1. Introduction to Struts
Andrew J. Dick
Red Hook Group
andrew@redhookgroup.com
Colorado Software Summit

2. What Is Struts?
?Framework for writing applications using
MVC architecture
?Open source
• Part of Apache’s Jakarta Project
• Current production version 1.0.2
?Model 2 architecture implementation
?Provides standard framework infrastructure
?Makes no presumptions about business and
application objects it deals with
• Could be EJBs, CORBA, directly from database, XML
tree

3. What Is MVC?
?Stands for Model-View-Controller
?Design paradigm
• Originated in the Smalltalk community
?Decouples data access code, business logic
code and presentation code
?Often ripple effects occur when changes are
required in applications without this separation

4. What Is MVC?
?MVC Components
?Model
• Application data
?View
• Translates Model into
readable form
?Controller
• Processes user input
• Initiates change in state
of Model
• In web design also
responsible for flow
control

5. Struts & MVC
?MVC implementation
?Model – Business Services, Transfer Objects
• Business Services populate and return Transfer
Objects
?View – JSPs, ActionForms
• JSP queries ActionForm for form data
?Controller – ActionServlet, Actions
• ActionServlet delegates control to Action class
instances

6. Struts Components
?ActionServlet ?ActionForms
?Actions ?Resource Management
?ActionMappings ?Tag Libraries
?ActionForwards ?Configuration
?ActionErrors ?Logging

7. What Is the ActionServlet
?Manages application flow of control
?Primary controller for Struts framework
?Performs initialization for application such as
?Parses Struts configuration file
• Loads application message resources
• Initializes:
?Action mapping cache
?Application defined data sources
?Servlet mapping information

8. What Does the ActionServlet
Do?
?For each user request
?Identifies action to invoke from URI
?Instantiates ActionForm bean if required by
mapping configuration
• Initialized with submitted form’s field values
?Calls the Action’s perform method
• May have to load and instantiate Action first
?HTTP GET and POST treated identically

9. ActionServlet Processing
?Segment of Struts ActionServlet request
processing
? * Copyright (c) 1999-2001 The Apache Software Foundation. All rights
reserved
protected void process(HttpServletRequest request,
HttpServletResponse response)
…
// Acquire the Action instance to process this request
Action actionInstance = processActionCreate(mapping, request);
…
ActionForward forward
= processActionPerform(actionInstance, mapping,
formInstance, request, response);
…
processActionForward(forward, mapping, formInstance,
request, response);

10. Struts 1.1 ActionServlet
?Introduction of Request Processor
?Handles much of the functionality of the
ActionServlet in Struts 1.0
?Allows developers to more easily customize the
request handling behavior

11. What Is an Action?
?Bridge between HTTP request and business
services
?Typically performs single task or business
operation
?Alternatively can group cohesive actions
together within an Action class
?Reduces number of required Action classes

12. How Is an Action Used?
?Implements perform() method
?Executed by ActionServlet according to
defined ActionMappings
?Single instance per Action class type
?Therefore must be threadsafe

13. What Does an Action Do?
?Processes request parameters
?Invokes appropriate business service
?Prepares business service results
?Determines path to follow
?Uses ActionMapping to determine where to
dispatch the user based on
• Request parameters
• Business service results

14. Action Relationships
ActionForm uses Action queries ActionMapping
invokes
Business Service

15. Action Interactions
ActionServlet Action ActionForm Business Service ActionMapping
1: perform
2: getInput
3: saveInput
4: findForward
5: return forward

16. Example Action
public ActionForward perform(ActionMapping mapping,
ActionForm form,
HttpServletRequest req,
HttpServletResponse resp)
throws IOException, ServletException {
…
final EditPersonForm editPersonForm = (EditPersonForm) form;
final String action = editPersonForm.getSelected();
if (WebConstants.SAVE.equals(action)) {
savePerson(editPersonForm.getModifiedPerson());
return mapping.findForward(quot;savequot;);
}
else {
// Initial pass - forward to the view
return mapping.findForward(quot;viewquot;);
}

