Java Ee Architecture

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Java EE Client-Server Architecture: 5 Layers

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1) Data Source Layer
2) Data Mapping Layer
3) Business Logic Layer/Domain Logic Layer/EJB Container Layer
4) Web Container Layer
5) Client Presentation Layer

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Data Source Layer (technologies)

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Relational DBMS such as DB2, Oracle DBMS, SQL Server

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Data Mapping Layer

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JDBC (Java Database Connectivity), Entity EJBs

load into memory

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Business Logic Layer/Domain Logic Layer/EJB Container Layer (technologies)

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* Enterprise JavaBeans (EJB)


* http://www.tutorialspoint.com/ejb/
* a development architecture for building highly scalable & robust enterprise level applications to be deployed on a J2EE compliant Application Server (e.g., JBOSS, Web Logic, etc.)

* Business Logic

* the part of the program that encodes the real-world business rules that determine how data can be created, stored, & manipulated
* see wiki

* EJB Container

* provides a run-time environment for EJBs within the application server
* acts an an intermediary b/t the business logic within the bean and the rest of the application-server environment

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Web Container Layer (technologies)

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Servlets
JavaServer Faces (JSF)
JavaServer Pages (JSP)

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JavaServer Page (JSP)

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A JSP is a template for a Web page with dynamic content created by using Java code and special server-side HTML tags, along with standard HTML.

WIKI
a technology that helps software developers create dynamically generated web pages based on HTML, XML, or other document types

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JavaServer Faces (JSF)

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a Java specification for building component-based user interfaces for web applications

MVC

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Java Servlet Struts Framework (Apache Struts)

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a web app framework for developing Java EE web apps

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Client Presentation Layer (technologies)

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JavaScript
XML
AJAX
XHTML
CSS
XSLT
DOM

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AJAX

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Asynchronous JavaScript and XML

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DOM

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Document Object Model

The Document Object Model (DOM) is a cross-platform and language-independent convention for representing and interacting with objects in HTML, XHTML and XML documents.

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XSLT

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XSLT (Extensible Stylesheet Language Transformations) is a language for transforming XML documents into other XML documents,[1] or other objects such as HTML for web pages, plain text or into XSL Formatting Objects which can then be converted to PDF, PostScript and PNG.[2]

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Container

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Containers are basically run-time environments that provide components with specific services.

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Web Container

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Web containers provide run-time support to clients by processing requests through invoking JSPs and servlets and returning results from the components to the client.

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EJB Containers

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EJB containers provide automated support for transaction and state management of EJB components, as well as look up and security services.

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HTTP

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HTTP is the protocol used on top of the TCP/IP protocol to enable the communication between the Client and the Server in a Request/Response-oriented manner over a network (e.g., Internet).

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HTTP (notes)

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...
 Is an application-level protocol for distributed, collaborative, hypermedia information systems.
 Is a request/response-oriented protocol.
 Is connectionless (CL-mode)
 Is stateless (the new version has improved on this capability)
 Is based on a Web server – sometimes referred to as HTTPD, for HTTP daemon.

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URL

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Uniform Resource Locator (URL) uniquely identifies a Web resource – an HTML page, a JSP page, a Servlet, an image, etc.
 Format: protocol://hostname<:port>/identifiers
 Example: http://manta.cs.vt.edu:80/cs5704/Course.html#CourseDescription

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URI

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Uniform Resource Identifier (URI) is a formatted string that identifies a Web resource via name, location, or any other characteristic relative to a known base.


 Example:
 /cs5704/Course.html#CourseDescription
where http://manta.cs.vt.edu:80 is the base (server) address.

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URI benefit

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 By referring to only a partial address, URI, you keep your HTML tags and JSP servlet code from being tied to a single machine name.
 Therefore, URIs provide maintainability of your code.

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HTTP: GET

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“get a file and return its contents"

The GET method means retrieve whatever information (in the form of an entity) is identified by the Request-URI

conditional GET

partial GET

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HTTP: POST

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Happens, usually, when you fill out an HTML form and click the Submit button.

Designed to send large amounts of data to the server.
 May have multiple connections to the server. The first is to send the request; subsequent ones may then be used to send the data to the server.

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POST

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The POST method is used to request that the origin server accept the entity enclosed in the request as a new subordinate of the resource identified by the Request-URI in the Request-Line.

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applet

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An Applet is a small Java program, which is downloaded and executed entirely within a Java Runtime Environment (JRE) *on the client machine.*

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servlet

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A Servlet is a small Java program, which is executed entirely within a Java Virtual Machine (JVM) *on the Server computer.*

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JSPs are run in a _____-side component called a ___ __________ which translate them into Java Servlets

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JSPs are run in a server-side component known as a JSP container, which translates them into Java Servlets.

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a JSP page exists in 3 forms

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1) JSP Source code (.jsp)
2) Java Source Code (The JSP constainer translates the JSP source code into Java Servlet source code)
3) Compiled Java Class (.class)

.jsp-->.java-->.class

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EJB defn

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An EJB is a component Java program that implements business logic in a distributed enterprise application.

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4 things provided by EJB Container

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1. Security,
2. Concurrency,
3. Transaction Support, and
4. Memory management, swapping unused EJBs from memory to secondary storage.

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2 types EJBs

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1) Session
2) Entity

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Session EJBs

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1. Executes methods on behalf of a client
2. Does not directly represent shared data in the database, although it may
3. Can direct and participate in transactions

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Entity EJBs

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1. Represents data in a database
2. Can participate in transactions
3. Allows shared access from multiple users

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MVC Paradigm - Model

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1. Objects of different classes provide services related to the application domain
2. Business logic implementation

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MVC Paradigm - View

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1. The display of the application’s state
2. Presentation layer

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MVC Paradigm - Controller

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1. The user interaction between the Model and the View.
2. Adapts the Model-layer objects to those needed by the View layer and mediate among various parts of the View layer by dealing with navigation and error-handling and reporting duties.