J2EE Basics

Refernces:

• http://java.sun.com/javaee/5/docs/tutorial/doc/
• http://java.sun.com/javaee/technologies/

Web Component

• JSP - Script
• Servlets - Class files (compiled)
• JSF - Framework based on JSP + Servlets

• Html + Server utility classes
  • these are not considered web components but can be bundled with the web components

- May include java beans that talk to the business tier

Web Service support

• web based application - open XML standards + transports
• JEE provides XML API and tools

Web services - method + parameters

Document oriented - document containing service data

XML - cross platform, extensible, text based

SOAP - Simple Object Access Protocol

• Envelope* describes message and how to process

• Body* Encoding rules to express app, defined data types, convention used to represent request and response

WSDL - Web Service Definition Language

XML format for describing network services

• description, name, location, communication mechanism (transport)
• can be stored in UDDI or published - web

UDDI + ebXML - allows publishing of services

Business Component

• EJB Enterprise beans that solve business needs
  • Stores and retrieves information from the EIS (Enterprise Information System)

Enterprise Information System

may contain:

• ERP - Enterprise resource planning
• Mainframe transaction processing
• Database
• Other legacy

Java EE Containers

• component based - organises business logic into components
• provides underlying services
• requires assembly into a module and deployment
  • specifying component settings for each component e.g. transaction management, JNDI, remote connectivity
• Transaction model allows relationships of methods to be defined
• JNDI - unified naming and lookup mechanism across directory services
• Remote connectivity - manages low level connectivity clients -> EJB

Security can be configured differently in different environments

Container manages non configurable items

• EJB + servlet live cycle
• DB pooling
• Persistence
• Access to JEE API

JEE Server = EJB container + Web Container

Deployment

• Functional components + optional deployment descriptors
• via platform specific tools - specifying user access + DB access

Packaging

• JEE app = EAR file (Enterprise Archive - standard jar format)

/Web module (.war)
/Application client module (.jar)
/Resource Adaptor (.rar)
/EJB module (.jar)
/META-INF/application.xml - JEE deployment configuration - root of web app, protable naming mappings
/META-INF/sun-application.xml - runtime - app specific runtime e.g. caching options

Deployment configuration can be changed without need to modify code and rebuild

Deployment roles

• Tool provider - provider of development, packaging tools
• Application component provider - develops beans/applets/clients etc
  • Enterprise Bean developer
  • Web component developer
  • Application client developer - client jar file
• Application assembler - assembles war,jar files into ear + writes deployment descriptors
• Application deployer + administrator - configures deploys application, administers servers, JEE, network etc.

Simplifies System integration

• platform independent system integration solution
• unified application model across tiers with EJB
• simplified request/response - Servlets/JSP
• reliable security model - JAAS
• XML data interchange - JAXP, SAAJ, JAX-WS
• interoperability - JCA
• easy DB connectivity - JDBC
• enterprise application integration with JMS, JTA, JNDI

Protocols

Standard web based protocols:

• TCP
• HTTP 1.0
• SSL 3.0
• RMI (Remote Method Invocation) Serialisation + JRMP (Java Remote Messaging Protocol)
  • OMG protocols (Object Management Group)
  • CORBA (Common Object request Broker Architecture)
    • Defines interface in IDL (Interface Definition Language)
    • IDL compiled into client and server stubs
  • ORB (Object Request Broker)
    • Communicates using IIOP (Internet Inter Orb Protocol)

Requires:

• Java IDL - idlj - hava compiler - generates java stubs from IDL
• RMI-IIOP - RMI implementation over IIOP

From [URL="http://en.wikipedia.org/wiki/RMI-IIOP"]wikipedia [/URL]

Both CORBA and RMI-IIOP use the same GIOP communication standard. If required, it is possible to generate the IDL definitions for the involved RMI-IIOP data structures and use these definitions to arrange the interoperability between the RMI-IIOP and plain CORBA applications.

There is a program that will generate the idl: http://java.sun.com/j2se/1.4.2/docs/guide/rmi-iiop/rmi_iiop_pg.html

So though RMI-IIOP is CORBA compiant it needs work for corba clients to integrate.

java IDL is the typical way to integrate with an existing CORBA application.

java EJB is RMI-IIOP and CORBA can integrate but needs IDL to be generated (with the help of rmic)

http://java.sun.com/javase/6/docs/technotes/guides/idl/jidlFAQ.html

• Java IDL - existing CORBA application - mainly CORBA/C++ based.
• RMI-JRMP - (Application Servers see below). Designed for java.
• RMI-IIOP - Used by Application Servers - part of spec. Mostly java based but want to maintain legacy applications.

Data formats

• HTML
• Image files: gif + jpeg
• JAR
• Class
• XML