Guide to Web Development with Java

Transcription

1 Guide to Web Development with Java

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3 Tim Downey Guide to Web Development with Java Understanding Website Creation

4 Tim Downey Computing and Information Sciences Florida Inernational University SW 8th Street Miami, FL USA ISBN e-isbn DOI / Springer London Dordrecht Heidelberg New York British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Control Number: Springer-Verlag London Limited 2012 Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms of licenses issued by the Copyright Licensing Agency. Enquiries concerning reproduction outside those terms should be sent to the publishers. The use of registered names, trademarks, etc., in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant laws and regulations and therefore free for general use. The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made. Printed on acid-free paper Springer is part of Springer Science+Business Media (

5 To Bobbi, my sweetheart, with all my love.

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7 Preface I have been teaching web development for 14 years. I started with Perl. I can still remember the behemoth programs that contained all the logic and HTML. I remember using a text editor to write the program. Debugging consisted of a lot of print statements. It was a fun time, full of exploration, but I do not miss them. Nine years ago, I made the move to Java and Java servlets. Life became much simpler with the use of NetBeans. It has been a critical component in developing web applications using Java. Debugging a web application in NetBeans is just as easy as debugging any Java application. This book is meant for students who have a solid background in programming, but who do not have any database training. Until six years ago, my students used a glorified HashMap to save data. Then, a former student gave me the word: Hibernate. For anyone with a programming background in Java, using Hibernate to save data to a relational database is a simple task. I have always been a proponent of automating the common tasks that web applications perform. There are many packages that can simplify the job of a web developer: Log4j, BeanUtils and Hibernate. I have created additional classes that can automate additional tasks. The book uses HTML, HTML Forms, Cascading Style Sheets (CSS) and XML as tools. Each topic will receive an introduction, but the full scope of the area will not be explored. The focus of the book is on Java servlets that use Java Server Pages and connect to a MySQL database using Hibernate. No SQL will be covered in the book, because SQL is not needed. A short section in the Appendix explains some basic SQL concepts for those who want to see what Hibernate is doing. Web services are useful tools for developers. Complex features can be added to a web application by using web services. The development environments for Java now have tools and wizards that simplify accessing a service, but there is still plenty of work left for the programmer. The book has eight chapters. In a typical one-semester course, the first five chapters can be covered in detail. Chapter 7 only requires the sections on HTML tables and CSS style sheets from Chap. 6. One of the web service applications from Chap. 8 uses the shopping cart application from Chap. 7. While it might not be feasible to vii

8 viii Preface cover all eight chapters in a single semester, it is possible to pick and choose topics from Chaps. 6, 7 and 8. Chapter 1 introduces the browser-server communication process, HTML, Tomcat and dynamic pages using Java Server Pages. The chapter does not go into depth in any of these topics, but introduces enough material to be able to write simple pages that send data to the web. Chapter 2 introduces the concept of a controller. The controller is in charge of directing data to the next page. The controller makes it easier to add new pages to the application. It is better to write the controller as a Java program, known as a servlet, rather than as a Java Server Page. The details of developing a servlet are covered, including modifying the configuration file of the web application to allow access to the servlet. Chapter 3 introduces Java beans and member variables. Java beans provide support for encapsulating the data. In later chapters, the data in the bean can be stored in a database. Member variables are troublesome in servlets; they can cause errors that are hard to debug. A helper class is introduced to allow the application to use member variables. Some member variables use the same class for all servlets; other member variables use a different class for each servlet. Inheritance is used to separate the first group into a base class that can be reused by all servlets. The member variables in the second group must be placed in a class that changes for each servlet. The first three chapters introduce the basic structure of web applications. Chapter 4 adds features to the web application and provides code for simplifying some of the common tasks of a controller. The Log4j package is added to the web application and a logger is added to the controller. Students learn how easy it is to add external resources to an application. Some of the features of the application can be streamlined: eliminating the need for hidden fields by using the session, automating the controller logic, filling the bean from the request parameters. Chapter 5 completes the picture of a web application. Required validation and data persistence are introduced. Both are implemented using the Hibernate package. By the end of the chapter, the student will understand how most websites work. The student will be able to gather data, validate it, save it to a database and retrieve it. Chapter 6 contains additional HTML tags and introduces cascading style sheets. Most of Chap. 6 can be covered at any time in the course, for those who want to allow the students to create more interesting-looking websites early in the course. Chapter 7 covers HTML cookies and completes the coverage of Hibernate by removing records from the database and validating a few fields at a time. Half of the chapter is devoted to developing a shopping cart. Generics are used to create a shopping cart that can be used with any bean. The first seven chapters are for creating web applications from the ground up; Chap. 8 is about accessing resources that someone else created. Three applications are developed that access web services. One application is developed that creates Java classes from database tables that already exist. Once the Java classes exist, all the techniques from the book can be used to access the database.

