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准备工作

引入pom

<dependency><groupId>com.alibaba</groupId><artifactId>fastjson</artifactId><version>1.2.78</version>
</dependency><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><version>1.18.22</version></dependency>    

实体bean

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {private Integer id;//姓名private String name;
}

1.JSONObject获取所有的key

技巧：
JSONObject获取key：↓JSONObject obj；for (Map.Entry<String, Object> entry : cutReceiveAlarmMessageObject.entrySet()) {String s = entry.getKey();}

2.集合中实体对象转换 list中Enrey转Dto

list中Enrey转Dto：↓List<WarningNoticeDto> warningNoticeDtoList = warningNoticeList.getInfo().getList().stream().map(this::getEntryToDto).collect(Collectors.toList());/*** entry转DTO* @param warningNotice entry* @return dto*/private WarningNoticeDto getEntryToDto(WarningNotice warningNotice) {WarningNoticeDto warningNoticeDto = new WarningNoticeDto();BeanUtils.copyProperties(warningNotice, warningNoticeDto);return warningNoticeDto;}

3.字符串转List

import com.alibaba.fastjson.TypeReference;
import com.alibaba.fastjson.JSONObject;String str = "[{"id": 5,"nodeIdArr": "[\"221\",\"222\"]","nodeNameArr": "[\"enb_221\",\"2222\"]","upperLimitOfTheBusyTimeThreshold": 9,"lowerLimitOfTheBusyTimeThreshold": 2,"dateRangeBeginTime": 1701648000000,"dateRangeEndTime": 1701682200000,"createTime": 1701676594000,"updateTime": 1701737385000,"activeState": "1"},{"id": 6,"nodeIdArr": "[\"2003\",\"501\",\"10010\"]","nodeNameArr": "[\"CityA\",\"501\",\"Vir1\"]","upperLimitOfTheBusyTimeThreshold": 9,"lowerLimitOfTheBusyTimeThreshold": 2,"dateRangeBeginTime": 1701648000000,"dateRangeEndTime": 1701682200000,"createTime": 1701676641000,"updateTime": 1701737382000,"activeState": "1"}]"
List<BusyTimeIndicatorAlarmThreshold> busyTimeIndicatorAlarmThresholdList = new ArrayList<>();
busyTimeIndicatorAlarmThresholdList = JSONObject.parseObject(str, new TypeReference<List<BusyTimeIndicatorAlarmThreshold>>() {});

方式一、List busyTimeIndicatorAlarmThresholdList = new ArrayList<>();
busyTimeIndicatorAlarmThresholdList = JSONObject.parseObject(str, new TypeReference<List>() {});

方式二、List userList = JSONArray.parseArray(str, User.class);

4.json字符串转JSONObject

@Test
public void jsonStrConverJSONObject(){String str = "{\"id\":1,\"name\":\"tom\"}";JSONObject jsonObject = JSONObject.parseObject(str);System.out.println(jsonObject);     
}

输出：{“name”:“tom”,“id”:1}

5.list根据ids数组过滤list

@Test
public void listFilter() {List<User> list = new ArrayList<>();list.add(new User(1, "a"));list.add(new User(2, "b"));list.add(new User(3, "c"));list.add(new User(4, "d"));list.add(new User(5, "e"));list.add(new User(6, "f"));list.add(new User(7, "g"));list.add(new User(8, "h"));list.add(new User(9, "i"));list.add(new User(10, "j"));//注意：数组类型必须使用Integer才可以，使用int会判断失败Integer[] arr = new Integer[]{1,2,5,6,9};List<User> filterList = list.stream().filter(item -> Arrays.asList(arr).contains(item.getId())).collect(Collectors.toList());filterList.stream().forEach(System.out::println);
}

6.json字符串转JavaBean对象

@Test
public void jsonStrConverBean(){String str = "{\"id\":1,\"name\":\"tom\"}";User user = JSONObject.parseObject(str, User.class);System.out.println(user);   
}

输出：User(id=1, name=tom)

7.json对象转javabean

@Test
public void JSONObjectConverBean(){JSONObject jsonObject = new JSONObject();jsonObject.put("id", 1);jsonObject.put("name", "tom");User user = JSONObject.toJavaObject(jsonObject, User.class);System.out.println(user);   
}

输出：User(id=1, name=tom)

