How to convert a map to a JSON string in Java?

To convert a Map to a JSON string, you can use JSON libraries such as Jackson or Fastjson. Below is an example code using the Jackson library:

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.util.HashMap;
import java.util.Map;

public class MapToJsonExample {
    public static void main(String[] args) {
        // 创建一个Map对象
        Map<String, Object> map = new HashMap<>();
        map.put("name", "John");
        map.put("age", 30);
        map.put("city", "New York");

        // 创建ObjectMapper对象
        ObjectMapper mapper = new ObjectMapper();

        try {
            // 将Map对象转换为JSON字符串
            String json = mapper.writeValueAsString(map);
            System.out.println(json);
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
    }
}

The output is:

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

Before using the Jackson library, it is necessary to import the relevant dependencies. If using Maven, you can add the following dependencies in the pom.xml file.

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.12.1</version>
</dependency>