This PR ensures that Togglz 4 is able to work with DynamoDB tables which were previously managed by Togglz 3 or lower.

Problem

As part of Release 4.0.0-M3, this commit upgraded the DynamoDBStateRepository from AWS SDK version 1 to version 2. Before the upgrade, the toggle feature state was stored in DynamoDB using com.amazonaws.services.dynamodbv2.document.Item.withJSON:

String json = objectMapper.writeValueAsString(FeatureStateStorageWrapper.wrapperForFeatureState(featureState));
Item featureStateEntry =
  new Item()
    .withPrimaryKey(primaryKeyAttribute, featureState.getFeature().name())
    .withJSON(FEATURE_STATE_ATTRIBUTE_NAME, json);
table.putItem(featureStateEntry);

As a result of using withJSON, the DynamoDB client unpacked the JSON string and turned it into a map. Here is an example using Togglz 2.9.8:

After the upgrade, the DynamoDBStateRepository instead stores the toggle feature state as a (JSON) string with AttributeValue.builder().s(json).build():

String json = objectMapper.writeValueAsString(FeatureStateStorageWrapper.wrapperForFeatureState(featureState));
UpdateItemRequest request = UpdateItemRequest.builder()
  .tableName(tableName)
  .key(Map.of(primaryKeyAttribute, AttributeValue.builder()
    .s(featureState.getFeature().name())
    .build()))
  .attributeUpdates(Map.of(FEATURE_STATE_ATTRIBUTE_NAME, AttributeValueUpdate.builder()
    .action(AttributeAction.PUT)
    .value(AttributeValue.builder()
      .s(json)
      .build())
    .build()))
  .build();
dynamoDbClient.updateItem(request);

Here is an example of the same feature using Togglz 4.3.0:

The change breaks backwards compatibility. Togglz 4 cannot read features from a table which was managed by Togglz 3 or lower. The object mapper will throw a NullPointerException.

Proposed solution

The main goal of the proposed solution is to be compatible with Togglz 3 and lower and with existing releases of Togglz 4.
To achieve this, the read method DynamoDBStateRepository.getFeatureState is adapted to understand both representations: The string representation of version 4 and the map representations of versions 3 and lower.
The write method DynamoDBStateRepository.setFeatureState remains unchanged and still stores feature state as a (JSON) string.

As a result, a feature is automatically "migrated" from the old map representation to the new string representation when it is changed with setFeatureState. Until all features have been changed at least one, a DynamoDB table can contain some features with the old representation and some features with the new representation.