序列化/反序列化Map< String，Object>与杰克逊 [英] Serialize/Deserialize Map<String, Object> with Jackson

问题描述

我有一个如下所示的类

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

我希望能够制作杰克逊从对象到JSON的回程往返。我可以将对象序列化为罚款并收到以下输出：

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
    }
}

我遇到的问题因为序列化映射中的值没有任何类型信息，所以它们不能正确反序列化。例如，在上面的示例中，enumValue1应该反序列化为枚举值，而是反序列化为String。我已经看到了基于各种类型的类型的示例，但在我的场景中，我不知道类型是什么（它们将是用户生成的对象，我不会事先知道）所以我需要成为能够使用键值对序列化类型信息。我怎么能用杰克逊来完成这个？

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，我使用的是杰克逊版本2.4.2。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，因此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

我认为实现你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.

在这里你是一个运行的例子，你将需要适应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某种东西类似于：

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"
  } ]
} ]

并且将被正确反序列化，并且断言将通过。

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

Bytheway有更多方法可以做到这一点，请查看在 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。

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