web applications internet engineering spring 2014 bahador bakhshi ce & it department, amirkabir...

Web Applications

Internet Engineering

Spring 2014

Bahador Bakhshi

CE & IT Department, Amirkabir University of Technology

OutlineMVC Design PatternMultilayer DesignMultitier ArchitectureIntroduction to Java EEServletJSP

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Web Application Development(Large) Applications cannot be developed in ad-

hoc manner We need design & architecture (SW engineering)

Concept separation, Component, Relations, …

There are so many architectural patterns ETL, MFT, EAI, TDS, …

http://en.wikipedia.org/wiki/Architectural_pattern Two common architectures in web applications

MVC Multi-layer (Multi-tier)

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MVC: Model-View-Controller Model

Does all the computational work All communication with the model is via methods It is input/output free, contains data, system state

Controller (of states sequences) Handles events/requests affecting model or view

User inputs/requests go to the controller Available commands are determined by controller (based on model) Tells the model what to do

View Show the results from model or controller

Examples: Calculator, Email Client, Word Processor5

Advantages of MVCSeparation of concerns

Computation is not intermixed with I/O Code is cleaner and easier to understand

Flexibility The GUI (if one is used) can be completely

revamped without touching the model in any wayReusability

The same model used for different controller & view

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MVC Interactions?!

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MVC Interactions (cont’d)

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model

view controller

event event is passed to the controller

controller updates model

controller updates view

view queries model

model signals changes

MVC for (simple) Web ApplicationsModel

Database tables (persistent data) Session information (current stat data) Parts of processing

View (X)HTML CSS

Controller Client-side scripting Part of processing by server side scripting

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MVC? MVC works fine for desktop application

The origin is from graphical application development 1970s

Consider large & distributed web application, e.g., online transactions, e-banking, … View Model interactions?!!

View is in user’s browser Model is in back-end server

User Controller interaction? User don’t have direct access to controller

Complicated processing on huge data Model cannot both hold data & process it

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Layering ApproachMVC Difficulties are due to triangular topology

Linearize the topology Layering approach

Common layering in web applications Presentation Layer Business logic Layer Data (management/resource) Layer

These layers are purely abstractions Not correspond to physical distribution

All layers may or may not be on the same machine

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Multilayer Architecture

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Presentation Layer User interface of the application

GUI HTML based browser

Displays information (processing output) which are get from the business logic layer

Gets user’s requests and pass them (with required data) to the business logic layer

The user interface of web applications can be made up client side & server side codes

What is this layer in Gmail?

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Business Logic LayerThe work that the application needs to do

Processing/Computing/Calculations

Receives requests from presentation layerFetches required data from data layerProcess the request & dataOutput is sent back to the presentation layerWhat does this layer do in Gmail?

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Data LayerProvides data access interface to business logic

Hide data storage details Hide heterogeneity of underlining systems

Communicating with data store systems Database server Messaging system

What is this layer in Gmail?

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Multilayer Multi-tierShould/Can all layers be implemented in a

single physical machine (single tier)?Yes, If application is (fairly) simple

Web server, HTML, CSS, PHP, Processing, MySQL, … all on the same machine

No, If application is huge & complex Web server on machine 1 Data base on machine 2

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Multitier ArchitectureTwo-tier Architecture:

Two layers are physically separated from the third, forming two physically separated tiers

Three-tier Architecture: The three abstract logical layers are separated into

three physically distributed tiers

N-tire Architecture: Each abstract logical layer is implemented using

multiple physical tiers

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Two-Tier 1: Fat clientCombining the presentation layer with the

business logic layer in a physical tierThis separation can be seen as the traditional

client-server architecture Client = Process + View Server = Data

This architecture effectively makes the client “fat” and the server “thin”

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Two-Tier Fat Client Characteristics Deployment costs are high

Many fat clients

Business logic migration or data base modification (changes in database driver, database type, …) costs are high Changing the business logic layer involves

recompiling and redeploying the client tier

Network performance suffers Huge raw data transfer (query & response)

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Two-Tier 2: Thin ClientClient (e.g., browser)

HTTP request Mainly for presentation of information Serving mainly static (D)HTML pages

Server (web server & DB server) HTTP response Server side programming: CGI & PHP, … Data base server: MySql

The suitable architecture for web applicationsHow about complex computing on huge data?!

