Struts Intro Course by Kamalakar Dandu

8/2/2019 Struts Intro Course by Kamalakar Dandu

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Project Refinery, Inc. 1

STRUTSPart of the Jakarta Project

Sponsored by theApache Software Foundation

Developed by: Roger W Barnes of Project Refinery, Inc.

Introduction to Struts


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STRUTS Objectives

Course Overview

Unit 1 - Model-View-Controller Design

PatternUnit 2 - Model Components

Unit 3 - View Components

Unit 4 - Controller ComponentsUnit 5 - Tag Libraries


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STRUTS Objectives

Unit 6 - STRUTS Configuration File

Unit 7 - Web Application Descriptor File

Unit 8 - Application Resources FileUnit 9 Resources


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Model-View-Controller DesignPattern

Unit 1


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STRUTS MVC Design Pattern

Central controller mediates applicationflow

Controller delegates to appropriatehandler

Handlers are tied to model components

Model encapsulates business logicControl forwarded back through the

Controller to the appropriate View


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3 Major Components in STRUTS

Servlet controller (Controller)

Java Server Pages (View)Application Business Logic (Model)

Controller bundles and routes HTTPrequest to other objects in framework

Controller parses configuration file




Configuration file contains actionmappings (determines navigation)

Controller uses mappings to turn HTTPrequests into application actions

Mapping must specify

A request pathObject type to act upon the request


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Model Components

Unit 2



STRUTS Model Components

Model divided into concepts

Internal state of the system

Actions that can change that state Internal state of system represented by

JavaBeans

Enterprise JavaBeans




JavaBeans and Scope Page visible within a single JSP page, for the

lifetime of the current request

Request visible within a single JSP page, as wellas to any page or servlet that is included in thispage, or forwarded to by this page

Session visible to all JSP pages and servletsthat participate in a particular user session, across

one or more requests Application - visible to all JSP pages and servlets

that are part of a web application




ActionForm Beans Extends the ActionForm class

Create one for each input form in the application

If defined in the ActionMapping configuration file,the Controller Servlet will perform the following: Check session for instance of bean of appropriate class

If no session bean exists, one is created automatically

For every request parameter whose name corresponds

to the name of a property in the bean, the correspondingsetter method will be called

The updatedActionForm bean will be passed to theAction Class perform() method when it is called, makingthese values immediately available


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When coding ActionForm beans consider: The ActionForm class itself requires no specific

methods to be implemented. It is used to identifythe role these particular beans play in the overallarchitecture. Typically, an ActionForm bean willhave only property getter and property settermethods, with no business logic

The ActionForm object also offers a standard

validation mechanism. If you override a "stub"method, and provide error messages in thestandard application resource, Struts willautomatically validate the input from the form


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Continued Define a property (with associated getXxx() and

setXxx() methods) for each field that is present inthe form. The field name and property name mustmatch according to the usual JavaBeansconventions

Place a bean instance on your form, and usenested property references. For example, you

have a "customer" bean on your Action Form, andthen refer to the property "customer.name" in yourJSP view. This would correspond to the methodscustomer.getName() andcustomer.setName(string Name) on your

customer bean


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System State Beans

Actual state of a system is normally representedas a set of one or more JavaBeans classes,

whose properties define the current state A shopping cart system, for example, will include a

bean that represents the cart being maintained foreach individual shopper, and will (among other

things) include the set of items that the shopperhas currently selected for purchase


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Business Logic Beans Should encapsulate the functional logic of your

application as method calls on JavaBeansdesigned for this purpose

For maximum code re-use, business logic beansshould be designed and implemented so that theydo not know they are being executed in a webapplication environment

For small to medium sized applications, businesslogic beans might be ordinary JavaBeans thatinteract with system state beans passed asarguments, or ordinary JavaBeans that access adatabase using JDBC calls


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Business Logic Beans - Continued

For larger applications, these beans willoften be stateful or stateless Enterprise

JavaBeans (EJBs)


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Accessing Relational Databases

Struts can define the datasources for anapplication from within its standard

configuration file

A simple JDBC connection pool is alsoprovided


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View Components

Unit 3


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STRUTS View Components

Internationalized Messages Struts builds upon Java platform to provide

assistance for building internationalized and localizedapplications Locale - fundamental Java class that supports

internationalization

ResourceBundle - supports messages in multiple languages

PropertyResourceBundle - standard implementation ofResourceBundle that allows you to define resources using

the same "name=value" syntax used to initialize propertiesfiles

MessageFormat - allows you to replace portions of amessage string with arguments specified at run time

