Google Git
Sign in
apache / struts-archive / cd87efd9c6e09100c5a393a5ed766cd277d9ff55 / . / build-legacy / core / xdocs / faqs / newbie.xml
blob: 046f90c9dca17b34ca9129ea1eff30007a789efa [file] [log] [blame]
<?xml version="1.0"?>
<document url="./newbie.xml">
<properties>
<title>Newbie FAQ - Apache Struts</title>
</properties>
<body>
<section href="faq" name="Newbie FAQ"/>
<section href="contents" name="Index">
<p>
Here are answers to the most common questions people ask when using
Struts on their first project.
<strong>For an in-depth, searchable FAQ, visit our friends at
<a href="http://www.jguru.com/faq/home.jsp?topic=Struts">JGuru</a>.</strong>
</p>
<ul>
<li>
<a href="#reload">Why was reload removed from Struts 1.1?</a>
</li>
<li>
<a href="#modules">What is a modular application? What does
module-relative mean?</a>
</li>
<li>
<a href="#naming">Why are some of the class and element names
counter-intuitive?</a>
</li>
<li>
<a href="#actionForms">Whither ActionForms?</a>
</li>
<li>
<a href="#actionFormInterface">Why is ActionForm a base class rather than an interface?</a>
</li>
<li>
<a href="#multiple">Can I use multiple HTML form elements with the same
name?</a>
</li>
<li>
<a href="#multipleSubmits">Can I have multiple submit buttons on the same
form?</a>
</li>
<li><a href="#checkbox">Why are my checkboxes not being set from ON to
OFF?</a>
</li>
<li><a href="#focus">Why doesn't the focus feature on the &lt;html:form>
tag work in every circumstance?</a>
</li>
<li>
<a href="#javascript.submit">How do I use JavaScript to submit a form? </a>
</li>
<li>
<a href="#javascript">How do I use JavaScript to ... </a>
</li>
<li>
<a href="#reset">Do I need to implement reset and set all my form
properties to their initial values?</a>
</li>
<li>
<a href="#scriptlets">Can't I just create some of my JavaBeans in the JSP
using a scriptlet?</a>
</li>
<li>
<a href="#otherBeans">Can I use other beans or hashmaps with ActionForms?</a>
</li>
<li>
<a href="#tags">Why do the Struts tags provide for so little
formatting?</a>
</li>
<li>
<a href="#layout">Why don't the Struts taglibs offer more layout options?</a>
</li>
<li>
<a href="#link">Why does the &lt;html:link> tag URL-encode javascript and
mailto links?"</a>
</li>
<li>
<a href="#authenticate">How can I authenticate my users?</a>
</li>
<li>
<a href="#pager">How can I scroll through list of pages like the search
results in google?</a>
</li>
<li>
<a href="#minimization">Why does the option tag render selected="selected"
instead of just "selected"?
</a></li>
<li><a href="#jsp">Do I have to use JSPs with my application?</a></li>
<li>
<a href="#formbeans">Do ActionForms have to be true JavaBeans?</a>
</li>
<li>
<a href="#separate">Do I have to have a separate ActionForm bean
for every HTML form?</a>
</li>
<li>
<a href="#prepopulate">How can I prepopulate a form?</a>
</li>
<li>
<a href="#noForm">Can I have an Action without a form?</a>
</li>
<li>
<a href="#requiredif">Can you give me a simple example of using the requiredif Validator rule?</a>
</li>
<li>
<a href="#validate">When is the best time to validate input?</a>
</li>
<li>
<a href="#avoidValidate">How can I avoid validating a form before data is entered?</a>
</li>
<li>
<a href="#wizard">How can I create a "wizard" workflow?</a>
</li>
<li>
<a href="#chaining">How can I "chain" Actions?</a>
</li>
</ul>
<p>
If you like to <a href="helping.html">contribute</a>,
there is a list of <a href="#undocumented"> undocumented questions</a>
at the end of this page.
</p>
</section>
<section href="reload" name="Why was reload removed from Struts 1.1?">
<p>
The problem with ReloadAction was that Struts was trying to act like a
container, but it couldn't do a proper job of it. For example, you
can't reload classes that have been modified, or (portably) add new
classes to a running web application (even if the container supported it).
</p>
<p>
Meanwhile, as 1.1 was being developed, work progressed on things
like Tomcat's reload command via the Manager webapp. This feature allows
you to quickly reload-on-demand, complete with saving and restoring your
session). It started to make even less sense for Struts to half-implement
a feature that containers are implementing fully.
</p>
<p>
A more minor point is that freezing the configuration information at application
startup time allows Struts to safely access the mapping information without
bothering with synchronization. The "startup-only" strategy creates a modest
but real improvement in performance for all users.
</p>
<p>So, ReloadAction is not supported in 1.1 for two reasons:</p>
<ul>
<li>
It never did let you reload everything that you would really
want to -- particularly changed classes -- so many people
ended up having to reload the webapp anyway.
</li>
<li>
Containers are starting to offer reload-on-demand features
which does the same thing as the Struts ReloadAction, only better.
</li>
<li>
Not supporting ReloadAction lets Struts avoid doing synchronization
locks around all the lookups (like figuring out which action to use,
or the destination of an ActionForward) so applications can run a
little faster.
</li>
</ul>
<p>
Of course, if someone came up with an implementation that solved these
problems without creating any others, we would not be opposed to including
a new ReloadAction.
</p>
</section>
<section href="modules" name="What is a modular application? What does module-relative mean?">
<p>
Since Struts 1.1, the framework supports multiple application modules. All applications have at
least one root, or default, module. Like the root directory in a file system, the default application
has no name. (Or is named with an empty string, depending your viewpoint.) Developing an application
with only a default module is no different from how applications were developed under Struts 1.0.
