杰克逊反序列化问题与数组和对象 [英] Jackson deserialization issues with arrays and objects

问题描述

我遇到了一个问题，我的JSON响应可以是对象或对象数组

I'm running into a problem where my JSON response can be object or an array of objects

单个值的Foobar示例：

Foobar example with a single value:

{
    "foo": {"msg": "Hello World" }
}

带数组的Foobar示例：

Foobar example with an array:

{
    "foo": [
           { "msg": "Hello World" },
           { "msg": "Goodbye World" }
         ]
}

我希望强制单值进入任何数组但到目前为止，我发现转换所有数据的唯一方法单个值作为数组。

I want the force the single value into any array but so far, the only way I found converted all single values as arrays.

ACCEPT_SINGLE_VALUE_AS_ARRAY

ACCEPT_SINGLE_VALUE_AS_ARRAY

http://wiki.fasterxml.com/JacksonFeaturesDeserialization

我一直在寻找一个对单个属性做同样事情的注释，但到目前为止谷歌还没有找到任何例子。

I've been looking around for an annotation that does the same thing for a single property but so far google hasn't turned up any examples.

之前有没有人遇到过这个问题，我真的不想把所有东西重写为数组，以使RestTemplate与一个有缺陷的服务一起工作。

Has anyone run into this problem before, I really don't want to rewrite everything as arrays to make RestTemplate work with a buggy service.

推荐答案

我希望强制将单个值放入任何数组，但到目前为止，我找到的唯一
方式将所有单个值转换为数组。

这不应该是这种情况。对于给定的ObjectMapper， ACCEPT_SINGLE_VALUE_AS_ARRAY 属性 是 打开/关闭，但其行为完全由目标属性管理正在映射JSON值。

This simply shouldn't be the case. The ACCEPT_SINGLE_VALUE_AS_ARRAY property is on/off for a given ObjectMapper, but its behavior is entirely governed by the target property the JSON value is being mapped to.

• 当ACCEPT_SINGLE_VALUE_AS_ARRAY打开时，将JSON值映射到Java集合属性不会导致错误。


• 当ACCEPT_SINGLE_VALUE_AS_ARRAY打开时，将JSON值映射到Java基本属性（也）不会导致错误。

以下代码说明：

class Foo {
    private String msg;

    // Constructor, setters, getters
}

class Holder {
    private List<Foo> foo;
    private Foo other;

    // Constructors, setters, getters
}

public class FooTest {

    @org.junit.Test
    public void testCollectionFromJSONValue() throws Exception {
        final InputStream stream = Thread.currentThread()
                .getContextClassLoader().getResourceAsStream("foo.json");

        final String json = IOUtils.toString(stream);

        final ObjectMapper mapper = new ObjectMapper();
        mapper.configure(
                DeserializationConfig.Feature.ACCEPT_SINGLE_VALUE_AS_ARRAY,
                true);
        final Holder holder = mapper.readValue(json, Holder.class);
        System.out.println(holder);
    }
}

这取决于以下JSON：

Which relies on the following JSON:

{
    "foo": {
        "msg": "Hello World"
    },
    "other": {
        "msg": "Goodbye"
    }
}

运行代码将显示foo属性已成功反序列化为列表，而other属性被反序列化为（基本）Foo类型。

Running the code will show that the "foo" property is successfully deserialized into a list, whereas the "other" property gets deserialized into a (basic) Foo type.

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