Java JSON映射<；字符串>；每个基本数据类型的转换

此代码的目的是将未知数量的参数和未知数量的值转换为

映射

（键-参数名称，值-可能的参数值列表），假设每种类型都将解析为字符串

问题是数字和其他格式没有解析成字符串，而且

jsonField.getValue（）

不是值节点（

jsonField.getValue（）.isValueNode（）

返回

false

），所以我不能使用

jsonField.getValue（）.asText（）

，因为它返回

null

我的做法：

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.apache.commons.collections4.map.ListOrderedMap;

public ListOrderedMap<String, ArrayList<String>> convertParamsFromJson(String jsonParams) throws IOException {

    ListOrderedMap<String, ArrayList<String>> convertedParams = new ListOrderedMap<>();
    Iterator<Entry<String, JsonNode>> fieldsFromJson = convertFromJson(jsonParams).fields();
    ObjectMapper mapper = new ObjectMapper();

    while (fieldsFromJson.hasNext()) {
        Entry<String, JsonNode> jsonField = fieldsFromJson.next();
        String paramName = jsonField.getKey();
        String paramValue = jsonField.getValue();
        if (jsonField.getValue().isArray()) {
            convertedParams.put(paramName, mapper.convertValue(paramValue, ArrayList.class));
        }
    }

    return convertedParams;
}

预期产出：

  <[MapEntry[key="firstparam", value=["1"]],
    MapEntry[key="secondparam", value=["a","b","c","d"]],
    MapEntry[key="thirdparam", value=["1","2","3"]],
    MapEntry[key="fourthparam", value=["true", "false"]]]>

输出：

  <[MapEntry[key="firstparam", value=[1]],
    MapEntry[key="secondparam", value=["a", "b", "c", "d"]],
    MapEntry[key="thirdparam", value=[1,2,3]],
    MapEntry[key="fourthparam", value=[true, false]]]>

---

默认情况下

Jackson

库将

JSON

原语转换为合适的类型。考虑下面的例子：

import com.fasterxml.jackson.databind.ObjectMapper;
import java.util.List;
import java.util.Map;

public class JsonApp {

    public static void main(String[] args) throws Exception {
        String json = "{\"firstParam\":[1],\"secondParam\": [\"a\",\"b\",\"c\",\"d\"],\"thirdParam\": [1,2,3],\"fourthParam\":[true,false]}";

        ObjectMapper mapper = new ObjectMapper();
        Map<String, List<Object>> map = mapper.readValue(json, Map.class);
        map.forEach((k, v) -> {
            System.out.print(k + " => ");
            v.forEach(i -> System.out.print(i + " (" + i.getClass().getSimpleName() + "), "));
            System.out.println();
        });
    }
}

但是，我们可以通过使用

TypeReference

提供需要实现的类型，强制将列表项转换为

String

：

import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

public class JsonApp {

    public static void main(String[] args) throws Exception {
        String json = "{\"firstParam\":[1],\"secondParam\": [\"a\",\"b\",\"c\",\"d\"],\"thirdParam\": [1,2,3],\"fourthParam\":[true,false]}";

        TypeReference<LinkedHashMap<String, List<String>>> mapOfStringListsType = new TypeReference<LinkedHashMap<String, List<String>>>() {};
        ObjectMapper mapper = new ObjectMapper();
        Map<String, List<String>> map = mapper.readValue(json, mapOfStringListsType);
        map.forEach((k, v) -> {
            System.out.print(k + " => ");
            v.forEach(i -> System.out.print(i + " (" + i.getClass().getSimpleName() + "), "));
            System.out.println();
        });
    }
}

---

简要介绍一下jackson文档，或者使用自定义的

ObjectMapper

，或者将默认值设置为使用自定义反序列化规则，以便始终映射到字符串，即使json具有不同的类型。我不知道这是如何实现的。

firstParam => 1 (Integer), 
secondParam => a (String), b (String), c (String), d (String), 
thirdParam => 1 (Integer), 2 (Integer), 3 (Integer), 
fourthParam => true (Boolean), false (Boolean), 

import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

public class JsonApp {

    public static void main(String[] args) throws Exception {
        String json = "{\"firstParam\":[1],\"secondParam\": [\"a\",\"b\",\"c\",\"d\"],\"thirdParam\": [1,2,3],\"fourthParam\":[true,false]}";

        TypeReference<LinkedHashMap<String, List<String>>> mapOfStringListsType = new TypeReference<LinkedHashMap<String, List<String>>>() {};
        ObjectMapper mapper = new ObjectMapper();
        Map<String, List<String>> map = mapper.readValue(json, mapOfStringListsType);
        map.forEach((k, v) -> {
            System.out.print(k + " => ");
            v.forEach(i -> System.out.print(i + " (" + i.getClass().getSimpleName() + "), "));
            System.out.println();
        });
    }
}

firstParam => 1 (String), 
secondParam => a (String), b (String), c (String), d (String), 
thirdParam => 1 (String), 2 (String), 3 (String), 
fourthParam => true (String), false (String),