sys:treeselect

Question

选择学校后可以选择班级
如何可以动态获取选择后的学校id

<div class="control-group">

        <label class="control-label">学校：</label>
        <div class="controls">
            <sys:treeselect id="orgId" name="orgId" value="${orgId}"
                labelName="" labelValue="${orgName}" title="学校"
                url="/torg/tOrg/tree?type=0" cssClass="" allowClear="true"
                notAllowSelectParent="true" />
        </div>
    </div>
    <div class="control-group">
        <label class="control-label">班级：</label>
        <div class="controls">
            <sys:treeselect id="banjiId" name="banji" value="${banji}"
                labelName="banji" labelValue="${banji}" title="班级"
                url="/banji/banji/classList?OrgId=？？？" cssClass="" allowClear="true"
                notAllowSelectParent="true" />
        </div>
    </div>