17. How Is an Action Configured?
<action-mappings>
<action path=quot;/person/editPersonquot;
type=quot;com.redhook.examples.genealogy.web.EditPersonActionquot;
scope=quot;requestquot;
name=quot;edit.person.formquot;
input=quot;/person/editPerson.jspquot;
validate=quot;truequot;>
<forward name=quot;savequot;
path=quot;/common/welcome.doquot;
redirect=quot;truequot;/>
<forward name=“viewquot;
path=quot;/common/editPerson.jspquot;/>
</action>
</action-mappings>

18. Struts 1.1 Actions
?Method perform() replaced by
execute()
?Backwards compatible
?Change necessary to support declarative
exception handling
?Addition of DispatchAction class
?Supports multiple business methods instead of a
single execute() method
• Allows easy grouping of related business methods

19. What Is an ActionMapping?
?Encapsulates mapping information
?Used to hold information that the ActionServlet
knows about a mapping
?Allows meta information to be passed to
Action object
?e.g. Configuration mappings for an Action

20. How Is an ActionMapping
Used?
?Passed to Action class when perform()
invoked
?Can be queried by Action class for information
?Used to determine where user should be
forwarded or redirected

21. ActionMapping Interactions
ActionServlet Action ActionMapping Business Service ActionForward JSP
1: perform
2: Invoke
3: findForward
4: return
5: get URI
6: forward

22. Example ActionMapping -
Usage
?Used to look up ActionForwards with a
lookup name
try {
delegate.createPerson(personInfo);
return mapping.findForward(“save”);
}
?Can also be used to retrieve input source
catch (final DuplicatePersonException duplicatePersonException) {
ActionErrors errors = new ActionErrors();
ActionError error = new ActionError(“error.duplicate.name”);
errors.add(“name”, error);
saveErrors(request, errors);
return mapping.findForward(mapping.getInput());
}

23. How Is an ActionMapping
Configured?
?Parent element of Action in the application
configuration
<action-mappings>
<action path=“/editPerson”>
…
<forward name=“save” path=“/person/viewPersonProfile.do”
redirect=“true”/>
</action>
<action path=“/findPerson”>
…
<forward name=“view” path=“/person/displayList.jsp”/>
</action>
…
</action-mappings>

24. What Is an ActionForward?
?Logical abstraction of a web resource
?Minimizes coupling of an application to physical
resources
?Encapsulates URI that ActionServlet can
redirect control to
?Three properties
• Name – lookup key
• Path – URI
• Redirect – whether to redirect or forward

25. How Is an ActionForward
Used?
?Defined as local to an action or global to the
application
?Look up via ActionMapping class
?findForward
?Can also be dynamically created by
specifying URI

26. ActionForward Interactions
ActionServlet Action ActionMapping Business Service ActionForward JSP
1: perform
2: Invoke
3: findForward
4: return
5: get URI
6: forward

27. Example ActionForward
public ActionForward perform(…) throws IOException,
ServletException {
…
String action = form.getSelected();
ActionForward forward;
if (action.equals(“login”)) {
forward = mapping.findForward(“login”);
}
else {
forward = new ActionForward(
“http://authserver:7001/authcontrol”, true);
}
return forward;
}

28. How Is an ActionForward
Configured?
? Can be configured globally
<global-forwards>
<forward name=quot;welcomequot;
path=quot;/common/welcome.doquot;
redirect=quot;truequot;/>
</global-forwards>
? Or relative to an action
<action>
…
<forward name=quot;viewquot; path=quot;/common/welcome.jspquot;/>
</action>

29. What Is an ActionError?
?Represents an error condition detected
during application workflow
?Passed through the system in a container
object
?ActionErrors

30. How Is an ActionError Used?
?Created in ActionForm validate() or
Action perform() method
?Created with error message key and
parameters
?Added to error container with key
?Represents form field causing the error
?ActionErrors is a request scope object
?Only exists until the input JSP is redisplayed with
the error messages

31. What Does an ActionError Do?
?Used to transport error messages to the user
?Supports internationalization of error
messages
?Allows user to be notified of multiple error
conditions
?Prevents a cycle of submit, display error,
resubmit, display next error…

32. ActionError Relationships
Action ActionForm
Creates Creates
ActionError JSP
Displays
0..*
ActionErrors

33. ActionError Interactions
Client ActionServlet ActionForm JSP
1: Submit
2: Validate
3: new ()
ActionErrors
4: new ()
ActionError
5: Add
6: return
7: Forward
8: Get error
9: Get message
10: Display message

