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问题描述

我有一个类似下面的类

public class MyClass {
   private String val1;
   private String val2;
   private Map<String,Object> context;
   // Appropriate accessors removed for brevity.
   ...
}

我希望能够与 Jackson 从对象到 JSON 再返回.我可以很好地序列化上面的对象并收到以下输出:

I'm looking to be able to make the round trip with Jackson from object to JSON and back. I can serialize the object above fine and receive the following output:

{
    "val1": "foo",
    "val2": "bar",
    "context": {
        "key1": "enumValue1",
        "key2": "stringValue1",
        "key3": 3.0
    }
}

我遇到的问题是,由于序列化映射中的值没有任何类型信息,因此它们没有正确反序列化.例如,在上面的示例中, enumValue1 应反序列化为枚举值,但反序列化为字符串.我已经看到了基于各种事物的类型的示例,但在我的场景中,我不知道类型是什么(它们将是我事先不知道的用户生成的对象)所以我需要能够使用键值对序列化类型信息.我如何与 Jackson 一起完成此任务?

The issue I'm running into is that since the values in the serialized map do not have any type information, they are not deserialized correctly. For example, in the sample above, enumValue1 should be deserialized as an enum value but is instead deserialized as a String. I've seen examples for basing what type on a variety of things, but in my scenario, I won't know what the types are (they will be user generated objects that I won't know in advance) so I need to be able to serialize the type information with the key value pair. How can I accomplish this with Jackson?

为了记录,我使用的是 Jackson 2.4.2 版.我用来测试往返的代码如下:

For the record, I'm using Jackson version 2.4.2. The code I'm using to test the round trip is as follows:

@Test
@SuppressWarnings("unchecked")
public void testJsonSerialization() throws Exception {
    // Get test object to serialize
    T serializationValue = getSerializationValue();
    // Serialize test object
    String json = mapper.writeValueAsString(serializationValue);
    // Test that object was serialized as expected
    assertJson(json);
    // Deserialize to complete round trip
    T roundTrip = (T) mapper.readValue(json, serializationValue.getClass());
    // Validate that the deserialized object matches the original one
    assertObject(roundTrip);
}

由于这是一个基于 Spring 的项目,映射器的创建方式如下:

Since this is a Spring based project, the mapper is being created as follows:

@Configuration
public static class SerializationConfiguration {

    @Bean
    public ObjectMapper mapper() {
        Map<Class<?>, Class<?>> mixins = new HashMap<Class<?>, Class<?>>();
        // Add unrelated MixIns
        ..

        return new Jackson2ObjectMapperBuilder()
                .featuresToDisable(SerializationFeature.WRITE_DATE_KEYS_AS_TIMESTAMPS)
                .dateFormat(new ISO8601DateFormatWithMilliSeconds())
                .mixIns(mixins)
                .build();
    }
}

推荐答案

我认为实现您想要的最简单的方法是使用:

I think the simplest way of achieve what you want is using:

ObjectMapper.enableDefaultTyping(ObjectMapper.DefaultTyping.NON_FINAL);

这将在序列化的 json 中添加类型信息.

This will add type information in the serialized json.

这是一个正在运行的示例,您需要适应 Spring:

Here you are a running example, that you will need to adapt to Spring:

public class Main {

    public enum MyEnum {
        enumValue1
    }

    public static void main(String[] args) throws IOException {
        ObjectMapper mapper = new ObjectMapper();

        MyClass obj = new MyClass();
        obj.setContext(new HashMap<String, Object>());

        obj.setVal1("foo");
        obj.setVal2("var");
        obj.getContext().put("key1", "stringValue1");
        obj.getContext().put("key2", MyEnum.enumValue1);
        obj.getContext().put("key3", 3.0);

        mapper.enableDefaultTyping(ObjectMapper.DefaultTyping.NON_FINAL);
        String json = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(obj);

        System.out.println(json);

        MyClass readValue = mapper.readValue(json, MyClass.class);
        //Check the enum value was correctly deserialized
        Assert.assertEquals(readValue.getContext().get("key2"), MyEnum.enumValue1);
    }

}

该对象将被序列化为类似于:

The object will be serialized into something similar to:

[ "so_27871226.MyClass", {
  "val1" : "foo",
  "val2" : "var",
  "context" : [ "java.util.HashMap", {
    "key3" : 3.0,
    "key2" : [ "so_27871226.Main$MyEnum", "enumValue1" ],
    "key1" : "stringValue1"
  } ]
} ]

并且会被正确反序列化,断言会通过.

And will be deserialized back correctly, and the assertion will pass.

顺便说一下,还有更多方法可以做到这一点,请查看 https://github.com/FasterXML/jackson-docs/wiki/JacksonPolymorphicDeserialization 了解更多信息.

Bytheway there are more ways of doing this, please look at https://github.com/FasterXML/jackson-docs/wiki/JacksonPolymorphicDeserialization for more info.

我希望它会有所帮助.

这篇关于Jackson:反序列化为 Map<String, Object>每个值都有正确的类型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!

08-06 22:56
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