如何用杰克逊解析嵌套数组? [英] How to parse nested arrays with Jackson?

问题描述

我曾经成功地解析以下.json文件:

I used to successfully parse the following .json file:

[
    {
        "latitude": 49.419459253939316,
        "longitude": 8.676411621072491
    },
    {
        "latitude": 49.41946061080915,
        "longitude": 8.676411644939083
    },
    {
        "latitude": 49.420365910782735,
        "longitude": 8.676438042403413
    }
]

以下 Jackson脚本输出点的List.

private static <T> List<T> parseFile(final String fileName, 
                                     Class<T> contentType) {
    // ...
    InputStream inputStream = // Open file
    ObjectMapper objectMapper = new ObjectMapper();
    try {
        TypeFactory typeFactory = objectMapper.getTypeFactory();
        CollectionType collectionType = typeFactory
            .constructCollectionType(List.class, contentType);
        return objectMapper.readValue(inputStream, collectionType);
    } catch (IOException e) {
        e.printStackTrace();
    }
    return null;
}

现在，数据集变得更加复杂.点的List变为点的List的List. 我是用这种方式构造的-如果不正确，请纠正我.

Now the dataset gets more complicated. The List of points becomes a List of List of points. I structured it this way - please correct me if this is not correct.

[
    [
        {
            "latitude": 49.419459253939316,
            "longitude": 8.676411621072491
        },
        {
            "latitude": 49.41946061080915,
            "longitude": 8.676411644939083
        },
        {
            "latitude": 49.420365910782735,
            "longitude": 8.676438042403413
        }
    ],
    [
        {
            "latitude": 49.40460334213399,
            "longitude": 8.670034018853409
        },
        {
            "latitude": 49.404608057285145,
            "longitude": 8.670028775634165
        },
        {
            "latitude": 49.40506145685422,
            "longitude": 8.66955817506422
        }
    ]
]

我准备了以下POJO来将数据存储到:

I prepared the following POJOs to store the data into:

public class GeoPoint {
    public double latitude;
    public double longitude;
}

...

public class ThreePoints {
    public List<GeoPoint> points;  
}

如何更改上面的Jackson解析器，以便它可以处理嵌套数组?杰克逊能否将数据解析为嵌套的类结构，例如ThreePoints.class?

How do I have to change the above Jackson parser so it can handle the nested arrays? Can Jackson parse the data into a nested class structure such as the ThreePoints.class?

推荐答案

您可以编写一个简单的自定义反序列化器

You can write a simple custom deserializer

要将其反序列化到您的班级:

To deserialize it to your class:

public class GeoPoint {
    public double latitude;
    public double longitude;
}

public class ThreePoints {
    public List<GeoPoint> points;
}

编写自定义反序列化器:

Write a custom deserializer:

class ThreePointsDeserializer extends StdDeserializer<ThreePoints> {

    protected ThreePointsDeserializer() {
        super(ThreePoints.class);
    }


    @Override
    public ThreePoints deserialize(JsonParser parser, DeserializationContext ctx)
            throws IOException, JsonProcessingException {
        ThreePoints result = new ThreePoints();
        GeoPoint[] points = parser.getCodec().readValue(parser, GeoPoint[].class);
        result.points = Arrays.asList(points);
        return result;
    }
}

使用该反序列化器:

SimpleModule module = new SimpleModule();
module.addDeserializer(ThreePoints.class, new ThreePointsDeserializer());

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

TypeFactory tf = mapper.getTypeFactory();
CollectionType collectionType = tf.constructCollectionType(List.class, ThreePoints.class);

List<ThreePoints> result = mapper.readValue(YOUR_DATA, collectionType);

这篇关于如何用杰克逊解析嵌套数组?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！