An architecture for webb applications, J2EE

A quick look at Java 2 Enterprise Edition

J2EE Overview

A framework for Enterprise Applications Scalable Distributed Transactional Losely coupled Multi-tired Portable Secure Access to different systems

J2EE Overview

Built on top of Java 2 Standard Edition, J2SE Access to all of J2SE-APIs 100% Java

J2EE Overview

J2EE is a specifaction, not a produkt No vendor lock in

Several implementations BEA (Weblogic) IBM (Websphere) Oracle (Oracle9iAS and OC4J) JBoss Ironflare (Orion) Jakarta Tomcat

J2EE Overview – Content of J2EE Enterprise Java Beans, EJB Java Servlets Java Server Pages, JSP Java Messaging Service, JMS Java Database Connectivity, JDBC JavaMail Java Transaction API, JTA Connector Architecture

J2EE Overview – Content of J2EE RMI/IIOP Java Naming and Directory Interface, JNDI Webservices, in version 1.4

J2EE Overview – Benefits of J2EE Separates business logic from system code Separates busines logic from presentation Deploy-time configuration Scalable from start Distributed from start Component model on the server = easier

team work Declarative security and transactions

Containers and Components

Containers and Components

A J2EE Application server provides containers for all components of J2EE

There is one container per J2EE component The Application server runs the entire J2EE

solution

Containers and Components

The Application server handles all system level programming Security

Authorization – Is the user allowed to do this operation? Authentication – Is the user who he says? Validate credentials

Transactions Threading Object life time management Caching Object persistence Database Connection pooling

Containers and Components

Several clients – one system

Enterprise Java Beans

The core of J2EE Server side components Three base types of EJB

Session Beans Entity Beans Message Driven Beans

Transactional components Bean managed or Container managed

Deploy time configuration of security and transactions

Enterprise Java Beans - Architecture

Enterprise Java Beans – Session Beans Stateless and statefull beans Handles busines logic Acts as frontend for Entity beans

Enterprise Java Beans – Entity Beans Handels data Mapped on Database tables Container managed (CMP) and Bean

Managed Persistence (BMP) CMP releaves the developer from writing SQL

code Minimizes the risk for database lock-in.

EJB-QL – a query language for EJBs

Enterprise Java Beans – Message Driven Beans Activated by a JMS queue Asynchronous execution No need for the client to wait for an answer

Java Messaging Service, JMS

A messaging API for Java A Sender sends a message to a JMS Queue A Listener listens for messages on a Queue Guarantied delivery Asynchronous processing

After the Sender has sent its message there is no need to wait for the Listener to get it

Great for scalability Good for operations that doesn’t have to occur at once, for

example logging

JavaMail

A high level API for sending and receiving mail No need to know everything about the underlying

protocolls Support for IMAP, POP and SMTP

Java Transaction API, JTA

The easy way to handle complex transactions You can have transactions between different

components A mailserver, a database and a JMS system can

participate in the same transaction, given that they support it

Based on XA The mechanism behind the transactions of

EJBs

Java Connector Architecture, JCA Hook into existing legacy systems You can write a connector for basically

anything Anything with a Connector can be plugged

into the J2EE Server Simplifies system integration

RMI/IIOP

Integration with other systems through Corba Call your J2EE Components from Visual

Basic, Delphi, C++ and C Java might not be the best or only choice for your

clients

Java Naming and Directory Interface, JNDI Very fundamental functionality in J2EE The way that distributed objects are located Any kind of objects can be stored in JNDI All objects are stored in a hierarchical way The way the Home interface for EJBs are

located

Java Naming and Directory Interface, JNDI Used to store connection pools for JDBC Context.lookup(“java:comp/env/jdbc/Pool1”)

Private context from within components Defined with a <resource-ref> in deployment

descriptors Context.lookup(“Pool1”)

Global context from the outside

Web Development

The web is static by nature Based on HTTP A stateless network environment The stateless nature is what have made the

Internet into what it is today

HTTP

A very simple and readable protocol Text based

Several methods GET

The basic request to get a page POST

Used from forms in the web pages DELETE HEAD

HTTP

A typical browser request for www.dn.se/index.html Connect to www.dn.se GET /index.html HTTP/1.0 Disconnect

CGI

Common Gateway Interface An early interface for making the web more

dynamic Executes programs on the server Cumbersome programming and bad resource

management Basically each request starts a new process on the

server

Java Servlets

Extensions of the web server One of the front ends to the J2EE system Generates HTML with print statements Good for implementing control logic Support for sessions Multithreaded by nature Not so good for generation nice layout

Java Server Pages (JSP)

HTML with embedded Java code Good for presentation Compiled to a Servlet at runtime Easy for web designers to use Support for Java Beans and Custom tags

Servlets and JSP

Servlets and JSPs are often used together The Servlet handles the request The Servlets calls Java Beans or EJBs to

handle the business logic The Servlest forwards to a JSP The JSP handles the Presentation Model View Controller, MVS

Other technologies for the web Microsoft Active Server Pages

Embed VB code in your HTML Similar to JSPs

PHP Quite like ASP, but open source and available on

all platform. Used at many sites today Coldfusion Webobjects (Mac) Zope

Next time

The next session will be all about Servlet programming