如果不使用jackson，则无法将hashmap转换为字符串

import java.util.HashMap;

public class HashMapToString {
    public static void main(String[] args) {
        HashMap<String, String> map = new HashMap<>();
        map.put("key1", "value1");
        map.put("key2", "value2");

        String result = map.toString();
        System.out.println(result);
    }
}

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

public class HashMapToJson {
    public static void main(String[] args) {
        HashMap<String, String> map = new HashMap<>();
        map.put("key1", "value1");
        map.put("key2", "value2");

        StringBuilder jsonBuilder = new StringBuilder();
        jsonBuilder.append("{");
        for (Map.Entry<String, String> entry : map.entrySet()) {
            jsonBuilder.append("\"")
                       .append(entry.getKey())
                       .append("\":\"")
                       .append(entry.getValue())
                       .append("\",");
        }
        if (map.size() > 0) {
            jsonBuilder.deleteCharAt(jsonBuilder.length() - 1); // Remove the last comma
        }
        jsonBuilder.append("}");

        String jsonString = jsonBuilder.toString();
        System.out.println(jsonString);
    }
}

import com.google.gson.Gson;
import java.util.HashMap;

public class HashMapToJsonWithGson {
    public static void main(String[] args) {
        HashMap<String, String> map = new HashMap<>();
        map.put("key1", "value1");
        map.put("key2", "value2");

        Gson gson = new Gson();
        String jsonString = gson.toJson(map);
        System.out.println(jsonString);
    }
}