Since Struts 1.1, you can add additional modules to your application, each of which can have their
own configuration files, messages resources, and so forth. Each module is developed in the same way as
the default module. Applications that were developed as a single module can added to a multiple
module application, and modules can promoted to a standalone application without change. For more
about configuring your application to support multiple modules, see
<a href="../userGuide/configuration.html#dd_config_modules">Configuring Applications</a> in the
User Guide.
</p>
<p>
But to answer the question =:0), a modular application is a Struts application that uses more than
one module. Module-relative means that the URI starts at the application-module level, rather than at
the application-context level, or the absolute-URL level.
</p>
<ul>
<li>Absolute URL: http://localhost/myApplication/myModule/myAction.do</li>
<li>context-relative: /myModule/myAction.do</li>
<li>module-relative: /myAction.do</li>
</ul>
</section>
<section href="naming" name="Why are some of the class and element names counter-intuitive?">
<p>
The framework grew in the telling and as it evolved some of the names
drifted.
</p>
<p>The good thing about a nightly build, is that everything becomes
available to the community as soon as it is written. The bad thing about
a nightly build is that things like class names get locked down early and
then become difficult to change.
</p>
</section>
<section href="actionForms" name="Wither ActionForms?">
<p>
<a href="http://www.mail-archive.com/struts-user@jakarta.apache.org/msg19281.html">http://www.mail-archive.com/struts-user@jakarta.apache.org/msg19281.html</a><br/>
<a href="http://www.mail-archive.com/struts-user@jakarta.apache.org/msg19338.html">http://www.mail-archive.com/struts-user@jakarta.apache.org/msg19338.html</a><br/>
<a href="http://www.mail-archive.com/struts-user@jakarta.apache.org/msg20833.html">http://www.mail-archive.com/struts-user@jakarta.apache.org/msg20833.html</a><br/>
</p>
</section>
<section href="actionFormInterface" name="Why is ActionForm a base class rather than an interface?">
<p>
The MVC design pattern is very simple to understand but much more difficult
to live with. You just need this little bit of Business Logic in the View
logic or you need just that little bit of View logic in the Business tier and
pretty soon you have a real mess.
</p>
<p>
Making ActionForm a class takes advantage of the single
inheritance restriction of Java to it makes it more difficult for people to do
things that they should not do.
</p>
<p>
ActionForms implemented as interfaces encourage making the property types match
the underlying business tier instead of Strings, which violates one of the
primary purposes for ActionForms in the first place (the ability to reproduce
invalid input, which is a fundamental user expectation).
ActionForms as an interface would also encourage using existing DAO objects as
ActionForms by adding ‘implements ActionForm’ to the class. This violates
the MVC design pattern goal of separation of the view and business logic.
</p>
<p>
Since the goal of struts is to enforce this separation, it just makes more sense
for Struts to own the ActionForm.
</p>
</section>
<section href="JavaBeans" name="Do ActionForms have to be true JavaBeans?">
<p>
The utilities that Struts uses (Commons-BeanUtils since 1.1) require that ActionForm properties follow
the JavaBean patterns for mutators and accessors (get*,set*,is*). Since Struts uses the Introspection API
with the ActionForms, some containers may require that all the JavaBean patterns be followed, including
declaring "<code>implements Serializable</code>" for each subclass. The safest thing is to review the
<a href="../userGuide/preface.html#javabeans">JavaBean specification</a> and follow all the prescribed patterns.</p>
</section>
<section href="multiple" name="Can I use multiple HTML form elements with the same name?">
<p>
Yes. Define the element as an array and Struts will autopopulate it like any other.
</p>
<pre>
<code>
private String[] id= {};
public String[] getId() { return this.id; }
public void setItem(String id[]) {this.id = id;}
</code>
</pre>
<p>
And so forth
</p>
</section>
<section href="multipleSubmits" name="Can I have multiple submit buttons on the same form?">
<p>
<strong>Yes</strong>. The issue is that only one action class can be
associated with a single form. So the real issue is how do I decode
multiple submit types to a single <code>Action</code> class.
There is more than one way to achieve this functionality.</p>
<p>
The way that is suggested by struts is right out of the javadoc for
<a href="../api/org/apache/struts/actions/LookupDispatchAction.html">
<code>LookupDispatchAction</code></a>.
Basically, <code>LookupDispatchAction</code> is using the keys from
<code>ApplicationProperties.resources</code> as keys to a map of actions
available to your <code>Action</code> class. It uses
<a href="http://java.sun.com/j2se/1.3/docs/guide/reflection/">reflection</a> to
decode the request and invoke the proper action. It also takes advantage of
the struts <a href="../userGuide/struts-html.html#submit">
<code>&lt;html:submit&gt;</code></a> tags and is straight forward to implement.</p>
<p>
You can roll your own with JavaScript events and <code>javascript:void
(document.forms["myform"].submit)</code> on any html element. This gives you
control of how you want your page to look. Again you
will have to decode the expected action in the <code>execute</code> method of
your action form if you choose this route.</p>
</section>
<section href="focus" name="Why doesn't the focus feature on the &lt;html:form> tag work in every circumstance?">
<p>
Unfortunately, there is some disagreement between the various browsers, and different versions of the same browser, as to how the focus can be set.
The &lt;html:form> tag provides a quick and easy JavaScript that will set the focus on a form
for most versions of most browsers.
If this feature doesn't work for you, then you should set the focus using your own JavaScript.
The focus feature is a convenient "value-add" -- not a core requirement of the tag.
