Building Web Applications With The Struts Framework

1

• Building Web Applications With The Struts
  Framework
• Session WE06 11/20/2002 1000-1100
• Craig R. McClanahan
• Senior Staff Engineer
• Sun Microsystems, Inc.

2
Session Outline

• Web Applications Backgrounder
• The Model-View-Controller Architecture
• The Struts Framework
• Building A Web Application With Struts
• Resources

3

• Web Applications Backgrounder

4
Web Applications Backgrounder

• Web applications run over the HTTP protocol
• Request/response oriented
• Stateless
• Web applications use varied presentation (markup)
  languages, and talk to varied client hardware
  devices
• Standard HTML -- not!
• Varying dynamic and JavaScript capabilities
• Wireless devices vary in capabilities, language
  dialect, and input device support

5
Simple Solutions ... for Simple Problems

• For relatively simple applications, a simple
  architecture works fine
• For each page in the user interface ...
• Create a servlet, JSP page, or something similar
• The page includes
• Logic to create the user interface
• Logic to retrieve required information from the
  database
• Logic to perform the appropriate business
  transaction
• Logic to update the corresponding database
  information
• And it's all mixed together in one source file
• This works fine for a Guest Book app, but what
  about something bigger?

6
What About Large Scale Applications?

• Disparate skill sets required
• Presentation Layer-- User interface design,
  visual appearance, interaction model
• Application Layer Functional business logic to
  perform required transactions
• Persistence Layer Databases, directory servers,
  messaging, Enterprise JavaBeansTM (EJBs)
• Application Deployment Networks, firewalls,
  public key infrastructures, load balancing,
  failover
• We need a fundamental organizing principle
• The Model-View-Controller (MVC) architecture

7

• The Model-View-Controller (MVC) Architecture

8
The Model-View-Controller Architecture

• Divides the overall functionality of an
  application into three layers
• Model Layer Contains the functional business
  logic of the application, as well as a
  representation of the persistently stored data
  backing the application
• View Layer Contains the user interface,
  including mechanisms to accept user input and
  render results
• Controller Layer Contains the logic that
  manages the flow of individual requests,
  dispatching to the appropriate business logic
  component

9
The Model Layer

• Functional business logic
• Should be modelled as JavaBeans or Session EJBs
• Should be reusable in non-web environments
• API exposes public methods for each logical unit
  of work (while hiding the details)
• Persistent data storage
• Should manage permanent storage of application
  data
• Typically shared across many applications
• API should expose data retrieval and storage
  operations (while hiding the mechanisms)

10
The View Layer

• Creation of the user interface
• Typically in HTML or an XML-based dialect
• Normally a combination of static and dynamic
  content
• Actual content varies depending on
• Device or browser type
• User preferences / personalization
• Internationalization and localization
  requirements
• Accessibility requirements

11
The Controller Layer

• Incoming requests flow through a common path
• Received by common component
• Standardized request pre-processing
• Dispatch to request-specific model component
  (business logic)
• Forward to business-logic-specified view
  component
• Standardized request post-processing
• Often called Model 2 Design in the JSP/Servlet
  community
• In modern design pattern terminology, Struts
  implements the front controller pattern.

12

• The Struts Framework An Implementation of the
  MVC Architecture

13
The Struts Framework Architecture

14
The Struts Framework Model Layer

• Struts does not restrict implementation
  techniques for model layer
• JDBC-accessed databases
• Enterprise JavaBeans
• O-R mapping tools
• Optional JDBC connection pool available
• Common design pattern
• Action acquires information from persistence tier
• Exposes information as request/session attributes
• View layer pulls data from attributes for display

15
The Struts Framework View Layer

• Form Bean maintains state of form input fields
  across requests
• ActionForm Standard JavaBean design pattern
• DynaActionForm Property names and types defined
  in Struts configuration file
• In addition to properties, form beans define two
  standard methods
• reset() -- Reset form properties to initial state
• validate() -- Perform field-level validations
• Form bean properties are typically Strings
• Allows redisplay of invalid input

