The lifecycle of ActionForm invoked by the RequestProcessor is as follows:

Retrieve or Create Form Bean associated with Action
"Store" FormBean in appropriate scope (request or session)
Reset the properties of the FormBean
Populate the properties of the FormBean
Validate the properties of the FormBean
Pass FormBean to Action

 
 

We can make message resources definitions file (properties file) available to Struts framework environment by adding this file to struts-config.xml.

<message-resources parameter="com.login.struts.ApplicationResources"/>

 
 

An ActionForm represents an HTML form that the user interacts with over one or more pages. You will provide properties to hold the state of the form with getters and setters to access them. Whereas, using DynaActionForm there is no need of providing properties to hold the state. Instead these properties and their type are declared in the struts-config.xml

The DynaActionForm bloats up the Struts config file with the xml based definition. This gets annoying as the Struts Config file grow larger.

The DynaActionForm is not strongly typed as the ActionForm. This means there is no compile time checking for the form fields. Detecting them at runtime is painful and makes you go through redeployment.

ActionForm can be cleanly organized in packages as against the flat organization in the Struts Config file.

ActionForm were designed to act as a Firewall between HTTP and the Action classes, i.e. isolate and encapsulate the HTTP request parameters from direct use in Actions. With DynaActionForm, the property access is no different than using request.getParameter( .. ).

DynaActionForm construction at runtime requires a lot of Java Reflection (Introspection) machinery that can be avoided.

 
 

Exceptions in Struts are handled in two ways:

Programmatic exception handling :
Explicit try/catch blocks in any code that can throw exception. It works well when custom value (i.e., of variable) needed when error occurs.

Declarative exception handling :You can either define <global-exceptions> handling tags in your struts-config.xml or define the exception handling tags within <action></action> tag. It works well when custom page needed when error occurs. This approach applies only to exceptions thrown by Actions.

 
 

<bean:message>: is used to retrive keyed values from resource bundle. It also supports the ability to include parameters that can be substituted for defined placeholders in the retrieved string.

<bean:message key="prompt.customer.firstname"/>

<bean:write>: is used to retrieve and print the value of the bean property. <bean:write> has no body.

<bean:write name="customer" property="firstName"/>

 
 

<html:errors/> tag displays all the errors. <html:errors/> iterates over ActionErrors request attribute.

 
 

The various Struts tag libraries are:

HTML Tags
Bean Tags
Logic Tags

Template Tags
Nested Tags
Tiles Tags

 
 

A specialized subclass of ActionForm that allows the creation of form beans with dynamic sets of properties (configured in configuration file), without requiring the developer to create a Java class for each type of form bean.

 
 

In this case the global forward is not used. Instead the <action> element’s <forward> takes precendence.

 
 

The SwitchAction class provides a means to switch from a resource in one module to another resource in a different module. SwitchAction is useful only if you have multiple modules in your Struts application. The SwitchAction class can be used as is, without extending.