JSP嵌入EL表达式？

我想在jsp页面里使用EL表达式的值做一个减法运算， ${tmp.id.rainDate}-${cropPlant}，其中rainDate，cropPlant都是java.util.Date型，
例如rainDate是2012-05-06，cropPlant是2012-05-05，想在单元格里显示 1 ，可是得到的确是2012-05-06 - 2012-05-05，各位帮忙看看
怎么解决？
<table width="960" border="1" bordercolor="#999999" cellpadding="0" cellspacing="0">

                            <colgroup span="17" style="FONT-WEIGHT:bold; FONT-SIZE:12px; COLOR:#003366">
                            </colgroup>

                            <logic:iterate name="ls" indexId="index" id="tmp">
                                <tr>
                                    <TD width="212" style="WIDTH: 100px">
                                        ${tmp.id.rainDate }
                                    </TD>
                                    <TD width="190" style="WIDTH: 50px">
                                        ${tmp.id.rainDate}-${cropPlant}
                                    </TD>
                                    <TD width="135" style="WIDTH: 50px">
                                        ${tmp.id.rainValid }
                                    </TD>
                                    <TD width="135" style="WIDTH: 50px">
                                        ${tmp.id.irrigationData }
                                    </TD>
                                    <TD width="135" style="WIDTH: 50px">
                                        ${tmp.id.etData }
                                    </TD>
                                    <TD width="139" style="WIDTH: 50px">
                                        ${tmp.id.humidityData }
                                    </TD>
                                </tr>
                            </logic:iterate>
                        </table>

${(tmp.id.rainDate-cropPlant)}
这样试试

1、${tmp.id.rainDate}-${cropPlant} 这相当于是两个EL表达式 中间通过-连接； “-”是html；

2、日期类型不能直接相减

3、可以这样 两个日期的毫秒值相减（cropPlant.time---->cropPlant.getTime()）
${tmp.id.rainDate.time - cropPlant.time}

4、EL表达式能完成的任务比较弱，因此复杂的计算建议在model/控制器完成

那就 ${(tmp.id.rainDate.time-cropPlant.time)/1000*60*60*24}

当然也可以考虑使用可以自定义EL表达式方法方式实现