weboi - student guide struts

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Object Innovations Course 114

William W. Provost

Student Guide Revision 1.1.1

Jakarta Struts


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Jakarta Struts

Rev. 1.1.1 Copyright © 2003-2004 Object Innovations, Inc., and William W. Provost iiAll Rights Reserved

Jakarta Struts

Rev. 1.1.1

Student Guide

Information in this document is subject to change without notice. Companies, names and data

used in examples herein are fictitious unless otherwise noted. No part of this document may be

reproduced or transmitted in any form or by any means, electronic or mechanical, for any

purpose, without the express written permission of Object Innovations.

Other product and company names mentioned herein are the trademarks or registered trademarks

of their respective owners.

Copyright © 2003 Object Innovations, Inc. and William W. Provost All rights reserved.

Object Innovations, Inc.

290 Turnpike Rd., Suite 413,

Westborough, MA 01581-2843

877-558-7246www.objectinnovations.com

Printed in the United States of America.


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Table of Contents (Overview)

Course Overview

Chapter 1 Struts Architecture

Chapter 2 Action Mappings

Chapter 3 Form Beans

Chapter 4 Persistent Data

Chapter 5 Struts Tag Libraries

Chapter 6 The JSP Standard Tag Library

Chapter 7 Internationalization and Localization

Chapter 8 Validating Input

Chapter 9 Under the Hood

Chapter 10 Best Practices

Chapter 11 Tiles

Appendix A Learning Resources


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Prerequisites

• Struts is a framework for Web application

development using Java servlets and JSPs.

• This course treats Struts in depth and therefore

requires students to have several skill sets coming

into the class:

− HTML page authoring, at least at a basic level of fluency

−

Java programming, including fluent use of Java classes,interfaces, inner classes, etc.

− Java servlets programming, including interactive Web

applications, session attributes, initialization parameters,

configuration and context

− JavaServer Pages (JSP) development, preferably to the

level of good familiarity with standard actions and custom

tags

• Some experience with will XML is helpful in

managing Struts configuration files.

− This is not absolutely critical, however.


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Labs

• The module relies on hands-on experience in various

topics and techniques.

• All lab code is 100% Pure Java, written to build and

run on the J2SE SDK, version 1.4.

• Students will also work with a number of file types,

all written to the applicable Java or W3C standard:

− HTML pages (.html)

− Java Server Pages (.jsp) and fragments

− SQL scripts (.sql)

− XML documents (.xml)


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Lab Installation

• The installation files for this course have been

provided to you by your courseware vendor, training

coordinator, or instructor.

− We’ll refer to an installation root directory, which may be a

shared network drive, or possibly the root directory of a CD-

ROMs or floppy disk which you’ve been given.

− Your instructor can direct you as to where to find this

material.

• Assure that the J2SE SDK 1.4.1 is installed on your

system, and that its bin directory is included in your

path.

− You should be able to run the following command with

substantially the same output as shown:

java –versionjava version "1.4.1"

...

• Run the Install.bat script to install the module.

− Let the script run to completion, even if you notice a few

error messages appear in console output during the install.

−

You can test for complete installation by checking the resultsas described on the following pages.


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Directory Structure for All Courses

• The install scripts will create all the required files in

and under a standard target directory:

− c:\OI for Windows systems

− $HOME/OI for Linux systems

• This is Object Innovations’ course root directory,

shared by this module along with others from the OI

curriculum.− In some cases your instructor may direct you to perform a

custom installation to some other destination.

− Throughout the student guide we will use c:\OI to represent

this directory.


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Directory Structure for the Module

• Each module will install to a combination of this

shared course root and its own module root directory

c:\OI\Struts.

− Under this root, the Examples directory holds code

examples, including all the starting, intermediate and answer

versions of all the labs.

− The Demos directory is home to files that relate to in-class

demonstrations, many of which will lead up to furtherdevelopment in labs.

− The Labs directory holds one subdirectory for each lab in the

course, named for the course module and lab number. This is

where you will do the bulk of your lab work, with some

reference to code in the Examples directory.

− The Docs directory holds HTML documentation giving an

overview of the course’s lab and example software. Theindex.html file is a good starting point for browsing the

course software, giving links to file sources, sample results,

and presentations: live XML presentations for browsers that

support it, and screenshots for browsers that don’t.

