Transcript Training - Day 2

Training - Day 2
The Web
Agenda
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Introduction to Struts
JSP – Java Server Pages
The Struts Tag Libraries
JSTL – JSP Standard Template Library
Advanced Struts Features
DisplayTag
What is Struts?
• Struts is an open source framework that
provides a “Model 2” paradigm, a variation of
MVC, for web programming.
– Business logic execution
– Presentation logic
• Multiple frameworks
– Struts Action Framework
– Struts Shale Framework
– Lots of extensions…
How Does Struts Work?
• Java Servlets are designed to handle
requests made by Web browsers
• Java Server Pages are designed to create
dynamic Web pages that can turn normal web
sites into live applications
• Struts uses a special Servlet as a
switchboard to route requests from Web
browsers to the appropriate Server Page.
• This makes Web applications much easier to
design, create, and maintain.
Continued
• A web application has a deployment descriptor called
web.xml
• Describes the configuration of your web application
– Welcome pages (the file that is shown in a directory when
none is specified by the request),
– Mappings to servlets (path or extension name), and
parameters to those servlets.
• Here is where you configure the Struts ActionServlet
as the servlet that will handle all requests for a given
mapping (usually the extension .do).
Continued
• In the Struts configuration file, you associate paths
with the controller components of your application,
known as Action classes
– Login ==> LoginAction class
– This tells the Struts ActionServlet that when the incoming
request is http://myhost/myapp/Login.do it should invoke
your controller component LoginAction
• Note the extension .do in this URL.
• The extension causes your container (Tomcat) to call
the ActionServlet, which sees the word “Login" as the
thing you want to do
• The configuration is referenced, and your LoginAction
is executed.
Continued
• For each Action, you also configure Struts with the names of the
resulting page(s) that can be shown as a result of that action.
• There can be more than one view as the result of an action
– one for success
– one for failure, etc
• Your Action is based on these logical result mapping names
• It reports back to the ActionServlet using words like "success",
"failure", "ready", "ok", etc
• The Struts system knows how to forward to the proper specific
page
• This has the added advantage of reconfiguration of the view
layer by simply editing the Struts XML configuration file
• At this point Struts knows how to delegate to your controller
components, and what to show as a result of your controller
processing
• The "model" part of the application is completely up to you, and
is called from within your controller components
Continued
• You may also associate a Java Bean with an action in the Struts
configuration file
• The Java Bean is used as a repository for form or display data
that can be communicated between the view and controller layer
• These Beans are automatically made visible to your controller
components (like LoginAction) and any view page that is
associated with that controller
• You must be using some sort of server-side technology (JSP in
our case) for the view layer to see this data (plain HTML won't
work).
• The client feeds the data back through normal form submission
(POST/GET) methods, and Struts updates that data in the Bean
before calling your controller components
Notes to remember
• It is important to remember that this Struts
mechanism, or lifecycle, is only in effect when the
ActionServlet is handling the request
• Since this only happens when a request is submitted
that causes your container to call ActionServlet, you
must be sure that any page that relies on Struts is
done through a request that will map to the
ActionServlet.
Looking at some of the pieces
• Actions
• Forms
• Views
MVC – The Controller
• Acts as a bridge between an
application’s model and views.
• When an application receives a request,
the controller invokes an Action.
• Actions are controllers with a specific
responsibility, and an application will be
made up of multiple Actions.
Action Example
• Let’s take a look at the MovieAction.java
file in the exercises project.
MVC – The Model
• ActionForms are the model in the Struts
mindset. This is not your application’s
model.
• This is where data is passed from an
Action to a view.
• Basically, just a simple java bean.
ActionForm Example
• Let’s take a look at the MovieForm.java
file in the exercises project.
Web Domain Objects
• Helper object that cleans up the code in ActionForms
and on JSP pages - help to not lock you in to Struts
– Not a part of Struts
– Something we use on SIT team
• A place for fields that might be needed on a web
page, but should not be associated with a true
domain object (gets saved to a database).
• Provides a hook for web validation.
• If you don’t have extra fields or need web validation,
just use the real domain object.
• Let’s take a look at the WebRental.java file in the
exercises project.
MVC – The View
• We uses Java Server Pages (JSP) as the
view technology, rather than JSF or VT, etc.
• Use an ActionForm/Request to retrieve data.
