnterprise Information System (EIS) TierEnterprise Java Bean(EJB)Enterprise Java Bean (EJB) (contd.)Enterprise Application with many EJBsRoles in EJB DevelopmentTypes of Enterprise Java BeansSession BeansEntity BeanEntity Bean (contd.)The life cycles of enterprise beansLife Cycle DifferencesSession beanContents of an Enterprise BeanContainer ServicesCompilation and DeploymentSummaryDistributed System Using Java 2 Enterprise Edition (J2EE)B.RamamurthyIntroductionSun Microsystems provides specifications for a comprehensive suite of technologies to solve large scale distributed system problems.This suite is the Java 2 Enterprise Edition, commonly known as J2EE.In this discussion we will discuss the architecture of J2EE and how it can be used to develop distributed multi-tiered applications.J2EE SuiteJ2EE (Java2 Enterprise Edition) offers a suite of software specification to design, develop, assemble and deploy enterprise applications.It provides a distributed, component-based, loosely coupled, reliable and secure, platform independent and responsive application environment.J2EE Suite (contd.)Core technology: Container infrastructure, language and environment supportXML and services technologyThe Java API for Webservices (JAX-WS)The Java API for XML-based RPC (JAX-RPC)SOAP with Attachments API for Java (SAAJ)The Java API for XML Registries (JAXR)Web TechnologyJava ServletsJavaServer PagesJavaServer Pages Standard Tag LibraryEnterprise Java Bean (EJB) technologySession beansEntity beansEnterprise JavaBeans Query LanguagePlain old java objects (POJO)Platform servicesSecurityTransactionsResourcesConnectorsJava messagingDistributed Multi-tiered ApplicationsServices, clients (people and application) and data are distributed geographically across many platforms and many machines.Multiple tiers:Client-tier (browser or client-application)Web-tier (web-server: Java Server Pages)Business-tier (logic; Examples: Enterprise Java Beans)Enterprise-Information-System (EIS) tier (database)J2EE-based ApplicationThe J2EE APIs enable distributed systems and applications through the following: Unified application model across tiers with enterprise beans Simplified response and request mechanism with JSP pages and servlets Reliable security model with JAAS XML-based data interchange integration with JAXP Simplified interoperability with the J2EE Connector Architecture Easy database connectivity with the JDBC API Enterprise application integration with message-driven beans and JMS, JTA, and JNDI Java persistent API;J2EE Technology ArchitectureServerplatformJTS JMAPI JNDI JMS JDBCJAXP JAAS…Enterprise Java Beans ComponentsJava ServerpagesServletsApplication clientsWeb clientsIIOP,othershtmlEnterprise Application Model (2007)Enterprise model (J2EE) todayJ2EE clientsWeb clientsDynamic web pages with HTML, rendered by web browsers.Can include applets.Communicates with server typically using HTTP.Application clientsUser interface using GUI components such as Swing and AWT. Directly accesses the business logic tier.Web-tier ComponentsClient can communicate with the business tier either directly or through servlets ot JSP that are located in the web-tier.Web-tier can help in pre-processing and allows distribution of the functionality.Servlets are special classes to realize the request-response model (get, post of HTTP).JSP is a developer-friendly wrapper over the servlet classes.Business-tier ComponentsThis is defined by the logic that pertains to the (business) application that is being developed.Enterprise Java Beans (EJB) can be used to implement this tier.This tier receives the data from the web-tier and processes the data and sends it to the EIS-tier and takes the data from the EIS and sends it to the web-tier.Enterprise Information System (EIS) TierIn general this corresponds to the database (relational database) and other information management system.The other information management systems may include Enterprise Resource Planning (ERP) and legacy system connected through open database connectivity.Enterprise Java Bean(EJB)An enterprise bean is a server-side component that contains the business logic of an application. At runtime, the application clients execute the business logic by invoking the enterprise bean's methods.Main goal of Enterprise Java Bean (EJB) architecture is to free the application developer from having to deal with the system level aspects of an application. This allows the bean developer to focus solely on the logic of the application.Enterprise Java Bean (EJB) (contd.)Deployable unit of code.At run-time, an enterprise bean resides in an EJB container.An EJB container provides the deployment environment and runtime environment for enterprise beans including services such as security, transaction, deployment, concurrency etc.Process of installing an EJB in a container is called EJB deployment.Enterprise Application with many EJBsWebClientApplClientEJB1EJB2EJB3EJB4EJB5EJB6Lets consider a shopping front application and figure out thepossible components (EJBs)Roles in EJB DevelopmentBean developer: Develops bean component.Application assembler: composes EJBs to form applicationsDeployer: deploys EJB applications within an operation environment.System administrator: Configures and administers the EJB computing and networking infrastructure.EJB Container Provider and EJB server provider: Vendors specializing in low level services such as transactions and application mgt.Types of Enterprise Java BeansPlain old java beansSession beansEntity Beans (for database access)Plain old java objects (POJO)Session BeansFor transient functionsRepresents “conversational” stateTypically one per requestData is non-persistentLifetime is limited by the client’s: once the client exits, the session bean and data are gone.Simple and easy to program.Light-weight.Entity Bean“Transactional” in behaviorCan be shared among clientsPersistent: data exists permanently