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N-Tier Architecture In N-tier deployments, presentation layer, business

logic layer, and data layer are separated into respective physical tiers 3 tier: client + server + data base

Presentation layer is implemented by parts in both client & server sides E.g., dynamic web page using Ajax + PHP 4 tier: Browser + Web server + Application Server + Database

server

Complicated Bussing logic layer itself can be distributed multi-tier application N-tier

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HTML Client (browser)

Web Server

Application Server

Database Server

Typical Web Application N-tier Architecture

N-Tier Architecture Characteristics Migration costs are low

Each tier can be upgraded independently, e.g. Business logic application migration Database switching Web server switch OS upgrade

Inter-Tier communication performance overhead

Server side maintenance costs are high

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Multilayer/Multitier ImplementationMany common requirements in applications

Object creation & garbage collection, Transaction Logging and audit, Security, and much more

These are not implemented by neither OS nor Application developer They are called middleware

Application servers provide middleware services Application components live inside application servers

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Application ServersExisting technologies can be classified into

three broad categories:Java based platform (Java Enterprise Edition) .NET FrameworkOther web application development

frameworks PHP frameworks: Zend, … Ruby on Rail …

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What is Java EE?Java Platforms:

Java Card: Smart card version Java ME (Micro Edition): Embedded systems, e.g.

Mobile handheld Java SE (Standard Edition): Desktop application

development Java EE (Enterprise Edition): Enterprise distributed

application software development Java EE add libraries to SE for fault-tolerant,

distributed, multi-tier, … based components Until java 5, it has been called J2EE

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Java EEJava EE provides technologies (libraries) for

enterprise level web applicationsJava EE technologies for web applications:

Servlet JavaServer Pages (JSP) JavaServer Faces (JSF) Enterprise Java Beans (EJB)

Many other facilities (via libraries & JVM) Remote method invocation, Security, Database

connectors, XML, …30

Java EE Components: Business LogicEJB: Enterprise version of Java Beans

Java classes that are designed to be reusable standalone software components All data (properties) are private

Exposed by public getter & setter method Public method to process the data

Enterprise version: automated (provided by container) concurrency, life-time management, security, transaction, … Simplify developing complex application

Can be used everywhere, not necessarily web application

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Java EE Components: PresentationClient side

Client can use HTML, Java Applet, Java Application, …Server side

Servlets are special classes to realize request-response model (get, post,… of HTTP) External server side code

JSP is a developer-friendly wrapper over servlet classes Embed server side code

Faces & Facelets similar to JSP but uses custom tags which can be converted to anything

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Java EE Multi-tier Architecture

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Java EE Containers Requirements from different aspects

All java codes must run a virtual machine To run Servlet & JSP we need something like PHP runtime

environment Application server (middleware) is need in business logic

These different terms are named container in Java EE terminology The runtime support for Java EE application components Provides a view of the underlying Java EE API

Security, Logging, Remote Method Invocation, …

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Java EE Container Architecture

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Web ContainerApplet Container

Application ClientContainer

EJB Container

Java Servlets

JSP

Databases and

Other Resources

EJBs

App.Client

Applet

JSF

Browser

JRE

Tomcat, JRun, … GlassFish, BEA, …


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What is Servlet?! A Java application that runs on the web server in

response to HTTP requests (GET, …) A normal java application +

Read/Write access to HTTP headers Access to HTML Forms Sessions, Cookies, …

Similar to CGI, output is sent to client Servlet is used to generate dynamic content to return to

browser: HTML, XML, …

Each servlet runs as separated thread inside servlet container

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The Servlet Model

Browser

Java Enabled

Web Server

Servlet container

HTTP Get/Post

HTMLXML

ResourcesJavaBeansDatabase

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Servlet

Servlet

Why Servlet: Servlets vs. CGI Scripts Servlets do what CGI scripts do; so, why should I

learn/use it? Because, it is better approach More efficient

No new process per request (as CGI), with servlets, servlet is loaded at first time, container stays running and handles each request with a lightweight Java thread

