Difference between modelAttribute and commandName attributes in form tag in spring?

Question

In Spring 3, I have seen two different attribute in form tag in jsp

<form:form method="post" modelAttribute="login"> 

in this the attribute modelAttribute is the name of the form object whose properties are used to populate the form. And I used it in posting a form and in controller I have used @ModelAttribute to capture value, calling validator, applying business logic. Everything is fine here. Now

<form:form method="post" commandName="login"> 

What is expected by this attribute, is it also a form object whose properties we are going to populate?

Answer 1

If you look at the source code of FormTag (4.3.x) which backs your <form> element, you'll notice this

/**  * Set the name of the form attribute in the model.  * <p>May be a runtime expression.  */ public void setModelAttribute(String modelAttribute) {     this.modelAttribute = modelAttribute; }  /**  * Get the name of the form attribute in the model.  */ protected String getModelAttribute() {     return this.modelAttribute; }  /**  * Set the name of the form attribute in the model.  * <p>May be a runtime expression.  * @see #setModelAttribute  */ public void setCommandName(String commandName) {     this.modelAttribute = commandName; }  /**  * Get the name of the form attribute in the model.  * @see #getModelAttribute  */ protected String getCommandName() {     return this.modelAttribute; } 

They are both referring to the same field, thus having same effect.

But, as the field name indicates, modelAttribute should be preferred, as others have also pointed out.

Answer 2

OLD WAY = commandName

... <spring:url value="/manage/add.do" var="action" />     <form:form action="${action}" commandName="employee">         <div>             <table> .... 

NEW WAY = modelAttribute

.. <spring:url value="/manage/add.do" var="action" />     <form:form action="${action}" modelAttribute="employee">         <div>             <table> ..