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Building Web Applications With The Struts Framework Session WE06 – 11/20/2002 – 10:00-11:00 Craig R. McClanahan Senior S

Building Web Applications With The Struts Framework Session WE06 – 11/20/2002 – 10:00-11:00 Craig R. McClanahan Senior Staff Engineer Sun Microsystems, Inc. Session Outline. Web Applications Backgrounder The Model-View-Controller Architecture The Struts Framework

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Building Web Applications With The Struts Framework Session WE06 – 11/20/2002 – 10:00-11:00 Craig R. McClanahan Senior S

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  1. Building Web Applications With The Struts Framework Session WE06 – 11/20/2002 – 10:00-11:00 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: • “{0} is not a valid credit rating” • 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 --> View --> Action • Welcome Page has link to logon page: • <html:link page=”/logon.jsp”>...</html:link> • Logon page instantiates LogonForm bean • Form submit goes to “/logon” action • View --> Action --> View --> Action • Setup action “/editRegistration?action=Edit” 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) <%@ page contentType=”text/html;charset=”UTF-8” %> <%@ taglib uri=”/WEB-INF/struts-bean.tld” prefix=”bean” %> <%@ taglib uri=”/WEB-INF/struts-html.tld” prefix=”html” %> <html:html locale=”true”> <head> <title> <bean:message key=”logon.title”/> </title> <html:base/> </head>

  33. Sample Application – View Layer (logon.jsp) <body bgcolor=”white”> <html:errors/> <html:form action=”/logon” focus=”username” onsubmit=”return validateLogonForm(this);”> <table border=”0” width=”100%”> <tr> <th align=”right”> <bean:message key=”prompt.username”/> </th> <td align=”left”> <html:text property=”username” size=”16”/> </td> </tr>

  34. Sample Application – View Layer (logon.jsp) <tr> <th align=”right”> <bean:message key=”prompt.password”/> </th> <td align=”left”> <html:password property=”password” size=”16”/> </td> </tr> </table></html:form> <html:javascript formName=”logonForm” dynamicJavascript=”true” staticJavascript=”false”/> <script language=”Javascript” .../> </body></html:html>

  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) <struts-config> <form-beans> ... <form-bean name=”logonForm” type=”org.apache.struts.action.DynaActionForm”> <form-property name=”username” type=”java.lang.String”/> <form-property name=”password” type=”java.lang.String”/> </form-bean> <form-bean name=”registrationForm” type=”org.apache.webapp.example.RegistrationForm”/> ... </form-beans>

  37. Sample Application – Struts Configuration (struts-config.xml) <global-forwards> <forward name=”logoff” path=”/logoff.do”/> <forward name=”logon” path=”/logon.do”/> <forward name=”registration” path=”/registration.jsp”/> <forward name=”success” path=”/mainMenu.jsp”/> </global-forwards>

  38. Sample Application – Struts Configuration (struts-config.xml) <action-mappings> <action path=”/editRegistration” type=”org.apache.struts.webapp.example.EditRegistrationAction” name=”registrationForm” scope=”request” validate=”false”> <forward name=”success” path=”/registration.jsp”/> </action> <action path=”/saveRegistration” type=”org.apache.struts.webapp.example.SaveRegistrationAction” name=”registrationForm” scope=”request” validate=”true” input=”registration”/>

  39. Sample Application – Struts Configuration (struts-config.xml) <action path=”/logon” type=”org.apache.struts.webapp.example.LogonAction” input=”request” name=”logonForm” scope=”request”/> ... </action-mappings> <controller> <set-property property=”inputForward” value=”true”/> </controller> <message-resources parameter=”org.apache.struts.example.ApplicationResources”/>

  40. Sample Application – Struts Configuration (struts-config.xml) <plug-in className=”org.apache.struts.webapp.example.memory.MemoryDatabasePlugIn”> <set-property property=”pathname” value=”/WEB-INF/database.xml”/> </plug-in> <plug-in className=”org.apache.struts.validator.ValidatorPlugIn”> <set-property property=”pathnames” value=”/WEB-INF/validator-rules.xml, /WEB-INF/validation.xml”/> </plug-in> </struts-config>

  41. Sample Application – Struts Configuration (validation.xml) <form-validation> <formset> <form name=”logonForm”> <field property=”username” depends=”minlength,...”> <arg0 key=”prompt.username”/> <arg1 key=”${var:minlength}” name=”minlength” resource=”false”/> <var><var-name>minlength</var-name> <var-value>3</var-value></var> ... </field> ... </form> ... </formset> </form-validation>

  42. Sample Application – Webapp Configuration (web.xml) <web-app> <servlet> <servlet-name>Controller</servlet-name> <servlet-class> org.apache.struts.action.ActionServlet </servlet-class> <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>

  43. Sample Application – Webapp Configuration (web.xml) <servlet-mapping> <servlet-name>Controller</servlet-name> <url-pattern> *.do </url-pattern> </servlet-mapping> ... </web-app>

  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.address[“mailing”].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-struts.sxi • Powerpoint: • http://www.apache.org/~craigmcc/apachecon-2002-struts.ppt

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