Migrate UUID values from legacy binary type 3 to standard

.README.md

MongoDB migration: From legacy UUID represenation (binary type 3) to standard (type 4)

You may face the need to migrate your data, because legacy format was a default choice for a long time in Spring Boot/Data MongoDB and the official MongoDB driver itself (more details here).

So, here is the Java solution based on utilitites from Mongo's org.bson:bson to perform the migration.

MongoDBUuidRepresentationMigrator.java

import org.bson.BsonBinary;
import org.bson.Document;
import org.bson.internal.UuidHelper;
import org.bson.types.Binary;

import java.util.LinkedList;
import java.util.Map;
import java.util.Queue;
import java.util.UUID;

import static org.bson.BsonBinarySubType.UUID_LEGACY;
import static org.bson.BsonBinarySubType.UUID_STANDARD;
import static org.bson.UuidRepresentation.JAVA_LEGACY;
import static org.bson.UuidRepresentation.STANDARD;

public class MongoDBUuidRepresentationMigrator {
    public static boolean convertUuidValuesFromLegacyToStandardFor(Document rootDocument) {
        boolean docWasChanged = false;
        Queue<Document> queue = new LinkedList<>();
        queue.offer(rootDocument);

        while (!queue.isEmpty()) {
            Document document = queue.remove();
            for (Map.Entry<String, Object> kv : document.entrySet()) {
                String fieldName = kv.getKey();
                Object fieldValue = kv.getValue();
                if (fieldValue instanceof Binary && ((Binary) fieldValue).getType() == UUID_LEGACY.getValue()) {
                    migrateUuidRepresentationFromLegacyToStandard(document, fieldName);
                    docWasChanged = true;
                } else if (fieldValue instanceof Document) {
                    queue.add(document);
                }
            }
        }
        return docWasChanged;
    }

    private static void migrateUuidRepresentationFromLegacyToStandard(Document document, String key) {
        Binary legacyBinary = (Binary) document.get(key);
        UUID uuid = new BsonBinary(legacyBinary.getType(), legacyBinary.getData()).asUuid(JAVA_LEGACY);
        document.put(key, new BsonBinary(UUID_STANDARD, UuidHelper.encodeUuidToBinary(uuid, STANDARD)));
    }
}