Introduction to Struts 1.3

Introduction to Jakarta Struts 1.3
Ilio Catallo – info@iliocatallo.it

Outline
¤ Model-View-Controller vs. Web applications
¤ From MVC to MVC2
¤ What is Struts?
¤ Struts Architecture
¤ Building web applications with Struts
¤ Setting up the Controller
¤ Writing Views
¤ References
2

Model-View-Controller vs.
Web applications
3

Model-View-Controller
design pattern
¤ In the late seventies, software architects saw applications
as having three major parts:
¤ The part that manages the data (Model)
¤ The part that creates screens and reports (View)
¤ The part that handles interactions between the user and the
other subsystems (Controller)
¤ MVC turned out to be a good way to design applications
¤ Cocoa (Apple)
¤ Swing (Java)
¤ .NET (Microsoft)
4

Model-View-Controller
design pattern
5
View
Controller
Model
State query
Change notification
Event
Method
invocation

Model-View-Controller vs.
Web applications
¤ What is the reason not to use the same MVC pattern also
for web applications?
¤ Java developers already have utilities for:
¤ building presentation pages, e.g., JavaServer Pages (View)
¤ handling databases, e.g., JDBC and EJB (Model)
¤ But…
¤ the HTTP protocol imposes limitations on the applicability of
the MVC design pattern
¤ we don’t have any component to act as the Controller
6

HTTP limitations
¤ The MVC design pattern requires a push protocol for the
views to be notified by the model
¤ HTTP is a pull protocol: no request implies no response
¤ The MVC design pattern requires a stateful protocol to
keep track of the state of the application
¤ HTTP is stateless
7

HTTP limitations: Struts solutions
¤ HTTP is stateless: we can implement the MVC design
pattern on top of the Java Servlet Platform
¤ the platform provides a session context to help track users in
the application
¤ HTTP is a pull protocol: we can increase the Controller
responsibility. It will be responsible for:
¤ state changes
¤ state queries
¤ change notifications
8

Model-View-Controller 2
design pattern
¤ The resulting design pattern is sometimes called MVC2 or
Web MVC
¤ Any state query or change notification must pass through
the Controller
¤ The View renders data passed by the Controller rather than
data returned directly from the Model
9
View Controller Model

What is Jakarta Struts?
¤ Jakarta Struts is an open source framework
¤ It provides a MVC2-style Controller that helps turn raw
materials like web pages and databases into a coherent
application
¤ The framework is based on a set of enabling
technologies common to every Java web application:
¤ Java Servlets for implementing the Controller
¤ JavaServer Pages for implementing the View
¤ EJB or JDBC for implementing the Model
10

Struts Main Components:
ActionForward, ActionForm, Action
¤ Each web application is made of three main
components:
¤ Hyperlinks lead to pages that display data and other
elements, such as text and images
¤ HTML forms are used to submit data to the application
¤ Server-side actions which performs some kind of business
logic on the data
12

ActionForward, ActionForm, Action
¤ Struts provides components that programmers can use to
define hyperlinks, forms and custom actions:
¤ Hyperlinks are represented as ActionForward objects
¤ Forms are represented as ActionForm objects
¤ Custom actions are represented as Action objects
13

ActionMapping
¤ Struts bundles these details together into an
ActionMapping object
¤ Each ActionMappinghas its own URI
¤ When a specific resource is requested by URI, the
Controller retrieves the corresponding ActionMapping
object
¤ The mapping tells the Controller which Action, ActionForm
and ActionForwards to use
14

ActionServlet
¤ The backbone component of the Struts framework is
ActionServlet (i.e., the Struts Controller)
¤ For every request, the ActionServlet:
¤ uses the URI to understand which ActionMapping to use
¤ bundles all the user input into an ActionForm
¤ call the Action in charge of handling the request
¤ reads the ActionForwardcoming from the Action and
forward the request to the JSP page what will render the
result
15