− Also, under each example, lab, or demo project, there will be

a Docs directory with generated javadoc for the Java code.

This can be browsed directly or can be found through the

index file mentioned above.


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Jakarta Struts

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Table of Contents (Detailed)

Chapter 1: Struts Architecture........................................................................................ 1

Servlets and JSPs ............................................................................................................ 3The Model-View-Controller Pattern............................................................................... 4

Benefits of MVC............................................................................................................. 5

MVC for Web Applications............................................................................................ 6The Command Pattern .................................................................................................... 7

Jakarta Struts................................................................................................................... 8

Handling Requests .......................................................................................................... 9Handling Requests – Java View ................................................................................... 10

More XML, Less Java!................................................................................................. 11

Declarations in web.xml ............................................................................................... 12The Struts Configuration .............................................................................................. 13

Handling Requests – XML View.................................................................................. 14Example – A 2-Page Web Application......................................................................... 15JavaBeans...................................................................................................................... 18

JavaBeans in Struts ....................................................................................................... 19

Working with Forms..................................................................................................... 20

Validation...................................................................................................................... 21Relational Data and Other Models................................................................................ 22

Presentation Technology............................................................................................... 23

Tiles .............................................................................................................................. 24The Tomcat Web Server............................................................................................... 25

Starting and Stopping Tomcat ...................................................................................... 26

The Ant Build Tool....................................................................................................... 27Course Exercises – File Organization........................................................................... 28

Development Process.................................................................................................... 29Environment and Setup................................................................................................. 30

Example – Building and Deploying.............................................................................. 31

Modules ........................................................................................................................ 34Learning Struts.............................................................................................................. 35

Designing Web Applications........................................................................................ 36

UML.............................................................................................................................. 37

Notation ........................................................................................................................ 38Case Study – Love Is Blind .......................................................................................... 39

The Struts Application.................................................................................................. 40Design Diagram ............................................................................................................ 41Summary....................................................................................................................... 42

Chapter 2: Action Mappings ......................................................................................... 43

The Command Pattern for the Web.............................................................................. 45

The Action Class........................................................................................................... 46Declaring Action Mappings.......................................................................................... 47

The Element ................................................................................................. 48


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Example – Elliptical Math ............................................................................................ 49

Example – A Calculator................................................................................................ 54The ForwardAction Class ............................................................................................. 57

Declaring a Forward ..................................................................................................... 58

Global Forwards ........................................................................................................... 59

Example – Querying LoveIsBlind................................................................................ 60Case Study – Next Steps............................................................................................... 64

More on the Love-is-Blind Domain.............................................................................. 65

Lab 2A .......................................................................................................................... 66Other Action Subtypes.................................................................................................. 67

Declarative Exception Handling................................................................................... 68

Global Exceptions......................................................................................................... 69Exception Handlers....................................................................................................... 70

The Standard Exception Handler.................................................................................. 71

The Periscope................................................................................................................ 72Example – Exceptions in Calculator............................................................................. 73

Example – Exceptions in Ellipsoid............................................................................... 76Lab 2B........................................................................................................................... 77

Summary....................................................................................................................... 78

Chapter 3: Form Beans .................................................................................................. 85

Working with HTML Forms......................................................................................... 87

Managing Information .................................................................................................. 88

What Not to Do............................................................................................................. 89Form Beans ................................................................................................................... 91

The Action Form Class................................................................................................. 92

Declaring an Action Form ............................................................................................ 93Relationship to Input..................................................................................................... 94

Relationship to Actions................................................................................................. 95Relationship to the Model............................................................................................. 96

Relationship to Output.................................................................................................. 97

Example – Ellipsoid Form Bean................................................................................... 98Example – Dropping Exceptions ................................................................................ 100

Lab 3A ........................................................................................................................ 103

Lab 3B......................................................................................................................... 104Declaring Form Properties.......................................................................................... 105

The DynaActionForm Class ....................................................................................... 106

Map-Backed Forms..................................................................................................... 107

Lab 3C (Optional)....................................................................................................... 108

Validation.................................................................................................................... 109Strong Typing? ........................................................................................................... 110

Form Bean Design ...................................................................................................... 111Coarse-Grained Action Forms .................................................................................... 112

The reset Method ........................................................................................................ 113

Summary..................................................................................................................... 114

Chapter 4: Persistent Data........................................................................................... 123

Many Models for Models ........................................................................................... 125


