Java -fastjson api

目录

• 构造 json 对象
• 转JSON字符串时保留null
• JSON串 转换为 map 及 JSONObject

构造 json 对象

需求：构造以下请求体

{
  "attrSelectionVO": [
    {
      "attrAccessId": "eea99a0894504a2b89f3cfeb4be051d3",
      "attrValueList": [
        {
          "attrValue": "输送型",
          "attrValueAccessId": "52d54de77b224cc8b5f9af647c938b10",
        }
      ],
      "attributeName": "皮带形状",
      "constraintCondition": 1,
      "mergedRangeParamValue": null,
      "paramName": null,
      "paramValue": null,
      "selectionSort": 2,
      "type": 0
    }
  ],
  "categoryCode": "C02"
}

实现方式一：

@Test
    public  void test01(){
        JSONObject requBody = new JSONObject();
        JSONArray attrSelectionVOArray = new JSONArray();
        requBody.put("attrSelectionVO", attrSelectionVOArray);
        requBody.put("categoryCode","C02");

        JSONObject attrSelectionVOEle = new JSONObject();
        attrSelectionVOEle.put("attrAccessId", "eea99a0894504a2b89f3cfeb4be051d3");

        JSONArray attrValueListArray = new JSONArray();
        JSONObject attrValueListEle = new JSONObject();
        attrValueListEle.put("attrValue", "输送型");
        attrValueListEle.put("attrValueAccessId", "52d54de77b224cc8b5f9af647c938b10");
        attrValueListArray.add(attrValueListEle);
        attrSelectionVOEle.put("attrValueList", attrValueListArray);

        attrSelectionVOEle.put("attributeName", "皮带形状");
        attrSelectionVOEle.put("constraintCondition", 1);
        attrSelectionVOEle.put("mergedRangeParamValue", null);
        attrSelectionVOEle.put("paramName", "null");
        attrSelectionVOEle.put("paramValue", "null");
        attrSelectionVOEle.put("type", 0);
        
        attrSelectionVOArray.add(attrSelectionVOEle);
        System.out.println(requBody.toJSONString());
    }

实现方式二：

    @Test
    public  void test02(){
        JSONObject requBody = new JSONObject();
        JSONArray attrSelectionVOArray = requBody.putArray("attrSelectionVO");
        requBody.put("categoryCode","C02");

        JSONObject attrSelectionVOEle = attrSelectionVOArray.addObject();
        attrSelectionVOEle.put("attrAccessId", "eea99a0894504a2b89f3cfeb4be051d3");

        JSONArray attrValueListArray = attrSelectionVOEle.putArray("attrValueList");
        JSONObject attrValueListEle = attrValueListArray.addObject();

        attrValueListEle.put("attrValue", "输送型");
        attrValueListEle.put("attrValueAccessId", "52d54de77b224cc8b5f9af647c938b10");

        attrSelectionVOEle.put("attributeName", "皮带形状");
        attrSelectionVOEle.put("constraintCondition", 1);
        attrSelectionVOEle.put("mergedRangeParamValue", null);
        attrSelectionVOEle.put("paramName", "null");
        attrSelectionVOEle.put("paramValue", "null");
        attrSelectionVOEle.put("type", 0);

        System.out.println(requBody.toJSONString());
    }

总结：

方式二的 putArray() 及 putObject() 可以在调用对象上返回一个空的 JSONArray 和 空的JSONObject，让我们不再去new对象及关注何时做映射，比方式一灵活

转JSON字符串时保留null

构造以下JSON串，保留 null：

{
  "attrSelectionVO": [
    {
      "attrAccessId": "eea99a0894504a2b89f3cfeb4be051d3",
      "paramName": null,
      "paramValue": null
    }
  ],
  "categoryCode": "C02"
}

实现：

@Test
public void test1() {
    Map<String, Object> map1 = new HashMap<>();

    map1.put("categoryCode", "C02");

    List<Map<String, Object>> attrSelectionVO = new ArrayList<>();
    Map<String, Object> attrSelectionVOEle = new HashMap<>();

    attrSelectionVOEle.put("attrAccessId", "eea99a0894504a2b89f3cfeb4be051d3");
    attrSelectionVOEle.put("paramName", null);
    attrSelectionVOEle.put("paramValue", null);

    attrSelectionVO.add(attrSelectionVOEle);

    map1.put("attrSelectionVO", attrSelectionVO);

    String s = JSON.toJSONString(map1, SerializerFeature.WriteMapNullValue);
    System.out.println(s);
}

com.alibaba.fastjson.serializer.SerializerFeature.WriteMapNullValue： fast json 的序列化策略，保留 null 值

https://blog.csdn.net/luoww1/article/details/66973627/
https://blog.csdn.net/weixin_39827470/article/details/109235313
https://blog.csdn.net/weixin_44326073/article/details/128924032

JSON串 转换为 map 及 JSONObject

转map:

@Test
public void test4() {
    String s = "{\n" +
            "  \"attrSelectionVO\": [\n" +
            "    {\n" +
            "      \"attrAccessId\": \"eea99a0894504a2b89f3cfeb4be051d3\",\n" +
            "      \"paramName\": null,\n" +
            "      \"paramValue\": null\n" +
            "    }\n" +
            "  ],\n" +
            "  \"categoryCode\": \"null\"\n" +
            "}";

    Map<String, Object> stringObjectMap = JSON.parseObject(s, new TypeReference<Map<String, Object>>() {
    });

    System.out.println(stringObjectMap);  //out: {categoryCode=null, attrSelectionVO=[{"attrAccessId":"eea99a0894504a2b89f3cfeb4be051d3"}]}
    System.out.println(JSON.toJSONString(stringObjectMap)); //out:{"categoryCode":"null","attrSelectionVO":[{"attrAccessId":"eea99a0894504a2b89f3cfeb4be051d3"}]}
    }

问题：值为 null 的转换为map 后 键不见了

转 JSONObject:

@Test
public void test3() {
    String s = "{\n" +
            "  \"attrSelectionVO\": [\n" +
            "    {\n" +
            "      \"attrAccessId\": \"eea99a0894504a2b89f3cfeb4be051d3\",\n" +
            "      \"paramName\": null,\n" +
            "      \"paramValue\": null\n" +
            "    }\n" +
            "  ],\n" +
            "  \"categoryCode\": \"null\"\n" +
            "}";

    JSONObject jsonObject = JSON.parseObject(s);
    System.out.println(jsonObject); //out: {"categoryCode":"null","attrSelectionVO":[{"attrAccessId":"eea99a0894504a2b89f3cfeb4be051d3"}]}
    System.out.println(JSON.toJSONString(jsonObject,SerializerFeature.WriteMapNullValue)); //out: {"categoryCode":"null","attrSelectionVO":[{"attrAccessId":"eea99a0894504a2b89f3cfeb4be051d3","paramName":null,"paramValue":null}]}
}

转换完毕后 值为null 的键依然存在

https://blog.csdn.net/qq_45854465/article/details/120873554