Set - 3

Question 16 :

Do ActionForms have to be true JavaBeans?

Answer :

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.
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.
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:

private {type} fieldName;
public {type} getFieldName() {
return (this.fieldName);
}

public void setFieldName({type} fieldName) {
this.fieldName = fieldName;
}

NOTE - you MUST 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.)
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 java.beans.BeanInfo class associated with your form bean. Normally, however, it is much more convenient to follow the standard conventions.
WARNING - 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:
* Using getter and setter method names that do not match - if you have a getFoo() method for your getter, but a setBar() 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".
* Using more than one setter method with the same name - The Java language lets you "overload" methods, as long as the argument types are different. For example, you could have a setStartDate(java.util.Date date) method and a setStartDate(String date) 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.
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: indexedprops.html


Question 17 :

Do I have to have a separate ActionForm bean for every HTML form?

Answer :

This is an interesting question. As a newbie, it is a good practice to create a new ActionForm for each action sequence. You can use DynaActionForms to help reduce the effort required, or use the code generation facilities of your IDE.
Some issues to keep in mind regarding reuse of form beans are as follows:
* Validation - You might need to use different validation rules depending upon the action that is currently being executed.
* Persistence - Be careful that a form populated in one action is not unexpectedly reused in a different action. Multiple entries in struts-config.xml for the same ActionForm 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.
* Checkboxes - 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 false value.
* Workflow - 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 (ActionForms, Actions, etc.) prior to being able to put together a smooth workflow environment using a single form bean.
As you get more comfortable, there are a few shortcuts you can take in order to reuse your ActionForm beans. Most of these shortcuts depend on how you have chosen to implement your Action / ActionForm combinations.


Question 18 :

How can I prepopulate a form?

Answer :

The simplest way to prepopulate a form is to have an Action whose sole purpose is to populate an ActionForm and forward to the servlet or JSP to render that form back to the client. A separate Action would then be use to process the submitted form fields, by declaring an instance of the same form bean name. 
The struts-example example application that is shipped with Struts illustrates this design pattern nicely. Note the following definitions from the struts-config.xml file: 
...

<form-beans>
...
<-- Registration form bean -->
<form-bean name="registrationForm" type="org.apache.struts.webapp.example.RegistrationForm"/>
...
</form-beans>
...
<action-mappings>
...
<-- Edit user registration -->
<action path="/editRegistration" type="org.apache.struts.webapp.example.EditRegistrationAction" name="registrationForm" scope="request" validate="false"/>
...
<-- Save user registration -->
<action path="/saveRegistration" type="org.apache.struts.webapp.example.SaveRegistrationAction" name="registrationForm" input="registration" scope="request"/>
...
</action-mappings>

Note the following features of this approach:
* Both the /editRegistration and /saveRegistration actions use the same form bean.
* When the /editRegistration action is entered, Struts will have pre-created an empty form bean instance, and passed it to the execute() 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.
* When the setup action completes configuring the properties of the form bean, it should return an ActionForm that points at the page which will display this form. If you are using the Struts JSP tag library, the action attribute on your <html:form> tag will be set to /saveRegistration in order for the form to be submitted to the processing action.
* Note that the setup action (/editRegistration) 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.
* The processing action (/saveRegistration), on the other hand, leaves out the validate attribute, which defaults to true. 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 ActionForward named "registration" in this case, because the example webapp uses the inputForward attribute in the element -- see the documentation describing struts-config.xml for more information) instead of calling your processing action.


Question 19 :

Can I have an Action without a form?

Answer :

Yes. If your Action 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 Action with no ActionForm is the LogoffAction in the struts example application:

<action path="/logoff" type="org.apache.struts.webapp.example.LogoffAction">
	<forward name="success" path="/index.jsp"/>
</action>

This action needs no data other than the user's session, which it can get from the Request, and it doesn't need to prepare any view elements for display, so it does not need a form.

However, you cannot use the <html:form> tag without an ActionForm. Even if you want to use the <html:form> 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.


Question 20 :

Can you give me a simple example of using the requiredif Validator rule?

Answer :

First off, there's an even newer Validator rule called validwhen, 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:

<form name="medicalStatusForm">
<field property="pregnancyTest" depends="validwhen">
<arg0 key="medicalStatusForm.pregnancyTest.label"/>
<var>
<var-name>test</var-name>
<var-value>((((sex == 'm') OR (sex == 'M')) AND (*this* == null)) OR (*this* != null))</test></var>
</field>

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:

<form name="medicalStatusForm">
<field property="pregnancyTest" depends="requiredif">
<arg0 key="medicalStatusForm.pregnancyTest.label"/>
<var>
<var-name>field[0]</var-name>
<var-value>sex</var-value>
</var>
<var>
<var-name>fieldTest[0]</var-name>
<var-value>EQUAL</var-value>
</var>
<var>
<var-name>fieldValue[0]</var-name>
<var-value>F</var-value>
</var>
<var>
<var-name>field[1]</var-name>
<var-value>sex</var-value>
</var>
<var>
<var-name>fieldTest[1]</var-name>
<var-value>EQUAL</var-value>
</var>
<var>
<var-name>fieldValue[1]</var-name>
<var-value>f</var-value>
</var>
<var>
<var-name>fieldJoin</var-name>
<var-value>OR</var-value>
</var>
</field>

<field
property="testResult" depends="requiredif">
<arg0 key="medicalStatusForm.testResult.label"/>
<var>
<var-name>field[0]</var-name>
<var-value>pregnancyTest</var-value>
</var>
<var>
<var-name>fieldTest[0]</var-name>
<var-value>NOTNULL</var-value>
</var>
</field>
</form>