CREATE TABLE `t_category` (
  `cid` char(32) NOT NULL,
  `cname` varchar(50) DEFAULT NULL,
  `pid` char(32) DEFAULT NULL,
  `desc` varchar(100) DEFAULT NULL,
  `orderBy` int(11) NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`cid`),
  UNIQUE KEY `cname` (`cname`),
  KEY `FK_t_category_t_category` (`pid`),
  KEY `orderBy` (`orderBy`),
  CONSTRAINT `FK_t_category_t_category` FOREIGN KEY (`pid`) REFERENCES `t_category` (`cid`)
) ENGINE=InnoDB AUTO_INCREMENT=48 DEFAULT CHARSET=utf8;

public List<Category> findAll() throws SQLException {
	/*
	 * 1. 查询出所有一级分类
	 */
	String sql = "select * from t_category where pid is null order by orderBy";
	List<Map<String,Object>> mapList = qr.query(sql, new MapListHandler());
	
	List<Category> parents = toCategoryList(mapList);
	
	/*
	 * 2. 循环遍历所有的一级分类，为每个一级分类加载它的二级分类 
	 */
	for(Category parent : parents) {
		// 查询出当前父分类的所有子分类
		List<Category> children = findByParent(parent.getCid());
		// 设置给父分类
		parent.setChildren(children);
	}
	return parents;
}

<script language="javascript">
$(function() {
....
<c:forEach items="${parents}" var="parent">
  <c:forEach items="${parent.children}" var="child">
	bar.add("${parent.cname}", "${child.cname}", "/goods/BookServlet?method=findByCategory&cid=${child.cid}", "body");
  </c:forEach>
</c:forEach>

});
</script>