9 Preface ix My goal is for students to understand how it all fits together. Sometimes I want them to know the details and sometimes I want them to just use the tools. In the beginning, I want them to learn how things work. Chapters 1, 2 and 3 introduce how websites work. Later, I want them to simplify as much as possible. Chapter 4 shows them how to use Java to automate some of the common tasks. Chapters 5 and 8 teach them to use tools to validate data, access a database and implement web services. Chapters 6 and 7 show them the details of advanced HTML elements and shopping carts. The book develops a framework for implementing websites. There are many frameworks on the market. I want students to understand how a framework might be implemented at the code level and to understand the problems that frameworks must solve. In the future, when they are introduced to other frameworks, they will understand them better. I am grateful to the community of web developers who have provided all the excellent tools for creating web applications: Apache, Tomcat, Hibernate, Java Servlets, Java Server Pages, NetBeans, Eclipse, Log4j, Apache Commons, Google web services, FedEx web services, PayPal web services, JBoss Community. I am thankful to Bobbi, my sweetheart, for all of her love and support. Without Bobbi, this book would not have been finished. I also want to thank Kip Irvine for encouraging me to write. Without Kip, this book would not have been started. Miami Tim Downey

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11 Contents 1 Browser-Server Communication Hypertext Transfer Protocol Request Format Response Format Content Type Markup Language Hypertext Markup Language Basic Tags for a Web Page What Is the HT in HTML? HTML Forms Form Elements Representing Data Transmitting Data over the Web Processing Form Data Web Application JSP Initialising Form Elements The Truth About JSPs Servlet for a JSP Handling a JSP Tomcat and IDEs Web Project Summary Chapter Review Controllers Sending Data to Another Form Action Attribute Hidden Field Technique Sending Data to Either of Two Pages xi

12 xii Contents 2.2 Using a Controller Controller Details JSP Controller JSPs Versus Servlets Controller Servlet Servlet Access Servlet Directory Structure Web Servlet Annotation Servlet Engine for a Servlet Servlets in IDEs Class Files Summary Chapter Review Java Beans and Controller Helpers Application: Start Example Java Bean Creating a Data Bean Using the Bean in a Web Application Application: Data Bean Mapping: Data Bean Controller: Data Bean Accessing the Bean in the JSP JSPs: Data Bean Application: Default Validation Java Bean: Default Validation Controller: Default Validation Member Variables in Servlets Threads The Problem with Member Variables Local Versus Member Variables Application: Shared Variable Error Controller: Shared Variable Error Reorganising the Controller Creating the Helper Base Creating the Controller Helper JSPs: Reorganised Controller Controller: Reorganised Controller Application: Reorganised Controller Model, View, Controller Summary Chapter Review

