java - Jackson JSON objectmapper 反序列化为 LinkedHashMap 而不是 HashMap

Question

我有一个带有内部 map 的 POJO。我希望将其从 JSON 反序列化为 HashMap，但 Jackson 将内部映射从 JSON 反序列化为 LinkedHashMap。我可以通过将Map的类型从“Map”更改为“HashMap”来强制它使用HashMap，但我想知道是否有办法告诉Jackson反序列化为Map的特定实现？

这是 JSON:

{
    "transforms": {
        "variable_name1": [{
            "min": 100,
            "max": 200,
            "value": 0.6
        }],
        "variable_name2": [{
            "min": 100,
            "max": 200,
            "value": 0.6
        }],
        "variable_name3": [{
            "min": 100,
            "max": 200,
            "value": 0.6
        }]
    }
}

以及 Transforms 类:

public class Transformer {
    Map<String, List<Transform>> transforms;

    public Transformer() {
        transforms = new HashMap<String, List<Transform>>();
    }

    public void setTransforms(Map<String, List<Transform>> transforms) {
        this.transforms = transforms;
    }
}

我如何使用 ObjectMapper:

try(Reader reader = new InputStreamReader(TransformTester.class.getResourceAsStream("transforms.json"), "UTF-8")) {
            ObjectMapper objMapper = new ObjectMapper();
            Transformer tr = objMapper.readValue(reader, Transformer.class);
}

Answer 1

如果您想要其他类型，您可以实现 Jackson 转换器并用它注释您的类。

public static class TransformConverter implements Converter<Map<String,List>,Map<String,List>>{

    @Override
    public Map<String,List> convert(Map<String,List> map) {
        return new HashMap<>(map);
    }

    @Override
    public JavaType getInputType(TypeFactory typeFactory) {
        return typeFactory.constructMapType(Map.class, String.class, List.class);
    }

    @Override
    public JavaType getOutputType(TypeFactory typeFactory) {
        return typeFactory.constructMapType(Map.class, String.class, List.class);
    }
}



public static class Transformer {
    @JsonDeserialize(converter = TransformConverter.class)
    Map<String, List<Transform>> transforms;
//rest of your class
}