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JDBC........................................................................................................................... 126

Connection, Statement, and ResultSet........................................................................ 127Sample Code ............................................................................................................... 128

Two Paths to a Connection ......................................................................................... 129

Many Paths to a DataSource....................................................................................... 130

The Struts DataSource Manager................................................................................. 131The Element........................................................................................ 132

MySQL ....................................................................................................................... 133

MySQL Server Setup.................................................................................................. 134MySQL Database Setup.............................................................................................. 135

Example – Web Retailing........................................................................................... 136

Multi-Tier Architecture............................................................................................... 140Business Logic Beans ................................................................................................. 141

Persistence Code ......................................................................................................... 142

EJB.............................................................................................................................. 143Demo – A Database for LoveIsBlind ......................................................................... 144

Lab 4 ........................................................................................................................... 149Summary..................................................................................................................... 150

Chapter 5: Struts Tag Libraries.................................................................................. 153

Building View Components........................................................................................ 155

Struts Tag Libraries .................................................................................................... 156

Deployment of Custom Tags...................................................................................... 157

Struts Tag Library Namespaces.................................................................................. 158Attributes for Struts Tags............................................................................................ 159

The HTML Tag Library.............................................................................................. 160

Building Forms ........................................................................................................... 161The Tag ................................................................................................. 162

The Tag, et. al. ........................................................................................ 163Forms and Form Beans............................................................................................... 164

Scenarios for Data Transfer ........................................................................................ 165

Scope and Duration of Form Data .............................................................................. 166Demo – LoveIsBlind Forms ....................................................................................... 167

Managing Hyperlinks ................................................................................................. 174

Example – Links in the Results Page.......................................................................... 175The Tag................................................................................................ 176

The Logic Tag Library................................................................................................ 177

Other Struts Tag Libraries .......................................................................................... 178

Case Study – Next Steps............................................................................................. 179

Lab 5 ........................................................................................................................... 180Summary..................................................................................................................... 181

Chapter 6: The JSP Standard Tag Library ............................................................... 187

The JSP Standard Tag Library.................................................................................... 189The JSP Expression Language.................................................................................... 190

Using JSP Expressions................................................................................................ 191

EL Syntax ................................................................................................................... 192JSTL Namespaces....................................................................................................... 193


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The JSTL Core Library............................................................................................... 194

Example – Odds and Evens ........................................................................................ 195The JSTL Formatting Library..................................................................................... 197

Example – Date and Time .......................................................................................... 198

The JSTL SQL Library............................................................................................... 200

Example – The Web Retailer...................................................................................... 201The JSTL XML Library.............................................................................................. 203

Example – Rental Housing ......................................................................................... 204

Mixing JSTL and Struts Tags ..................................................................................... 207Using EL with Struts Tags.......................................................................................... 208

Case Study – Next Steps............................................................................................. 209

Lab 6A ........................................................................................................................ 210Lab 6B......................................................................................................................... 211

Summary..................................................................................................................... 212

Chapter 7: Internationalization and Localization ..................................................... 219

Such Long Words! ...................................................................................................... 221

i18n in Java ................................................................................................................. 222Locales........................................................................................................................ 223

Determining Locale .................................................................................................... 224Time Zones ................................................................................................................. 225

Resource Bundles ....................................................................................................... 226

Finding a Resource Bundle......................................................................................... 227

i18n in Struts Configuration ....................................................................................... 228i18n in Struts Actions and Forms ............................................................................... 229

i18n in Struts Tag Libraries and JSTL........................................................................ 230

Example – The Calculator .......................................................................................... 231Example – The Language of Love.............................................................................. 232

i18n in Validation ....................................................................................................... 234Lab 7 ........................................................................................................................... 235

Summary..................................................................................................................... 236

Chapter 8: Validating Input ........................................................................................ 239

We All Seek Validation .............................................................................................. 241Where, When, and How?............................................................................................ 242

Validation in Web Applications ................................................................................. 243

Validate and Repeat .................................................................................................... 244Validation in Struts ..................................................................................................... 245

The Struts Validator.................................................................................................... 246

The ValidatorForm Class............................................................................................ 247

Dyna-This and Action-That …................................................................................... 248Validating ActionForm Subtypes ............................................................................... 249

Configuring Validation............................................................................................... 250

Validators.................................................................................................................... 251The “required” Validator ............................................................................................ 252