34. How Is an ActionError
Configured?
?Error messages defined in resource bundle
?ApplicationResources.properties by default
?Can be parameterized with up to five parameters
• e.g. error.invalid.date=Date {0} is not valid
?Error header and footer defined
?errors.header and errors.footer
?If present, added before and after error
messages

35. Example ActionError - Creation
?Created in ActionForm validate method
public ActionErrors validate(ActionMapping mapping,
HttpServletRequest request) {
ActionErrors errors = new ActionErrors();
try {
DateFormat.parse(getBirthDate());
}
catch (final ParseException parseException) {
ActionError error = new ActionError(“error.invalid.date”),
getBirthDate());
errors.add(“birthDate”, error);
}
return errors;
}

36. Example ActionError - Creation
?Can also be created in Action perform
method
?Generally if business validation is necessary
• e.g. Uniqueness of input
…
try {
personDelegate.createPerson(personInfo);
}
catch (final DuplicatePersonException duplicatePersonException) {
ActionErrors errors = new ActionErrors();
ActionError error = new ActionError(“error.duplicate.name”);
errors.add(“name”, error);
saveErrors(request, errors);
return mapping.findForward(mapping.getInput());
}

37. Example ActionError - Display
<form method=“post” action=“createPerson”>
<table>
…
<tr>
<td>Birthdate</td>
<td><input type=“text” name=“birthDate”/></td>
</tr>
<tr>
<td><html:errors/></td>
</tr>
<tr>
<td><input type=“submit” name=“Submit” value=“Create”></td>
</tr>
</table>
</form>

38. Struts 1.1 ActionErrors
?New ActionMessage super class introduced
?Used for more general purpose messages
• Action ‘Error’ implies improper to use for informational
or warning messages
?Introduction of declarative exception
handling
?Allows definition of exception handling policy
externally

39. What Is an ActionForm?
?Defines an abstract class for managing forms
?Standard callback for form validation
?Standard callback for resetting a form
?Supports form management by
?Capturing input data
?Validation of form data
?Returning error message on validation failure
?Transferring data to Action class
?Determining which action was submitted
• If multiple submits in the form

40. How Is an ActionForm Used?
?Defines accessors and mutators for form
being maintained
?Implements validate and reset methods
?Validate performs validation of data
• Only called if form configured for validation
?Reset allows recycling of forms
?Two levels of scope – session (default) and
request
?Session used to support multi-page wizards
?Form passed into Action class when invoked

41. What Does an ActionForm Do?
?When a form is submitted, the ActionServlet
will:
?Detect which ActionForm subclass is associated
with the mapping (if any)
?Find an existing instance or instantiate one
?Populate it with form data from the request
?Invoke the ActionForm’s validate method
?Pass the ActionForm instance to the Action
instance
• If validation successful

42. ActionForm Relationships
ActionForm invokes ActionServlet
populated from
creates
JSP displays ActionError ActionErrors

43. ActionForm Interactions
Client ActionServlet ActionForm JSP
1: submit
2: validate
3: new ()
ActionErrors
4: new ()
ActionError
5: add
6: return
7: forward
8: display errors

44. Example ActionForm
public ActionErrors validate(ActionMapping mapping,
HttpServletRequest request) {
ActionErrors errors = new ActionErrors();
try {
DateFormat.parse(getBirthDate());
} catch (final ParseException parseException) {
errors.add(“birthDate”,
new ActionError(“error.invalid.date”),
getBirthDate());
}
if ((getName() == null) || (getName().equals(“”))) {
errors.add(“name”, new ActionError(“error.name.required”));
}
return errors;
}

45. How Is an ActionForm
Configured?
<form-beans>
<form-bean name=“edit.person.formquot;
type=quot;com.redhook.examples.genealogy.web.EditPersonFormquot;/>
</form-beans>
…
<action path=quot;/person/editPersonquot;
type=quot;com.redhook.examples.genealogy.web.EditPersonActionquot;
name=“edit.person.formquot;
scope=quot;requestquot;
input=quot;/person/editPerson.jspquot;
validate=quot;truequot;>
<forward name=“savequot; path=quot;/common/welcome.doquot; redirect=quot;truequot;/>
</action>

