0.前言

1. 用到的依赖

  <!-- lombok -->
  <dependency>
      <groupId>org.projectlombok</groupId>
      <artifactId>lombok</artifactId>
      <optional>true</optional>
  </dependency>
  <!-- hutool -->
  <dependency>
      <groupId>cn.hutool</groupId>
      <artifactId>hutool-all</artifactId>
      <version>5.7.15</version>
  </dependency>
  <!-- fastjson2 -->
  <dependency>
      <groupId>com.alibaba.fastjson2</groupId>
      <artifactId>fastjson2</artifactId>
      <version>2.0.21</version>
  </dependency>

2. 实体类

/**
 * @author 知否技术
 * @description
 * @date 2024-08-10 17:39
 */
@Data
@AllArgsConstructor
@NoArgsConstructor
@ToString
public class User {

  private Integer id;

  private String name;

  private Integer age;
}

3. 名词解读

• char : 字符
• String : 字符串
• Object : 对象

1.String 相关

1.1 String 转 char

String strChar = "知否技术";
char[] charArr = strChar.toCharArray();
log.info("charArr: {}", charArr);

1.2 String 转数组String str = "知否,技术";
String[] strArray = str.split(",");
for (String strElement : strArray) {
log.info("strElement: {}", strElement);
}

2.数组相关

2.1 数组转 String

String[] arr = { "张三", "李四", "知否君" };

1.hutool

import cn.hutool.core.util.ArrayUtil;

String[] arr = { "张三", "李四", "知否君" };
String str = ArrayUtil.toString(arr);
log.info("str: {}", str);

2.Arrays 和 Stream

import java.util.Arrays;
import java.util.stream.Collectors;

String str = Arrays.stream(arr).collect(Collectors.joining(","));
log.info("str: {}", str);

2.2 数组转 List

  String[] array = {"亚瑟","李白","后羿"};

1.Arrays

List<String> list = Arrays.asList(array);
log.info("list: {}", list);

注：通过该方式转成 List 之后，不能进行增删操作，只能进行查改操作，否则会抛异常

以下两种方式可以对转换之后的 List 进行增删改查操作：

2.ArrayList的构造器进行转

 ArrayList<String> list = new ArrayList<>(Arrays.asList(array));

3.Collections.addAll()

List<String> list = new ArrayList<>();
Collections.addAll(list, array);

2.3 数组转 Set

String[] arr = new String[]{"A", "B", "C", "C"};
Set<String> set = new HashSet<>(Arrays.asList(arr));
log.info("set: {}", set);

3.List相关3.1 List 转数组List<String> list = Arrays.asList("张三","李四");
String[] stringArray = list.toArray(new String[0]);
3.2 List 转 StringList<String> list = Arrays.asList("张三","李四");
String listToStr = String.join(",", list);
log.info("listToStr: {}", listToStr);

3.3 List 转 Map

1.Stream 流，key 相同，后面的覆盖前面的

List<User> users = Arrays.asList(new User(1, "张三", 18),new User(1, "张三", 99), new User(2, "李四", 20));
Map<Integer, User> map = users.stream().collect(Collectors.toMap(User::getId, Function.identity(),(key1, key2) -> key2));// key 相同，后面的覆盖前面的
log.info("map: {}", map);

2.Stream 流，key 相同，指定对象的属性作为返回 map的 key 和 value

List<User> users = Arrays.asList(new User(1, "张三", 18),new User(1, "张三", 99), new User(2, "李四", 20));
Map<String, Integer> map = users.stream().collect(Collectors.toMap(User::getName,User::getAge,(key1, key2) -> key2));
log.info("map: {}", map);

3.Stream 流，key 相同，根据对象属性分组

List<User> users = Arrays.asList(new User(1, "张三", 18),new User(1, "张三", 99), new User(2, "李四", 20));
Map<Integer, List<User>> map = users.stream().collect(Collectors.groupingBy(User::getId)); // 根据什么分组
log.info("map: {}", map);

3.4 List 转 Set

List<String> list = Arrays.asList("张三","李四");

1.使用 HashSet 构造函数

Set<String> set = new HashSet<>(list);

2.使用 Set 的 addAll 方法

Set<String> set = new HashSet<>();
set.addAll(list);

3.stream 流

Set<String> set = list.stream().collect(Collectors.toSet());

3.5 List 转 JSONArray

List<User> users = Arrays.asList(new User(1, "张三", 18), new User(2, "李四", 20));

1.hutool

JSONArray jsonArray = JSONUtil.parseArray(users);