Struts Control Flow
16
Controller
(ActionServlet)
Action
(ActionMapping,
ActionForm)
JSP page
(with HTML
form)
JSP page
(result page)
HTTP
request
HTTP
response
①
②
③
④ Model
(e.g., EJB)
ActionForward
⑤
Controller Model

Struts main component responsibilities
Class Description
ActionForward A user’s gesture or view selection
ActionForm The data for a state change
ActionMapping The state change event
ActionServlet The part of the Controller that receives
user gestures and stare changes and
issues view selections
Action classes The part of the Controller that interacts
with the model to execute a state
change or query and advises
ActionServlet of the next view to select
17

Building Web applications with
Struts
Setting up the Controller
18

Setting up the Controller:
The big picture
19
struts-
config.xml
web.xml
ActionMapping 1 ActionMapping N

Servlet Container (1/3)
¤ The web.xml deployment descriptor file describes how to
deploy a web application in a servlet container (e.g., Tomcat)
¤ The container reads the deployment descriptor web.xml, which
specifies:
¤ which servlets to load
¤ which requests are sent to which servlet
20

¤ Struts implements the Controller as a servlet
¤ Like all servlets it lives in the servlet container
¤ Conventionally, the container is configured to sent to
ActionServlet any request that matches the pattern
*.do
¤ Remember: Any valid extension or prefix can be used,
.do is simply a popular choice
21

web.xml (snippet)
<servlet-mapping>
<servlet-name>action</servlet-name>
<url-pattern>*.do</url-pattern>
</servlet-mapping>
22
¤ Forward any request that matches the pattern *.do to
the servlet named action (i.e., the Struts controller)

Struts Controller:
struts-config.xml
¤ The framework uses the struts-config.xml file as a
deployment descriptor
¤ It contains all the ActionMappings definedfor the web
application
¤ At boot time, Struts reads it to create a database of objects
¤ At runtime, Struts refers to the object created with the
configuration file, not the file itself
23

Struts Controller:
ActionForm (1/4)
¤ A JavaBean is a reusable software component which
conform to a set of design patterns
¤ The access to the bean’s internal state is provided through
two kinds of methods: accessors and mutators
¤ JavaBeans are used to encapsulate many objects into a
single object
¤ They can be passed around as a single bean object instead
of as multiple individual objects
24

Struts Controller:
ActionForm (2/4)
¤ Struts model ActionForms as JavaBeans
¤ The ActionForm has a corresponding property for each field
on the HTML form
¤ The Controller matches the parameters in the HTTP
request with the properties of the ActionForm
¤ When they correspond, the Controller calls the setter
methods and passes the value from the HTTP request
25

Struts Controller:
ActionForm (3/4)
LoginForm.java
pubic class LoginForm extends org.apache.struts.action.ActionForm {
private String username;
private String password;
public String getUsername() {return this.username;}
public String getPassword() {return this.password;}
public void setUsername(String username) {this.username =
username;}
public void setPassword(String password) {this.password =
password;}
}
26
¤ An ActionForm is a JavaBean that extends
org.apache.struts.action.ActionForm

Struts Controller:
ActionForm (4/4)
Specifying a new ActionForm in struts-config.xml
<form-beans>
<form-bean name=”loginForm"
type=”app.LoginForm"/>
</form-beans>
27
¤ Define a mapping between the actual ActionForm and
its logical name

Struts Controller:
ActionForwards
Specifying new ActionForwardsin struts-config.xml
<forward name="success" path="/success.html"/>
<forward name=”failure" path="/success.html"/>
<forward name=”logon" path=”/Logon.do"/>
28
¤ Define a mapping between the resource link and its
logical name
¤ Once defined, throughout the web application it is
possible to reference the resource via its logical name

Struts Controller:
Action
¤ Actions are Java classes that extend
org.apache.struts.Action
¤ The Controller populates the ActionForm and then passes it
to the Action
¤ the entry method is perform (Struts 1.0) or execute (Struts 1.1+)
¤ The Action is generally responsible for:
¤ validating input
¤ accessing business information
¤ determining which ActionForward to return to the Controller
29