The “intRange” Validator ........................................................................................... 253

Rules ........................................................................................................................... 254Demo – Validating Semi-Axis Lengths...................................................................... 255


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Is Necessary?......................................................................................... 259

Reporting Errors ......................................................................................................... 260Example – Highlighting Invalid Fields....................................................................... 261

Case Study – Almost Home! ...................................................................................... 264

Coarse-Grained Beans and Validation........................................................................ 265

Multi-Page Validation................................................................................................. 266Lab 8A ........................................................................................................................ 267

Client-Side Validation ................................................................................................ 268

Demo – Client-Side Validation................................................................................... 269Limitations on the Client Side .................................................................................... 270

Implementing a Validator ........................................................................................... 271

Example – Positive Numbers...................................................................................... 272Implementing validate ()............................................................................................. 274

Lab 8B (Optional)....................................................................................................... 275

Summary..................................................................................................................... 276

Chapter 9: Under the Hood ......................................................................................... 285

Digging Deeper........................................................................................................... 287Global Objects ............................................................................................................ 288

The Globals Keys........................................................................................................ 289Examples – JSP Access to Globals............................................................................. 290

Struts Modules ............................................................................................................ 291

Struts, Servlets, and JSP ............................................................................................. 292

Know Thy Source ....................................................................................................... 293The ActionServlet Class ............................................................................................. 294

ActionServlet Cohorts................................................................................................. 295

The RequestProcessor Class ....................................................................................... 296The Action Class......................................................................................................... 297

Struts Configuration in Depth..................................................................................... 298Configuring Action Mappings.................................................................................... 299

Controller Configuration............................................................................................. 300

Plug-Ins....................................................................................................................... 301Implementing a Plug-In .............................................................................................. 302

org.apache.struts.config .............................................................................................. 303

Logging....................................................................................................................... 304The Commons Logging API....................................................................................... 305

Severity Levels ........................................................................................................... 306

Creating a Commons Log........................................................................................... 307

Log4J .......................................................................................................................... 308

Categories ................................................................................................................... 309Appenders ................................................................................................................... 310

Configuration .............................................................................................................. 311Logging Setup............................................................................................................. 312

Demo – Logging Configurations ................................................................................ 313

Demo – Logging in a Web Application...................................................................... 318org.apache.struts.util................................................................................................... 320

Commons BeanUtils ................................................................................................... 321


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Initializing Persistence Classes................................................................................... 322

Solutions ..................................................................................................................... 323Lab 9A ........................................................................................................................ 324

Lab 9B......................................................................................................................... 325

Summary..................................................................................................................... 326

Chapter 10: Best Practices........................................................................................... 333Effective Struts Development..................................................................................... 335

Cardinality .................................................................................................................. 336

One Form Bean to Many Anythings........................................................................... 337One View to Many Actions ........................................................................................ 338

Many Actions to One View ........................................................................................ 339

Example – Branching.................................................................................................. 340

One Action to Many Views ........................................................................................ 342Many Mappings to One Action?................................................................................. 343

Chaining Actions ........................................................................................................ 344

Dynamic Forwarding .................................................................................................. 346

The Mediator Tier....................................................................................................... 347Form Beans as Mediators ........................................................................................... 348

Leverage from the Business Tier ................................................................................ 349Reflection.................................................................................................................... 350

Using BeanUtils.......................................................................................................... 351

Lab 10A ...................................................................................................................... 352

Reusing Validation Rules ........................................................................................... 353Multipage Validation .................................................................................................. 354

Validating Immediate Inputs ...................................................................................... 355

Mapping-Based Validation ......................................................................................... 356Graceful Validation..................................................................................................... 357

Lab 10B....................................................................................................................... 358Summary..................................................................................................................... 359

Chapter 11: Tiles........................................................................................................... 365

Consistent Look and Feel ........................................................................................... 367

Reusable Layouts........................................................................................................ 368Reusable Content ........................................................................................................ 369

The Tiles Framework.................................................................................................. 370

Layouts........................................................................................................................ 371Instantiating Layouts................................................................................................... 372

Tiles ............................................................................................................................ 373

Body-Wrap Insertions................................................................................................. 374

Demo – Refactoring Love is Blind............................................................................. 375Tiles and Stylesheets................................................................................................... 381

Attributes .................................................................................................................... 382