If you do come up with a JavaScript that provides the final solution to this project,
please post your patch to this <a href="http://issues.apache.org/bugzilla/show_bug.cgi?id=13454">Bugzilla ticket</a>.
</p>
</section>
<section href="checkbox" name="Why are my checkboxes not being set from ON to OFF?">
<p>
A problem with a checkbox is that the browser will only include it in the request
when it is checked. If it is not checked, the HTML specification suggests that it
not be sent (i.e. omitted from the request). If the value of the checkbox is being
persisted, either in a session bean or in the model, a checked box can never
unchecked by a HTML form -- because the form can never send a signal to uncheck
the box. The application must somehow ascertain that since the element was not
sent that the corresponding value is unchecked.
</p>
<p>
The recommended approach for Struts applications is to use the reset method in the
ActionForm to set all properties represented by checkboxes to null or false. The
checked boxes submitted by the form will then set those properties to true. The
omitted properties will remain false. Another solution is to use radio buttons
instead, which always submit a value.
</p>
<p>
It is important to note that the HTML specification recommends this same
behavior whenever a control is not "successful". Any blank element in a HTML
form is not guaranteed to submitted. It is therefor very important to set the
default values for an ActionForm correctly, and to implement the reset method
when the ActionForm might kept in session scope.
</p>
</section>
<section href="javascript.submit" name="Can I use JavaScript to submit a form?">
<p>
You can submit a form with a link as below.
BTW, the examples below assume you are in an &lt;html:form&gt; block and 'myForm'
is picked up from the struts-config.xml name field of the action.
</p>
<pre><code>
&lt;a href='javascript:void(document.forms["myForm"].submit()&gt;My Link&lt;/a&gt;
</code></pre>
<p>
Now the trick in the action is to decode what action you intend to perform.
Since you are using JavaScript, you could set a field value and look for it in
the request or in the form.
</p>
<p>
... html/javascript part ...
</p>
<pre><code>
&lt;input type='hidden' value='myAction' /&gt;
&lt;input type='button' value='Save Meeeee'
onclick='document.forms["myForm"].myAction.value="save";
document.forms["myForm"].submit();' /&gt;
&lt;input type='button' value='Delete Meeeee'
onclick='document.forms["myForm"].myAction.value="delete";
document.forms["myForm"].submit();' /&gt;
</code></pre>
<p>
... the java part ...
</p>
<pre><code>
class MyAction extends ActionForm implements Serializable {
public ActionForward execute (ActionMapping map, ActionForm form,
HttpServletRequest req, HttpServletResponse) {
String myAction = req.getParameter("myAction");
if (myAction.equals("save") {
// ... save action ...
} else if (myAction.equals("delete") {
// ... delete action ...
}
}
}
}
</code></pre>
<p>
This is just one of many ways to achieve submitting a form and decoding the
intended action. Once you get used to the framework you will find other ways
that make more sense for your coding style and requirements. Just remember
this example is completely non-functional without JavaScript.
</p>
<p>
Here is a link
which utilizes the LookupDispatch action to submit forms with multiple actions
without javascript: <a href="http://husted.com/struts/tips/003.html">http://husted.com/struts/tips/003.html</a>
</p>
</section>
<section href="javascript" name="How do I use JavaScript to ...">
<p>
Struts is mainly a server-side technology.
We bundled in some JSP tags to expose the framework components to your
presentation page, but past that, the usual development process applies.
</p>
<p>
Interactive pages require the use of JavaScript.
(That's why it was invented.)
If you want things popping up or doing this when they click that,
you are outside the scope of Struts and back into the web
development mainstream.
</p>
<p>
You use JavaScript with Struts the same way you use with any presentation
page.
Since JavaScript is a client-side technology, you can use simple relative
references to your scripts.
If you need to fire a JavaScript from a HTML control, the Struts HTML tags
have properties for the JavaScript events.
</p>
<p>
A very good JavaScript resource is Matt Kruse's site at
<a href="http://www.mattkruse.com/javascript/">
http://www.mattkruse.com/javascript/</a>
</p>
</section>
<section href="reset" name="Do I need to implement reset and set all my form properties to their initial values?">
<p>
No.
You need to set checkbox properties to false if the ActionForm is being retained in session scope.
This is because an unchecked box does not submit an attribute.
Only checked boxes submit attributes.
If the form is in session scope, and the checkbox was checked, there is no way to turn it back off without the reset method.
Resetting the properties for other controls, or for a request scope form, is pointless.
If the form is in request scope, everything already just started at the initial value.
</p>
</section>
<section href="scriptlets" name="Can't I just create some of my JavaBeans in the JSP using a scriptlet?">
<p>
Struts is designed to encourage a
<a href="http://www.javaworld.com/javaworld/jw-12-1999/jw-12-ssj-jspmvc.html">
Model 2/MVC architecture</a>. But there is nothing that prevents you from using Model 1
techniques in your JavaServer Pages, so the answer to the question is "Yes, you can".
</p>
<p>
Though, using Model 1 techniques in a Struts application does go against the grain.
The approach recommended by most Struts developers is to create and populate whatever
objects the view may need in the Action, and then forward these through the request.
Some objects may also be created and stored in the session or application context,
depending on how they are used.
</p>
<p>
Likewise, there is nothing to prevent you from using scriptlets along with JSP
tags in your pages. Though, many Struts developers report writing very complex
scriplet-free applications and recommend the JSP tag approach to others.
</p>
<p>
For help with Model 1 techniques and scriptlets, you might consider joining the
<a href="http://archives.java.sun.com/jsp-interest.html">Javasoft JSP-interest
mailing list</a>, where there are more people still using these approaches.
</p>
</section>
<section href="otherBeans" name="Can I use other beans or hashmaps with ActionForms?">
<p>
Yes. There are several ways that you can use other beans or hashmaps with ActionForms.
