Java实现Json和String之间的转换

我们将围绕fastjson中的JSONObject这个类来谈转换

 <dependency>
 <groupId>com.alibaba</groupId>
 <artifactId>fastjson</artifactId>
 <version>1.2.15</version>
 </dependency>

String转成JSON

String json = "{"abc":"1","hahah":"2"}";
JSONObject jsonObject = JSONObject.parseObject(content);

一句话就能解决，非常便捷。
想要取出值，可以对`jsonObject`进行操作：

jsonObject.getString("abc");

结果为：`1`
将String转为list后转为JSON

List<String> list = new ArrayList<String>(); 
list.add("username"); 
list.add("age"); 
list.add("sex"); 
JSONArray array = new JSONArray(); 
array.add(list); 

将String转为map后转为JSON

Map<String, String> map = new HashMap<String, String>();
 map.put("abc", "abc");
map.put("def", "efg");
JSONArray array_test = new JSONArray();
array_test.add(map);
 JSONObject jsonObject = JSONObject.fromObject(map);

特别注意:从JSONObject中取值，碰到了数字为key的时候，如

{
 "userAnswer": {
 "28568": {
 "28552": {
 "qId": "28552",
 "order": "1",
 "userScore": {
 "score": 100
 },
 "answer": {
 "28554": "28554"
 },
 "qScore": "100.0",
 "qtype": "SingleChoice",
 "sId": "28568"
 }
 }
 },
 "paperType": "1",
 "paperOid": "28567",
 "instanceId": 30823,
 "remainingTime": -1,
 "examOid": "28570"
}

获取“userAnswer”的value,再转成JSON,可仿照如下形式：

JSONObject userJson = JSONObject.parseObject(jsonObject.getString("userAnswer"));

但是想获取key"28568"就没这么容易了。直接像上述的写法，会报错。
我们浏览fastjson中的源码，总结下，应该如下写：

JSONObject question = (JSONObject) JSONObject.parseObject(section.getString("28568"), Object.class);

整体代码：

dao代码很容易，就不贴出来了。

package com.xiamenair.training.business.service;
import com.alibaba.fastjson.JSONObject;
import com.xiamenair.training.business.dao.elearningdao.ELearningExamInstanceDao;
import com.xiamenair.training.business.dao.masterdao.ELearningChoiceRecordDao;
import com.xiamenair.training.business.model.LasChoiceRecord;
import com.xiamenair.training.business.model.entity.elearning.LasExamInstance;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Service;
import java.math.BigDecimal;
import java.sql.Blob;
import java.sql.SQLException;
import java.text.SimpleDateFormat;
import java.util.*;
@Service
public class ChoiceRecordService {
 //查询数据Dao
 @Autowired
 private ELearningChoiceRecordDao eLearningChoiceRecordDao;
 //转储数据Dao
 @Autowired
 private ELearningExamInstanceDao eLearningExamInstanceDao;
 private ChoiceRecordService() {
 }
 private static class SingletonRecordInstance {
 private static final LasChoiceRecord choiceRecord = new LasChoiceRecord();
 }
 public static LasChoiceRecord getMapInstance() {
 return SingletonRecordInstance.choiceRecord;
 }
 private static SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");
 /**
 * 定时任务，每天定时将E学网考试数据分析并转储
 *
 * @param : instanceIdList
 * @return : void
 * @author : 28370·皮育才
 * @date : 2018/11/20
 **/
 @Scheduled(cron = "00 00 01 * * ?")
 public void analysisChoiceRecord() {
 //获取前一天的时间
 Date date = new Date();
 Calendar calendar = Calendar.getInstance();
 calendar.setTime(date);
 calendar.add(calendar.DATE, -1);
 date = calendar.getTime();
 String dateString = simpleDateFormat.format(date);
 List<BigDecimal> instanceIdList = eLearningExamInstanceDao.findInstanceIdByFinishTime(dateString);
 if(0 != instanceIdList.size()){
 LasChoiceRecord lasChoiceRecord = getMapInstance();
 instanceIdList.stream().forEach(instanceId -> {
 Blob answerBlob = eLearningExamInstanceDao.findUserAnswer(instanceId);
 Long userId = eLearningExamInstanceDao.findUserId(instanceId);
 String content = null;
 try {
 content = new String(answerBlob.getBytes((long) 1, (int) answerBlob.length()));
 } catch (SQLException e) {
 e.printStackTrace();
 System.out.println("SQLEXCEPTION:" + e);
 }
 JSONObject jsonObject = JSONObject.parseObject(content);
 //针对本section的"公共"属性直接设置
 lasChoiceRecord.setUserId(userId);
 lasChoiceRecord.setPaperType(jsonObject.getString("paperType"));
 lasChoiceRecord.setPaperId(jsonObject.getString("paperOid"));
 lasChoiceRecord.setExamInstanceId(jsonObject.getString("instanceId"));
 lasChoiceRecord.setRemainingTime(jsonObject.getString("remainingTime"));
 lasChoiceRecord.setExamId(jsonObject.getString("examOid"));
 //针对section中的题目进行细化循环拆分
 JSONObject userJson = JSONObject.parseObject(jsonObject.getString("userAnswer"));
 Set sectionSet = userJson.keySet();
 Iterator<String> setIt = sectionSet.iterator();
 analyzeAnswer(lasChoiceRecord, userJson, setIt);
 });
 }
 }
 private void analyzeAnswer(LasChoiceRecord lasChoiceRecord, JSONObject userJson, Iterator<String> setIt) {
 while (setIt.hasNext()) {
 //对每个question进行再次拆分出题目
 JSONObject section = (JSONObject) JSONObject.parseObject(userJson.getString(setIt.next()), Object.class);
 Set questionSet = section.keySet();
 Iterator<String> queIt = questionSet.iterator();
 while (queIt.hasNext()) {
 JSONObject question = (JSONObject) JSONObject.parseObject(section.getString(queIt.next()), Object.class);
 String userAnswer = question.getString("answer");
 String userScore = question.getString("userScore");
 lasChoiceRecord.setQuestionId(question.getString("qId"));
 lasChoiceRecord.setRecordId(UUID.randomUUID().toString());
 eLearningChoiceRecordDao.save(lasChoiceRecord);
 }
 }
}
}