2.fastjson

JSONArray jsonArray = JSON.parseArray(JSON.toJSONString(users));

4.Set 相关

Set<String> neSet = new HashSet();
neSet.add("张三");
neSet.add("李四");

4.1 Set 转 List

1.构造函数

List<String> result = new ArrayList<>(set);

2.stream 流

List<String> list = set.stream().collect(Collectors.toList());

4.2 Set 转数组

1.toArray

String[] strArray = set.toArray(new String[set.size()]);

2.stream 流

String[] strArray = set.stream().toArray(java[]::new);

5.Object 相关

5.1 Object 转 JSONObject

User obj = new User(1, "张三", 18);

1.hutool

JSONObject jsonObject   = JSONUtil.parseObj(obj);
log.info("map:{}",jsonObject);

2.fastjson

JSONObject jsonObject = JSON.parseObject(JSON.toJSONString(obj));
log.info("map:{}",jsonObject);

5.2 Oject 转 Map

hutool

Map<String, Object> map = BeanUtil.beanToMap(new User(1, "张三", 18));
log.info("map:{}",map);

6.Map 相关

Map<String, Object> map = new HashMap<>();
map.put("name","张三");
map.put("age",18);

6.1 Map 转 JSONObject

1.hutool

JSONObject jsonObject = JSONUtil.toBean(JSONUtil.toJsonStr(map), JSONObject.class);
log.info("jsonObject:{}",jsonObject);

2.fastjson

JSONObject jsonObject = new JSONObject(map);
log.info("map:{}",jsonObject);

6.2 Map 转 Object

hutool

User user = JSONUtil.toBean(JSONUtil.toJsonStr(map), User.class);
log.info("user:{}",user);

6.3 Map 转 JSONString

1.hutool

String mapToStr = JSONUtil.toJsonStr(map);
log.info("mapToStr:{}",mapToStr);

2.fastjson

String mapToStr = JSONObject.toJSONString(map);
log.info("mapToStr:{}",mapToStr);

7.JSON 相关

7.1 JSON 字符串转 JSONObject

1.hutool

String jsonStr = "{\"id\": 1, \"name\": \"知否君\"}";
JSONObject jsonObject = JSONUtil.parseObj(jsonStr);
log.info("jsonObject:{}",jsonObject);

2.fastjson

String jsonStr = "{\"id\": 1, \"name\": \"知否君\"}";
JSONObject jsonObject = JSON.parseObject(jsonStr);
log.info("jsonObject:{}",jsonObject);

7.2 JSON 字符串转 JSONArray

1.hutool

String jsonStr = "[{\"id\": 1, \"name\": \"知否君\"}, {\"id\": 2, \"name\": \"李白\"}]";
JSONArray jsonArray = JSONUtil.parseArray(jsonStr);
log.info("jsonArray:{}",jsonArray);

2.fastjson

String jsonStr = "[{\"id\": 1, \"name\": \"知否君\"}, {\"id\": 2, \"name\": \"李白\"}]";
JSONArray jsonArray = JSON.parseArray(jsonStr);
log.info("jsonArray:{}",jsonArray);

7.3 JSON 字符串转 Object

1.hutool

String jsonStr = "{\"id\": 1, \"name\": \"知否君\"}";
User user = JSONUtil.toBean(jsonStr, User.class);
log.info("user:{}",user);

2.fastjson

String jsonStr = "{\"id\": 1, \"name\": \"知否君\"}";
User user = JSON.parseObject(jsonStr, User.class);
log.info("user:{}",user);

7.4 JSON 转 Map

1.hutool

String jsonStr = "{\"id\": 1, \"name\": \"知否君\"}";
Map map = JSONUtil.toBean(jsonStr, Map.class);
log.info("map:{}",map);

2.fastjson

String jsonStr = "{\"id\": 1, \"name\": \"知否君\"}";
Map map = JSON.parseObject(jsonStr, Map.class);
log.info("map:{}",map);

7.5 JSON 字符串转 List

1.hutool

String jsonStr = "[{\"id\": 1, \"name\": \"知否君\"}, {\"id\": 2, \"name\": \"李白\"}]";
List<User> list = JSONUtil.toList(jsonStr, User.class);
log.info("list:{}", list);

2.fastjson

String jsonStr = "[{\"id\": 1, \"name\": \"知否君\"}, {\"id\": 2, \"name\": \"李白\"}]";
List<User> list = JSON.parseArray(jsonStr, User.class);
log.info("list:{}", list);

java8

编程7

java · 目录

#java

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