More Convenient Servlets have an extensive infrastructure for automatically

parsing and decoding HTML form data, reading and setting HTTP headers, handling cookies, tracking sessions, …

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Why Servlet: Servlets vs. CGI Scripts More Portable

Servlets are written in the Java programming language and follow a standard API. Servlets are supported directly or by a plugin on virtually every major web server

More Secure CGI programs are often executed by general-purpose operating

system shells, however, servlets run in container which impose more security enforcement (sand boxing)

More powerful It is java & its container provide mechanisms to use other java

application, e.g. EJB multi-layer architecture

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Why Servlet: Its Role in Java EE

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How does Servlet Work? There is a mapping between URL & Servlet classes, e.g.

/1/2/3 abc.class The “web.xml” file (we see later)

When there is a request for URL (/1/2/3/), container calls service method of the class (abc.class) Multiple concurrent requests Multiple threads running the service method

The service method calls do??? method according to the type of requests E.g., doGet for GET method

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Assumption: servlet is already loaded in RAM

How does Servlet Work? (cont’d) The method accesses to the request information

HTTP headers, form data, cookies, sessions, … Through objects which are passed to the method by

container

The method processes the request Normal java application, DB access, using EJB, …

The method generates output Setting response headers, setting cookies, updating session,

printing HTML to output stream, … Using the objects which are provided by container

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The “Hello World” Exampleimport java.io.*;import javax.servlet.*;import javax.servlet.http.*;

public class HelloWorld extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException{ response.setContentType("text/html"); PrintWriter out = response.getWriter(); out.println("<html>"); out.println("<body>"); out.println("<h1>Hello World!</h1>"); out.println("</body>"); out.println("</html>"); }}

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JavaServer Pages (JSP)JSP technology is an extension of servlet

Simplify web application development by java We have not to create whole HTML by println

JSPs are easier to develop than servlets

It is the embed version of servlet in HTML Contains static HTML elements + JSP tags in .jsp file

Java code inside the tags creates dynamic content Very similar to PHP, but using Java codes

When JSP runs, a servlet is created It runs on the same container that runs Servlets

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JSP Invocation

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JSP Advantages In comparison to Servlet

Only dynamic part are java coded, not whole HTML Separation between HTML (Presentation) & Bussing logic

Develop java code & include them in HTML by JSP tags Automatic recompilation of modified pages As powerful as servlet (it becomes servlet finally!)

In comparison to interpreted scripts (PHP) JSP is compiled & kept in memory Better performance Converted to Servlet (a complete Java program) More complex

logic implementation

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What is New in JSP? JSP = HTML + tag + Java Servlet We already know HTML + Java + Servlet

So, what do we want to learn about JSP?

Tags!!! Okay, we know it <% %> (or something like that)

JSP is finished! There is nothing to learn ( or ? )

But, wait!! A servlet is composed of some sections imports, variable & method declaration, doGet, … How do we specify which tag in JSP is which part of the servlet class?!

Yes! Tags!!! Different tags for different purposes

We want to learn! ( :P)

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JSP Tag Examples JSP Comment:

<%-- Blah --%> Developer comment that is not sent to the client

JSP Expression: <%= Java Value %> Expression that is evaluated and sent to the client each time the

page is requested

JSP Scriptlet: <% code %> The code is inserted into the servlet's _jspService

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The Hello World Example<HTML><BODY>Hello World! The time is now <%= new java.util.Date() %></BODY></HTML>

Is converted to out.print("<HTML> <BODY> Hello World! The time is now ");out.print(new java.util.Date());out.print("</BODY> </HTML>");

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Summary Q8) How are complex/big web applications developed?

We need architectures & design patterns to help us

Q8.1) Design patterns & Architecture? MVC & Multi-layer are common approaches

Q8.2) Deployment architecture? Multi-layer is typically deployed in multi-tier architecture

Q8.3) What does Java EE provide? Servlet & JSP & Some other things (we didn’t see)

Q8.4) Servlet? A java class that run to handle HTTP requests

Q8.5) JSP? Embed version of the Servlet with specially tags for different purposes

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ReferencesThe “Core Servlet” Bookwww.j2eetutorials.50webs.com

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http://www.j2eetutorials.50webs.com/

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