Unexpected Serialization behaviour with configured Jackson Object Mapper

Question

[Related to Unexpected serialization behavior with configured Jackson ObjectMapper. I was asked to pose the question again.]

I am using Jackson 2.10.5 to serialize the same java.util.Date object twice.

The first time, with a basic Jackson ObjectMapper, I see the timestamp.

Then I construct a new ObjectMapper and configure it. I get a different result, the class name and the timestamp in a JSON list.

The configuration is intended to tell the ObjectMapper to include the class name of every object except java.util.Date as a JSON property.

Why is the Date object serialized differently between the two cases? Any advice how I am using the PolymorphicTypeMapper incorrectly would be appreciated.

The use case for this is as a JSON provider for Jersey. I have a way of generating and configuring an ObjectMapper at launch time, but the ability to configure per-write is just for the test code above.

Here's the test code:

private PolymorphicTypeValidator getPTV() {
    return BasicPolymorphicTypeValidator.builder()
            .denyForExactBaseType(Date.class)
            .build();
}


@Test
public void serializationTest() {
    try {
        Date now = new Date();

        // Create an object mapper and serialize the date
        ObjectMapper om = new ObjectMapper();
        String serialized1 = om.writeValueAsString(now); // result: 1605744866827

        ObjectMapper om2 = new ObjectMapper();
        om2.activateDefaultTypingAsProperty(getPTV(), ObjectMapper.DefaultTyping.EVERYTHING, "@class");
        String serialized2 = om2.writeValueAsString(now); // result: ["java.util.Date",1605744866827]

        Logger.getLogger(SerializationTest.class).info(serialized1);
        Logger.getLogger(SerializationTest.class).info(serialized2);

        Assert.assertEquals("Unexpected change in serialization", serialized1, serialized2);

    } catch (JsonProcessingException e) {
        Assert.fail("Exception thrown: "+e);
    }
}

And here is the output:

INFO  2020-11-19 07:55:41,799 [main] <> test.SerializationTest : 1605801341571
INFO  2020-11-19 07:55:41,800 [main] <> test.SerializationTest : ["java.util.Date",1605801341571]

org.junit.ComparisonFailure: Unexpected change in serialization 
Expected :1605801341571
Actual   :["java.util.Date",1605801341571]

dbp dbp · Accepted Answer · 2020-11-19T23:01:23

This was a misunderstanding on my part.

The type validator is only refererenced for deserialization. It controls the classes that can be deserialized from their class information.

Unexpected Serialization behaviour with configured Jackson Object Mapper

1 Answers