struts intro
TRANSCRIPT
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
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
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
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
Struts Components?ActionServlet?Actions ?ActionMappings?ActionForwards?ActionErrors
?ActionForms?Resource Management?Tag Libraries?Configuration?Logging
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
What Does the ActionServletDo?
?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
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 requestAction actionInstance = processActionCreate(mapping, request);…ActionForward forward
= processActionPerform(actionInstance, mapping,formInstance, request, response);
…processActionForward(forward, mapping, formInstance,
request, response);
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
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
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
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
Action Relationships
Business Service
Action ActionMappingActionForm queriesuses
invokes
Action InteractionsBusiness Service ActionMappingActionServlet ActionFormAction
saveInput 3:
findForward 4:
return forward 5:
getInput 2:
perform 1:
Example Actionpublic 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("save");
}else {
// Initial pass - forward to the viewreturn mapping.findForward("view");
}
How Is an Action Configured?<action-mappings>
<action path="/person/editPerson"type="com.redhook.examples.genealogy.web.EditPersonAction"scope="request"name="edit.person.form"input="/person/editPerson.jsp"validate="true">
<forward name="save" path="/common/welcome.do" redirect="true"/>
<forward name=“view" path="/common/editPerson.jsp"/>
</action></action-mappings>
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
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
How Is an ActionMappingUsed?
?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
ActionMapping InteractionsBusiness ServiceActionMapping ActionForwardActionServlet Action JSP
Invoke 2:
findForward 3:
get URI 5:
return 4:
perform 1:
forward 6:
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 sourcecatch (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());
}
How Is an ActionMappingConfigured?
?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>
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
How Is an ActionForwardUsed?
?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
ActionForward InteractionsBusiness ServiceActionMapping ActionForwardActionServlet Action JSP
Invoke 2:
findForward 3:
get URI 5:
return 4:
perform 1:
forward 6:
Example ActionForwardpublic 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;}
How Is an ActionForwardConfigured?
? Can be configured globally<global-forwards>
<forward name="welcome" path="/common/welcome.do" redirect="true"/>
</global-forwards>
? Or relative to an action<action>
…<forward name="view" path="/common/welcome.jsp"/>
</action>
What Is an ActionError??Represents an error condition detected
during application workflow?Passed through the system in a container
object?ActionErrors
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
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…
ActionError Relationships
ActionErrors
ActionError
ActionFormAction
JSP
Displays
0..*
CreatesCreates
ActionError InteractionsActionServlet
ActionErrors
ActionForm
ActionError
Client JSP
Submit 1:
return 6:
Add 5:
Get error 8:
new () 3:
Validate 2:
Get message 9:
new () 4:
Display message 10:
Forward 7:
How Is an ActionErrorConfigured?
?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
Example ActionError - Creation?Created in ActionForm validate methodpublic 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;}
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());
}
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>
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
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
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
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
ActionForm Relationships
ActionServlet
ActionErrors
ActionForm
ActionErrorJSP
populated from
displays
invokes
creates
ActionForm InteractionsActionServlet
ActionError
ActionErrors
ActionFormClient JSP
submit 1:
return 6:
new () 4:
new () 3:
add 5:
validate 2:
display errors 8:
forward 7:
Example ActionFormpublic 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;}
How Is an ActionFormConfigured?
<form-beans><form-bean name=“edit.person.form"
type="com.redhook.examples.genealogy.web.EditPersonForm"/></form-beans>…<action path="/person/editPerson"
type="com.redhook.examples.genealogy.web.EditPersonAction"name=“edit.person.form"scope="request"input="/person/editPerson.jsp"validate="true">
<forward name=“save" path="/common/welcome.do" redirect="true"/></action>
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
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
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
ResourceManagement –ApplicationResources.properties
# Titlestitle.welcome=Genealogy Tree
# Labelslabel.first.name=First Name:
# Linkslink.add.person=Add a new person
# Resourcesresource.image.save=/images/save.gif
# Errorserror.invalid.date=Date {0} is not valid.
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 MessageResourcesMessageResources messages = getResources();Locale locale = getLocale(request);messages.getMessage(“label.name", locale);
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
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' %>
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
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
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
Template Tag Library?Allows atomic views to be created?i.e. Section, Header, Footer, Content
?Views can then be added to a defined layout
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
Configuration?Two aspects to Struts configuration?web.xml?struts-config.xml
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>…
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>
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>
Configuration –Struts-config.xml
<struts-config><form-beans>
<form-bean name="edit.person.form"type="com.redhook.examples.genealogy.web.EditPersonForm"/>
</form-beans><global-forwards>
<forward name="welcome" path="/common/welcome.do" redirect="true"/></global-forwards><action-mappings>
<action path="/person/editPerson"type="com.redhook.examples.genealogy.web.EditPersonAction"name="edit.person.form"scope="request"input="/person/editPerson.jsp"validate="true">
<forward name="save" path="/common/welcome.do" redirect="true"/></action>
</action-mappings></struts-config>
Configuration –Struts-config.xml
<struts-config><form-beans>
<form-bean name=“edit.person.form"type="com.redhook.examples.genealogy.web.EditPersonForm"/>
</form-beans><global-forwards>
<forward name="welcome" path="/common/welcome.do" redirect="true"/></global-forwards><action-mappings>
<action path="/person/editPerson"type="com.redhook.examples.genealogy.web.EditPersonAction"scope="request"name=“edit.person.form"input="/person/editPerson.jsp"validate="true">
<forward name="save" path="/common/welcome.do" redirect="true"/></action>
</action-mappings></struts-config>
Configuration –Struts-config.xml
<struts-config><form-beans>
<form-bean name="edit.person.form"type="com.redhook.examples.genealogy.web.EditPersonForm"/>
</form-beans><global-forwards>
<forward name="welcome" path="/common/welcome.do" redirect="true"/></global-forwards><action-mappings>
<action path="/person/editPerson"type="com.redhook.examples.genealogy.web.EditPersonAction"scope="request"name="edit.person.form"input="/person/editPerson.jsp"validate="true">
<forward name="save" path="/common/welcome.do" redirect="true"/></action>
</action-mappings></struts-config>
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
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
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
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
Resources?JSP and Tag Libraries for Web Development
by Wellington L.S. da Silva, New Riders PublishingISBN: 0-73571-095-3
?Programming Jakarta StrutsBy Chuck Cavaness, O’Reilly & Associates (October 2002)ISBN: 0-59600-328-5
?Struts in Action: A Practical Guide to the Leading Java Web Frameworkby Ted Husted et al., Manning Publications CompanyISBN: 1930110502
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 [email protected]