</p>
<ul>
<li>
ActionForms can have other beansor hashmaps as properties
</li>
<li>
"Value Beans" or "Data Transfer Objects" (DTOs) can be used independently of
ActionForms to transfer data to the view
</li>
<li>
ActionForms can use Maps to support "dynamic" properties (since Struts 1.1)
</li>
</ul>
<p>
ActionForms (a.k.a. "form beans") are really just Java beans (with a few
special methods) that Struts creates and puts into session or request scope for you.
There is nothing preventing you from using other beans, or including
them in your form beans. Here are some examples:
</p>
<p>
<em>Collections as properties</em> Suppose that you need to display a pulldown list of
available colors on an input form in your application. You can include a string-valued
<code>colorSelected</code> property in your <code>ActionForm</code> to represent the user's
selection and a <code>colorOptions</code> property implemented as a <code>Collection</code>
(of strings) to store the available color choices. Assuming that you have defined the getters
and setters for the <code>colorSelected</code> and <code>colorOptions</code> properties
in your <code>orderEntryForm</code> form bean, you can render the
pulldown list using:
</p>
<pre><code>
&lt;html:select property="colorSelected"&gt;
&lt;html:options property="colorOptions" name="orderEntryForm"/&gt;
&lt;/html:select&gt;
</code></pre>
<p>
The list will be populated using the strings in the <code>colorOptions</code>
collection of the <code>orderEntryForm</code> and the value that the user selects
will go into the <code>colorSelected</code> property that gets posted to the subsequent
<code>Action</code>. Note that we are assuming here that the <code>colorOptions</code>
property of the <code>orderEntryForm</code> has already been set.
</p>
<p>
See <a href="#prepopulate">How can I prepopulate a form?</a> for instructions on how to set
form bean properties before rendering edit forms that expect properties to be pre-set.
</p>
<p>
<em>Independent DTO</em> An <code>Action</code> that retrieves a list of open orders (as an
<code>ArrayList</code> of <code>Order</code> objects) can use a DTO independently of any
form bean to transfer search results to the view. First, the Action's
<code>execute</code> method performs the search and puts the DTO into the request:
</p>
<pre><code>
ArrayList results = businessObject.executeSearch(searchParameters);
request.setAttribute("searchResults",results);
</code></pre>
<p>
Then the view can iterate through the results using the "searchResults" request key to
reference the DTO:
` </p>
<pre><code>
&lt;logic:iterate id="order" name="searchResults" type="com.foo.bar.Order"&gt;
&lt;tr&gt;&lt;td&gt;&lt;bean:write name="order" property="orderNumber"/&gt;&lt;td&gt;
&lt;td&gt;..other properties...&lt;/td&gt;&lt;/tr&gt;
&lt;/logic:iterate&gt;
</code></pre>
<p>
See also: <a href="../userGuide/building_controller.html#map_action_form_classes">Map-Backed ActionForms</a> (since Struts 1.1)
</p>
</section>
<section href="tags" name="Why do the Struts tags provide for so little formatting?">
<p>
<em>The Struts tags seem to provide only the most rudimentary functionality.
Why is there not better support for date formatting and advanced string handling?</em>
</p>
<p>
Three reasons:
</p>
<p>
First, work started on the JSTL and we didn't want to duplicate the effort.
</p>
<p>
Second, work started on Java Server Faces, and we didn't want to duplicate that effort either.
</p>
<p>
Third, in a Model 2 application, most of the formatting can be handled in the ActionForms (or in the business tier),
so all the tag has to do is spit out a string.
This leads to better reuse since the same "how to format" code does not need to be repeated in every instance.
You can "say it once" in a JavaBean and be done with it.
</p>
</section>
<section href="layout" name="Why don't the Struts taglibs offer more layout options?">
<p>
Since the Struts tags are open source, you can extend them to provide whatever additional formatting you may need.
If you are interested in a pre-written taglib that offers more layout options, see the
<a href="http://struts.application-servers.com">struts-layout taglib</a>.
</p>
<p>
In the same arena, there is a well regarded contributor taglib that can help you create
<a href="http://sourceforge.net/projects/struts-menu/">Menus for your Struts applications</a>.
</p>
</section>
<section href="link" name="Why does the &lt;html:link> tag URL-encode javascript and mailto links?">
<p>
The &lt;html:link> tag is not intended for use with client-side references like those used to launch Javascripts or email clients.
The purpose of link tag is to interject the context (or module) path into the URI so that your server-side links are not dependent on your context (or module) name.
It also encodes the link, as needed, to maintain the client's session on the server.
Neither feature applies to client-side links, so there is no reason to use the &lt;html:link> tag.
Simply markup the client-side links using the standard <a/> tag.
</p>
</section>
<section href="authenticate" name="How can I authenticate my users?">
<p>
<a href="http://www.mail-archive.com/struts-user@jakarta.apache.org/msg24504.html">http://www.mail-archive.com/struts-user@jakarta.apache.org/msg24504.html</a><br/>
<a href="http://www.mail-archive.com/struts-user@jakarta.apache.org/msg22949.html">http://www.mail-archive.com/struts-user@jakarta.apache.org/msg22949.html</a>
</p>
</section>
<section href="pager" name="How can I scroll through list of pages like the search results in google?">
<p>Many Struts developers use the Pager from the JSPTags site.</p>
<p><a href="http://jsptags.com/tags/navigation/pager/">http://jsptags.com/tags/navigation/pager/</a></p>
</section>
<section href="minimization" name="Why does the option tag render selected=selected instead of just selected?">
<p>
Attribute minimization (that is, specifying an attribute with no value) is
a place where HTML violates standard XML syntax rules. This matters a lot
for people writing to browsers that support XHTML, where doing so makes
the page invalid.It's much better for Struts to use the expanded syntax,
which works the same on existing browsers interpreting HTML, and newer
browsers that expect XHTML-compliant syntax. Struts is following the
behavior recommended by the <a href="http://www.w3.org/TR/xhtml1/#h-4.5">
XHTML specification</a></p>
</section>
<section href="jsp" name="Do I have to use JSPs with my application?">
<p>
The short answer to this question is: No, you are not limited to
JavaServer Pages.
