SSC - Communication and Networking

SSC - Web developmentModel-View-Controller for Java web application

development

Shan He

School for Computational ScienceUniversity of Birmingham

Module 06-19321: SSC

SSC - Communication and Networking

Outline

Outline of Topics

Java Server Pages (JSP)

Model-View-Controller (MVC)

Java Enterprise applications

SSC - Communication and Networking

Java Server Pages (JSP)

What is Java Server Pages

I JSPs: “a Java technology that provides a simplified, fast wayto create easily maintain, information-rich, dynamic Webpages based on HTML, XML, or other document types.”

I Viewed as a high-level abstraction of Java servlets: translatedinto servlets at runtime from the JSP source file

I Requires a Servlet container, e.g., TomcatI Life cycle of JSP: very similar to Java Servlet:

I Step 1: JSP Page Translation: Translated as Servlet sourcecode

I Step 2: JSP Page Compilation: Compiled as Servlet classI Other steps are similar to Java Servlet

SSC - Communication and Networking

Java Server Pages (JSP)

What is Java Server Pages

_jspInit()

JSP Page (.jsp)

_jspService()

Servlet class (.class)

_jspDestroy()

Finalisation and garbage collection

Request

Response

Servlet container

Servlet source (.java)

Translate

Compile

SSC - Communication and Networking

Java Server Pages (JSP)

How to write JSPI Java Code inside HTML using special JSP tags, called JSP

Scriting elementsI Three categories of JSP Scriting elements:

I Declaration Tags: define varaibales and methods in JSP, startwith <%! and end with %> , e.g.,

<%!

String username = Shan;

%>I Expression Tags: produce output (a String object) that can be

used to display result on JSP, start with <%= and end with

%> , e.g., <%=name %>

I Scriptlets: start with <% and end with %> , e.g.,

<%

java.util.Date date = new java.util.Date();

%>

SSC - Communication and Networking

Java Server Pages (JSP)

JSP vs Java Servlet

I Differences:I Java Servlet is “HTML in Java”, while JSP is “Java in

HTML”.I Servlets run faster compared to JSP since JSP needs to be

translated and compiled before execution.I More convenient to write JSP to generate HTML

I Q: When to use JSP?

I A: When there is not much data process and manipulation,otherwise use Model-View-Controller design pattern, whereJSP used as View and Servlet as controller

SSC - Communication and Networking

Model-View-Controller (MVC)

Java web application development: problems

I Many software systems are essentially to retrieve data from adata store, e.g., a database and display it for the user:

I The user changes the data using an user interfaceI The system stores the updates in the data store

I Most straightforward design: combines user interface and datastore to reduce the amount of coding and to improveapplication performance

I Problems:I user interface tends to change much more frequently than the

data storage system.I mixed up the presentation (the user interface) and application

logic (data store).

SSC - Communication and Networking

Model-View-Controller (MVC)

What is Model-View-Controller (MVC)?

I MVC: a design pattern for efficiently relating the userinterface to underlying data models.

I Three main components:I Model: represents the underlying data structures in a software

application and the functions to retrieve, insert, and updatethe data. Note: No information about the user interface.

I View: a collection of classes representing the elements in theuser interface for the user to see on the screen

I Controller: classes connecting the model and the view, and isused to communicate between classes in the model and view.

SSC - Communication and Networking

Model-View-Controller (MVC)

What is Model-View-Controller (MVC)?

ModelView

Controller

User

Manipulates

Request

Updates

Return results

SSC - Communication and Networking

Model-View-Controller (MVC)

Advantages of MVC

I Better complexity management:I Software separate presentation (view) from application logic

(model)I Consequently, code is cleaner and easier to understandI Enable large teams of developers for parallel development

I Flexibility: Presentation or user interface can be completelyrevamped without touching the model

I Reusability: The same model can used for other applicationwith different user interfaces

SSC - Communication and Networking

Model-View-Controller (MVC)

MVC for Java Web Application

I Model: Plain Old Java Object (POJO) or Java Beans

I View: Java Server Pages (JSP)I Controller: Java Sevlet, which decides:

I what application logic code to be applied in the modelI which JSP page is appropriate to present those particular

results and forwards the request there

I A Java Sevlet Controller:I handles incoming requestsI instantiates of model and invokes the correct application logic

in the model for the requestI forwards the results from the model and request from the user

to the appropriate view (JSP file) −→ RequestDispatcher

I You can use request.setAttribute or

session.setAttribute to pass the results to view

SSC - Communication and Networking

Model-View-Controller (MVC)

MVC for Java Web Application

Model(POJO/Bean)

View(JSP pages)

Controller(Servlet)

User

Instantiate/invoke

Request

Forward Request/results

Return results

SSC - Communication and Networking

Java Enterprise applications

What is Enterprise applications?

I Enterprise applications: “ large-scale, multi-tiered, scalable,reliable, and secure network applications”

I Three Tier architecture consists of:I Presentation Tier: usually consists of clients and components

that handle the interaction between clients and the applicationtier

I Application Tier (Business/Logic Tier): coordinatesapplication, e.g., its business logic, decisions, calculations andevaluations, moves data between the presentation and datatiers.

I Data Tier (Enterprise Information Systems Tier): retrieves andstores data.

SSC - Communication and Networking

Java Enterprise applications

Enterprise applications 3-Tier architecture

Java Enterprise Application Three Tier Architecture

Ap

plic

atio

n t

ier

Pres

enta

tion

tie

rD

ata

tier

Browser with dynamic web pages

Desktop applications

Servlet/JSP/JSF componets

EJB/POJO

JDBC/Hibernate/JDO etc.

SSC - Communication and Networking

Java Enterprise applications

Tools for Java Enterprise Application Development

I Java EE: the one your are learning but need learned moreI Spring Framework: one of the most popular open source

application development framework for developing Javaenterprise applications.

I Consists of many modules to simply developmentI The key concept - Inversion of control: the control flow of a

program is inverted, e.g., instead the programmer controls theflow of a program, the external source, e.g., Spring Frameworktakes control of it.

I The fundamental functionality - dependency injection: objectsdo not create other objects on which they rely to do theirwork. Instead, they get the objects from by a externalframework component.

I The basic idea: to simplify development complexity by loosingcouplings/dependencies between classes

SSC - Communication and Networking

Java Enterprise applications

Links

I Java EE vs Spring

I Spring Tutorial - Eclipse

I Spring Tutorial - Netbean

I Spring guides