MessageResources - lets you treat a set of resource bundles

like a database, and allows you to request a particularmessage string for a particular Locale


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ApplicationResources.properties

Contains the messages in the defaultlanguage for your server. If your default

language is English, you might have anentry like this: prompt.hello=Hello

ApplicationResources_xx.properties

Contains the same messages in thelanguage whose ISO language code is "xx"


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Forms and FormBean interactions

HTML Forms and their limitations

Errors not easily handled


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Building Forms with Struts

The taglib directive tells the JSP page compiler

where to find the tag library descriptorfor the

Struts tag library message tag is used to look up internationalized

message strings from a MessageResources

object containing all the resources for thisapplication

The errors tag displays any error messages thathave been stored by a business logic component,or nothing if no errors have been stored


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Building Forms with Struts continued The form tag renders an HTML element,

based on the specified attributes

The form tag also associates all of the fields withinthis form with a request scoped FormBean that isstored under the key FormName

The form bean can also be specified in the Strutsconfiguration file, in which case the Name and

Type can be omitted here The text tag renders an HTML element of

type "text

The submit and reset tags generate thecorresponding buttons at the bottom of the form


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Input field types supported checkboxes

hidden fields

password input fields radio buttons

reset buttons

select lists

options submit buttons

text input fields

textareas


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Useful Presentation Tags [logic] iterate repeats its tag body once for each

element of a specified collection (which can be anEnumeration, a Hashtable, a Vector, or an array of

objects) [logic] present depending on which attribute is

specified, this tag checks the current request, andevaluates the nested body content of this tag only

if the specified value is present [logic] notPresent the companion tag to present,

notPresent provides the same functionality whenthe specified attribute is not present
http://../Java%20Docs/STRUTS/Docs/struts-logic.htmlhttp://../Java%20Docs/STRUTS/Docs/struts-logic.htmlhttp://../Java%20Docs/STRUTS/Docs/struts-logic.htmlhttp://../Java%20Docs/STRUTS/Docs/struts-logic.htmlhttp://../Java%20Docs/STRUTS/Docs/struts-logic.htmlhttp://../Java%20Docs/STRUTS/Docs/struts-logic.html


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Useful Presentation Tags continued [html] link generates a HTML element as an

anchor definition or a hyperlink to the specifiedURL, and automatically applies URL encoding to

maintain session state in the absence of cookiesupport

[html] img generates a HTML element withthe ability to dynamically modify the URLs

specified by the "src" and "lowsrc" attributes in thesame manner that can

[bean] parameter retrieves the value of thespecified request parameter, and defines theresult as a page scope attribute of type String or

String
http://../Java%20Docs/STRUTS/Docs/struts-html.htmlhttp://../Java%20Docs/STRUTS/Docs/struts-html.htmlhttp://../Java%20Docs/STRUTS/Docs/struts-bean.htmlhttp://../Java%20Docs/STRUTS/Docs/struts-bean.htmlhttp://../Java%20Docs/STRUTS/Docs/struts-html.htmlhttp://../Java%20Docs/STRUTS/Docs/struts-html.html


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Automatic Form Validation

Struts offers an additional facility to validate theinput fields it has received

To utilize this feature, override the validate()method in your ActionForm class

The validate() method is called by the controllerservlet after the bean properties have been

populated, but before the corresponding actionclass's perform() method is invoked


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Page Composition with Includes The development of the various segments

of a site is easier if you can divide up the

work, and assign different developers tothe different segments

Use the includecapability of JavaServerPages technology to combine the results

into a single result page, or use the includetag provided with Struts


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Page Composition with Includes continued There are three types of includeavailable,

depending on when you want the combination ofoutput to occur: An directive can include a

file that contains java code or jsp tags

The include action() is processed at request time, and ishandled transparently by the server

The bean:include tag takes either a an argument"forward" representing a logical name mapped to the jspto include, or the "id" argument, which represents a pagecontext String variable to print out to the jsp page
http://../Java%20Docs/STRUTS/Docs/struts-bean.htmlhttp://../Java%20Docs/STRUTS/Docs/struts-bean.html


