how to disable buttons based on a condition in jsp?

Try using JSTL construction like this:

<input type="button" <c:if test="${variable == false}"><c:out value="disabled='disabled'"/></c:if>">

For more examples see http://www.ibm.com/developerworks/java/library/j-jstl0211/index.html

Or simply you could do it using el directly like this:

<input type="button" ${ condition ? 'disabled="disabled"' : ''}/>

As an example:

<input type="button" ${ someVariable eq 5  ? 'disabled="disabled"' : ''}/>

My approach would be something like this:

 <c:choose>
    <c:when test="${condition == true}">
      <input type="button" disabled="disabled"/>
    </c:when>
    <c:otherwise>
      <input type="button" />
    </c:otherwise>
 </c:choose>