杰克逊 - 如何处理（反序列化）嵌套的JSON？

问题描述

{
  vendors: [
    {
      vendor: {
        id: 367,
        name: "Kuhn-Pollich",
        company_id: 1,
      }
    },
    {
      vendor: {
        id: 374,
        name: "Sawayn-Hermann",
        company_id: 1,
      }
  }]
}

我有一个Vendor对象，可以从单个vendorjson中正确反序列化，但我想将其反序列化为 Vendor [] ，I只是想不通如何让杰克逊合作。任何提示？

I have a Vendor object that can properly be deserialized from a single "vendor" json, but I want to deserialize this into a Vendor[], I just can't figure out how to make Jackson cooperate. Any tips?

推荐答案

您的数据存在问题，因为您的数组中有内部包装器对象。据推测，您的供应商对象旨在处理 id ， name ， company_id ，但这些多个对象中的每一个也都包含在一个具有单个属性 vendor 的对象中。

Your data is problematic in that you have inner wrapper objects in your array. Presumably your Vendor object is designed to handle id, name, company_id, but each of those multiple objects are also wrapped in an object with a single property vendor.

我假设你正在使用杰克逊模型。

I'm assuming that you're using the Jackson Data Binding model.

如果有，那么有两件事需要考虑：

If so then there are two things to consider:

第一种是使用特殊的Jackson配置属性。杰克逊 - 从1.9开始我认为，如果你使用旧版本的杰克逊，这可能无法使用 - 提供。它设计用于将结果包装在您要丢弃的顶级单属性对象中的情况。

The first is using a special Jackson config property. Jackson - since 1.9 I believe, this may not be available if you're using an old version of Jackson - provides UNWRAP_ROOT_VALUE. It's designed for cases where your results are wrapped in a top-level single-property object that you want to discard.

所以，请玩：

objectMapper.configure(SerializationConfig.Feature.UNWRAP_ROOT_VALUE, true);

第二种是使用包装器对象。即使在丢弃外部包装器对象之后，仍然存在将 Vendor 对象包装在单个属性对象中的问题。使用包装器解决这个问题：

The second is using wrapper objects. Even after discarding the outer wrapper object you still have the problem of your Vendor objects being wrapped in a single-property object. Use a wrapper to get around this:

class VendorWrapper
{
    Vendor vendor;

    // gettors, settors for vendor if you need them
}

同样，您也可以定义一个包装类来处理外部对象，而不是使用 UNWRAP_ROOT_VALUES 。假设您有正确的供应商， VendorWrapper 对象，您可以定义：

Similarly, instead of using UNWRAP_ROOT_VALUES, you could also define a wrapper class to handle the outer object. Assuming that you have correct Vendor, VendorWrapper object, you can define:

class VendorsWrapper
{
    List<VendorWrapper> vendors = new ArrayList<VendorWrapper>();

    // gettors, settors for vendors if you need them
}

// in your deserialization code:
ObjectMapper mapper = new ObjectMapper();
JsonNode rootNode = mapper.readValue(jsonInput, VendorsWrapper.class);

VendorsWrapper的对象树类似于你的JSON：

The object tree for VendorsWrapper is analogous to your JSON:

VendorsWrapper:
    vendors:
    [
        VendorWrapper
            vendor: Vendor,
        VendorWrapper:
            vendor: Vendor,
        ...
    ]

最后，您可以使用杰克逊将其解析为 JsonNodes ，丢弃外部节点，以及 ArrayNode 中的每个 JsonNode ，调用：

Finally, you might use the Jackson Tree Model to parse this into JsonNodes, discarding the outer node, and for each JsonNode in the ArrayNode, calling:

mapper.readValue(node.get("vendor").getTextValue(), Vendor.class);

这可能导致代码减少，但似乎并不比使用两个包装器更笨拙。

That might result in less code, but it seems no less clumsy than using two wrappers.

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