13 Contents xiii 4 Enhancing the Controller Logging in Web Applications Logging with Log4j Configuring Log4j Retrieving the Logger Adding a Logger in the Bean Eliminating Hidden Fields Retrieving Data from the Session Specifying the Location of the JSPs JSPs in the Directory Where the Controller Is Mapped JSPs in a Different Visible Directory JSPs in a Hidden Directory JSPs in the Controller s Directory Where Should JSPs Be Located? Controller Logic Decoding Button Names Executing the Correct Button Method Filling a Bean Application: Enhanced Controller JSPs: Enhanced Controller ControllerHelper: Enhanced Controller Controller: Enhanced Controller Libraries in IDEs Summary Chapter Review Hibernate Required Validation Regular Expressions Hibernate Validation Implementing Required Validation Application: Required Validation POST Requests POST Versus GET Application: POST Controller Controller: POST Controller ControllerHelper: POST Controller JSPs: Updating the JSPs with POST Saving a Bean to a Database Hibernate JAR Files Hibernate Persistence: Configuration Closing Hibernate Persistent Annotations Accessing the Database Making Data Available Data Persistence in Hibernate

14 xiv Contents 5.6 Application: Persistent Data Controller: Persistent Data ControllerHelper: Persistent Data Hibernate Configuration Files XML File File Location Simplified Controller Helper Summary Chapter Review Advanced HTML and Form Elements Images HTML Design In-line and Block Tags General Style Tags Layout Tags Cascading Style Sheets Adding Style Defining Style Custom Layout with CSS Form Elements Input Elements Textarea Element Select Elements Bean Implementation Application: Complex Elements Controller: Complex Elements ControllerHelper: Complex Elements Edit.jsp: Complex Elements Java Bean: Complex Elements Confirm.jsp, Process.jsp: Complex Elements Using Advanced Form Elements Initialising Form Elements Map of Checked Values Automating the Process Application: Initialised Complex Elements Java Bean: Initialised Complex Elements HelperBase: Initialised Complex Elements ControllerHelper: Initialised Complex Elements Edit.jsp: Initialised Complex Elements Validating Multiple Choices Application: Complex Validation Java Bean: Complex Validation Edit.jsp: Complex Validation

15 Contents xv 6.10 Saving Multiple Choices Application: Complex Persistent ControllerHelper: Complex Persistent Java Bean: Complex Persistent Process.jsp: Complex Persistent Summary Chapter Review Accounts, Cookies and Carts Retrieving Rows from the Database Finding a Row Validating a Single Property Application: Account Login Java Bean: Account Login Login.jsp: Account Login ControllerHelper: Account Login Removing Rows from the Database Application: Account Removal Process.jsp: Account Removal ControllerHelper: Account Removal Cookie Definition Cookie Class Application: Cookie Test JSPs: Cookie Test Showing Cookies Setting Cookies Deleting Cookies Finding Cookies Cookie Utilities Path Specific Cookies Application: Account Cookie Edit.jsp: Account Cookie Process.jsp: Account Cookie ControllerHelper: Account Cookie Shopping Cart Catalogue Item Create Catalogue Database Shopping Cart Bean Application: Shopping Cart ControllerHelper: Shopping Cart BrowseLoop.jsp: Shopping Cart Cart.jsp: Shopping Cart Process.jsp: Shopping Cart Shopping Cart: Enhancement

16 xvi Contents 7.10 Persistent Shopping Cart Application: Persistent Shopping Cart Bean: Persistent Shopping Cart JSPs: Persistent Shopping Cart ControllerHelper: Persistent Shopping Cart Summary Chapter Review Web Services and Legacy Databases Application: Google Maps Bean: Google Maps Service Method: Google Maps Process Method: Google Maps Process.jsp: Google Maps Properties File: Google Maps FedEx: Rate Service FedEx: Overview Application: FedEx Bean: FedEx JSPs: FedEx ControllerHelper: FedEx PayPal Web Service Application: PayPal ControllerHelper: PayPal JSPs: PayPal Legacy Database Eclipse Tools Summary Chapter Review Appendix Integrated Development Environments NetBeans Eclipse CLASSPATH and Packages Usual Suspects What Is a Package? JAR File Problems Hibernate MySQL Driver Hibernate Annotations MySQL

17 Contents xvii 9.5 Auxiliary Classes Annotations Cookie Utility Enumerations Helper Base Hibernate Helper InitLog4j Servlet PersistentBase Class Webapp Listener Glossary Bibliography Index

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