java生成json

当我们用sql查出来一些值，想要把它打包成一个JSON格式，例如我们查出的数据如下

班级 姓名  年龄 性别 身高 
1班    AAA   11    男     296cm
1班    BBB  11     男    296cm
2班    CCC   11     男    296cm
2班    DDD  11     男     296cm
2班     EEE  11     男     296cm
3班     FFF  11     男     296cm

要将他变成JSON格式

{
        "school": [{
                        "班级": "1班",
                        "student": [{
                                "姓名": "AAA",
                                "年龄": "11",
                                "性别": "男",
                                "身高": "296cm"
                        }, {
                                "姓名": "BBB",
                                "年龄": "11",
                                "性别": "男",
                                "身高": "296cm"
                        }]
                },{
                        "班级": "2班",
                        "student": [{
                                "姓名": "CCC",
                                "年龄": "11",
                                "性别": "男",
                                "身高": "296cm"
                        }, {
                                "姓名": "DDD",
                                "年龄": "11",
                                "性别": "男",
                                "身高": "296cm"
                        }, {
                                "姓名": "EEE",
                                "年龄": "11",
                                "性别": "男",
                                "身高": "296cm"
                        }]
                },{
                        "班级": "3班",
                        "student": [{
                                "姓名": "FFF",
                                "年龄": "11",
                                "性别": "男",
                                "身高": "296cm"
                        }]
                }]
}

代码如下

Map<String, Object> schoolMap = new HashMap<>();
        if (manifest.size() != 0){
            List<Map<String, Object>> chalssList = new ArrayList<>();
            for (int i = 0; i < t.size(); i++) {
                Map<String, Object> classMap = new HashMap<>();
                List<student>studentList = new ArrayList;
                if (*.size() !=0){
                    // 假设数据已经从数据库中查询出来并存储在List>中
                    List<Map<String, String>> contentList = new ArrayList<>();
                    for (int j = 0; j < /.size(); j++) {
                        Map<String, String> data = new HashMap<>();
                        data.put("姓名", student.get(j).getName);
                        data.put("年龄", student.get(j).getAge);
                        data.put("性别", student.get(j).getSex);
                        data.put("身高", student.get(j).getLength());
                        contentList.add(data);
                    }
                    String class = student.getClass();
                    classMap.put("班级", class);
                    classMap.put("content", student);
                }
                chalssList.add(manifestMap);
            }
            schoolMap.put("school", school);
        }
        ObjectMapper objectMapper = new ObjectMapper();
        String json = null;
        try {
            json = objectMapper.writeValueAsString(schoolMap);
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
        System.out.println("json格式："+json);