Struts DynaActionForm example

The Struts DynaActionForm class is an interesting feature to let you create a form bean dynamically and declaratively. It enables you to create a 「virtual」 form bean in Struts configuration file instead of create a real Java form bean class. It can avoid you to create many simple but tedious form bean classes.

For example, a DynaActionForm contains a 「username」 property.

<form-bean name="dynaUserForm"   
    type="org.apache.struts.action.DynaActionForm">
    <form-property name="username" type="java.lang.String"/>
</form-bean>

The different between 「DynaActionForm」 and 「ActionForm」

• DynaActionForm is not required to create a real Java class (just declare in Struts config file), but ActionForm does.
• In DynaActionForm, form validation is implement in Action class, while ActionForm is implement inside its own class.

DynaActionForm example

The Struts <html:text> textbox example will be refactor to use the 「DynaActionForm」 instead of normal 「ActionForm」.

1. struts-config.xml

Declare the 「DynaActionForm」 in Struts configuration file and link it to the Action class like normal.

struts-config.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE struts-config PUBLIC 
"-//Apache Software Foundation//DTD Struts Configuration 1.3//EN" 
"http://jakarta.apache.org/struts/dtds/struts-config_1_3.dtd">
 
<struts-config>
 
    <form-beans>
        <!--<form-bean
            name="userForm"
            type="com.mkyong.common.form.UserForm"/>
        -->
        <form-bean name="dynaUserForm"   
              type="org.apache.struts.action.DynaActionForm">
              <form-property name="username" type="java.lang.String"/>
        </form-bean>

    </form-beans>
 
    <action-mappings>
 
            <action
            path="/LoginPage"
            type="org.apache.struts.actions.ForwardAction"
            parameter="/pages/login.jsp"/>
 
        <action
            path="/Login"
            type="com.mkyong.common.action.UserAction"
            name="dynaUserForm"
            >   
 
            <forward name="success" path="/pages/welcome.jsp"/>
            <forward name="failed" path="/pages/login.jsp"/>
            
        </action>
    </action-mappings>
 
    <message-resources
        parameter="com.mkyong.common.properties.Common" />
 
</struts-config>

2. Action

Move all the form validation method to Action class, and get the 「DynaActionForm」 property via the 「get()」 method.

UserAction.java

package com.mkyong.common.action;
 
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
import org.apache.struts.action.ActionMessage;
import org.apache.struts.action.ActionMessages;
import org.apache.struts.action.DynaActionForm;
 
public class UserAction extends Action{
 
    public ActionForward execute(ActionMapping mapping,ActionForm form,
        HttpServletRequest request,HttpServletResponse response) 
        throws Exception {
 
        DynaActionForm userForm = (DynaActionForm)form;
        
        ActionMessages errors = new ActionMessages();

        //do the form validation in action class
        if( userForm.get("username") == null || 
                         ("".equals(userForm.get("username")))) {

           errors.add("common.name.err",
                    new ActionMessage("error.common.name.required"));

        }
 
        saveErrors(request,errors);
        
        if(errors.isEmpty()){
            return mapping.findForward("success");
        }else{
            return mapping.findForward("failed");
        }
       
    }
 
}

Conclusion

Should you go for DynaActionForm? This feature can save you a lot time to create ActionForm class, but, it has limitation and sometime you have to use a real ActionForm to do certain tasks. In large project environment, maintenance always is the 1st priority to consider, you have to create a 「Form standard」 to follow, it’s not practical to mix use of both, unless you have a very solid reason to support. Personally, i seldom use the DynaActionForm, with Eclipse IDE, the ActionForm is not so hard to create after all.