</p>
<p>
The longer answer is that you can use any type of presentation technology
which can be returned by a web server or Java container.
The list includes but is not limited to:
</p>
<ul>
<li>
JavaServer Pages,
</li>
<li>
HTML pages,
</li>
<li>
WML files,
</li>
<li>
Java servlets,
</li>
<li>
Velocity templates, and
</li>
<li>
XML/XLST
</li>
</ul>
<p>
Some people even mix and match apparently unrelated technologies,
like PHP, into the same web application.
</p>
</section>
<section href="formbeans" name="Do ActionForms have to be true JavaBeans?">
<p>ActionForms are added to a servlet scope (session or request)
as beans. What this means is that, for certain functionality to
be available, your ActionForms will have to follow a few simple
rules.</p>
<p>First, your ActionForm bean must have a zero-arguments
constructor. This is required because Struts must be able to
dynamically create new instances of your form bean class, while
knowing only the class name. This is not an onerous restriction,
however, because Struts will also populate your form bean's
properties (from the request parameters) for you.</p>
<p>Second, the fields of your form bean are made available to the
framework by supplying public getter and setter methods that
follow the naming design patterns described in the JavaBeans
Specification. For most users, that means using the following
idiom for each of your form bean's properties:</p>
<pre>
private {type} fieldName;
public {type} getFieldName() {
return (this.fieldName);
}
public void setFieldName({type} fieldName) {
this.fieldName = fieldName;
}
</pre>
<p><strong>NOTE</strong> - you <em>MUST</em> obey the capitalization
conventions shown above for your ActionForm properties to be recognized.
The property name in this example is "fieldName", and that must also be
the name of the input field that corresponds to this property. A bean
property may have a "getter" method and a "setter" method (in a form bean,
it is typical to have both) whose name starts with "get" or "set",
followed by the property name with the first character capitalized.
(For boolean properties, it is also legal to use "is" instead of "get"
as the prefix for the getter method.)</p>
<p> Advanced JavaBeans users will know that you can tell the system
you want to use different names for the getter and setter methods, by
using a <code>java.beans.BeanInfo</code> class associated with your form
bean. Normally, however, it is much more convenient to follow the
standard conventions.</p>
<p><strong>WARNING</strong> - developers might be tempted to use one of
the following techniques, but any of them will cause your property not
to be recognized by the JavaBeans introspection facilities, and therefore
cause your applications to misbehave:</p>
<ul>
<li><em>Using getter and setter method names that do not
match</em> - if you have a <code>getFoo()</code> method for your
getter, but a <code>setBar()</code> method for your setter, Java
will not recognize these methods as referring to the same property.
Instead, the language will think you have a read-only property named
"foo" and a write-only property named "bar".</li>
<li><em>Using more than one setter method with the same
name</em> - The Java language lets you "overload" methods, as long
as the argument types are different. For example, you could have a
<code>setStartDate(java.util.Date date)</code> method and a
<code>setStartDate(String date)</code> method in the same class, and
the compiled code would know which method to call based on the
parameter type being passed. However, doing this for form bean
properties will prevent Java from recognizing that you have a
"startDate" property at all.</li>
</ul>
<p>There are other rules to follow if you want other features of your
form beans to be exposed. These include indexed attributes and mapped
attributes. They are covered in detail in other areas of the Struts
documentation, in particular:</p>
<a href="indexedprops.html">indexedprops.html</a>
<p>For a complete explanation of what a JavaBean is, and everything it can
do, see the JavaBeans Specification (version 1.01) at:</p>
<a href="http://java.sun.com/products/javabeans/docs/beans.101.pdf">
http://java.sun.com/products/javabeans/docs/beans.101.pdf</a>
</section>
<section href="separate"
name="Do I have to have a separate ActionForm bean for every HTML form?">
<p>This is an interesting question. As a newbie, it is a good
practice to create a new <code>ActionForm</code> for each action
sequence. You can use <code>DynaActionForm</code>s to help reduce
the effort required, or use the code generation facilities of your
IDE.</p>
<p>Some issues to keep in mind regarding reuse of form beans
are as follows:</p>
<ul>
<li><em>Validation</em> - You might need to use different
validation rules depending upon the action that is currently
being executed.</li>
<li><em>Persistence</em> - Be careful that a form populated in
one action is not <strong>unexpectedly</strong> reused in a
different action. Multiple <code>&lt;form-bean&gt;</code>
entries in <code>struts-config.xml</code> for the same
<code>ActionForm</code> subclass can help (especially if you
store your form beans in session scope). Alternatively,
storing form beans in request scope can avoid unexpected
interactions (as well as reduce the memory footprint of your
application, because no server-side objects will need to be
saved in between requests.</li>
<li><em>Checkboxes</em> - If you do as recommended and reset
your boolean properties (for fields presented as checkboxes),
and the page you are currently displaying does not have a
checkbox for every boolean property on the form bean, the
undisplayed boolean properties will always appear to have a
<code>false</code> value.</li>
<li><em>Workflow</em> - The most common need for form bean
reuse is workflow. Out of the box, Struts has limited support
for workflow, but a common pattern is to use a single form bean
with all of the properties for all of the pages of a workflow.
