CS6320 – J2EE L. Grewe

MOTIVATION: E-commerce and Enterprise Computing Models Four models for e-commerce and enterprise computing: Four models for e-commerce and enterprise computing: Business to businessBusiness to business Business to customerBusiness to customer Customer to customerCustomer to customer Intra-businessIntra-business Implementation technology has gone through two-tier to component- based n-tier architecture. Implementation technology has gone through two-tier to component- based n-tier architecture.

Why N-tier Systems Architecture Different presentations of the same business data. Different presentations of the same business data. Change the business logic, or database type or schema without impacting the clients. Change the business logic, or database type or schema without impacting the clients. Hide middle tier (business logic) behind a firewall. Hide middle tier (business logic) behind a firewall. Database connection pools. Database connection pools. Selectively upgrade parts of the architecture without rewriting the entire application. Selectively upgrade parts of the architecture without rewriting the entire application.

N-tier Systems

Java™2 Platform, Enterprise Edition (J2EE) J2EE is introduce to reduce the cost and complexity of developing n-tired enterprise applications J2EE is introduce to reduce the cost and complexity of developing n-tired enterprise applications J2EE defines a complete platform that guarantees services in such areas as: J2EE defines a complete platform that guarantees services in such areas as: SecuritySecurity Transaction ManagementTransaction Management Resource ManagementResource Management Naming and DirectoryNaming and Directory MessagingMessaging Concurrency controlConcurrency control InteroperabilityInteroperability

J2EE Architecture The J2EE runtime environment consists of four major parts: The J2EE runtime environment consists of four major parts: Application componentsApplication components ContainersContainers Resource manager driversResource manager drivers Database supportDatabase support

J2EE Application Components J2EE defines four application component types: J2EE defines four application component types: Application clientsApplication clients AppletsApplets Servlets and JavaServer pages (JSP)Servlets and JavaServer pages (JSP) Enterprise JavaBeans™ components (EJB)Enterprise JavaBeans™ components (EJB)

J2EE Containers J2EE supports four separate types of containers, corresponding to the four types of components: J2EE supports four separate types of containers, corresponding to the four types of components: Application client containersApplication client containers Applet containersApplet containers Web containersWeb containers Enterprise bean containersEnterprise bean containers All types of containers must provide Java 2 Platform Standard Edition (J2SE) compatible runtime environment All types of containers must provide Java 2 Platform Standard Edition (J2SE) compatible runtime environment

J2EE Architecture

Benefits of J2EE Architecture J2EE server core manages resources and transactions and includes the java 2 platform virtual machine J2EE server core manages resources and transactions and includes the java 2 platform virtual machine J2EE platform services may be implemented on a single system or distributed over disparate platforms. J2EE platform services may be implemented on a single system or distributed over disparate platforms. J2EE-compliant servers guarantee the seamless and correct execution of all components and middleware services. J2EE-compliant servers guarantee the seamless and correct execution of all components and middleware services. Developers do not need to manage the integration of service implementations from various vendors (it is the J2EE platform vendor’s responsibility). Developers do not need to manage the integration of service implementations from various vendors (it is the J2EE platform vendor’s responsibility).

Other benefits of J2EE Architecture Service API are specified as Enterprise Java technology interfaces, which may be plugged seamlessly into the server Service API are specified as Enterprise Java technology interfaces, which may be plugged seamlessly into the server The application server provides services such as: The application server provides services such as: Load balancingLoad balancing ReplicationReplication Database connection poolingDatabase connection pooling Thread poolingThread pooling CachingCaching J2EE is vendor independent – Application builders can choose from a variety of server implementations. J2EE is vendor independent – Application builders can choose from a variety of server implementations.

Component-based Server Development The application server may be implemented using reusable components. The application server may be implemented using reusable components. Server components: Server components: Have well-defined business interfaces for their clients.Have well-defined business interfaces for their clients. Interact with the container through well- defined API.Interact with the container through well- defined API. J2EE technology provides a set of vendor- independent programming interfaces for the implementation of the container (middle tier). J2EE technology provides a set of vendor- independent programming interfaces for the implementation of the container (middle tier).

Component-based Server Development EJB technology forms one core of the J2EE architecture. EJB technology forms one core of the J2EE architecture. Presentation logic is implemented using servlets and JSP. Presentation logic is implemented using servlets and JSP. Business logic objects are implemented as EJB and/or servlets. Business logic objects are implemented as EJB and/or servlets. Data layer represented with EJB. Data layer represented with EJB.

J2EE Containers J2EE containers provide: J2EE containers provide: An environment and context for J2EE components to execute.An environment and context for J2EE components to execute. Resource management and other system services to the components.Resource management and other system services to the components. Operating system processes. Operating system processes. Threads. Threads. Container services are exposed to components through interfaces (the container itself is specified using interfaces). Container services are exposed to components through interfaces (the container itself is specified using interfaces).

J2EE Connectors Connectors are used to integrate various existing information systems in a J2EE- based application. Connectors are used to integrate various existing information systems in a J2EE- based application.

J2EE Connectors Leverage investments in existing enterprise systems. Leverage investments in existing enterprise systems. A connector is a vendor-specific bridge used to link an existing system to the J2EE system. A connector is a vendor-specific bridge used to link an existing system to the J2EE system. Connectors manage (and hide) all the logic used to integrate with proprietary systems and present their services as JavaBeans components. Connectors manage (and hide) all the logic used to integrate with proprietary systems and present their services as JavaBeans components.

J2EE Applications A J2EE application is a collection of software components that are engineered to be distributed across multiple tires of an N-tier system. These software components are implemented as EJB. A J2EE application is a collection of software components that are engineered to be distributed across multiple tires of an N-tier system. These software components are implemented as EJB. J2EE applications may play the role of a client or a server depending on which tier they are deployed. J2EE applications may play the role of a client or a server depending on which tier they are deployed. J2EE applications are not required to be distributed, but they should be engineered so that they may be deployed on a distributed system. J2EE applications are not required to be distributed, but they should be engineered so that they may be deployed on a distributed system.

J2EE Application Components There are two types of J2EE application components: Web components for handling presentation logic and EJB components for handling the business logic. There are two types of J2EE application components: Web components for handling presentation logic and EJB components for handling the business logic. Web components are implemented as JSP or servlets. These components shield the first-tier clients from the complexity of the application server.Web components are implemented as JSP or servlets. These components shield the first-tier clients from the complexity of the application server. JSP presents application server services in a form that is usable by any browser-based client.JSP presents application server services in a form that is usable by any browser-based client. Servlets manage the presentation of application server services for clients such as Java appplets, Java applications and Web browsers.Servlets manage the presentation of application server services for clients such as Java appplets, Java applications and Web browsers.