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Controller Components

Unit 4


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STRUTS Controller Components

Struts includes a Servlet thatimplements the primary function ofmapping a request URI to anAction

class (ActionServlet)


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Your primary responsibilities are: Write anAction class (that is, an extension of the

Action class) for each logical request that may bereceived

Write the action mapping configuration file (inXML) that is used to configure the controllerservlet (struts-config.xml)

Update the web application deployment descriptor

file (in XML) for your application to include thenecessary Struts components

Add the appropriate Struts components to yourapplication


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Action Classes:

TheAction class defines a perform method

that you override

public ActionForward perform(ActionMapping

mapping, ActionForm form, HttpServletRequest

request, HttpServletResponse response)

throws IOException, ServletException;


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The goal of anAction class is to

process this request, and then to returnanActionForward object that identifies

the JSP page (if any) to which controlshould be forwarded to generate thecorresponding response


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A typicalAction class will implement thefollowing logic in its perform() method Validate the current state of the user's session

If validation has not yet occurred, validate the formbean properties as necessary

Perform the processing required to deal with thisrequest

Update the server-side objects that will be used to

create the next page of the user interface Return an appropriateActionForward object that

identifies the JSP page to be used to generate thisresponse, based on the newly updated beans


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Design issues to remember when codingAction classes include the following The controller Servlet creates only one instance of

yourAction class, and uses it for all requests.Thus, you need to code yourAction class so that itoperates correctly in a multi-threadedenvironment, just as you must code a Servlet'sservice() method safely

The most important principle that aids in thread-safe coding is to use only local variables, notinstance variables, in yourAction class


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Design issues to remember when codingAction classes include the followingcontinued The beans that represent the Model of your

system may throw exceptions due to problemsaccessing databases or other resources. Youshould trap all such exceptions in the logic of yourperform() method, and log them to the application

logfile As a general rule, allocating scarce resources and

keeping them across requests from the same user(in the user's session) can cause scalabilityproblems


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The ActionMapping Implementation type - Fully qualified Java class name of theAction

implementation class used by this mapping.

name - The name of the form bean defined in the config

file that this action will use path - The request URI path that is matched to select

this mapping. See below for examples of how matchingworks.

unknown - Set to true if this action should be configuredas the default for this application, to handle all requests

not handled by another action. Only one action can bedefined as a default within a single application.

validate - Set to true if the validate() method of the actionassociated with this mapping should be called.


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The Actions Mapping Configuration File

The developer's responsibility is to create an XMLfile named struts-config.xml, and place it in the

WEB-INF directory of your application The outermost XML element must be

Inside of the element, there two

important elements that you use to describe youractions:


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This section contains your form beandefinitions. You use a element foreach form bean, which has the following

important attributes: name: The name of the request or session level

attribute that this form bean will be stored as

type: The fully-qualified Java classname of your formbean


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This section contains your action definitions. Youuse an element for each of your actionsyou would like to define. Each action element has

requires the following attributes to be defined: path: The application context-relative path to the action

type: The fully qualified java classname of your Actionclass

name: The name of your element to usewith this action


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One more section of good use is the section, which specifies data sourcesthat your application can use.This is how youwould specify a basic data source for your

application inside of struts-config.xml:


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The Web Application DeploymentDescriptor

The final step in setting up the application

is to configure the application deploymentdescriptor (stored in file WEB-INF/web.xml)

to include all the Struts components that

are required


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Tag Libraries

Unit 5


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STRUTS Tag Libraries

HTML Tags

Bean Tags

Logic TagsTemplate Tags

Custom Tags


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HTML Tags

The tags in the Struts HTML library form abridge between a JSP view and the othercomponents of a Web application. Since adynamic Web application often depends ongathering data from a user, input forms playan important role in the Struts framework.Consequently, the majority of the HTML tagsinvolve HTML forms. Other important issuesaddressed by the Struts-HTML tags are

messages, error messages, hyperlinking andinternationalization.


