Support enum avro serialization with default value (#391)

Author: Sonic-Rage

avro/src/main/java/com/fasterxml/jackson/dataformat/avro/schema/AvroSchemaHelper.java

@@ -264,21 +264,29 @@ public static Schema parseJsonSchema(String json) {
     /**
      * Constructs a new enum schema
      *
+     * @param intr Introspector to use to find default enum value
      * @param bean Enum type to use for name / description / namespace
      * @param values List of enum names
+     *
      * @return An {@link org.apache.avro.Schema.Type#ENUM ENUM} schema.
      */
-    public static Schema createEnumSchema(BeanDescription bean, List<String> values)
+    public static Schema createEnumSchema(AnnotationIntrospector intr,
+            BeanDescription bean, List<String> values)
     {
         final JavaType enumType = bean.getType();
+        @SuppressWarnings("unchecked")
+        Class<Enum<?>> rawEnumClass = (Class<Enum<?>>) enumType.getRawClass();
+        final Enum<?> defaultEnumValue = intr.findDefaultEnumValue(bean.getClassInfo(),
+                rawEnumClass.getEnumConstants());
+        final String namespace = getNamespace(enumType, bean.getClassInfo());
         final Schema avroSchema;
-        
         try {
             avroSchema = Schema.createEnum(
                 getName(enumType),
                 bean.findClassDescription(),
-                getNamespace(enumType, bean.getClassInfo()),
-                values);
+                namespace,
+                values,
+                defaultEnumValue != null ? defaultEnumValue.toString() : null);
         } catch (SchemaParseException spe) {
             final String msg = String.format("Problem generating Avro `Schema` for Enum type %s: %s",
                     ClassUtil.getTypeDescription(enumType), spe.getMessage());

avro/src/main/java/com/fasterxml/jackson/dataformat/avro/schema/EnumVisitor.java

@@ -41,7 +41,8 @@ public Schema builtAvroSchema() {
         }
 
         BeanDescription bean = _provider.getConfig().introspectClassAnnotations(_type);
-        Schema schema = AvroSchemaHelper.createEnumSchema(bean, new ArrayList<>(_enums));
+        Schema schema = AvroSchemaHelper.createEnumSchema(_provider.getAnnotationIntrospector(),
+                bean, new ArrayList<>(_enums));
         _schemas.addSchema(_type, schema);
         return schema;
     }

avro/src/test/java/com/fasterxml/jackson/dataformat/avro/AvroTestBase.java

@@ -244,6 +244,7 @@ public Image(String uri, String title, int w, int h, Size s)
       public void setSize(Size s) { _size = s; }
     }
 
+    // public because needed by "AvroAliasTest"
     public enum Size { SMALL, LARGE; }
 
     /*

avro/src/test/java/com/fasterxml/jackson/dataformat/avro/EnumTest.java

@@ -1,7 +1,17 @@
 package com.fasterxml.jackson.dataformat.avro;
 
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
 import org.junit.jupiter.api.Test;
 
+import org.apache.avro.Schema;
+import org.apache.avro.Schema.Type;
+
+import com.fasterxml.jackson.annotation.JsonEnumDefaultValue;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.dataformat.avro.schema.AvroSchemaGenerator;
+
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 
@@ -35,6 +45,19 @@ protected static class EmployeeStr {
         public String gender;
     }
 
+    protected enum ABC {
+        A,
+        B,
+        @JsonEnumDefaultValue
+        C; 
+    }
+
+    protected static class ABCDefaultClass {
+        public String name;
+        @JsonProperty(required = true)
+        public ABC abc;
+    }
+
     private final AvroMapper MAPPER = newMapper();
 
     @Test
@@ -127,4 +150,35 @@ public void test_avroSchemaWithString_fromStringValueToEnumValue() throws Except
         assertEquals(Gender.F, output.gender);
     }
 
+    // [dataformats-binary#388]: Default value for enums with class
+    @Test
+    public void testClassEnumWithDefault() throws Exception
+    {
+        AvroSchemaGenerator gen = new AvroSchemaGenerator();
+
+        MAPPER.acceptJsonFormatVisitor(ABCDefaultClass.class, gen);
+        AvroSchema schema = gen.getGeneratedSchema();
+        assertNotNull(schema);
+
+        String json = schema.getAvroSchema().toString(true);
+        assertNotNull(json);
+
+        // And read it back too just for fun
+        AvroSchema s2 = MAPPER.schemaFrom(json);
+        assertNotNull(s2);
+
+        Schema avroSchema = s2.getAvroSchema();
+
+        // String name, int value
+        assertEquals(Type.RECORD, avroSchema.getType());
+        Schema.Field f = avroSchema.getField("abc");
+        assertNotNull(f);
+        assertEquals("abc", f.name());
+
+        assertEquals(Type.ENUM, f.schema().getType());
+        assertEquals(ABC.C.toString(), f.schema().getEnumDefault());
+        assertEquals(Stream.of(ABC.values())
+                               .map(ABC::name)
+                               .collect(Collectors.toList()), f.schema().getEnumSymbols());
+    }   
 }