16
The Struts Framework View Layer

• Internationalization Support enables
  locale-specific applications
• Locale Standard Java class representing a
  choice of language and/or country
• MessageFormat Standard Java class representing
  an individual message with replaceable
  parameters
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• MessageResources Struts abstraction around sets
  of messages for supported locales
• ActionErrors / ActionMessages Struts
  collections of localized messages

17
The Struts Framework View Layer

• JSP Custom Tag Libraries If you are using JSP
  pages for your presentation
• struts-bean.tld Fundamental bean manipulation
  and internationalization
• struts-html.tld Smart HTML elements
• struts-logic.tld Basic conditionals and
  iteration
• struts-template.tld Basic layout management

18
The Struts Framework View Layer

• Standard tag libraries added in Struts 1.1
• struts-nested.tld -- Nested variants of
  standard tags that resolve relative references
  against beans
• struts-tiles.tld Full features layout
  management library
• Contributed libraries added in Struts 1.1
• struts-xxx-el.tld Versions of standard Struts
  tag libraries that support the expression
  language syntax of JSP Standard Tag Library

19
The Struts Framework View Layer

• Validation Framework
• No-code-required field level validations
• Configured in an XML document included in the web
  application
• Optionally generates client side JavaScript to
  enforce validation rules
• Extensible architecture

20
The Struts Framework Controller Layer

• ActionServlet Standard implementation of
  controller
• At application startup, reads configuration file
  and initializes resources
• Struts 1.1 PlugIn General start/stop hook
• On each request, implements the standard Struts
  request processing lifecycle (in Struts 1.1,
  implemented in RequestProcessor)
• Specialization / customization via subclassing
• Struts 1.1 Sub-application modules support

21
The Struts Framework Controller Layer

• Action Standard base class for business logic
  components and adapters
• Mapped to logical names by request processor
• Single instance per application (must be thread
  safe)
• Instantiated as needed, like servlets
• Implements the Command Pattern
• execute() -- Invoked for each request
• Can (but typically does not) create response
  content directly
• Typically returns ActionForward to select
  resource to prepare response

22
The Struts Framework Controller Layer

• Standard Request Processing Lifecycle 1
• processLocale() -- Record user's locale
  preference (if not already present)
• processPreprocess() -- general purpose
  pre-processing hook
• processMapping() -- select Action to be utilized
• processRoles() -- perform security role-based
  restrictions on action execution
• processActionForm() -- Create or acquire an
  appropriate ActionForm instance

23
The Struts Framework Controller Layer

• Standard Request Processing Lifecycle 2
• processPopulate() -- Copy the request parameters
  into the form bean properties
• processValidate() -- Call form bean's validate()
  method
• processActionCreate() -- Create or acquire an
  appropriate Action instance
• processActionPerform() -- Call action's execute()
  method
• processActionForward() -- Process returned
  ActionForward instance (if any)

24
The Struts Framework Controller Layer

• XML Configuration Document (/WEB-INF/struts-config
  .xml)
• Standard place to configure all aspects of the
  application's behavior
• DTD included for optional (but recommended)
  validation
• Logical-to-physical mappings for Actions,
  ActionForms, and ActionForwards
• General configuration settings
• Struts 1.1 Configuration Document per module if
  more than one

25
The Struts Framework Commons Libraries

• Non-Struts Specific Logic Factored Out
• commons-beanutils Generic bean property
  manipulation
• commons-collections Extensions to standard
  Java2 collections classes
• commons-dbcp Optional JDBC connection pool
• commons-digester XML parsing for configuration
  files
• commons-fileupload Support library for HTML
  file uploads

26
The Struts Framework Commons Libraries

• Non-Struts Specific Logic Factored Out
• commons-logging Application logging wrapper
• commons-pool Object pooling library
• commons-resources Message resources support
  library
• Commons-validator Field validation framework