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HTML Tags

HTML "form" tags

button

cancel

checkboxes

file

hidden

image

multibox

password input fields radio buttons

reset buttons

HTML "form" tags

select lists withembedded

option

options submit buttons

text input fields

textareas

HTML Tags T i l HTML F


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HTML Tags Typical HTML Form

First Name

Street Address

CityState

Postal Code

HTML Tags T i l St t F


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HTML Tags Typical Struts Form

B T


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Bean Tags The "struts-bean" tag library provides substantial enhancements to

the basic capability provided by , as discussed in the

following sections:

Bean Properties - Extended syntax to refer to JavaBean properties withsimple names (same as the standard JSP tags and), nested names (a property named address.city

returns the value retrieved by the Java expression

getAddress().getCity()), and indexed names (a property namedaddress[3] retrieves the fourth address from the indexed "address"

property of a bean).

Bean Creation - New JSP beans, in any scope, can be created from avariety of objects and APIs associated with the current request, or withthe servlet container in which this page is running.

Bean Output - Supports the rendering of textual output from a bean (orbean property), which will be included in the response being created by

your JSP page.

Bean Tags


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Bean TagsTag Name Description

cookie Define a scripting variable based on the value(s) of the specified request cookie.

define Define a scripting variable based on the value(s) of the specified bean property.

header Define a scripting variable based on the value(s) of the specified request header.

include Load the response from a dynamic application request and make it available as a bean.

message Render an internationalized message string to the response.

page Expose a specified item from the page context as a bean.

parameter Define a scripting variable based on the value(s) of the specified request parameter.

resource Load a web application resource and make it available as a bean.

size Define a bean containing the number of elements in a Collection or Map.

struts Expose a named Struts internal configuration object as a bean.

write Render the value of the specified bean property to the current JspWriter.

Bean Tag Example


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Bean Tag Example

Logic Tags


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Logic Tags

The Logic tag library contains tags that areuseful in managing conditional generationof output text, looping over objectcollections for repetitive generation of

output text, and application flowmanagement.

Logic Tags


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Logic Tags For tags that do value comparisons (equal, greaterEqual,

greaterThan, lessEqual, lessThan, notEqual), thefollowing rules apply:

The specified value is examined. If it can be convertedsuccessfully to a double or a long, it is assumed that the ultimate

comparison will be numeric (either floating point or integer).

Otherwise, a String comparison will be performed. The variable to be compared to is retrieved, based on the

selector attribute(s) (cookie, header, name, parameter, property)

present on this tag. It will be converted to the appropriate type forthe comparison, as determined above.

A request time exception will be thrown if the specified variablecannot be retrieved, or has a null value.

The specific comparison for this tag will be performed, and thenested body content of this tag will be evaluated if thecomparison returns a true result.

Logic Tags


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Logic Tags For tags that do substring matching (match,

notMatch), the following rules apply: The specified variable is retrieved, based on the

selector attribute(s) (cookie, header, name, parameter,property) present on this tag. The variable is

converted to a String, if necessary.

A request time exception will be thrown if the specifiedvariable cannot be retrieved, or has a null value.

The specified value is checked for existence as asubstring of the variable, in the position specified bythe location attribute, as follows: at the beginning (iflocation is set to start), at the end (if location is set toend), or anywhere (if location is not specified).

Logic Tags


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Logic TagsTag Name Description

empty Evaluate the nested body content of this tag if the requested variable is either null or an empty string.

equal Evaluate the nested body content of this tag if the requested variable is equal to the specified value.

forward Forward control to the page specified by the specified ActionForward entry.

greaterEqual Evaluate the nested body content of this tag if requested variable is greater than or equal to specified value.

greaterThan Evaluate the nested body content of this tag if the requested variable is greater than the specified value.

iterate Repeat the nested body content of this tag over a specified collection.

lessEqual Evaluate the nested body content of this tag if requested variable is greater than or equal to specified value.

lessThan Evaluate the nested body content of this tag if the requested variable is less than the specified value.

match Evaluate the nested body content of this tag if specified value is an appropriate substring of requested variable.

messagesNotPresent Generate the nested body content of this tag if the specified message is not present in this request.

messagesPresent Generate the nested body content of this tag if the specified message is present in this request.

notEmpty Evaluate the nested body content of this tag if the requested variable is neither null nor an empty string.

notEqual Evaluate the nested body content of this tag if the requested variable is not equal to the specified value.

notMatch Evaluate the nested body content of tag if specified value not an appropriate substring of requested variable.

notPresent Generate the nested body content of this tag if the specified value is not present in this request.

present Generate the nested body content of this tag if the specified value is present in this request.

redirect Render an HTTP Redirect

Logic Tags Example


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Logic Tags - Example

Template Tags


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Template Tags

The Template tag library contains threetags: put, get, and insert. Put tags putcontent into request scope, which is

retrieved by a get tag in a different JSPpage (the template). That template isincluded with the insert tag.