The Tiles Context........................................................................................................ 383Page Inheritance.......................................................................................................... 384

Definitions .................................................................................................................. 385

Advantages of Definitions .......................................................................................... 386Aggregation and Inheritance....................................................................................... 387


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The Tiles Plug-In ........................................................................................................ 388

Extending Definitions................................................................................................. 389Forwarding to Definitions........................................................................................... 390

Dynamic Page Description ......................................................................................... 391

Performance ................................................................................................................ 392

Lab 11 ......................................................................................................................... 393Summary..................................................................................................................... 394

Appendix A: Learning Resources............................................................................... 397


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Jakarta Struts Chapter 7

Rev. 1.1 Copyright © 2003 Object Innovations, Inc., and William W. Provost 219All Rights Reserved

Chapter 7

Internationalization and

Localization


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Internationalization and Localization

Objectives

After completing this unit you will be able to:

• Describe the Java 2 Standard Edition framework for

internationalization and localization.

• Explain how Struts builds on this framework:

− Configuration of resource bundles as defaults, or undersimple key names, in the application context.

− Consistent use of message keys, instead of literal values,throughout the Struts tag libraries.

• Use internationalization features in your Struts

applications:

− Define user-visible strings in resource bundles.

− Provide user feedback based on message keys.

− Use Struts and Java standard tag libraries to presentcompletely localized user interfaces.


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Such Long Words!

• The unwieldy terms internationalization and

localization refer to the development effort required

to make a piece of software usable in multiple

countries and locales.

− This means managing multiple written languages, and inthe this chapter we’ll look at how to create locale-specificresource bundles that can be swapped in based on the user’sor application’s chosen locale.

− It also involves formatting output according to localconventions, even where language is not an issue per se.Although we will not study it in detail, the JSTL formattingtag library provides excellent support for this.

• To save ink and breath, many developers eventually

find their way to the term i18n – an extremely terse

phrase which is perhaps an overcompensation.− There are 18 letters between the first and last letters of the

word ‘internationalization.’


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i18n in Java

• The J2SE provides complete support for

internationalization, although the APIs are not the

most facile things in the world.

• The framework is based on a handful of classes in the

java.util package:

− Locale

−

TimeZone

− ResourceBundle

• We’ll consider each of these briefly, although for

Struts purposes it will be resource bundles that are

the most interesting.


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Locales

• In order to produce output that will make the most

sense to a human user, an application first needs to

understand a few things about that user’s locale:

− The language he or she reads and writes. This will influencethe language used in application messages and output.

− The place from which he or she is using the application. Thiswill affect the format in which certain output is produced.

− The time zone from which he or she is using the application.This will affect date and time values, rather than formats.

• Java software uses the java.util.Locale class to

encapsulate the first two factors.

− This class can produce and parse a string representation thatcombines two-letter codes for language and country.

− Both of these code sets are standardized by the ISO – seeISO-639 and ISO-3166, respectively.

− The resulting string representation is of the form “xx-XX”,where “xx” is the lowercase language code and “XX” is theuppercase country code.

− For example, this chapter was written in “en-US”.


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Determining Locale

• The application can set its locale preference.

− This is typically in response to some user input – perhaps aconfiguration performed once when a user creates a profile.

− This may also be done purely for testing purposes.

• Much more likely for Web applications is that the

locale will be provided by the browser or other user

agent.− Popular browsers will rely on the operating system to provide

locale information, and will provide that locale to theapplication per request.

− They also have preferences screens that allow the user tochoose another locale or language in which he or she would

prefer to interact with Web applications.

− In this way, applications that don’t set a locale at all can beassured that locale-dependent behaviors will be tailoredcorrectly for the current user.


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Time Zones

• Java software uses the java.util.TimeZone class to

encapsulate information about a time zone.

− Again, there is a common string representation as well, inthis case specified as part of the Java standard platform.

− Two formats are possible: a terse one stating “GMT” plus orminus some number of hours, and a verbose one in which thenames of places are written longhand and separated by

slashes, as in “America/Los_Angeles”.

• As with locales, the prevailing time zone can be set by

application code, but it is much more common to get

it from the client side.


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Resource Bundles

• A resource bundle is a collection of named resources

dedicated to a specific locale.

− An application will commonly deploy several resource bundles, one for each locale or language supported – forexample separate bundles for US English, UK English,French and Spanish.

