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.