STRUTS
Part of the Jakarta Project
Sponsored by the
Apache 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
Pattern
Unit 2 - Model Components
Unit 3 - View Components
Unit 4 - Controller Components
Unit 5 - Tag Libraries
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STRUTS Objectives
Unit 6 - STRUTS Configuration File
Unit 7 - Web Application Descriptor File
Unit 8 - Application Resources File
Unit 9 – Resources
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Model-View-Controller Design
Pattern
Unit 1
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STRUTS MVC Design Pattern
Central controller mediates application
flow
Controller delegates to appropriate
handler
Handlers are tied to model components
Model encapsulates business logic
Control forwarded back through the
Controller to the appropriate View
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STRUTS MVC Design Pattern
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STRUTS MVC Design Pattern
3 Major Components in STRUTS
Servletcontroller (Controller)
Java Server Pages (View)
Application Business Logic (Model)
Controller bundles and routes HTTP
request to other objects in framework
Controller parses configuration file
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STRUTS MVC Design Pattern
Configuration file contains action
mappings (determines navigation)
Controller uses mappings to turn HTTP
requests into application actions
Mapping must specify
A request path
Object type to act upon the request
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Model Components
Unit 2
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STRUTS Model Components
Model divided into concepts
Internalstate of the system
Actions that can change that state
Internal state of system represented by
JavaBeans
Enterprise JavaBeans
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STRUTS Model Components
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 well
as to any page or servlet that is included in this
page, or forwarded to by this page
Session – visible to all JSP pages and servlets
that 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
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STRUTS Model Components
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 corresponding
setter method will be called
The updated ActionForm bean will be passed to the
Action Class perform() method when it is called, making
these values immediately available
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STRUTS Model Components
When coding ActionForm beans consider:
The ActionForm class itself requires no specific
methods to be implemented. It is used to identify
the role these particular beans play in the overall
architecture. Typically, an ActionForm bean will
have only property getter and property setter
methods, with no business logic
The ActionForm object also offers a standard
validation mechanism. If you override a "stub"
method, and provide error messages in the
standard application resource, Struts will
automatically validate the input from the form
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STRUTS Model Components
Continued
Define a property (with associated getXxx() and
setXxx() methods) for each field that is present in
the form. The field name and property name must
match according to the usual JavaBeans
conventions
Place a bean instance on your form, and use
nested property references. For example, you
have a "customer" bean on your Action Form, and
then refer to the property "customer.name" in your
JSP view. This would correspond to the methods
customer.getName() and
customer.setName(string Name) on your
customer bean
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STRUTS Model Components
System State Beans
Actual state of a system is normally represented
as 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 for
each individual shopper, and will (among other
things) include the set of items that the shopper
has currently selected for purchase
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STRUTS Model Components
Business Logic Beans
Should encapsulate the functional logic of your
application as method calls on JavaBeans
designed for this purpose
For maximum code re-use, business logic beans
should be designed and implemented so that they
do not know they are being executed in a web
application environment
For small to medium sized applications, business
logic beans might be ordinary JavaBeans that
interact with system state beans passed as
arguments, or ordinary JavaBeans that access a
database using JDBC calls
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STRUTS Model Components
Business Logic Beans - Continued
For larger applications, these beans will
often be stateful or stateless Enterprise
JavaBeans (EJBs)
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STRUTS Model Components
Accessing Relational Databases
Struts can define the datasources for an
application from within its standard
configuration file
A simple JDBC connection pool is also
provided
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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 localized
applications
Locale - fundamental Java class that supports
internationalization
ResourceBundle - supports messages in multiple languages
PropertyResourceBundle - standard implementation of
ResourceBundle that allows you to define resources using
the same "name=value" syntax used to initialize properties
files
MessageFormat - allows you to replace portions of a
message 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 particular
message string for a particular Locale
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STRUTS View Components
ApplicationResources.properties
Contains the messages in the default
language for your server. If your default
language is English, you might have an
entry like this: prompt.hello=Hello
ApplicationResources_xx.properties
the same messages in the
Contains
language whose ISO language code is "xx"
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STRUTS View Components
Forms and FormBean interactions
HTML Forms and their limitations
Errors not easily handled
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STRUTS View Components
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STRUTS View Components
Building Forms with Struts
The taglib directive tells the JSP page compiler
where to find the tag library descriptor for the
Struts tag library
message tag is used to look up internationalized
message strings from a MessageResources