− Each such bundle will have the same set of keys, but

different values for those keys.

− The application relies on lookups into these bundles to present a locale-specific interface from the same Java code.

• The java.util.ResourceBundle class encapsulates a

resource bundle as loaded into memory.

− Keys are always strings, but values can be of any Java type,

including primitives and objects.

• More conveniently, bundles of message strings can be

implemented in properties files that simply list the

strings in “name=value” format, one per text line.

− This is still backed by a Java class, actually, which is java.util.PropertyResourceBundle.

• In either case, the placement of the artifact issignificant: the Java package and class name, or the

subdirectory path and name of a properties file, will

be used to identify it as a bundle for a certain

purpose.


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Finding a Resource Bundle

• When a Java class or JSP requests a localized

resource such as a message string, it does so by

providing:

− The message key

− The bundle’s base name

− The desired locale (or it relies on the prevailing default)

• Resource-management code in the J2SE runtimeresolves this request by finding the correct resource

bundle.

− The base name combined with the locale gives the name of aconcrete bundle, and the runtime searches for a bundle of thiscalculated name.

−

The actual algorithm is a good bit more complex, allowingfor more or less specific locale suffices to be used in bundlenames. (For instance a bundle might be dedicated to alanguage only, and not to a locale.)

− Also, an ordered list of preferred locales may be supplied bya browser, rather than a single default locale.

− We will not delve into all the tricks and twists of i18n

resource management and deployment in this chapter.


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i18n in Struts Configuration

• The Struts framework further simplifies the

deployment of message resources.

• Resource bundles are deployed within the application

in the standard manner.

− As with just about everything else in Struts, the Strutsfeatures are built on existing standards, without hiding orcompromising those standards.

− Application code can still use the usual J2SE i18n APIs.

• Message bundles can be declared in the

configuration, using top level elements of type

.

− These elements map bundles by a key name into theapplication context. The key can be omitted to declare a

default resource bundle.

− The parameter attribute connects this key (or default) to aresource bundle by the usual Java i18n base name.

• This does nothing of real value for the application’s

Java code, but it puts message bundles into objects

that can be easily discovered and read by tag

libraries.

− Both Struts and Java standard tag libraries can use bundles published in this way – Struts implicitly, JSTL explicitly.


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i18n in Struts Actions and Forms

• Controller code is of course not responsible for

presenting localized messages.

• It is often required to produce those messages,

however.

• With i18n thoroughly supported in Struts – through

presentation tags, in generic actions and other

components, and in the Struts Validator – application

code can speak entirely in terms of message keys.

− When reporting an error, it is a key that’s passed to the globalERRORS object.

− The same is true for placing a general-purpose message in theMESSAGES object.


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i18n in Struts Tag Libraries and JSTL

• The Struts tag libraries support internationalization

everywhere that a literal message might be produced

to the output stream.

− HTML tags can use message keys for captions, titles, andalternate text. For convenience, most tags offer pairs ofattributes, such as title (literal) and titleKey (resource key to

be dereferenced), only one of which will be used.

−

The tag provides a simple and directmeans of producing a message of a certain key.

− Throughout, the default resource bundle (localized accordingto client preference, if possible) is used, or can be overridden

by a separate attribute (the attribute name varies).

• JSTL provides the formatting library, which offers

several tags dedicated to localized processing:

− Date, time, number and currency formatting.

− Production of localized messages.

− does more or less the same job as

, although again the Struts tag is a step

easier to use because it assumes the use of the Struts defaultresource bundle, where the JSTL tag would need it to be

declared in a separate attribute or separate tag.


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Example – The Calculator

• We’ve seen a few examples of localized strings

already – although at runtime only a default resource

bundle is deployed.

• One such example is the Calculator application,

which reports exceptional conditions using the

application-defined error.serverException key.

• See Examples\Calculator\Step3:

− Config\struts-config.xml:

− Config\classes\application.properties:

error.serverException=

An error was encounteredin processing this request. The calculator memoryhas been cleared; you can try again!

− View\Calculator.jsp:


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Example – The Language of Love

• A more ambitious example of internationalizing an

application is found in Examples\Amour .

• This is a variant of an earlier version of Love is Blind

in which the initial walk-in query is presented

entirely using resource strings.

− The JSPs use the JSTL formatting tags, bypassing the Strutsconfiguration to look up the resource bundle by the standard

J2SE algorithm.

