如果不使用jackson，则无法将hashmap转换为字符串

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

public class HashMapToString {
    public static void main(String[] args) {
        // 创建一个HashMap
        Map<String, String> hashMap = new HashMap<>();
        hashMap.put("key1", "value1");
        hashMap.put("key2", "value2");
        hashMap.put("key3", "value3");

        // 将HashMap转换为字符串
        StringBuilder stringBuilder = new StringBuilder();
        stringBuilder.append("{");
        for (Map.Entry<String, String> entry : hashMap.entrySet()) {
            stringBuilder.append("\"").append(entry.getKey()).append("\":\"").append(entry.getValue()).append("\",");
        }
        stringBuilder.deleteCharAt(stringBuilder.length() - 1);
        stringBuilder.append("}");

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