46. Struts 1.1 ActionForms
?Dynamic Forms introduced
?Configured in configuration file rather than
coding
?Version exists that works with validator package
to provide automatic validation

47. Struts 1.1 Validation
?Validator framework from Jakarta
?Part of Commons sub-project
?Struts 1.1 includes this by default
?Allows declarative validation for many fields
• e.g. Formats
?Dates, Numbers, Email, Credit Card, Postal Codes
• Lengths
?Minimum, maximum
• Ranges
?Can also be configured for Struts 1.0

48. Struts Resource Management
?Centralizes resource administration for
?Internationalization
?Error treatment
?Standard labeling
?By default ApplicationResources.properties
?Can be changed in web.xml configuration
?Must be located on class path
• Typically in WEB-INF/classes

49. ResourceManagement –
ApplicationResources.properties
# Titles
title.welcome=Genealogy Tree
# Labels
label.first.name=First Name:
# Links
link.add.person=Add a new person
# Resources
resource.image.save=/images/save.gif
# Errors
error.invalid.date=Date {0} is not valid.

50. Struts Resource Management
?Can be accessed from JSP through tag
libraries
<bean:message key=“label.first.name”/>
<html:img pageKey=“resource.image.save”/>
?Can also be accessed in Action objects
through MessageResources
MessageResources messages = getResources();
Locale locale = getLocale(request);
messages.getMessage(“label.namequot;, locale);

51. Struts & TagLibs
?Struts supports four tag libraries
?Not mandatory
• Renders cleaner pages
• Not limited to these four
?Provides flexible way to
• Access application and framework objects under
different scopes
• Render objects to output stream, handle validation
and processing errors
• Support internationalization capabilities
• Create page templates that support reusable design

52. Struts & TagLibs
?What is required to use them?
?web.xml tag library declaration for each library
<taglib>
<taglib-uri>/WEB-INF/tlds/struts-bean.tld</taglib-uri>
<taglib-location>
/WEB-INF/tlds/struts-bean.tld
</taglib-location>
</taglib>
?Taglib directive on each target page
<%@ taglib uri='/WEB-INF/tlds/struts-bean.tld'
prefix='bean' %>

53. Bean Tag Library
?Provides ways to access and expose beans
and properties in the application
?Provides internationalization functionality
?Includes parametric replacement
?Bean references can be created
?String constants can be defined

54. HTML Tag Library
?Provides support for rendering html controls
?Input controls, images, forms, etc.
?Includes support for:
?JavaScript event handling
?Cascading Style Sheets
?Navigation attributes
?Supports display of errors found during form
validation

55. Logic Tag Library
?Conditional generation of content
?Supports comparison properties equality to a
constant
?Conditional on presence (or lack) of variables or
properties
• Includes cookies, roles, etc.
?Navigational forwarding or redirection
?Iteration of collection elements

56. Template Tag Library
?Allows atomic views to be created
?i.e. Section, Header, Footer, Content
?Views can then be added to a defined layout

57. Struts & TagLibs
?Can also use other tag libraries
?Jakarta TagLibs
?JSTL
?Custom Tags
?Struts 1.1
?Tile TagLib supercedes Template TagLib
• Provides more extensive layout support
?Nested TagLib
• Extends base Struts Taglibs to support relation to
each other in a nested manner

58. Configuration
?Two aspects to Struts configuration
?web.xml
?struts-config.xml

59. Configuration – Web.xml
<web-app>
<servlet>
<servlet-name>action</servlet-name>
<servlet-class>org.apache.struts.action.ActionServlet</servlet-
class>
<init-param>
<param-name>application</param-name>
<param-value>ApplicationResources</param-value>
</init-param>
<init-param>
<param-name>config</param-name>
<param-value>/WEB-INF/struts-config.xml</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
…

60. Configuration – Web.xml
<web-app>
…
<servlet-mapping>
<servlet-name>action</servlet-name>
<url-pattern>*.do</url-pattern>
</servlet-mapping>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>

61. Configuration – Web.xml
<web-app>
…
<taglib>
<taglib-uri>/WEB-INF/tlds/struts-bean.tld</taglib-uri>
<taglib-location>
/WEB-INF/tlds/struts-bean.tld
</taglib-location>
</taglib>
</web-app>

