SSC - Web development Model-View-Controller for Java web application development

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SSC - Communication and Networking

SSC - Web development

Model-View-Controller for Java web application

development

Shan He

School for Computational Science University of Birmingham

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SSC - Communication and Networking Outline

Outline of Topics

Java Server Pages (JSP)

Model-View-Controller (MVC)

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SSC - Communication and Networking Java Server Pages (JSP)

What is Java Server Pages

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JSPs: “a Java technology that provides a simplified, fast way

to create easily maintain, information-rich, dynamic Web

pages based on HTML, XML, or other document types.”

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Viewed as a high-level abstraction of Java servlets: translated

into servlets at runtime from the JSP source file

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Requires a Servlet container, e.g., Tomcat

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Life cycle of JSP: very similar to Java Servlet:

I Step 1: JSP Page Translation: Translated as Servlet source code

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

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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

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How to write JSP

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Java Code inside HTML using special JSP tags, called JSP

Scriting elements

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Three categories of JSP Scriting elements:

I Declaration Tags: define varaibales and methods in JSP, start with <%! 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(); %>

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JSP vs Java Servlet

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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

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Q: When to use JSP?

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A: When there is not much data process and manipulation,

otherwise use Model-View-Controller design pattern, where

JSP used as View and Servlet as controller

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SSC - Communication and Networking Model-View-Controller (MVC)

Java web application development: problems

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Many software systems are essentially to retrieve data from a

data store, e.g., a database and display it for the user:

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

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Most straightforward design: combines user interface and data

store to reduce the amount of coding and to improve

application performance

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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).

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What is Model-View-Controller (MVC)?

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MVC: a design pattern for efficiently relating the user

interface to underlying data models.

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Three main components:

I Model: represents the underlying data structures in a software application and the functions to retrieve, insert, and update the data. Note: No information about the user interface. I View: a collection of classes representing the elements in the

user interface for the user to see on the screen

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

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What is Model-View-Controller (MVC)?

Model View Controller User Manipulates Request Updates Return results

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Advantages of MVC

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Better complexity management:

I Software separate presentation (view) from application logic (model)

I Consequently, code is cleaner and easier to understand I Enable large teams of developers for parallel development

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Flexibility: Presentation or user interface can be completely

revamped without touching the model

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Reusability: The same model can used for other application

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MVC for Java Web Application

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

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View: Java Server Pages (JSP)

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Controller: Java Sevlet, which decides:

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

results and forwards the request there

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A Java Sevlet Controller:

I handles incoming requests

I instantiates of model and invokes the correct application logic in the model for the request

I 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

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MVC for Java Web Application

Model (POJO/Bean) View (JSP pages) Controller (Servlet) User Instantiate/ invoke Request Forward Request/results Return results

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SSC - Communication and Networking Java Enterprise applications

What is Enterprise applications?

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Enterprise applications: “ large-scale, multi-tiered, scalable,

reliable, and secure network applications”

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Three Tier architecture consists of:

I Presentation Tier: usually consists of clients and components that handle the interaction between clients and the application tier

I Application Tier (Business/Logic Tier): coordinates

application, e.g., its business logic, decisions, calculations and evaluations, moves data between the presentation and data tiers.

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

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Enterprise applications 3-Tier architecture

Java Enterprise Application Three Tier Architecture

A p p lic ati o n ti er Pr es en ta ti on ti er D ata ti e r

Browser with dynamic

web pages Desktop applications

Servlet/JSP/JSF componets

EJB/POJO

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Tools for Java Enterprise Application Development

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Java EE: the one your are learning but need learned more

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Spring Framework: one of the most popular open source

application development framework for developing Java

enterprise applications.

I Consists of many modules to simply development

I The key concept - Inversion of control: the control flow of a program is inverted, e.g., instead the programmer controls the flow of a program, the external source, e.g., Spring Framework takes control of it.

I The fundamental functionality - dependency injection: objects do not create other objects on which they rely to do their work. Instead, they get the objects from by a external framework component.

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

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Links

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Java EE vs Spring

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Spring Tutorial - Eclipse

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Spring Tutorial - Netbean

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SSC - Web development Model-View-Controller for Java web application development