8.jsonObject转map

@Test
public void JSONObjectConverMap(){JSONObject jsonObject = new JSONObject();jsonObject.put("id", 1);jsonObject.put("name", "tom");Map<String,String> map = JSONObject.parseObject(jsonObject.toJSONString(), Map.class);System.out.println(map);   
}

输出：{name=tom, id=1}

9.List<User>转jsonArray

@Test
public void listConverjJsonArray(){List<User> list = new ArrayList<>();list.add(new User(1, "a"));list.add(new User(2, "b"));//错误写法，因为list.toString()输出[User(id=1, name=a), User(id=2, name=b)]。这东西无法json解析，会报错：com.alibaba.fastjson.JSONException: syntax error, pos 2, line 1, column 3[User(id=1, name=a), User(id=2, name=b)]//        JSONArray jsonArray =JSONArray.parseArray(list.toString());//正确写法，简写方式JSONArray jsonArray =JSONArray.parseArray(JSONObject.toJSONString(list));//正确写法，复杂方式//        JSONArray jsonArray = new JSONArray();//        JSONObject jsonObject = null;//        for (User user: list) {//            jsonObject = new JSONObject();//            jsonObject.put("id", user.getId());//            jsonObject.put("name", user.getName());//            jsonArray.add(jsonObject);//        }System.out.println(jsonArray);
}

10.jsonArray转成String[]

@Test
public void jsonArrayConverStringArray(){JSONArray jsonArray = new JSONArray();jsonArray.add(0, "100");jsonArray.add(1, "101");jsonArray.add(2, "102");System.out.println("jsonArray:" + jsonArray);String[] stringArr = new String[jsonArray.size()];for (int i = 0; i < jsonArray.size(); i++) {stringArr[i] = jsonArray.get(i).toString();}for(String str : stringArr) {System.out.println(str);}
}

问题：为啥使用int就判断失效，而使用Integer和String都能准确判断？

/*** 问题：为啥使用int就判断失效，而使用Integer和String都能准确判断？* 答案：不能将基本数据类型转化为List列表。
*/
@Test
public void test1() {int[] arr = new int[]{1,2,5,6,9};System.out.println(Arrays.asList(arr).contains(1)); //结果为falseInteger[] arr2 = new Integer[]{1,2,5,6,9};System.out.println(Arrays.asList(arr2).contains(1)); //结果为trueString[] arr3 = new String[]{"1","2","5","6","9"};System.out.println(Arrays.asList(arr3).contains("1")); //结果为true//验证答案如下,把arr、arr2、arr3分别返回查看返回泛型，能够看出Arrays.asList(arr)返回的居然是List<int[]>，问题就出在这，说明list里面包含的是一个个的int[]，用这个判断ints.contains(1)，肯定为falseList<int[]> ints = Arrays.asList(arr);List<Integer> integers = Arrays.asList(arr2);List<String> strings = Arrays.asList(arr3);
}

本人其他文章链接

1.java小工具util系列1：日期毫秒数转日期字符串
https://blog.csdn.net/a924382407/article/details/121955349

2.java小工具util系列2：获取字符modelStr在字符串str中第count次出现时的下标
https://blog.csdn.net/a924382407/article/details/121955455

3.java小工具util系列3：正则表达式匹配:匹配不包含@特殊字符的字符串
https://blog.csdn.net/a924382407/article/details/121955737

4.java小工具util系列4：String[] 转 List＜ Integer ＞
https://blog.csdn.net/a924382407/article/details/121956201

5.java小工具util系列5：基础工具代码(Msg、PageResult、Response、常量、枚举)
https://blog.csdn.net/a924382407/article/details/120952865

6.java小工具util系列6：java执行string返回boolean结果
https://blog.csdn.net/a924382407/article/details/117124536

7.java小工具util系列7：集合中实体对象转换 list中Enrey转Dto
https://blog.csdn.net/a924382407/article/details/121957545

8.java小工具util系列8：JSONObject获取key
https://blog.csdn.net/a924382407/article/details/121957607

9.java小工具util系列9：检测一个字符串是否是时间格式
https://blog.csdn.net/a924382407/article/details/123948881

10.java小工具util系列10：时间毫秒数、时间格式字符串、日期之间相互转化
https://blog.csdn.net/a924382407/article/details/124581851