Struts Controller:
Action
LoginAction.java
import javax.servet.http.*;
public class LoginAction extends org.apache.struts.action.Action {
public ActionForward execute(ActionMapping mapping, ActionForm
form,
HttpServletRequest req, HttpServletResponse
res) {
// Extract data from the form
LoginForm lf = (LoginForm) form;
String username = lf.getUsername();
String password = lf.getPassword();
// Apply business logic
UserDirectory ud = UserDirectory.getInstance();
if (ud.isValidPassword(username, password))
return mapping.findForward("success");
return mapping.findForward("failure");
}
} 30

Struts Controller:
struts-config.xml
struts-config.xml (snippet)
<form-beans>
<form-bean name="loginForm"
type="app.LoginForm"/>
</form-beans>
<action-mappings>
<action path="/login"
type="app.LoginAction"
name="loginForm">
<forward name="success" path="/success.jsp"/>
<forward name="failure" path="/failure.jsp"/>
</action>
</action-mappings>
31
Struts trims
automatically
the .do
extension

Building web applications with
Struts
Writing Views
32

Writing Views:
JavaServer Pages (JSP)
¤ JavaServer Pages is a technology that helps Java
developers create dynamically generated web pages
¤ A JSP page is a mix of plain old HTML tags and JSP scripting
elements
¤ JSP pages are translated into servlets at runtime by the JSP
container
33
JSP Scripting Element
<b> This page was accessed at <%= new Date() %></b>

Writing Views:
JSP tags
¤ JSP scripting elements require that developers mix Java
code with HTML. This situation leads to:
¤ non-maintainable applications
¤ no opportunity for code reuse
¤ An alternative to scripting elements is to use JSP tags
¤ JSP tags can be used as if they were ordinary HTML tags
¤ Each JSP tag is associated with a Java class
¤ It’s sufficient to insert the same tag on another page to reuse
the same code
¤ If the code changes, all the pages are automatically updated
34

Writing Views:
JSP Tag Libraries
¤ A number of prebuilt tag libraries are available for
developers
¤ Example: JSP Standard Tag Library (JSTL)
¤ Each JSP tag library is associated with a Tag Library
Descriptor (TLD)
¤ The TLD file is an XML-style document that defines a tag
library and its individual tags
¤ For each tag, it defines the tag name, its attributes, and the
name of the class that handles tag semantics
35

Writing Views:
JSP Tag Libraries
¤ JSP pages are an integral part of the Struts Framework
¤ Struts provides its own set of custom tag libraries
36
Tag library descriptor Purpose
struts-html.tld JSP tag extension for
HTML forms
struts-bean.tld JSP tag extension for
handling JavaBeans
struts-logic.tld JSP tag extension for
testing the values of
properties

Writing Views
login.jsp
<%@ taglib uri=”http://struts.apache.org/tags-html" prefix="html" %>
<html>
<head>
<title>Sign in, Please!</title>
</head>
<body>
<html:form action="/login" focus="username">
Username: <html:text property="username"/> <br/>
Password: <html:password property="password"/><br/>
<html:submit/> <html:reset/>
</html:form>
</body>
</html>
37
the taglib directive
makes accessible the
tag library to the JSP
page
JSP tag from the
struts-html tag
library

References
¤ Struts 1 In Action, T. N. Husted, C. Dumoulin, G. Franciscus,
D. Winterfeldt, , Manning Publications Co.
¤ JavaBeans, In Wikipedia, The Free
Encyclopedia,http://en.wikipedia.org/w/index.php?title=
JavaBeans&oldid=530069922
¤ JavaServer Pages, In Wikipedia, The Free
Encyclopediahttp://en.wikipedia.org/w/index.php?title=
JavaServer_Pages&oldid=528080552
38

Introduction to Struts 1.3

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