Add getter method(getMapper()) to Serializer class that uses ObjectMapper

[doljae]

Description

After creating the XXXSerializer class, I suggest to add a getter method that can access the ObjectMapper to adjust the configurations.

If ObjectMapper is not specified in the current Serializer class constructor, the ObjectMapper that has been set internally by default is used.

In this state, if the user wants to make minor modifications to the ObjectMapper, since it cannot be accessed, it is inconvenient to create an ObjectMapper with new settings and then create a new Serializer.

And I know that DefaultTyping of ObjectMapper of GenericJackson2JsonRedisSerializer has been changed from DefaultTyping.NON_FINAL to EVERYTHING since version 2.7.0 due to the issue & PR below.

• Add support for final/Kotlin classes in GenericJackson2JsonRedisSerializer [DATAREDIS-995] #1566
• 93c25b0

If there is a method that can access the ObjectMapper, it has the advantage of being able to flexibly change only the necessary parts of the default setting even after creating the Serializer.

Sample

Without getter()

// always make new ObjectMapper when add Modules or adjust configurations
final ObjectMapper mapper = new ObjectMapper()
    .registerModule(new ParameterNamesModule(JsonCreator.Mode.DEFAULT))
    .registerModule(new Jdk8Module())
    .registerModule(new JavaTimeModule())
    .configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false)
    .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

// duplicated -> same as default ObjectMapper configurations, 
mapper.activateDefaultTyping(mapper.getPolymorphicTypeValidator(),
                             DefaultTyping.EVERYTHING,
                             As.PROPERTY);

return new GenericJackson2JsonRedisSerializer(mapper);

If a getter() method is provided for the ObjectMapper, it can be used flexibly in the same way as the test code below.

@Test
void genericJackson2JsonRedisSerializerCanCustomizeObjectMapperAfterCreated() {

    GenericJackson2JsonRedisSerializer serializer = new GenericJackson2JsonRedisSerializer();

    serializer.getMapper() // add getter method for accessing ObjectMapper in Serializer
              .registerModule(new JavaTimeModule()) // just add module with default ObjectMapper
	      .configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false) // adjust configurations
	      .configure(DeserializationFeature.ADJUST_DATES_TO_CONTEXT_TIME_ZONE, false);
 
    ObjectWithOffsetDateTime source = new ObjectWithOffsetDateTime(1L, "doljae", OffsetDateTime.now());

    assertThat(serializer.deserialize(serializer.serialize(source))).isEqualTo(source);
}

Additional info

Regarding this, after folking the repository, I've already done some work targeting the GenericJackson2JsonRedisSerializer.

• https://github.com/doljae/spring-data-redis/commit/9422a2653197e16fcc57917a81ce045fe68488be

[doljae]

@mp911de
It's been about two weeks since you posted the issue, so I'm curious about your opinion.

[mp911de]

We do not want to expose the ObjectMapper from the serializer because that is a potential source for bugs and it leaks internal implementation details. Instead, please configure multiple serializers or create the serializer with a given ObjectMapper.