You will need a good understanding of the
environment (<code>ActionForm</code>s, <code>Action</code>s,
etc.) prior to being able to put together a smooth workflow
environment using a single form bean.</li>
</ul>
<p>As you get more comfortable, there are a few shortcuts you can
take in order to reuse your <code>ActionForm</code> beans. Most of
these shortcuts depend on how you have chosen to implement your
<code>Action</code> / <code>ActionForm</code> combinations.</p>
</section>
<section href="prepopulate"
name="How can I prepopulate a form?">
<p>The simplest way to prepopulate a form is to have an <code>Action</code>
whose sole purpose is to populate an <code>ActionForm</code> and forward
to the servlet or JSP to render that form back to the client. A separate
<code>Action</code> would then be use to process the submitted form fields,
by declaring an instance of the same form bean name.</p>
<p>The <em>struts-example</em> example application that is shipped
with Struts illustrates this design pattern nicely. Note the following
definitions from the <code>struts-config.xml</code> file:</p>
<pre>
...
&lt;form-beans&gt;
...
&lt;-- Registration form bean --&gt;
&lt;form-bean name="registrationForm"
type="org.apache.struts.webapp.example.RegistrationForm"/&gt;
...
&lt;/form-beans&gt;
...
&lt;action-mappings&gt;
...
&lt;-- Edit user registration --&gt;
&lt;action path="/editRegistration"
type="org.apache.struts.webapp.example.EditRegistrationAction"
name="registrationForm"
scope="request"
validate="false"/&gt;
...
&lt;-- Save user registration --&gt;
&lt;action path="/saveRegistration"
type="org.apache.struts.webapp.example.SaveRegistrationAction"
name="registrationForm"
input="registration"
scope="request"/&gt;
...
&lt;/action-mappings&gt;
</pre>
<p>Note the following features of this approach:</p>
<ul>
<li>Both the <code>/editRegistration</code> and
<code>/saveRegistration</code> actions use the same form bean.</li>
<li>When the <code>/editRegistration</code> action is entered, Struts
will have pre-created an empty form bean instance, and passed it to
the <code>execute()</code> method. The setup action is free to
preconfigure the values that will be displayed when the form is
rendered, simply by setting the corresponding form bean properties.
</li>
<li>When the setup action completes configuring the properties of the
form bean, it should return an <code>ActionForm</code> that points
at the page which will display this form. If you are using the
Struts JSP tag library, the <code>action</code> attribute on your
&lt;html:form&gt; tag will be set to <code>/saveRegistration</code>
in order for the form to be submitted to the processing action.</li>
<li>Note that the setup action (<code>/editRegistration</code>) turns off
validation on the form that is being set up. You will normally want
to include this attribute in the configuration of your setup actions,
because you are not planning to actually process the results -- you
simply want to take advantage of the fact that Struts will precreate
a form bean instance of the correct class for you.</li>
<li>The processing action (<code>/saveRegistration</code>), on the other
hand, leaves out the <code>validate</code> attribute, which defaults
to <code>true</code>. This tells Struts to perform the validations
associated with this form bean before invoking the processing action
at all. If any validation errors have occurred, Struts will forward
back to your input page (technically, it forwards back to an
<code>ActionForward</code> named "registration" in this case, because
the example webapp uses the <code>inputForward</code> attribute in the
<code>&lt;controller&gt;</code> element -- see the documentation
describing <code>struts-config.xml</code> for more information)
instead of calling your processing action.</li>
</ul>
</section>
<section href="noForm" name="Can I have an Action without a form?">
<p>
Yes. If your <code>Action</code> does not need any data and it does not need to make any
data available to the view or controller component that it forwards to, it doesn't need
a form. A good example of an <code>Action</code> with no <code>ActionForm</code> is the
<code>LogoffAction</code> in the struts example application:</p>
<pre>
&lt;action path="/logoff"
type="org.apache.struts.webapp.example.LogoffAction"&gt;
&lt;forward name="success" path="/index.jsp"/&gt;
&lt;/action&gt;
</pre>
<p>
This action needs no data other than the user's session, which it can get from the
<code>Request</code>, and it doesn't need to prepare any view elements for display,
so it does not need a form.
</p>
<p>
However, you cannot use the &lt;html:form&gt; <strong>tag</strong> without an ActionForm.
Even if you want to use the &lt;html:form&gt; tag with a simple Action that does not require input,
the tag will expect you to use some type of ActionForm, even if it is an empty subclass without any properties.
</p>
</section>
<section href="requiredif"
name="Can you give me a simple example of using the requiredif Validator rule?">
<p>First off, there's an even newer Validator rule called <code>validwhen</code>,
which is almost certainly what you want to use, since it is much easier and
more powerful. It will be available in the first release after 1.1 ships.
The example shown below could be coded with validwhen as:</p>
<pre>
&lt;form name="medicalStatusForm"&gt;
&lt;field
property="pregnancyTest" depends="validwhen"&gt;
&lt;arg0 key="medicalStatusForm.pregnancyTest.label"/&gt;
&lt;var&gt;
&lt;var-name&gt;test&lt;/var-name&gt;
&lt;var-value&gt;((((sex == 'm') OR (sex == 'M')) AND (*this* == null)) OR (*this* != null))&lt;/test&gt;
&lt;/var&gt;
&lt;/field&gt;
</pre>
<p>Let's assume you have a medical information form with three fields, sex, pregnancyTest, and testResult.
If sex is 'f' or 'F', pregnancyTest is required. If pregnancyTest is not blank, testResult is required.