27

• Building Web Applications With Struts

28
Building Web Applications With Struts

• Now that we understand the architecture of
  Struts, let's look at parts of an example app
  that is built with it
• Struts includes a canonical example that is
  useful in determining whether you have installed
  things correctly
• struts-example.war
• Application models (part of) an email portal site
  that lets you maintain multiple subscriptions

29
Sample Application Model Layer (Persistence
Tier)

• Modelled via a Data Access Object (DAO)
• org.apache.struts.webapp.example.UserDatabase
• public interface UserDatabase
• public User createUser(String username)
• public void close() throws Exception
• public User findUser(String username)
• public User findUsers()
• public void open() throws Exception
• public void removeUser(User user)
• public void save() throws Exception

30
Sample Application Model Layer (Persistence
Tier)

• Default implementation based on loading an XML
  document into memory
• o.a.s.e.memory.MemoryUserDatabase
• JDBC-based (or LDAP-based) implementation is easy
  to imagine, and would be transparent to the
  business logic
• Implementation selection implemented via a PlugIn
  ... see configuration file example later

31
Sample Application Model Layer (Business Logic)

• Two common Struts design patterns illustrated
• View --gt View --gt Action
• Welcome Page has link to logon page
• lthtmllink page/logon.jspgt...lt/htmllinkgt
• Logon page instantiates LogonForm bean
• Form submit goes to /logon action
• View --gt Action --gt View --gt Action
• Setup action /editRegistration?actionEdit
  pulls data from database and populates form
  bean
• Registration page /registration.jsp displays
  current data
• Form submit goes to /saveRegistration action

32
Sample Application View Layer (logon.jsp)

• lt_at_ page contentTypetext/htmlcharsetUTF-8
  gt
• lt_at_ taglib uri/WEB-INF/struts-bean.tld
• prefixbean gt
• lt_at_ taglib uri/WEB-INF/struts-html.tld
• prefixhtml gt
• lthtmlhtml localetruegt
• ltheadgt
• lttitlegt
• ltbeanmessage keylogon.title/gt
• lt/titlegt
• lthtmlbase/gt
• lt/headgt

33
Sample Application View Layer (logon.jsp)

• ltbody bgcolorwhitegt
• lthtmlerrors/gt
• lthtmlform action/logon focususername
• onsubmitreturn validateLogonForm(this)
  gt
• lttable border0 width100gt
• lttrgt
• ltth alignrightgt ltbeanmessage
  keyprompt.username/gt
• lt/thgt
• lttd alignleftgt
• lthtmltext propertyusername size16/gt
• lt/tdgt
• lt/trgt

34
Sample Application View Layer (logon.jsp)

• lttrgt
• ltth alignrightgt ltbeanmessage
  keyprompt.password/gt
• lt/thgt
• lttd alignleftgt
• lthtmlpassword propertypassword
• size16/gt
• lt/tdgt
• lt/trgt
• lt/tablegtlt/htmlformgt
• lthtmljavascript formNamelogonForm
• dynamicJavascripttrue
• staticJavascriptfalse/gt
• ltscript languageJavascript .../gt
• lt/bodygtlt/htmlhtmlgt

35
Sample Application Controller Layer

• No application logic required Struts does
  everything for you -)
• Controller functionality is configured via
  XML-based files
• struts-config.xml Struts controller
  configuration
• validation.xml Validator framework
  configuration
• web.xml Web application configuration

36
Sample Application Struts Configuration
(struts-config.xml)

• ltstruts-configgt
• ltform-beansgt
• ...
• ltform-bean namelogonForm
• typeorg.apache.struts.action.DynaActionForm
  gt
• ltform-property nameusername
• typejava.lang.String/gt
• ltform-property namepassword
• typejava.lang.String/gt
• lt/form-beangt
• ltform-bean nameregistrationForm
• typeorg.apache.webapp.example.RegistrationF
  orm/gt
• ...
• lt/form-beansgt