最近研究java的东西。之前靠着自己的摸索，实现了把java对象转成json格式的数据的功能，返回给前端。当时使用的是 JSONObject.fromObject(object) 方法把java对象换成json格式。也就是先有一个java实体类，例如叫User。然后从数据库查出列表数据，也就是一个List，里面的每一条数据都是一个User的实体对象。而如果前端需求变化，需要在当前这个接口中多返回一个字段时，就需要修改这个User实体类，新增字段。这样一来，所有用到这个User实体类的接口的地方，接口返回的json数据里都会有新增的这个字段。后来发现可以用一下方法根据需要动态拼接需要的字段。

package com.lin.domain;

import net.sf.json.JSONArray;
import net.sf.json.JSONObject;

public class Test {
  
    public static void main(String[] args) throws Exception {  
        JSONObject createJSONObject = createJSONObject();
        System.out.println(createJSONObject);
    }  
      
 // 创建JSONObject对象  
    private static JSONObject createJSONObject() {  
        JSONObject result = new JSONObject();  
        result.put("success", true);  
        result.put("totalCount", "30");  
        
        JSONObject user1 = new JSONObject();  
        user1.put("id", "12");  
        user1.put("name", "张三");  
        user1.put("createTime", "2017-11-16 12:12:12");  
   
        JSONObject user2 = new JSONObject();  
        user2.put("id", "13");  
        user2.put("name", "李四");  
        user2.put("createTime", "2017-11-16 12:12:15"); 
        
        JSONObject department = new JSONObject();
        department.put("id", 1);
        department.put("name","技术部");
        
        user1.put("department", department);
        user2.put("department", department);
          
        // 返回一个JSONArray对象  
        JSONArray jsonArray = new JSONArray();  
          
        jsonArray.add(0, user1);  
        jsonArray.add(1, user2);  
        result.element("data", jsonArray);  
          
        return result;  
    } 
}

返回的Json数据：

下面是真实的接口代码，从数据库中查询数据：

@ResponseBody
    @RequestMapping(value="/getRoleMenuList.do", method=RequestMethod.GET)
    public void getRoleMenuList(HttpServletRequest req, HttpServletResponse res, Integer roleId) throws IOException{
        res.setHeader("Content-type", "application/json;charset=UTF-8");
        res.setCharacterEncoding("UTF-8");
        ResListData rld = new ResListData();
        
        JSONObject result = new JSONObject();
        
        try {
            Map<String, Object> params1 = new HashMap<>();
            params1.put("roleId", roleId);
            params1.put("menuLevel", 1);
            List<RoleJuri> fMenuList = rjService.getRoleMenuList2(params1);    //一级菜单
            JSONArray firstList = new JSONArray(); 
            
            for(int i=0; i<fMenuList.size(); i++){
                RoleJuri firstMenu = fMenuList.get(i);
                JSONObject firstResult = new JSONObject();
                firstResult.put("id", firstMenu.getId());
                firstResult.put("name", firstMenu.getMenuName());
                firstResult.put("url", firstMenu.getMenuUrl());
                Map<String, Object> params2 = new HashMap<>();
                params2.put("roleId", roleId);
                params2.put("menuPId", firstMenu.getMenuId());
                List<RoleJuri> sMenuList = rjService.getRoleMenuList2(params2);    //二级菜单
                
                JSONArray secondList = new JSONArray();
                for(int j=0; j<sMenuList.size(); j++){
                    RoleJuri secondMenu = sMenuList.get(j);
                    JSONObject secondResult = new JSONObject();
                    secondResult.put("id", secondMenu.getId());
                    secondResult.put("name", secondMenu.getMenuName());
                    secondResult.put("url", secondMenu.getMenuUrl());
                    secondList.add(secondResult);
                }
                firstResult.put("children", secondList);
                firstList.add(firstResult);
            }
            if(fMenuList.size() > 0){    //查询到了一级菜单
                result.put("success", 1);
                result.put("data", firstList);
            }else{    //未查询到一级菜单
                result.put("success", 0);
                result.put("data", new Array());
                result.put("error", "未获取到菜单数据");
            }
        } catch (Exception e) {
            result.put("success", 0);
            result.put("data", new Array());
            result.put("error", "服务器运行错误");
        }
        res.getWriter().write(result.toString());
    }

返回的Json数据：

 

 参考：

https://www.cnblogs.com/libo0125ok/p/7905665.html

https://blog.csdn.net/javaQQ561487941/article/details/84328669

https://www.cnblogs.com/LearnAndGet/p/10009646.html