object containing all the resources for this
application
The errors tag displays any error messages that
have been stored by a business logic component,
or nothing if no errors have been stored
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STRUTS View Components
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 within
this form with a request scoped FormBean that is
stored under the key FormName
The form bean can also be specified in the Struts
configuration 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 the
corresponding buttons at the bottom of the form
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STRUTS View Components
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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STRUTS View Components
Useful Presentation Tags
[logic] iterate repeats its tag body once for each
element of a specified collection (which can be an
Enumeration, a Hashtable, a Vector, or an array of
objects)
[logic] present depending on which attribute is
specified, this tag checks the current request, and
evaluates 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 when
the specified attribute is not present
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STRUTS View Components
Useful Presentation Tags – continued
[html] link generates a HTML element as an
anchor definition or a hyperlink to the specified
URL, and automatically applies URL encoding to
maintain session state in the absence of cookie
support
[html] img generates a HTML element with
the ability to dynamically modify the URLs
specified by the "src" and "lowsrc" attributes in the
same manner that can
[bean] parameter retrieves the value of the
specified request parameter, and defines the
result as a page scope attribute of type String or
String
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STRUTS View Components
Automatic Form Validation
Struts offers an additional facility to validate the
input fields it has received
To utilize this feature, override the validate()
method in your ActionForm class
The validate() method is called by the controller
servlet after the bean properties have been
populated, but before the corresponding action
class's perform() method is invoked
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STRUTS View Components
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 to
the different segments
Use the include capability of JavaServer
Pages technology to combine the results
into a single result page, or use the include
tag provided with Struts
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STRUTS View Components
Page Composition with Includes – continued
There are three types of include available,
depending on when you want the combination of
output to occur:
An directive can include a
file that contains java code or jsp tags
The include action () is processed at request time, and is
handled transparently by the server
The bean:include tag takes either a an argument
"forward" representing a logical name mapped to the jsp
to include, or the "id" argument, which represents a page
context String variable to print out to the jsp page
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Controller Components
Unit 4
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STRUTS Controller Components
Strutsincludes a Servlet that
implements the primary function of
mapping a request URI to an Action
class (ActionServlet)
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STRUTS Controller Components
Your primary responsibilities are:
Write an Action class (that is, an extension of the
Action class) for each logical request that may be
received
Write the action mapping configuration file (in
XML) that is used to configure the controller
servlet (struts-config.xml)
Update the web application deployment descriptor
file (in XML) for your application to include the
necessary Struts components
Add the appropriate Struts components to your
application
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STRUTS Controller Components
Action Classes:
The Action 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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STRUTS Controller Components
The goal of an Action class is to
process this request, and then to return
an ActionForward object that identifies
the JSP page (if any) to which control
should be forwarded to generate the
corresponding response
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STRUTS Controller Components
A typical Action class will implement the
following logic in its perform() method
Validate the current state of the user's session
If validation has not yet occurred, validate the form
bean properties as necessary
Perform the processing required to deal with this
request
Update the server-side objects that will be used to
create the next page of the user interface
Return an appropriate ActionForward object that
identifies the JSP page to be used to generate this
response, based on the newly updated beans
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STRUTS Controller Components
Design issues to remember when coding
Action classes include the following
The controller Servlet creates only one instance of
your Action class, and uses it for all requests.
Thus, you need to code your Action class so that it
operates correctly in a multi-threaded
environment, just as you must code a Servlet's
service() method safely
The most important principle that aids in thread-
safe coding is to use only local variables, not
instance variables, in your Action class
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STRUTS Controller Components
Design issues to remember when coding
Action classes include the following –
continued
The beans that represent the Model of your
system may throw exceptions due to problems
accessing databases or other resources. You
should trap all such exceptions in the logic of your
perform() 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 scalability
problems
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STRUTS Controller Components
The ActionMapping Implementation
type - Fully qualified Java class name of the Action
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 matching
works.
unknown - Set to true if this action should be configured
as the default for this application, to handle all requests
not handled by another action. Only one action can be
defined as a default within a single application.
validate - Set to true if the validate() method of the action
associated with this mapping should be called.
