Fix DocumentToStringConverter UUID representation when calling toJson.

This commit makes sure to use an Encoder having UuidRepresentation set when calling org.bson.Document#toJson, preventing CodecConfigurationException from being raised.

Future versions will make sure the UUID string representation matches the Java default one.

Closes #3546.
Original pull request: #3551.

Author: christophstrobl

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/MongoConverters.java

@@ -32,6 +32,9 @@
 
 import org.bson.BsonTimestamp;
 import org.bson.Document;
+import org.bson.UuidRepresentation;
+import org.bson.codecs.Codec;
+import org.bson.internal.CodecRegistryHelper;
 import org.bson.types.Binary;
 import org.bson.types.Code;
 import org.bson.types.Decimal128;
@@ -45,11 +48,12 @@
 import org.springframework.data.convert.WritingConverter;
 import org.springframework.data.mongodb.core.query.Term;
 import org.springframework.data.mongodb.core.script.NamedMongoScript;
-import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.NumberUtils;
 import org.springframework.util.StringUtils;
 
+import com.mongodb.MongoClientSettings;
+
 /**
  * Wrapper class to contain useful converters for the usage with Mongo.
  *
@@ -236,9 +240,13 @@ enum DocumentToStringConverter implements Converter<Document, String> {
 
 		INSTANCE;
 
+		private final Codec<Document> codec = CodecRegistryHelper
+				.createRegistry(MongoClientSettings.getDefaultCodecRegistry(), UuidRepresentation.JAVA_LEGACY)
+				.get(Document.class);
+
 		@Override
 		public String convert(Document source) {
-			return source.toJson();
+			return source.toJson(codec);
 		}
 	}
 

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/convert/MappingMongoConverterUnitTests.java

@@ -2181,6 +2181,15 @@ public void readAndConvertDBRefNestedByMapCorrectly() {
 		assertThat(((LinkedHashMap) result.get("cluster")).get("_id")).isEqualTo(100L);
 	}
 
+	@Test // GH-3546
+	void readFlattensNestedDocumentToStringIfNecessary() {
+
+		org.bson.Document source = new org.bson.Document("street", new org.bson.Document("json", "string").append("_id", UUID.randomUUID()));
+
+		Address target = converter.read(Address.class, source);
+		assertThat(target.street).isNotNull();
+	}
+
 	@Test // DATAMONGO-1902
 	void writeFlattensEmbeddedType() {