• Tag libraries can be used in conjunction with
JSP - JSTL and DisplayTag are common
examples.
• Examples coming up in the JSP/JSTL
sections.
Exercise: Actions and Forms
• There are TODO statements scattered
throughout
– MovieAction.java
– MovieForm.java
Wiring Application Logic
• Configuration of application logic is
done in the struts-config.xml file.
• Allows declarative logic in XML rather
than in the application code.
• Allows re-configuration of application
logic without recompilation.
Example
<?xml version="1.0" encoding="ISO-8859-1" ?>
<!DOCTYPE struts-config PUBLIC
"-//Apache Software Foundation//DTD Struts Configuration 1.2//EN"
"http://struts.apache.org/dtds/struts-config_1_2.dtd">
<struts-config>
<form-beans>
<form-bean name="logonForm" type="app.LogonForm"/>
</form-beans>
<action-mappings>
<action path="/Welcome" forward="/pages/Welcome.jsp"/>
<action path="/Logon"
forward="/pages/Logon.jsp"/>
<action
path="/LogonSubmit"
type="app.LogonAction"
name="logonForm"
scope="request"
validate="true"
input="/pages/Logon.jsp">
<forward name="success" path="/pages/Welcome.jsp"/>
<forward name="failure" path="/pages/Logon.jsp"/>
</action>
<action path="/Logoff" type="app.LogoffAction">
<forward name="success" path="/pages/Logoff.jsp"/>
</action>
</action-mappings>
<message-resources parameter="resources.application"/>
</struts-config>
Time to look at the trn
configuration file
• Let’s find the struts-config.xml file in the
exercises project and look at it
Exercise: Wire Struts
• Time for you to go in and complete all of
the TODO items in the struts-config.xml
for the trn project.
Application Resources
(Messages)
• Application Resources is a file that can
contain all text messages that appear in
an application.
• Provides a single point for all textual
messages: easy to keep consistent,
change out side of the code, etc.
• Makes it possible for i18n.
Example
application.title=My Application
group.error=The group {0} is invalid
error.username.missing=You must type in a username
error.password.missing=You must type in a password
username.message=Username:
password.message=Password:
submit.button.message=Save
Let’s take a look at the
ApplicationResources.properties file out in the
trn project.
Adding Struts to a Web App
•
Configuring Struts
<servlet>
<servlet-name>action</servlet-name>
<servlet-class>org.apache.struts.action.ActionServlet</servlet-class>
<init-param>
<param-name>application</param-name>
<param-value>edu.iu.uis.train.ApplicationResources</param-value>
</init-param>
<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>
<servlet-mapping>
<servlet-name>action</servlet-name>
<url-pattern>*.do</url-pattern>
</servlet-mapping>
•
Configuring the taglibs for Struts
<taglib>
<taglib-uri>http://struts.apache.org/tags-html-el</taglib-uri>
<taglib-location>/WEB-INF/struts-html-el.tld</taglib-location>
</taglib>
Java Server Pages
• If you can write HTML pages, you are
well on your way to writing JSP
• Combination of:
– HTML tags
– Struts HTML-EL tags
– JSTL tags
• Let’s take a look at MovieDetail.jsp
struts-html-el
• Contain tags that
– handle form HTML elements
– handle re-writing HREF’s
– display user interface errors
– deal with a user’s locale
<%@ taglib uri="http://struts.apache.org/tags-html-el"
prefix="html-el" %>
struts-html-el <html-el>
• Looks at browser’s locale setting and
enables i18n based on user’s locale.
<html-el:html locale=“true”>
struts-html-el <html-el:errors>
• Displays a single error message or all
error messages saved in the servlet
context
• Action object/Form object can add
errors as necessary
– We typically do this in a validation
<html-el:errors/>
<html-el:errors property=“projectName”/>
struts-html-el <html-el:form>
• Start an HTML form where all input is
sent to a Form object
• POSTS or GETS to an action in strutsconfig.xml
<html-el:form action=“/Movie.do”>
struts-html-el
• Form Input tags
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button
cancel
checkbox
hidden
multibox
option
options
password
radio
reset
select
submit
text
textarea
All of these are just like their HTML counterparts
with a property attribute that work with a Form
struts-html-el <html-el:link>
• Create <a href> and handle url rewriting
• Use to provide links to locations within
your application
<html-el:link href=“/Movie.do”>
some link text or image
</html-el:link>
struts-html-el <html-el:image>
Create an image for submitting
Probably going to be the standard way to do buttons in
the UIS look and feel
Note the property – this is how Struts knows if you
clicked the image
<html-el:image
src="images/buttonsmall_save.gif"
property="methodToCall.saveBanUser2" />
JSTL
• JSP Standard Tag Library
• Set of tags that should be available in
all compliant JSP containers
• Promotes rapid application development
at the web page layer
Why do we need JSTL?
