java版list-map实现 树结构 父子结构 通俗易懂

@Action("getModelCategoryTree")
public void getModelCategoryTree(HttpServletRequest request, HttpServletResponse response){
List<Map<String, Object>> newList = new ArrayList<Map<String, Object>>();//实例化最终的list
PrintWriter out = null;
try {
response.setHeader("Charset","UTF-8");
response.setContentType("application/json;charset=utf-8");
out = response.getWriter();
Map paramMap = new HashMap(); 
StringBuffer sb = new StringBuffer();
sb.append("select category_code id, category_name text, parent_code pid from bdm_model_category");
List<Map<String, Object>> pList = (List<Map<String, Object>>) runner.queryForMapList(sb.toString(),paramMap);

if(pList != null && pList.size() > 0){
//1、找到根节点
for(Map<String, Object> mapParent : pList){
String parentCode = String.valueOf(mapParent.get("pid"));
if(parentCode.equals("-1")){
//找到根节点map
Map<String, Object> mapChild = new HashMap<String, Object>(); 
mapChild.put("id", String.valueOf(mapParent.get("id")));
mapChild.put("text", String.valueOf(mapParent.get("text")));
mapChild.put("children", getChildModelCategory(mapParent, pList));
mapChild.put("state", "open");
newList.add(mapChild);
}
}
}
String jsonStr = Functions.java2json(newList);