<th><input type='checkbox' onClick='checkedAll();'/></th>

 checked = false;
 function checkedAll () {
   if (checked == false){checked = true}else{checked = false}
  
   for (i=0; i<document.forms[0].elements.length; i++){
      if (document.forms[0].elements.type == "checkbox") {
        document.forms[0].elements.checked = checked;
      }
   }
 }

 <html:multibox property="selectedItemIds" styleClass="checkbox" value="${item.сode}" onclick="switch(${item.сode})"/>

<td >
  <input type="checkbox" name="selectedItemIds" value="6472" onclick="switch(6472)" class="checkbox">
</td>
<td >
  <input type="checkbox" name="selectedItemIds" value="988" onclick="switch(988)" class="checkbox">
</td>