• A big reason is that writing your own
custom actions, or tags, can be a pain
• There was lots of reinventing the wheel
going on, for tasks like displaying a date
in a special format
• Many open source libraries sprung up,
but there was still no standard
• This fueled the fire behind JSTL
What do you get?
• Core
– Variables, logic and control flow, output
• XML
– Importing and parsing xml documents, xpath
• SQL
– Datasources, queries, updates, transactions
• i18n and Formatting
– Data/time formatting and i18n messaging
The Expression Language
• Very important part of JSTL
<c:if test="${book.orderQuantity > book.inStock}">
The book ${book.title} is currently out of stock.
</c:if>
• ${ … } are the expressions
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Access JavaBean properties using . (dot)
${book.title} translates to book.getTitle()
Access to Array and Collection elements using collection[]
Access to a Map value by key using map[“key”]
• EL searches each scope area if a scope isn’t specified
• Specific scope areas can be used:
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${pageScope.title}
${requestScope.title}
${sessionScope.title}
${applicationScope.title}
EL Operators
• Arithmetic
– +, -, *, / (or div), % (or mod) – note on XPath
• Relational
– == (or eq), != (or ne), < (or lt)
– > (or gt), <= (or le), >= (or ge)
• Logical
– && (or and), || (or or), ! (or not)
• Validation
– empty
• null values
• Collections or Arrays that are empty
• Strings that evaluate to “”
Implicit objects available in EL
• param and paramValues
– access HTTP request parameters
• header and headerValues
– request header information
• initParam (for the context init
parameters of the webapp)
• cookies
Automatic Type Conversion
• Authors do not have to worry about
converting types
• For example, a String parameter from a
request will be coerced to the
appropriate object or primitive
Taglib Directives
• Must be included on the page that you
want to use the tags
• Here is a directive for the core library
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
Variables
• <c:set var="name" scope="scope"
value="expression"/>
– The scope attribute is optional and defaults to page
• <c:set var="timezone"
scope="session">CST</c:set>
• <c:remove var="timezone"
scope="session"/>
Output
• <c:out value="expression" default="expression"
escapeXml="boolean"/>
– Default printed if its value null or an empty String
– escapeXml controls whether or not characters such as "<",
">", and "&" should be escaped
• Shortcut
– ${expression} can be used in some containers
Flow Control
• Iteration
• Condition
• Exception Handling
Iteration
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A loop with a start, end, and step (typical for statement)
<c:forEach var="name" varStatus="name"
begin="expression" end="expression" step="expression">
body content
</c:forEach>
•
A loop using an Iterator for a collection
<c:forEach var="name" items="expression" varStatus="name"
begin="expression" end="expression" step="expression">
body content
</c:forEach>
Example
<table>
<tr><th>Value</th><th>Square</th></tr>
<c:forEach var="x" begin="0"
end="10" step="2">
<tr>
<td>${x}</td>
<td>${x * x}</td>
</tr>
</c:forEach>
</table>
Another Example
<table>
<c:forEach items="${entryList}" var="blogEntry">
<tr><td align="left" class="blogTitle">
${blogEntry.title}
</td></tr>
<tr><td align="left" class="blogText">
${blogEntry.text}
</td></tr>
</c:forEach>
</table>
Conditionals
<c:if test="expression" var="name" scope="scope">
body content
</c:if>
<c:choose>
<c:when test="expression">
body content
</c:when>
...
<c:otherwise>
body content
</c:otherwise>
</c:choose>
Example
<c:choose>
<c:when test="${pageContext.request.scheme eq 'http'}">
This is an insecure Web session.
</c:when>
<c:when test="${pageContext.request.scheme eq 'https'}">
This is a secure Web session.
</c:when>
<c:otherwise>
You are using an unrecognized Web protocol. How did this happen?!