The entry in your validation.xml file would look like this:
</p>
<pre>
&lt;form name="medicalStatusForm"&gt;
&lt;field
property="pregnancyTest" depends="requiredif"&gt;
&lt;arg0 key="medicalStatusForm.pregnancyTest.label"/&gt;
&lt;var&gt;
&lt;var-name&gt;field[0]&lt;/var-name&gt;
&lt;var-value&gt;sex&lt;/var-value&gt;
&lt;/var&gt;
&lt;var&gt;
&lt;var-name&gt;fieldTest[0]&lt;/var-name&gt;
&lt;var-value&gt;EQUAL&lt;/var-value&gt;
&lt;/var&gt;
&lt;var&gt;
&lt;var-name&gt;fieldValue[0]&lt;/var-name&gt;
&lt;var-value&gt;F&lt;/var-value&gt;
&lt;/var&gt;
&lt;var&gt;
&lt;var-name&gt;field[1]&lt;/var-name&gt;
&lt;var-value&gt;sex&lt;/var-value&gt;
&lt;/var&gt;
&lt;var&gt;
&lt;var-name&gt;fieldTest[1]&lt;/var-name&gt;
&lt;var-value&gt;EQUAL&lt;/var-value&gt;
&lt;/var&gt;
&lt;var&gt;
&lt;var-name&gt;fieldValue[1]&lt;/var-name&gt;
&lt;var-value&gt;f&lt;/var-value&gt;
&lt;/var&gt;
&lt;var&gt;
&lt;var-name&gt;fieldJoin&lt;/var-name&gt;
&lt;var-value&gt;OR&lt;/var-value&gt;
&lt;/var&gt;
&lt;/field&gt;
&lt;field
property="testResult" depends="requiredif"&gt;
&lt;arg0 key="medicalStatusForm.testResult.label"/&gt;
&lt;var&gt;
&lt;var-name&gt;field[0]&lt;/var-name&gt;
&lt;var-value&gt;pregnancyTest&lt;/var-value&gt;
&lt;/var&gt;
&lt;var&gt;
&lt;var-name&gt;fieldTest[0]&lt;/var-name&gt;
&lt;var-value&gt;NOTNULL&lt;/var-value&gt;
&lt;/var&gt;
&lt;/field&gt;
&lt;/form&gt;
</pre>
</section>
<section href="validate" name="When is the best time to validate input?">
<p>
This is an excellent question. Let's step back a second and think about a
typical mid to large size application. If we start from the back end and work
toward the view we have:
</p>
<p>
1) Database: Most modern databases are going to validate for required
fields, duplicate records, security constraints, etc.</p>
<p>
2) Business Logic: Here you are going to check for valid data relationships
and things that make sense for the particular problem you are triing to
solve.</p>
<p>
... This is where struts comes into the picture, by now the system should be
pretty well bulletproof. What we are going to do is make validation friendlier
and informative. Rember it is OK to have duplicate validations...</p>
<p>
3) <code>ActionErrors validate(ActionMapping map, HttpServletRequest req)</code>
is where you can do your validation and feed back to the view,
information required to correct any errors. <code>validate</code> is run after
the form has been <code>reset</code> and after the <code>ActionForm</code>
properties have been set from corresponding view based input. Also remember you
can turn validation off with <code>validate="false"</code> in the
<code>action</code> mapping in the <code>struts-config.xml</code>. This is done
by returning an <code>ActionErrors</code> collection with messages from your
<code>ApplicationResources.properties</code> file.</p>
<p>
Here you have access to the request so you can see what kinds of action is
being requested to fine tune your validations. The &lt;html:error&gt; tag
allows you to dump all errors on your page or a particular error associated
with a particular property. The <code>input</code> attribute of the
<code>struts-config.xml</code> <code>action</code> allows you to send
validation errors to a particular jsp / html / tile page.</p>
<p>
4) You can have the system perform low level validations and client side
feedback using a <code>ValidatorForm</code> or its derivatives. This will
generate javascript and give instant feedback to the user for simple data entry
errors. You code your validations in the <code>validator-rules.xml</code>
file. A working knowledge of
<a href="http://etext.lib.virginia.edu/helpsheets/regex.html">regular
expressions</a> is necessary to use this feature effectively. For more
information, see
<a href="../userGuide/dev_validator.html">
User Guide</a></p>
</section>
<section href="avoidValidate"
name="How can I avoid validating a form before data is entered?">
<p>
The simplest way is to have two actions. The first one has the job of setting
the form data, i.e. a blank registration screen. The second action in our
writes the registration data to the database. Struts
would take care of invoking the validation and returning the user to the
correct screen if validation was not complete.
</p>
<p>
The EditRegistration action in the struts example application illustrates this:
</p>
<pre><code>
&lt;action path="/editRegistration"
type="org.apache.struts.webapp.example.EditRegistrationAction"
attribute="registrationForm"
scope="request"
validate="false"&gt;
&lt;forward name="success path="/registration.jsp"/&gt;
&lt;/action&gt;
</code></pre>
<p>
When the /editRegistration action is invoked, a registrationForm is created and added to the request,
but its validate method is not called. The default value of the <code>validate</code> attribute is
<code>true</code>, so if you do not want an action to trigger form validation, you need to remember
to add this attribute and set it to <code>false</code>.
