优化下面这段代码Map<String, List<Department>> listMap = all.stream().collect(Collectors.groupingBy(Department::getBigcode)); Set<Map.Entry<String, List<Department>>> entries = listMap.entrySet(); List<DepartmentVo> departmentVoList = new ArrayList<>(); for (Map.Entry<String, List<Department>> entry : entries) { DepartmentVo departmentVo = new DepartmentVo(); //大科室编号 String bigCode = entry.getKey(); List<Department> departmentList = entry.getValue(); //大科室名称 String bigName = departmentList.get(0).getBigname(); departmentVo.setDepcode(bigCode); departmentVo.setDepname(bigName); //接下来进行子列表操作 List<DepartmentVo> childDepartmentVoList = new ArrayList<>(); for (Department childDepartment : departmentList) { DepartmentVo childDepartmentVo = new DepartmentVo(); childDepartmentVo.setDepcode(childDepartment.getDepcode()); childDepartmentVo.setDepname(childDepartment.getDepname()); childDepartmentVoList.add(childDepartmentVo); } departmentVo.setChildren(childDepartmentVoList); departmentVoList.add(departmentVo); } return departmentVoList;

可以使用Stream API的flatMap操作来简化代码，如下所示：

List<DepartmentVo> departmentVoList = all.stream()
        .collect(Collectors.groupingBy(Department::getBigcode))
        .entrySet().stream()
        .map(entry -> {
            DepartmentVo departmentVo = new DepartmentVo();
            String bigCode = entry.getKey();
            List<Department> departmentList = entry.getValue();
            String bigName = departmentList.get(0).getBigname();
            departmentVo.setDepcode(bigCode);
            departmentVo.setDepname(bigName);
            List<DepartmentVo> childDepartmentVoList = departmentList.stream()
                    .map(childDepartment -> {
                        DepartmentVo childDepartmentVo = new DepartmentVo();
                        childDepartmentVo.setDepcode(childDepartment.getDepcode());
                        childDepartmentVo.setDepname(childDepartment.getDepname());
                        return childDepartmentVo;
                    })
                    .collect(Collectors.toList());
            departmentVo.setChildren(childDepartmentVoList);
            return departmentVo;
        })
        .collect(Collectors.toList());
return departmentVoList;

使用flatMap操作可以避免使用嵌套的循环，使代码更加简洁易懂。