62. Configuration –
Struts-config.xml
<struts-config>
<form-beans>
<form-bean name=quot;edit.person.formquot;
type=quot;com.redhook.examples.genealogy.web.EditPersonFormquot;/>
</form-beans>
<global-forwards>
<forward name=quot;welcomequot; path=quot;/common/welcome.doquot; redirect=quot;truequot;/>
</global-forwards>
<action-mappings>
<action path=quot;/person/editPersonquot;
type=quot;com.redhook.examples.genealogy.web.EditPersonActionquot;
name=quot;edit.person.formquot;
scope=quot;requestquot;
input=quot;/person/editPerson.jspquot;
validate=quot;truequot;>
<forward name=quot;savequot; path=quot;/common/welcome.doquot; redirect=quot;truequot;/>
</action>
</action-mappings>
</struts-config>

63. Configuration –
Struts-config.xml
<struts-config>
<form-beans>
<form-bean name=“edit.person.formquot;
type=quot;com.redhook.examples.genealogy.web.EditPersonFormquot;/>
</form-beans>
<global-forwards>
<forward name=quot;welcomequot; path=quot;/common/welcome.doquot; redirect=quot;truequot;/>
</global-forwards>
<action-mappings>
<action path=quot;/person/editPersonquot;
type=quot;com.redhook.examples.genealogy.web.EditPersonActionquot;
scope=quot;requestquot;
name=“edit.person.formquot;
input=quot;/person/editPerson.jspquot;
validate=quot;truequot;>
<forward name=quot;savequot; path=quot;/common/welcome.doquot; redirect=quot;truequot;/>
</action>
</action-mappings>
</struts-config>

64. Configuration –
Struts-config.xml
<struts-config>
<form-beans>
<form-bean name=quot;edit.person.formquot;
type=quot;com.redhook.examples.genealogy.web.EditPersonFormquot;/>
</form-beans>
<global-forwards>
<forward name=quot;welcomequot; path=quot;/common/welcome.doquot; redirect=quot;truequot;/>
</global-forwards>
<action-mappings>
<action path=quot;/person/editPersonquot;
type=quot;com.redhook.examples.genealogy.web.EditPersonActionquot;
scope=quot;requestquot;
name=quot;edit.person.formquot;
input=quot;/person/editPerson.jspquot;
validate=quot;truequot;>
<forward name=quot;savequot; path=quot;/common/welcome.doquot; redirect=quot;truequot;/>
</action>
</action-mappings>
</struts-config>

65. Struts 1.1 Configuration
?Adds support for
?Multiple application modules
?Declarative exceptions
?Plug in elements
?Multiple message resource elements
?Visual configuration tools can also be found
?Both commercial and open-source
• http://jakarta.apache.org/struts/resources/guis.html

66. Logging
?Important aspect of applications
?3rd party logging frameworks used pre JDK 1.4
• i.e. log4j
?Logging API introduced with JDK 1.4
• Similar to log4j
?Hierarchical categories
?Logging levels

67. Logging
?What does Struts provide?
?Nothing
?Jakarta project provides thin logging
wrapper
?Part of Commons subproject
?Provides wrappers for standard logging
frameworks
• JDK 1.4, log4j, etc.
?Can also develop wrapper for custom logging
API

68. Logging
?Why use Jakarta Common Logging?
?Can declaratively switch logging frameworks
?Implementation wrapper class declared in a
properties file
?Must still configure logging framework in
typical way
?i.e. log4j.properties
?Jakarta also provides logging tag library
?Useful for debugging
• Allows dump of scope attributes

69. Resources
?JSP and Tag Libraries for Web Development
by Wellington L.S. da Silva, New Riders Publishing
ISBN: 0-73571-095-3
?Programming Jakarta Struts
By Chuck Cavaness, O’Reilly & Associates (October 2002)
ISBN: 0-59600-328-5
?Struts in Action: A Practical Guide to the Leading
Java Web Framework
by Ted Husted et al., Manning Publications Company
ISBN: 1930110502

70. Websites
? http://jakarta.apache.org/struts/index.html
? http://www.husted.com/struts
? Sample app can be found at:
? http://www.redhookgroup.com/downloads/css/genealogy.zip
?Thank you.
?Any questions
?andrew@redhookgroup.com