#453 - Introduce converters to consume Postgres Json and convert these to String/byte[].

We now ship converters for Postgres' Json data type to map JSON to String and to byte[] for easier and safe consumption.

src/main/java/org/springframework/data/r2dbc/dialect/PostgresDialect.java

@@ -1,5 +1,7 @@
 package org.springframework.data.r2dbc.dialect;
 
+import io.r2dbc.postgresql.codec.Json;
+
 import java.net.InetAddress;
 import java.net.URI;
 import java.net.URL;
@@ -38,6 +40,9 @@ public class PostgresDialect extends org.springframework.data.relational.core.di
 
 	private static final Set<Class<?>> SIMPLE_TYPES;
 
+	private static final boolean JSON_PRESENT = ClassUtils.isPresent("io.r2dbc.postgresql.codec.Json",
+			PostgresDialect.class.getClassLoader());
+
 	private static final boolean GEO_TYPES_PRESENT = ClassUtils.isPresent("io.r2dbc.postgresql.codec.Polygon",
 			PostgresDialect.class.getClassLoader());
 
@@ -45,9 +50,6 @@ public class PostgresDialect extends org.springframework.data.relational.core.di
 
 		Set<Class<?>> simpleTypes = new HashSet<>(Arrays.asList(UUID.class, URL.class, URI.class, InetAddress.class));
 
-		// conditional Postgres JSON support.
-		ifClassPresent("io.r2dbc.postgresql.codec.Json", simpleTypes::add);
-
 		// conditional Postgres Geo support.
 		Stream.of("io.r2dbc.postgresql.codec.Box", //
 				"io.r2dbc.postgresql.codec.Circle", //
@@ -58,6 +60,9 @@ public class PostgresDialect extends org.springframework.data.relational.core.di
 				"io.r2dbc.postgresql.codec.Polygon") //
 				.forEach(s -> ifClassPresent(s, simpleTypes::add));
 
+		// conditional Postgres JSON support.
+		ifClassPresent("io.r2dbc.postgresql.codec.Json", simpleTypes::add);
+
 		SIMPLE_TYPES = simpleTypes;
 	}
 
@@ -106,14 +111,24 @@ public class PostgresDialect extends org.springframework.data.relational.core.di
 	@Override
 	public Collection<Object> getConverters() {
 
-		if (GEO_TYPES_PRESENT) {
-			return Arrays.asList(FromPostgresPointConverter.INSTANCE, ToPostgresPointConverter.INSTANCE, //
-					FromPostgresCircleConverter.INSTANCE, ToPostgresCircleConverter.INSTANCE, //
-					FromPostgresBoxConverter.INSTANCE, ToPostgresBoxConverter.INSTANCE, //
-					FromPostgresPolygonConverter.INSTANCE, ToPostgresPolygonConverter.INSTANCE);
+		if (!GEO_TYPES_PRESENT && !JSON_PRESENT) {
+			return Collections.emptyList();
 		}
 
-		return Collections.emptyList();
+		List<Object> converters = new ArrayList<>();
+
+		if (GEO_TYPES_PRESENT) {
+			converters.addAll(Arrays.asList(FromPostgresPointConverter.INSTANCE, ToPostgresPointConverter.INSTANCE, //
+					FromPostgresCircleConverter.INSTANCE, ToPostgresCircleConverter.INSTANCE, //
+					FromPostgresBoxConverter.INSTANCE, ToPostgresBoxConverter.INSTANCE, //
+					FromPostgresPolygonConverter.INSTANCE, ToPostgresPolygonConverter.INSTANCE));
+		}
+
+		if (JSON_PRESENT) {
+			converters.addAll(Arrays.asList(JsonToByteArrayConverter.INSTANCE, JsonToStringConverter.INSTANCE));
+		}
+
+		return converters;
 	}
 
 	private static class R2dbcArrayColumns implements ArrayColumns {
@@ -269,4 +284,28 @@ public class PostgresDialect extends org.springframework.data.relational.core.di
 		}
 	}
 
+	@ReadingConverter
+	private enum JsonToStringConverter implements Converter<Json, String> {
+
+		INSTANCE;
+
+		@Override
+		@NonNull
+		public String convert(Json source) {
+			return source.asString();
+		}
+	}
+
+	@ReadingConverter
+	private enum JsonToByteArrayConverter implements Converter<Json, byte[]> {
+
+		INSTANCE;
+
+		@Override
+		@NonNull
+		public byte[] convert(Json source) {
+			return source.asArray();
+		}
+	}
+
 }

src/test/java/org/springframework/data/r2dbc/convert/PostgresMappingR2dbcConverterUnitTests.java

@@ -18,6 +18,9 @@ package org.springframework.data.r2dbc.convert;
 import static org.assertj.core.api.Assertions.*;
 
 import io.r2dbc.postgresql.codec.Json;
+import io.r2dbc.spi.test.MockColumnMetadata;
+import io.r2dbc.spi.test.MockRow;
+import io.r2dbc.spi.test.MockRowMetadata;
 import lombok.AllArgsConstructor;
 
 import java.util.ArrayList;
@@ -72,6 +75,30 @@ public class PostgresMappingR2dbcConverterUnitTests {
 		assertThat(row).containsEntry(SqlIdentifier.unquoted("json_value"), Parameter.from(person.jsonValue));
 	}
 
+	@Test // gh-453
+	public void shouldConvertJsonToString() {
+
+		MockRow row = MockRow.builder().identified("json_string", Object.class, Json.of("{\"hello\":\"world\"}")).build();
+
+		MockRowMetadata metadata = MockRowMetadata.builder()
+				.columnMetadata(MockColumnMetadata.builder().name("json_string").build()).build();
+
+		ConvertedJson result = converter.read(ConvertedJson.class, row, metadata);
+		assertThat(result.jsonString).isEqualTo("{\"hello\":\"world\"}");
+	}
+
+	@Test // gh-453
+	public void shouldConvertJsonToByteArray() {
+
+		MockRow row = MockRow.builder().identified("json_bytes", Object.class, Json.of("{\"hello\":\"world\"}")).build();
+
+		MockRowMetadata metadata = MockRowMetadata.builder()
+				.columnMetadata(MockColumnMetadata.builder().name("json_bytes").build()).build();
+
+		ConvertedJson result = converter.read(ConvertedJson.class, row, metadata);
+		assertThat(result.jsonBytes).isEqualTo("{\"hello\":\"world\"}".getBytes());
+	}
+
 	@AllArgsConstructor
 	static class JsonPerson {
 
@@ -79,4 +106,14 @@ public class PostgresMappingR2dbcConverterUnitTests {
 
 		Json jsonValue;
 	}
+
+	@AllArgsConstructor
+	static class ConvertedJson {
+
+		@Id Long id;
+
+		String jsonString;
+
+		byte[] jsonBytes;
+	}
 }