杰克逊反序列化列表中的地图对象

Question

我在一个文件中有以下 JSON

[
    {"numberEnrolledPerMonthPerWeek":
        {
            {"year":"2011","numberEnrolled":0,"weeks":2},
            {"year":"2011","numberEnrolled":0,"weeks":3},
            {"year":"2011","numberEnrolled":0,"weeks":4},
            {"year":"2011","numberEnrolled":0,"weeks":5},
            {"year":"2011","numberEnrolled":0,"weeks":6},
            {"year":"2011","numberEnrolled":0,"weeks":7},
            {"year":"2011","numberEnrolled":0,"weeks":8},
            {"year":"2011","numberEnrolled":0,"weeks":9}        
        }
        ,"country":"Argentina"
    },
]

当我使用Jackson将其反序列化为Java对象时，我得到以下错误

org.codehaus.jackson.map.JsonMappingException: Can not deserialize instance of java.util.LinkedHashMap out of START_ARRAY token

我正在使用以下代码

object mapper mapper = new object mapper()；

List<EnrolledEnrolment> enrolments = mapper.readValue(new File("src/main/resources/data/jsonQueriesTestData1.txt"), 
        new TypeReference<List<EnrolledEnrolment>>(){});

我已经为初始数组使用了类型引用，但如何将类型引用用于对象EnrolledEnrolment内的hashmap。

private Map<Integer, Enrolled> numberEnrolledPerMonthPerWeek = new HashMap<Integer,Enrolled>();

当它尝试解析第二个数组时抛出错误？有什么想法吗？

谢谢

Answer 1

很难说原始帖子中没有实际错误，但我在尝试将JSON自动反序列化为对象时遇到了一个问题，其中JSON包含List中的Map。

我看到了这个错误:

com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of `java.util.LinkedHashMap` (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value

我修复了将@JsonDeserialize（转换器= JsonToMap转换器.class）添加到我的POJO中的地图中。

那堂课看起来像这样

public class JsonToMapConverter extends StdConverter<String, Map<String, MyPojo>> {

    @Override
    public Map<String, MyPojo> convert(String value) {
        try {
            return JsonUtil.convertJsonToMap(value, String.class, MyPojo.class);
        }
        catch (Exception e) {
            throw new RuntimeException(String.format("Failed to convert String to POJO [%s]", value));
        }
    }

}

实用方法看起来像

    public static <K,V> Map<K,V> convertJsonToMap(String json, Class<K> key, Class<V> value) throws IOException {
        JavaType type = mapper.getTypeFactory()
            .constructMapLikeType(Map.class, key, value);
        return mapper.readValue(json.getBytes(StandardCharsets.UTF_8), type);
    }