Apachecon 2002 Struts

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 Building A Web Application With Struts Resources

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

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?

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 JavaBeans TM (EJBs) Application Deployment – Networks, firewalls, public key infrastructures, load balancing, failover We need a fundamental organizing principle: The Model-View-Controller (MVC) architecture

The Model-View-Controller (MVC) Architecture

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

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)

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

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.

The Struts Framework – An Implementation of the MVC Architecture

The Struts Framework – Architecture

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

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

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

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

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

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

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

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

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

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)

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

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

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

Building Web Applications With Struts

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

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; }

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

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

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>

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>

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 >

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

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>

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>

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”/>

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 ”/>

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>

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>

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>

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

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

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)

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

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

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

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

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/

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/

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

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

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

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