Jackson json to map和camelcase键名

Question

我想通过杰克逊库将json转换为包含camelCase密钥的地图……比如……

从

{
    "SomeKey": "SomeValue",
    "AnotherKey": "another value",
    "InnerJson" : {"TheKey" : "TheValue"}
}

到这个。。。

{
    "someKey": "SomeValue",
    "anotherKey": "another value",
    "innerJson" : {"theKey" : "TheValue"}
}

我的代码...

public Map<String, Object> jsonToMap(String jsonString) throws IOException
{
    ObjectMapper mapper=new ObjectMapper();
    mapper.setPropertyNamingStrategy(PropertyNamingStrategy.CAMEL_CASE_TO_LOWER_CASE_WITH_UNDERSCORES);
    return mapper.readValue(jsonString,new TypeReference<Map<String, Object>>(){});
}

但这行不通...甚至其他属性命名策略也不适用于 json...如。。。

{
    "someKey": "SomeValue"
}

mapper.setPropertyNamingStrategy(new PropertyNamingStrategy.PascalCaseStrategy())

到

{
    "SomeKey": "SomeValue"
}

如何通过jackson获得camelCase地图键名...或者我应该手动循环映射和转换关键点还是有一些其他的方法？？？

提前感谢...

Answer 1

下面将使用任何“case格式”的键将json转换为使用camelCased键：

/**
 * Convert all property keys of the specified JSON to camelCase
 */
public static String toJsonWithCamelCasedKeys(String json) {
    ObjectMapper objectMapper = new ObjectMapper();
    objectMapper.registerModule(new SimpleModule()
      .addKeySerializer(String.class, new JsonSerializer<>() {
          @Override
          public void serialize(String value, JsonGenerator gen, SerializerProvider serializers) throws IOException {
              String key = CaseUtil.toCamelCase(value);
              gen.writeFieldName(key);
          }
      })
    );

    try {
        Map<String, Object> jsonMap = objectMapper.readValue(json, new TypeReference<>() {});
        return objectMapper.writeValueAsString(jsonMap);
    } catch (Exception e) {
        throw new JsonException("Error transforming JSON", e);
    }
}

… CaseUtil实现可能是这样的：

import java.util.Arrays;
import java.util.stream.Collectors;

public class CaseUtil {

    public static String toCamelCase(String s) {
        if (s == null) {
            return null;
        }
        else if (s.isBlank()) {
            return "";
        }

        return decapitaliseFirstLetter(
          String.join("", Arrays.stream(s.split("[-_\\s]"))
          .map(CaseUtil::capitaliseFirstLetter)
          .collect(Collectors.toList()))
        );
    }

    private static String capitaliseFirstLetter(String s) {
        return (s.length() > 0)
          ? s.substring(0, 1).toUpperCase() + s.substring(1)
          : s;
    }

    private static String decapitaliseFirstLetter(String s) {
        return (s.length() > 0)
          ? s.substring(0, 1).toLowerCase() + s.substring(1)
          : s;
    }

}

单元测试：

    @Test
    void jsonWithMiscCasedPropKeys_shouldConvertKeyToCamelCase() throws Exception {
        String inputJson =
            "{\"kebab-prop\": \"kebab\"," +
            "\"snake_prop\": \"snake\"," +
            "\"PascalProp\": \"pascal\"," +
            "\"camelCasedProp\": \"camel\"}";
        String expectedJson =
          "{\"kebabProp\": \"kebab\"," +
            "\"snakeProp\": \"snake\"," +
            "\"pascalProp\": \"pascal\"," +
            "\"camelCasedProp\": \"camel\"}";
        String actualJson = Json.toJsonWithCamelCasedKeys(inputJson);

        JSONAssert.assertEquals(expectedJson, actualJson, JSONCompareMode.LENIENT);
    }

Answer 2

您始终可以迭代地图的键并更新它们。但是，如果您只对使用驼峰大小写键生成JSON感兴趣，可以考虑下面描述的方法。

您可以有一个自定义密钥序列化器。它将在将Map实例序列化为JSON时使用：

public class CamelCaseKeySerializer extends JsonSerializer<String> {

    @Override
    public void serialize(String value, JsonGenerator gen, SerializerProvider serializers)
                throws IOException, JsonProcessingException {

        String key = Character.toLowerCase(value.charAt(0)) + value.substring(1);
        gen.writeFieldName(key);
    }
}

然后执行以下操作：

String json = "{\"SomeKey\":\"SomeValue\",\"AnotherKey\":\"another value\",\"InnerJson\":"
            + "{\"TheKey\":\"TheValue\"}}";

SimpleModule simpleModule = new SimpleModule();
simpleModule.addKeySerializer(String.class, new CamelCaseKeySerializer());

ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(simpleModule);

Map<String, Object> map = mapper.readValue(json, 
                                          new TypeReference<Map<String, Object>>() {});

String camelCaseJson = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(map);

输出将是:

{
  "someKey" : "SomeValue",
  "anotherKey" : "another value",
  "innerJson" : {
    "theKey" : "TheValue"
  }
}

使用这种方法，< code>Map的键将不会是camel大小写。但是它会给你想要的输出。

Answer 3

由于您使用的是地图/字典，而不是将JSON数据绑定到POJOs(与JSON数据匹配的显式Java类)，因此属性命名策略不适用:

类PropertyNamingStrategy…定义了JSON属性的名称（“外部名称”）是如何从POJO方法和字段的名称派生出来的（“内部名称”）

因此，您必须首先使用Jackson解析数据，然后迭代结果并转换键。

像这样更改代码：

public Map<String, Object> jsonToMap(String jsonString) throws IOException
{
    ObjectMapper mapper=new ObjectMapper();
    mapper.setPropertyNamingStrategy(PropertyNamingStrategy.CAMEL_CASE_TO_LOWER_CASE_WITH_UNDERSCORES);
    Map<String, Object> map = mapper.readValue(jsonString,new TypeReference<Map<String, Object>>(){});
    return convertMap(map);
}

并添加这些方法:

public String mapKey(String key) {
    return Character.toLowerCase(key.charAt(0)) + key.substring(1);
}

public Map<String, Object> convertMap(Map<String, Object> map) {
    Map<String, Object> result = new HashMap<String, Object>();
    for (Map.Entry<String, Object> entry : map.entrySet()) {
        String key = entry.getKey();
        Object value = entry.getValue();
        result.put(mapKey(key), convertValue(value));
    }
    return result;
}

public convertList(Lst<Object> list) {
    List<Object> result = new ArrayList<Object>();
    for (Object obj : list) {
        result.add(convertValue(obj));
    }
    return result;
}

public Object covertValue(Object obj) {
    if (obj instanceof Map<String, Object>) {
        return convertMap((Map<String, Object>) obj);
    } else if (obj instanceof List<Object>) {
        return convertList((List<Object>) obj);
    } else {
        return obj;
    }
}