37
Sample Application Struts Configuration
(struts-config.xml)

• ltglobal-forwardsgt
• ltforward namelogoff path/logoff.do/gt
• ltforward namelogon path/logon.do/gt
• ltforward nameregistration
• path/registration.jsp/gt
• ltforward namesuccess
• path/mainMenu.jsp/gt
• lt/global-forwardsgt

38
Sample Application Struts Configuration
(struts-config.xml)

• ltaction-mappingsgt
• ltaction path/editRegistration
• typeorg.apache.struts.webapp.example.EditRegi
  strationAction
• nameregistrationForm
• scoperequest validatefalsegt
• ltforward namesuccess
• path/registration.jsp/gt
• lt/actiongt
• ltaction path/saveRegistration
• typeorg.apache.struts.webapp.example.SaveRegi
  strationAction
• nameregistrationForm
• scoperequest validatetrue
• inputregistration/gt

39
Sample Application Struts Configuration
(struts-config.xml)

• ltaction path/logon
• typeorg.apache.struts.webapp.example.
  LogonAction
• inputrequest
• namelogonForm
• scoperequest/gt
• ...
• lt/action-mappingsgt
• ltcontrollergt
• ltset-property propertyinputForward
• valuetrue/gt
• lt/controllergt
• ltmessage-resources
• parameterorg.apache.struts.example.Application
  Resources/gt

40
Sample Application Struts Configuration
(struts-config.xml)

• ltplug-in classNameorg.apache.struts.webapp.ex
  ample.memory.MemoryDatabasePlugIngt
• ltset-property propertypathname
• value/WEB-INF/database.xml/gt
• lt/plug-ingt
• ltplug-in classNameorg.apache.struts.validator.
  ValidatorPlugIngt
• ltset-property propertypathnames
• value/WEB-INF/validator-rules.xml,
• /WEB-INF/validation.xml/gt
• lt/plug-ingt
• lt/struts-configgt

41
Sample Application Struts Configuration
(validation.xml)

• ltform-validationgt
• ltformsetgt
• ltform namelogonFormgt
• ltfield propertyusername
• dependsminlength,...gt
• ltarg0 keyprompt.username/gt
• ltarg1 keyvarminlength
• nameminlength
• resourcefalse/gt
• ltvargtltvar-namegtminlengthlt/var-namegt
• ltvar-valuegt3lt/var-valuegtlt/vargt
• ...
• lt/fieldgt
• ...
• lt/formgt
• ...
• lt/formsetgt
• lt/form-validationgt

42
Sample Application Webapp Configuration
(web.xml)

• ltweb-appgt
• ltservletgt
• ltservlet-namegtControllerlt/servlet-namegt
• ltservlet-classgt
• org.apache.struts.action.ActionServlet
• lt/servlet-classgt
• ltinit-paramgt
• ltparam-namegtconfiglt/param-namegt
• ltparam-valuegt
• /WEB-INF/struts-config.xml
• lt/param-valuegt
• lt/init-paramgt
• ltload-on-startupgt 1 lt/load-on-startupgt
• lt/servletgt

43
Sample Application Webapp Configuration
(web.xml)

• ltservlet-mappinggt
• ltservlet-namegtControllerlt/servlet-namegt
• lturl-patterngt .do lt/url-patterngt
• lt/servlet-mappinggt
• ...
• lt/web-appgt

44

• Current Events

45
Struts 1.1 Release

• When? Real Soon Now
• What new features?
• Apache Commons Libraries
• DynaActionForm
• Declarative Exception Handling
• Nested Tag Library
• PlugIn API
• Sub-Application Module Support
• (Contributed) STRUTS-EL Tag Libraries