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STRUTS Controller Components
The Actions Mapping Configuration File
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
The outermost XML element must be
Inside of the element, there two
important elements that you use to describe your
actions:
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STRUTS Controller Components
This section contains your form bean
definitions. You use a element for
each 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 form
bean
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STRUTS Controller Components
This section contains your action definitions. You
use an element for each of your actions
you 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 Action
class
name: The name of your element to use
with this action
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STRUTS Controller Components
One more section of good use is the section, which specifies data sources
that your application can use.This is how you
would specify a basic data source for your
application inside of struts-config.xml:
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STRUTS Controller Components
Web Application Deployment
The
Descriptor
The final step in setting up the application
is to configure the application deployment
descriptor (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 Tags
Template Tags
Custom Tags
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HTML Tags
The tags in the Struts HTML library form a
bridge between a JSP view and the other
components of a Web application. Since a
dynamic Web application often depends on
gathering data from a user, input forms play
an important role in the Struts framework.
Consequently, the majority of the HTML tags
involve HTML forms. Other important issues
addressed by the Struts-HTML tags are
messages, error messages, hyperlinking and
internationalization.
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HTML Tags
HTML "form" tags HTML "form" tags
button select lists with
cancel embedded
checkboxes option
file options
hidden submit buttons
image text input fields
multibox textareas
password input fields
radio buttons
reset buttons
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HTML Tags – Typical HTML Form
First Name
Street Address
City
State
Postal Code
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HTML Tags – Typical Struts Form
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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 with
simple 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 named
address[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 a
variety of objects and APIs associated with the current request, or with
the servlet container in which this page is running.
Bean Output - Supports the rendering of textual output from a bean (or
bean property), which will be included in the response being created by
your JSP page.
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Bean Tags
Tag 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.
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Bean Tag Example
&unitnbr=
&onbase_dns=" >
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Logic Tags
The Logic tag library contains tags that are
useful in managing conditional generation
of output text, looping over object
collections for repetitive generation of
output text, and application flow
management.
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Logic Tags
For tags that do value comparisons (equal, greaterEqual,
greaterThan, lessEqual, lessThan, notEqual), the
following rules apply:
The specified value is examined. If it can be converted
successfully 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 for
the comparison, as determined above.
A request time exception will be thrown if the specified variable
cannot be retrieved, or has a null value.
The specific comparison for this tag will be performed, and the
nested body content of this tag will be evaluated if the
comparison returns a true result.
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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 specified
variable cannot be retrieved, or has a null value.
The specified value is checked for existence as a
substring of the variable, in the position specified by
the location attribute, as follows: at the beginning (if
location is set to start), at the end (if location is set to
end), or anywhere (if location is not specified).
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Logic Tags
Tag 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
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Logic Tags - Example
…
…
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Template Tags
The Template tag library contains three
tags: put, get, and insert. Put tags put
content into request scope, which is
retrieved by a get tag in a different JSP
page (the template). That template is
included with the insert tag.
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Template Tags
Insert Inserts (includes, actually) a
template. Templates are JSP pages that
include parameterized content. That
content 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.
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Custom Tags
'
unitnbr=''
userid='' >
Image Broker Link Test
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Custom Tags – tld File
doctype
com.pri.brokertag.ImageBrokerDoctype
value
true
true
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Custom Tags – Tag Class
public 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; }
} Project Refinery, Inc. 64
STRUTS Configuration File
Unit 6
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STRUTS Configuration File
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's
definition in "struts-config_1_0.dtd". The
outermost 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 important
attributes:
• name: A unique identifier for this bean, which will be used to
reference it in corresponding action mappings. Usually, this is also
the name of the request or session attribute under which this form
bean 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 action
element 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
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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 the
application is to configure the
application deployment descriptor
(stored in file WEB-INF/web.xml) to
include all the Struts components that
are required. Using the deployment
descriptor for the example application
as a guide, we see that the following
entries need to be created or modified.
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Web.xml File
imagebrokerWeb
action
org.apache.struts.action.ActionServlet
applicationimagebrokerWeb
configWEB-INF/struts-
config.xml
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Web.xml File - continued
action
*.do
index.html
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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 Resources File
Unit 8
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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 Broker
imagebrokerlink.title=pri Image Broker Link Test
imagelocationlist.title=Image Location List
imagelocationdetail.title=Image Location Detail
imagelocationinsert.title=Image Location Insert
errors.header=
errors.footer=
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Resources
Unit 9
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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/
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