Apachecon 2002 Struts

Building Web Applications With The Struts Framework

Session WE06 – 11/20/2002 – 10:00-11:00

Craig R. McClanahanSenior 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 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 JavaBeansTM (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


● 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


● 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


● 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


● 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


● 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


● 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


● 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)


● 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>


<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>


<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>


<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>


<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”/>


<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”/>


<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>

Current Events

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

Resources

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

Q & A

Technology

Apachecon 2002 Struts