− The rest of the page presentation is carefully resourced:

—

:...

• English- and French-language resource bundles have

been deployed.


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Example – The Language of Love

• Build and test the application – it should look normal

at first.

• Try setting a preference in your browser for the

locale “fr-FR” and then reload the query page …


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i18n in Validation

• In the next chapter we’ll take a long look at the Struts

Validator.

• It is here that internationalization first imposes itself

upon many Struts developers.

− Validation rules and the validator framework in general aremostly about generically handling problems.

−

This means declaring messages that should be handed back tothe user when problems arise.

− Message keys are the natural way to do this, and Struts’ philosophy on internationalization seems to be, “In for a penny, in for a pound.”

− So, where in other aspects of development one might chooseto forego internationalization for early iterations, when it

comes to validation there is really no other way to go about it(except to build one’s own validator).


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Lab 7

An Authentication Error Message

In this lab you will enhance the existing Love is Blind logon page.It currently does nothing to inform the user when authenticationfails – it is just shown repeatedly until the user gets it right or goesaway. You will add code to Logon.jsp to present an advisorymessage, and a key and value to the default resource bundle tosupport the JSP.

Detailed instructions are contained in the Lab 7 write-up at the endof the chapter.

Suggested time: 30-45 minutes.


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Summary

• On the other hand, Struts’ thoroughness with, and

insistence on, internationalization can be helpful.

• The use of a default resource bundle, and the

consistent use of message keys throughout the system,

makes it fairly simple to get internationalization

support involved in the very first iteration of a Struts

application.

• Many applications really never will grow to use

anything but their default bundles, but they will be

none the worse for having gotten into the system.

− Bear in mind that even if an application never needs to beinternationalized in the strictest sense, there can still beadvantages to having a string table in play.

−

Certain presentations – button captions, phrasing of usermessages, etc. – can be fine-tuned late in the development

process without difficulty, if message keys are usedconsistently in the application.

• Those that do need to support multiple languages and

locales can start to add new bundles.

− One great thing about the Java i18n framework is that once

the base names and keys for bundles and strings are knownand in use, the simple act of adding a resource bundle to theWAR file will activate resources for the new target language.

− No additional configuration of any sort is required.


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Lab 7

An Authentication Error Message

Introduction

In this lab you will enhance the existing Love is Blind logon page. It currently doesnothing to inform the user when authentication fails – it is just shown repeatedly until theuser gets it right or goes away. You will add code to Logon.jsp to present an advisorymessage, and a key and value to the default resource bundle to support the JSP.

Suggested Time: 30-45 minutes.

Root Directory: OI\Struts

Directories: Labs\Lab7 (do your work here)Examples\LoveIsBlind\Step7 (backup copy of starter files)Examples\LoveIsBlind\Step8 (contains lab solution)

Files: View\Member\Logon.jsp

Config\classes\application.properties

Instructions

1. Build and test the starter application. As you may already have noticed, if you flunkyour logon, the JSP just shows again, with password cleared. It’s a pretty good guesswhat’s happening, from the user’s perspective, but it’s hardly good presentation.

2. Review the code in oi\LIB\action\Authenticate.java , and note that on failure it sets arequest-scope attribute “authenticated” to “false”.

3. Open Logon.jsp and add code right after the page heading. Start by using with a test attribute of “${authenticated == ‘false’}” to see if authentication failed onthe recent request.

4. Inside the conditional tag, create a element, and inside it a with attribute baseName set to “application”. Tags occurring inside this one willdefault to look up keys in the application.properties bundle already deployed with

the application.

5. Finally, inside the bundle tag, add a tag with key equal to“error.invalidLogon”. This is a new key for the application, which will need to havea value defined.


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6. Open application.properties and define a message for the new key – something tothe effect that the user and password couldn’t be authenticated in the memberdatabase.

7. Build and retest the application, and provide a bad password for someone. Youshould see your message clearly in the re-displayed logon page. (This is the

Step8

answer code; the remaining steps are a quick experiment and are not reflectedanywhere in the example steps.)

Optional Steps

8. Try the same thing with , as follows.

9. You will need to declare the Struts bean tag library instead of the JSTL formattinglibrary.

10. You will still need the conditional, but then you can place a

tag with the same key attribute where the is currently.

11. You can remove the entirely, since the new tag will automaticallylook up the Struts default bundle as already configured.

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