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
@Test
public void test3(){
JSONObject jsonObject = new JSONObject();
jsonObject.put("aaa","111");
jsonObject.put("bbb","222");
JSONArray jsonArray = new JSONArray();
jsonArray.add(jsonObject);
//array转string
String 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);
UserInfo(id=200, name=jogging, age=null, email=null, area=null)