AVRO-4197: Fix schema bytes defaults

lang/java/avro/src/main/java/org/apache/avro/Schema.java

@@ -613,8 +613,8 @@ public Field(String name, Schema schema, String doc) {
      */
     public Field(String name, Schema schema, String doc, Object defaultValue) {
       this(name, schema, doc,
-          defaultValue == NULL_DEFAULT_VALUE ? NullNode.getInstance() : JacksonUtils.toJsonNode(defaultValue), true,
-          Order.ASCENDING);
+          defaultValue == NULL_DEFAULT_VALUE ? NullNode.getInstance() : JacksonUtils.toJsonNode(defaultValue, true),
+          true, Order.ASCENDING);
     }
 
     /**
@@ -623,8 +623,8 @@ public Field(String name, Schema schema, String doc, Object defaultValue) {
      */
     public Field(String name, Schema schema, String doc, Object defaultValue, Order order) {
       this(name, schema, doc,
-          defaultValue == NULL_DEFAULT_VALUE ? NullNode.getInstance() : JacksonUtils.toJsonNode(defaultValue), true,
-          Objects.requireNonNull(order));
+          defaultValue == NULL_DEFAULT_VALUE ? NullNode.getInstance() : JacksonUtils.toJsonNode(defaultValue, true),
+          true, Objects.requireNonNull(order));
     }
 
     public String name() {

lang/java/avro/src/main/java/org/apache/avro/util/internal/JacksonUtils.java

@@ -57,38 +57,47 @@ public class JacksonUtils {
   private JacksonUtils() {
   }
 
-  public static JsonNode toJsonNode(Object datum) {
+  public static JsonNode toJsonNode(Object object) {
+    return toJsonNode(object, false);
+  }
+
+  public static JsonNode toJsonNode(Object datum, boolean inSchemaContext) {
     if (datum == null) {
       return null;
     }
     try {
       TokenBuffer generator = new TokenBuffer(MAPPER, false);
-      toJson(datum, generator);
+      toJson(datum, generator, inSchemaContext);
       return MAPPER.readTree(generator.asParser());
     } catch (IOException e) {
       throw new AvroRuntimeException(e);
     }
   }
 
   @SuppressWarnings(value = "unchecked")
-  static void toJson(Object datum, JsonGenerator generator) throws IOException {
+  static void toJson(Object datum, JsonGenerator generator, boolean inSchemaContext) throws IOException {
     if (datum == JsonProperties.NULL_VALUE) { // null
       generator.writeNull();
     } else if (datum instanceof Map) { // record, map
       generator.writeStartObject();
       for (Map.Entry<Object, Object> entry : ((Map<Object, Object>) datum).entrySet()) {
         generator.writeFieldName(entry.getKey().toString());
-        toJson(entry.getValue(), generator);
+        toJson(entry.getValue(), generator, inSchemaContext);
       }
       generator.writeEndObject();
     } else if (datum instanceof Collection) { // array
       generator.writeStartArray();
       for (Object element : (Collection<?>) datum) {
-        toJson(element, generator);
+        toJson(element, generator, inSchemaContext);
       }
       generator.writeEndArray();
     } else if (datum instanceof byte[]) { // bytes, fixed
-      generator.writeBinary((byte[]) datum);// writeString(new String((byte[]) datum, StandardCharsets.ISO_8859_1));
+      if (inSchemaContext) {
+        // when writing schemas, bytes must be encoded to string
+        generator.writeString(new String((byte[]) datum, StandardCharsets.ISO_8859_1));
+      } else {
+        generator.writeBinary((byte[]) datum);
+      }
     } else if (datum instanceof CharSequence || datum instanceof Enum<?>) { // string, enum
       generator.writeString(datum.toString());
     } else if (datum instanceof Double) { // double

lang/java/avro/src/test/java/org/apache/avro/TestSchema.java

@@ -26,6 +26,7 @@
 import java.io.ObjectInputStream;
 import java.io.ObjectOutputStream;
 import java.net.URL;
+import java.nio.ByteBuffer;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.util.ArrayList;
@@ -59,6 +60,7 @@
 import org.junit.jupiter.api.Test;
 
 import static java.util.Objects.requireNonNull;
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
@@ -238,6 +240,15 @@ void serialization() throws IOException, ClassNotFoundException {
     }
   }
 
+  @Test
+  void byteArrayDefaultField() {
+    byte[] defaultBytes = new byte[] { 1, 2, 3 };
+    Schema.Field field = new Schema.Field("bytesField", Schema.create(Schema.Type.BYTES), "my bytes field", defaultBytes);
+    Schema rSchema = Schema.createRecord("myRecord", "myRecord docs", "me", false, List.of(field));
+    GenericData.Record rec = new GenericRecordBuilder(rSchema).build();
+    assertArrayEquals(defaultBytes, ((ByteBuffer) rec.get("bytesField")).array());
+  }
+
   @Test
   void reconstructSchemaStringWithoutInlinedChildReference() {
     String child = "{\"type\":\"record\"," + "\"name\":\"Child\"," + "\"namespace\":\"org.apache.avro.nested\","