46
Struts and JSTL

• JSP Standard Tag Library (JSTL) 1.0
• Expression language (customer.addressmailing
  .city)
• General purpose actions (out, set, remove, catch)
• Conditional actions (if, choose, when, otherwise)
• Iterator actions (forEach, forTokens)
• URL actions (import, url, redirect, param)
• Internationalization actions (message, setLocale,
  bundle, setBundle, message, param,
  requestEncoding)
• Formatting actions (timeZone, setTimeZone,
  formatNumber, parseNumber, formatDate, parseDate)

47
Struts and JSTL

• JSP Standard Tag Library (JSTL) 1.0, continued
• SQL actions (not relevant in an MVC framework
  environment)
• XML core actions (parse, out, set)
• XML flow control actions (if, choose, when,
  otherwise, forEach)
• XML transform actions (transform, param)
• The struts-xxx-el libraries are a bridge for
  Struts developers who want to leverage JSTL tags,
  and expression language syntax, now

48
Struts and JSF

• JavaServer Faces (currently under development in
  JSR-127)
• Goals
• Standard GUI component framework for web
  applications
• RenderKits for different rendering environments
  (browser vs. wireless device, different locales,
  etc.)
• Struts will provide an integration library
• Requires changes to view layer and
  struts-config.xml file only!
• Plugs in to RequestProcessor APIs

49

• Resources

50
This Presentation Online

• StarOffice 6.0
• http//www.apache.org/craigmcc/apachecon-2002-str
  uts.sxi
• Powerpoint
• http//www.apache.org/craigmcc/apachecon-2002-str
  uts.ppt

51
Internet Technologies

• Hypertext Markup Language (HTML) 4.01
• http//www.w3.org/TR/html4/
• Hypertext Transfer Protocol (HTTP) 1.1
• http//www.ietf.org/rfc/rfc2616.txt
• Uniform Resource Identifiers (URI)
• http//www.ietf.org/rfc/rfc2396.txt

52
Model Layer Standard Java APIs

• JavaBeans
• http//java.sun.com/products/javabeans/
• Java Database Connectivity (JDBC)
• http//java.sun.com/products/jdbc/
• Java Data Objects
• http//java.sun.com/products/jdo/
• http//jcp.org/jsr/detail/12.jsp
• Java Naming and Directory Interface
• http//java.sun.com/products/jndi/
• Enterprise JavaBeans (EJB)
• http//java.sun.com/products/ejb/

53
Model Layer Persistence Frameworks

• Castor
• http//castor.exolab.org/
• Java Data Objects
• http//java.sun.com/products/jdo/
• Object/Relational Bridge
• http//jakarta.apache.org/ojb/
• Torque
• http//jakarta.apache.org/turbine/torque/

54
View Layer Standard Java APIs

• Servlets
• http//java.sun.com/products/servlet/
• JavaServer Pages (JSP)
• http//java.sun.com/products/jsp/
• JSP Standard Tag Library (JSTL)
• http//java.sun.com/products/jsp/jstl/
• JavaServer Faces
• http//java.sun.com/j2ee/javaserverfaces/
• http//jcp.org/jsr/detail/127.jsp

55
Struts Resources

• The Struts and Commons Web Sites
• http//jakarta.apache.org/struts/
• http//jakarta.apache.org/commons/
• Recent Books About Struts
• Cavaness, Chuck Programming Jakarta Struts
  O'Reilly
• Goodwill, James Mastering Jakarta Struts John
  Wiley
• Husted, Ted Java Web Development With Struts
  Manning
• Spielman, Sue The Struts Framework Practical
  Guide for Programmers Morgan Kaufman
• Turner, James Struts Kick Start Sams

56
Design Patterns Resources

• The Java Blueprints Web Site
• http//java.sun.com/blueprints/
• Design Patterns Books
• Gamma, Erich (et. al.) Design Patterns Elements
  of Reusable Object-Oriented Software
  Addison-Wesley
• Alur, Deepak (et. al.) Core J2EE Patterns Best
  Practices and Design Strategies Prentice Hall

57

• Q A