后端 Java 对象转 json（不用第三方依赖的拼接方式）

需求：编写工具类要尽可能不用任意一个 jar 包依赖，或者尽可能精简

原有数据：

ArpsParams{actualProduction=[{mouth=2022-07, oilProdDaily=366088.33}, {mouth=2022-08, oilProdDaily=380806.78}], 
predictionSegment=[{mouth=2022-07, oilProdDaily=367832.31}, {mouth=2022-08, oilProdDaily=368310.88}], 
predictionProduction=[{mouth=2023-10, oilProdDaily=374462.45}, {mouth=2023-11, oilProdDaily=374949.65}, {mouth=2023-12, oilProdDaily=375437.49}, {mouth=2024-01, oilProdDaily=375925.96}, {mouth=2024-02, oilProdDaily=376415.07}], 
methodName='指数递减', formula='Q=367354.35*e^(--0.001*t)'}

现有要求转换成 JSON 形式显示：

{
  "actualProduction": [
    {
      "mouth": "2022-07",
      "oilProdDaily": 366088.33
    },
    {
      "mouth": "2022-08",
      "oilProdDaily": 380806.78
    }
  ],
  "predictionSegment": [
    {
      "mouth": "2022-07",
      "oilProdDaily": 367832.31
    },
    {
      "mouth": "2022-08",
      "oilProdDaily": 368310.88
    }
  ],
  "predictionProduction": [
    {
      "mouth": "2023-10",
      "oilProdDaily": 374462.45
    },
    {
      "mouth": "2023-11",
      "oilProdDaily": 374949.65
    },
    {
      "mouth": "2023-12",
      "oilProdDaily": 375437.49
    },
    {
      "mouth": "2024-01",
      "oilProdDaily": 375925.96
    },
    {
      "mouth": "2024-02",
      "oilProdDaily": 376415.07
    }
  ],
  "methodName": "指数递减",
  "formula": "Q=367354.35*e^(--0.001*t)"
}

方法一：引入第三方依赖，如 jackson-databind，然后使用：

import com.fasterxml.jackson.databind.ObjectMapper;

ObjectMapper objectMapper = new ObjectMapper();
String arpsParamsJson = objectMapper.writeValueAsString(arpsParams);
System.out.println(arpsParamsJson); // JSON样式

方法二：拼接，推荐使用 StringBuilder builder = new StringBuilder();

//        开始拼接：
StringBuilder builder = new StringBuilder("{");
//        实际数据 actualProduction：
List<Map<String, Object>> actual = arpsParams.getActualProduction();
builder.append("\"actualProduction\": [");
for (int i = 0; i < actual.size(); i++){
    // 获取 mouth 和 oilProdDaily 的值
    String mouth = (String) actual.get(i).get("mouth");
    Double oilProdDaily = (Double) actual.get(i).get("oilProdDaily");
    builder.append("{\"mouth\": \"" + mouth + "\",");
    builder.append("\"oilProdDaily\": " + oilProdDaily + "},");
}
int lastCommaIndex1 = builder.lastIndexOf(",");
if (lastCommaIndex1 != -1) {
    // 删除最后一个逗号
    builder.deleteCharAt(lastCommaIndex1);
}
builder.append("],");

//        拟合数据 predictionSegment：
List<Map<String, Object>> segment = arpsParams.getPredictionSegment();
builder.append("\"predictionSegment\": [");
for (int i = 0; i < segment.size(); i++){
    // 获取 mouth 和 oilProdDaily 的值
    String mouth = (String) segment.get(i).get("mouth");
    Double oilProdDaily = (Double) segment.get(i).get("oilProdDaily");
    builder.append("{\"mouth\": \"" + mouth + "\",");
    builder.append("\"oilProdDaily\": " + oilProdDaily + "},");
}
int lastCommaIndex2 = builder.lastIndexOf(",");
if (lastCommaIndex2 != -1) {
    builder.deleteCharAt(lastCommaIndex2);
}
builder.append("],");

//        预测数据 predictionProduction：
List<Map<String, Object>> production = arpsParams.getPredictionProduction();
builder.append("\"predictionProduction\": [");
for (int i = 0; i < production.size(); i++){
    // 获取 mouth 和 oilProdDaily 的值
    String mouth = (String) production.get(i).get("mouth");
    Double oilProdDaily = (Double) production.get(i).get("oilProdDaily");
    builder.append("{\"mouth\": \"" + mouth + "\",");
    builder.append("\"oilProdDaily\": " + oilProdDaily + "},");
}
int lastCommaIndex3 = builder.lastIndexOf(",");
if (lastCommaIndex3 != -1) {
    builder.deleteCharAt(lastCommaIndex3);
}
builder.append("],");

//        模型类型和表达式:
String methodName = arpsParams.getMethodName();
String formula = arpsParams.getFormula();
builder.append("\"methodName\": \"" + methodName + "\",\"formula\": \"" + formula + "\"}");

//        以JSON形式输出显示
System.out.println(builder);