</c:otherwise>
</c:choose>
Exception Handling
• Rudimentary exception handling within a JSP
page
• Any exceptions raised within the body content
of this tag will be caught and ignored, unless
var is specified (exception stuck in var) for
custom error handling
<c:catch var="name">
body content
</c:catch>
Formatting
<fmt:formatDate value="expression"
timeZone="expression"
type="field" dateStyle="style"
timeStyle="style"
pattern="expression"
var="name" scope="scope"/>
<fmt:setBundle basename="expression"
var="name" scope="scope"/>
<fmt:message key="expression" bundle="expression"
var="name" scope="scope"/>
Example
<table>
<fmt:timeZone value="US/Eastern">
<c:forEach items="${entryList}" var="blogEntry" varStatus="status">
<c:if test="${status.first}">
<tr>
<td align="left" class="blogDate">
<fmt:formatDate value="${blogEntry.created}" dateStyle="full"/>
</td>
</tr>
</c:if>
<tr>
<td align="left" class="blogTitle">${blogEntry.title}</td>
</tr>
<tr>
<td align="left" class="blogText">${blogEntry.text}
<font class="blogPosted">
[Posted <fmt:formatDate value="${blogEntry.created}"
pattern="h:mm a zz"/>]
</font>
</td>
</tr>
</c:forEach>
</fmt:timeZone>
</table>
Example Output
The rest of JSTL
• Check out the references for the rest of
the JSTL libraries
– The rest of FMT
– SQL
– XML
• Also take a look at some of the JSP files
in the exercises application for
examples.
Exercise: JSP and JSTL
• Movie.jsp has numerous TODO items
throughout. At this time, you should
have enough information to fix this file.
Advanced Struts Topics
• Using the Struts Dispatch Action
– A few examples
• An Action with and without Dispatch
• A struts-config.xml file with and without
• MainAction.java in the trn project
• Struts Request Processor
– Configured via a controller
<controller processorClass=
"edu.iu.uis.train.application.TrainingStrutsRequestProcessor" />
• Message Resources
– Support for i18n of your messages
<message-resources
parameter="edu.iu.uis.train.ApplicationResources" />
• Dynamic Forms (not something we use)
http://struts.apache.org//struts-doc1.2.9/userGuide/building_controller.html#dyna_action_form_classes
Other stuff…
• UIS Dispatch Base Action
– Method to call
DisplayTag
What can it do?
• Actually the display tag library can just... display
tables!
• Give it a list of objects and it will handle
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Column display
Sorting
Paging
Cropping
Grouping
Exporting
Smart linking
Decoration of a table in a customizable XHTML style
Displaying a List of Objects
<% request.setAttribute( "test", new TestList(10, false) ); %>
<display:table name="test">
<display:column property="id" title="ID" />
<display:column property="name" />
<display:column property="email" />
<display:column property="status" />
<display:column property="description" title="Comments"/>
</display:table>
What get’s displayed in a column
• A column will display whatever the
property value tells it to display by
calling the getter for that bean property
Getting access in EL
• If you assign an id attribute, you can use that in EL
<display:table id="row" name="mylist">
<display:column title="row number" >
${row_rowNum}
</display:column>
<display:column title="name" >
${row.first_name}&nbsp;
${row.last_name}
</display:column>
</display:table>
DisplayTag: Things to remember
• We store the data in session for faster
paging and sorting (listKey)
• If you need multiple links, you may need
to hardcode the entire url in the action
property
Looking at some code
• Let’s take a look at MovieDetail.jsp in
the exercises project for a real example
Exercise: DisplayTag
• In <webapp>/WEB-INF/jsp/movie finish
the display tag in MovieList.jsp
• There is a TODO that explains what
needs to be done
References
• Struts Action Framework
http://struts.apache.org/struts-action/
• Practical JSTL Part 1
http://today.java.net/pub/a/today/2003/10/07/jstl1.html
• IBM JSTL Tutorial Part 1
http://www-128.ibm.com/developerworks/java/library/j-jstl0211.html
• IBM JSTL Tutorial Part 2
http://www-128.ibm.com/developerworks/java/library/j-jstl0318/
• IBM JSTL Tutorial Part 3
http://www-128.ibm.com/developerworks/java/library/j-jstl0415/
• The Display Tag Library
http://displaytag.sourceforge.net/10/