关于java数据样品以及转换

关于集合

List<String>

List<String> list = duoMapper.selectName();

[
"alice1",
"alice2",
"alice3",
"alice4",
"alice5",
"alice6",
"alice7",
"alice8",
"alice9",
"alice10"
]

List<UserInfo>

List<UserInfo> list = duoMapper.selectName();

[{"id": null,"name": "alice1","age": 24,"email": null,"area": null},{"id": null,"name": "alice2","age": 27,"email": null,"area": null}
]

Map<String,Object>

map格式必须是两个，而且只能查一条数据，key若重复，将覆盖value

Map<String,Object> map = duoMapper.selectName();

select name,age from user_info limit 1

{
"name": "alice1",
"age": 24
}

LinkedHashMap是hashmap的子类，都属于map，数据格式一致

关于数组

        // 假设我们有一个整型数组int[] numbers = {1, 2, 3, 4, 5};// 使用for循环遍历数组并打印每个元素for (int i = 0; i < numbers.length; i++) {System.out.print(numbers[i]);}

12345

二维的话，双层

        // 二维数组int[][] matrix = {{1, 2, 3},{4, 5, 6},{7, 8, 9}};// 外层循环遍历行for (int i = 0; i < matrix.length; i++) {// 内层循环遍历列for (int j = 0; j < matrix[i].length; j++) {System.out.print(matrix[i][j] + " ");}System.out.println(); // 每打印完一行数据后换行}

1 2 3
4 5 6
7 8 9

没有任何符号包裹，裸数据

关于json

导入jar包

<dependency><groupId>com.alibaba</groupId><artifactId>fastjson</artifactId><version>1.2.33</version>
</dependency>

JSONObject

一种键值对的集合，写法类似map，所以key重复，value被覆盖，只有一组

        JSONObject jsonObject = new JSONObject();jsonObject.put("aaa","111");jsonObject.put("bbb","222");System.out.println(jsonObject);

{"aaa":"111","bbb":"222"}

JSONArray

一个

        JSONObject jsonObject = new JSONObject();jsonObject.put("aaa","111");jsonObject.put("bbb","222");JSONArray jsonArray = new JSONArray();jsonArray.add(jsonObject);System.out.println(jsonArray);

[{"aaa":"111","bbb":"222"}]

多个

        JSONObject jsonObject = new JSONObject();jsonObject.put("aaa","111");jsonObject.put("bbb","222");JSONObject jsonObject2 = new JSONObject();jsonObject2.put("ccc","333");jsonObject2.put("ddd","444");JSONArray jsonArray = new JSONArray();jsonArray.add(jsonObject);jsonArray.add(jsonObject2);System.out.println(jsonArray);

[{"aaa":"111","bbb":"222"},{"ccc":"333","ddd":"444"}]

关于json转换

array转json

JSONObject jsonObject3 = (JSONObject)jsonArray.get(i);
JSONObject jsonObject4 = jsonArray.getJSONObject(i);

array转string

    @Testpublic void test3(){JSONObject jsonObject = new JSONObject();jsonObject.put("aaa","111");jsonObject.put("bbb","222");JSONArray jsonArray = new JSONArray();jsonArray.add(jsonObject);//array转stringString str = JSONObject.toJSONString(jsonArray, SerializerFeature.WriteMapNullValue);System.out.println(str);}

[{"aaa":"111","bbb":"222"}]

json转string

        // 创建一个JSONObject对象JSONObject jsonObject = new JSONObject();jsonObject.put("name", "John Doe");jsonObject.put("age", 30);jsonObject.put("city", "New York");// 将JSONObject转换成字符串String jsonString = jsonObject.toString();// 输出转换后的字符串System.out.println(jsonString);

{"city":"New York","name":"John Doe","age":30}

string转json

        String result =  "{\"code\":200,\"message\":\"success\"}";JSONObject json = JSONObject.parseObject(result);System.out.println(json);

{"code":200,"message":"success"}

如果String有多组数据

String str = "[{\"name\":\"Alice\",\"age\":20},{\"name\":\"Bob\",\"age\":30}]";JSONArray jsonArray = JSON.parseArray(str);System.out.println(jsonArray);

[{"name":"Alice","age":20},{"name":"Bob","age":30}]

json转java对象

        String result =  "{\"id\":200,\"name\":\"jogging\"}";JSONObject jsonObject = JSONObject.parseObject(result);UserInfo userInfo = JSON.parseObject(jsonObject.toString(), UserInfo.class);System.out.println(userInfo);