</p>
</section>
<section href="wizard" name="How can I create a wizard workflow?">
<p>
The basic idea is a series of actions with next, back, cancel
and finish actions with a common bean. Using a LookupDispatchAction is
reccomended as it fits the design pattern well and can be internationalized
easily. Since the bean is shared, each choice made will add data to the
wizards base of information. A sample of struts-config.xml follows:
</p>
<pre><code>
&lt;form-beans&gt;
&lt;form-bean name="MyWizard"
type="forms.MyWizard" /&gt;
&lt;/form-beans&gt;
&lt;!-- the first screen of the wizard (next action only available) --&gt;
&lt;!-- no validation, since the finish action is not available --&gt;
&lt;actions&gt;
&lt;action path="/mywizard1"
type="actions.MyWizard"
name="MyWizard"
validate="false"
input="/WEB-INF/jsp/mywizard1.jsp"&gt;
&lt;forward name="next"
path="/WEB-INF/jsp/mywizard2.jsp" /&gt;
&lt;forward name="cancel"
path="/WEB-INF/jsp/mywizardcancel.jsp" /&gt;
&lt;/action&gt;
&lt;!-- the second screen of the wizard (back, next and finish) --&gt;
&lt;!-- since finish action is available, bean should validated, note
validation should not necessarily validate if back action requested, you
might delay validation or do conditional validation --&gt;
&lt;action path="/mywizard2"
type="actions.MyWizard"
name="MyWizard"
validate="true"
input="/WEB-INF/jsp/mywizard2.jsp"&gt;
&lt;forward name="back"
path="/WEB-INF/jsp/mywizard1.jsp" /&gt;
&lt;forward name="next"
path="/WEB-INF/jsp/mywizard3.jsp" /&gt;
&lt;forward name="finish"
path="/WEB-INF/jsp/mywizarddone.jsp" /&gt;
&lt;forward name="cancel"
path="/WEB-INF/jsp/mywizardcancel.jsp" /&gt;
&lt;/action&gt;
&lt;!-- the last screen of the wizard (back, finish and cancel only) --&gt;
&lt;action path="/mywizard3"
type="actions.MyWizard"
name="MyWizard"
validate="true"
input="/WEB-INF/jsp/mywizard3.jsp"&gt;
&lt;forward name="back"
path="/WEB-INF/jsp/mywizard2.jsp" /&gt;
&lt;forward name="finish"
path="/WEB-INF/jsp/mywizarddone.jsp" /&gt;
&lt;forward name="cancel"
path="/WEB-INF/jsp/mywizardcancel.jsp" /&gt;
&lt;/action&gt;
</code></pre>
<p>
The pieces of the wizard are as follows:
</p>
<p>
<strong>forms.MyWizard.java</strong> - the form bean holding the information required
</p>
<p>
<strong>actions.MyWizard.java</strong> - the actions of the wizard, note the use of
LookupDispatchAction allows for one action class with several methods. All the
real work will be done in the 'finish' method.
</p>
<p>
<strong>mywizard[x].jsp</strong> - the data collection jsp's
</p>
<p>
<strong>mywizarddone.jsp</strong> - the 'success' page
</p>
<p>
<strong>mywizardcancel.jsp</strong> - the 'cancel' page
</p>
</section>
<section href="chaining" name="How can I 'chain' Actions?">
<p>
Chaining actions can be done by simply using the proper mapping in your
forward entries in the struts-config.xml file. Assume you had the following
two classes:
</p>
<pre><code><![CDATA[
/* com/AAction.java */
...
public class AAction extends Action
{
public ActionForward
execute(ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response) throws
Exception
{
// Do something
return mapping.findForward("success");
}
}
]]></code></pre>
<pre><code><![CDATA[
/* com/BAction.java */
...
public class BAction extends Action
{
public ActionForward
execute(ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response) throws
Exception
{
// Do something else
return mapping.findForward("success");
}
}
]]></code></pre>
<p>
Then you can chain together these two actions with the Struts
configuration as shown in the following excerpt:
</p>
<pre><code><![CDATA[
...
<action-mappings type="org.apache.struts.action.ActionMapping">
<action path="/A"
type="com.AAction"
validate="false">
<forward name="success" path="/B.do" />
</action>
<action path="/B"
type="com.BAction"
scope="session"
validate="false">
<forward name="success" path="/result.jsp" />
</action>
</action-mappings>
...
]]></code></pre>
<p>
Here we are assuming you are using a suffix-based (<code>.do</code>) servlet
mapping, which is recommended since module support requires it. When you
send your browser to the web application and name the action
<code>A.do</code> (i.e. <code>http://localhost:8080/app/A.do</code>) it will
execute <code>AAction.execute()</code>, which will then forward to the
"success" mapping.
</p>
<p>
This causes the execution of <code>BAction.execute()</code> since the
<code>&lt;forward&gt;</code> entry for "success" in the configuration file
uses the <code>.do</code> suffix.
</p>
<p>
Of course it is also possible to chain actions programmatically, but the
power and ease of being able to "reroute" your web application's structure
using the XML configuration file is much easier to maintain.
</p>
<p>
As a rule, chaining Actions is <strong>not</strong> recommended.
If your business classes are properly factored, you should be able to call
whatever methods you need from any Action, without splicing them together
into a cybernetic Rube Goldberg device.
</p>
<p>
If you must chain Actions, be aware of the following:
calling the second Action from the first Action has the same effect as calling the second
Action from scratch.
If both of your Actions change the properties of a formbean,
the changes made by the first Action will be lost because Struts calls the reset() method on
the formbean when the second Action is called.
</p>
</section>
<section
href="undocumented"
name="If you would like to contribute, here is a list of
popular but undocumented questions">
<ul>
<li>How can I capture binary or formatted values, like dates or telephone numbers?</li>
<li>Why do my option lists disappear when validation fails?</li>
<li>Why can't I disable URL-encoding in the Struts taglibs?</li>
<li>Can I create dynamic ActionForwards?</li>
<li>How can I use my own (ActionForm, ActionForward, ActionMapping, ActionServlet) class?</li>
</ul>
</section>
</body></document>