Template Tags


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Template Tags

Insert Inserts (includes, actually) a

template. Templates are JSP pages thatinclude parameterized content. Thatcontent comes from put tags that are

children of insert tags.Put Puts content into request scope.

Get Gets the content from request scope

that was put there by a put tag.

Custom Tags


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Custom Tags

Image Broker Link Test

Custom Tags tld File


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Custom Tags tld File

doctypecom.pri.brokertag.ImageBrokerDoctypevaluetruetrue

Custom Tags Tag Class


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Custom Tags Tag Classpublic class ImageBrokerDoctype extends TagSupport {

private String value = null;public int doStartTag() throws JspException{

Hashtable ht = null;String keyword_count = null;int iCnt = 0;HttpServletRequest request = (HttpServletRequest)pageContext.getRequest();ht = (Hashtable) request.getAttribute("keyword_parms");keyword_count = (String)

request.getAttribute("queryobject_count");iCnt ++;ht.put("QueryObject" + iCnt, value);request.setAttribute("keyword_parms", ht);request.setAttribute("queryobject_count", new String(new

Integer(iCnt).toString()));return EVAL_PAGE; }

}


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STRUTS Configuration File

Unit 6



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The developer's responsibility is to

create an XML file named struts-config.xml, and place it in the WEB-INF

directory of your application. This format

of this document is constrained by it'sdefinition in "struts-config_1_0.dtd". Theoutermost XML element must be

.


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STRUTS Configuration File Inside of the element, there are two important elements

that are used to describe your actions:This section contains your form bean definitions. You use a element for each form bean, which has the following importantattributes:

name: A unique identifier for this bean, which will be used toreference it in corresponding action mappings. Usually, this is alsothe name of the request or session attribute under which this formbean will be stored.

type: The fully-qualified Java classname of your form bean.This section contains your action definitions. You use an element for each of your actions you would like to define. Each actionelement requires the following attributes to be defined: path: The application context-relative path to the action type: The fully qualified java classname of your Action class name: The name of your element to use with this

action

Struts-config.xml


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Struts config.xml


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Web Application Descriptor

File

Unit 7


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Web.xml File

The final step in setting up theapplication is to configure theapplication deployment descriptor

(stored in file WEB-INF/web.xml) toinclude all the Struts components thatare required. Using the deploymentdescriptor for the example application

as a guide, we see that the followingentries need to be created or modified.

Web xml File


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Web.xml File

imagebrokerWebactionorg.apache.struts.action.ActionServletapplicationimagebrokerWebconfigWEB-INF/struts-config.xml

Web.xml File - continued


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eb e co t ued

action*.do

index.html

Web.xml File - continued


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Web.xml File continued

WEB-INF/struts-bean.tld/WEB-INF/struts-bean.tld

WEB-INF/struts-html.tld/WEB-INF/struts-html.tld

WEB-INF/struts-logic.tld/WEB-INF/struts-logic.tld


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Application.properties File


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Application.properties File

error.cryptvalue.required=You must enter some text.error.lob.required=You must enter the Line of Business.error.unitnbr.required=You must enter the Unit Number.error.onbase_dns.required=You must enter the OnBase DNS.imagebroker.linkname=Project Refinery, Inc.imagebroker.title=pri Image Brokerimagebrokerlink.title=pri Image Broker Link Testimagelocationlist.title=Image Location Listimagelocationdetail.title=Image Location Detailimagelocationinsert.title=Image Location Inserterrors.header=errors.footer=


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Resources

Unit 9

Resources


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Resources

Main Struts Web Site http://jakarta.apache.org/struts/index.html

Struts User Guide http://jakarta.apache.org/struts/userGuide/index.html

Various Struts Resources

http://jakarta.apache.org/struts/resources.html

Ted Husted Web Site http://www.husted.com/struts/

Documents

Struts Intro Course by Kamalakar Dandu