Try using the form to stores, ie. the record id so the checked items can be retrieved from the form.
1. get result set and stores the record ID in the "id" property as a checkbox value, where getstring(1) is the record ID:
while (rs.next()) {
rec = new Sales();
rec.setId("<input type=\"checkbox\" name=\"selectedItems\"
value=\""+rs.getString(1)+"\" />"+rs.getString(1));

2. displays result and check box in the "id" property in jsp:
<display:table class="display1" style="border:1px solid #999"
name="requestScope.salesList" sort="list">
<display:column property="id" title="Row ID" sort="true" />

3. the updateSales form has the "selectedItems" properties
private String[] selectedItems = {};
public String[] getSelectedItems() {
return this.selectedItems;

4. In the action form, retrieves the selected items
String[] idList = updateSales.getSelectedItems();

5. now do whatever you wish with the list of selected items

Good luck!