List<Function> resultFunctionList = new ArrayList<Function>();
        List<Function> functionListTemp = new ArrayList<Function>();
        Subject currentUser = SecurityUtils.getSubject();
        User user = (User) currentUser.getPrincipal();
        List<Function> functionList = user.getFunctionList();
        functionListTemp = new ArrayList<Function>(functionList);
        Iterator<Function> iterator = functionListTemp.iterator();
        for (Function parent : functionListTemp) {
            if (oid.equals(parent.getOid())) {
                resultFunctionList.add(parent);
                for (Function child : functionListTemp) {
                    if (child.getPid().equals(parent.getOid())) {
                        if (parent.getChildren() == null) {
                            parent.setChildren(new ArrayList<Function>());
                        }
                        parent.getChildren().add(child);
                    }
                }
            }
        }
        return resultFunctionList;

parent.getChildren().add(child) 居然会改变functionList对象中的内容