implement null example serialization

Author: frantuma

modules/swagger-core/src/main/java/io/swagger/v3/core/jackson/MediaTypeSerializer.java

@@ -0,0 +1,43 @@
+package io.swagger.v3.core.jackson;
+
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.databind.JsonMappingException;
+import com.fasterxml.jackson.databind.JsonSerializer;
+import com.fasterxml.jackson.databind.SerializerProvider;
+import com.fasterxml.jackson.databind.ser.ResolvableSerializer;
+import io.swagger.v3.oas.models.media.MediaType;
+
+import java.io.IOException;
+
+public class MediaTypeSerializer extends JsonSerializer<MediaType> implements ResolvableSerializer {
+
+    private JsonSerializer<Object> defaultSerializer;
+
+    public MediaTypeSerializer(JsonSerializer<Object> serializer) {
+        defaultSerializer = serializer;
+    }
+
+    @Override
+    public void resolve(SerializerProvider serializerProvider) throws JsonMappingException {
+        if (defaultSerializer instanceof ResolvableSerializer) {
+            ((ResolvableSerializer) defaultSerializer).resolve(serializerProvider);
+        }
+    }
+
+    @Override
+    public void serialize(
+            MediaType value, JsonGenerator jgen, SerializerProvider provider)
+            throws IOException {
+
+        if (value.getExampleSetFlag() && value.getExample() == null) {
+            jgen.writeStartObject();
+            defaultSerializer.unwrappingSerializer(null).serialize(value, jgen, provider);
+            jgen.writeNullField("example");
+            jgen.writeEndObject();
+        } else {
+            defaultSerializer.serialize(value, jgen, provider);
+        }
+    }
+}
+
+

modules/swagger-core/src/main/java/io/swagger/v3/core/jackson/ModelResolver.java

@@ -1372,7 +1372,6 @@ private boolean resolveSubtypes(Schema model, BeanDescription bean, ModelConvert
                         .additionalProperties(subtypeModel.getAdditionalProperties())
                         .description(subtypeModel.getDescription())
                         .discriminator(subtypeModel.getDiscriminator())
-                        .example(subtypeModel.getExample())
                         .exclusiveMaximum(subtypeModel.getExclusiveMaximum())
                         .exclusiveMinimum(subtypeModel.getExclusiveMinimum())
                         .externalDocs(subtypeModel.getExternalDocs())
@@ -1398,6 +1397,9 @@ private boolean resolveSubtypes(Schema model, BeanDescription bean, ModelConvert
                         .xml(subtypeModel.getXml())
                         .extensions(subtypeModel.getExtensions());
 
+                if (subtypeModel.getExample() != null || subtypeModel.getExampleSetFlag()) {
+                    composedSchema.example(subtypeModel.getExample());
+                }
                 composedSchema.setEnum(subtypeModel.getEnum());
             } else {
                 composedSchema = (ComposedSchema) subtypeModel;

modules/swagger-core/src/main/java/io/swagger/v3/core/jackson/SchemaSerializer.java

@@ -30,13 +30,22 @@ public void serialize(
             Schema value, JsonGenerator jgen, SerializerProvider provider)
             throws IOException {
 
-        // handle ref schema serialization skipping all other props
         if (StringUtils.isBlank(value.get$ref())) {
-            defaultSerializer.serialize(value, jgen, provider);
+
+            if (value.getExampleSetFlag() && value.getExample() == null) {
+                jgen.writeStartObject();
+                defaultSerializer.unwrappingSerializer(null).serialize(value, jgen, provider);
+                jgen.writeNullField("example");
+                jgen.writeEndObject();
+            } else {
+                defaultSerializer.serialize(value, jgen, provider);
+            }
+
         } else {
+            // handle ref schema serialization skipping all other props
             jgen.writeStartObject();
             jgen.writeStringField("$ref", value.get$ref());
             jgen.writeEndObject();
         }
     }
-}
+}

modules/swagger-core/src/main/java/io/swagger/v3/core/jackson/mixin/MediaTypeMixin.java

@@ -18,6 +18,6 @@ public abstract class MediaTypeMixin {
     @JsonIgnore
     public abstract boolean getExampleSetFlag();
 
-    @JsonInclude(JsonInclude.Include.CUSTOM)
+    @JsonInclude(value = JsonInclude.Include.NON_NULL, content = JsonInclude.Include.ALWAYS)
     public abstract Object getExample();
 }

modules/swagger-core/src/main/java/io/swagger/v3/core/jackson/mixin/SchemaMixin.java

@@ -7,11 +7,6 @@
 
 import java.util.Map;
 
-/*
- TODO: this handles deserialization, but not serialization of "explicit" null value (as we are serializing non null fields)
- to handle it, a custom schema serializer / JsonFilter / BeanSerializerModifier must be added, using non null for all fields except example where the flag would
- be checked to serialize or skip null example field.
- */
 public abstract class SchemaMixin {
 
     @JsonAnyGetter
@@ -23,6 +18,6 @@ public abstract class SchemaMixin {
     @JsonIgnore
     public abstract boolean getExampleSetFlag();
 
-    @JsonInclude(JsonInclude.Include.CUSTOM)
+    @JsonInclude(value = JsonInclude.Include.NON_NULL, content = JsonInclude.Include.ALWAYS)
     public abstract Object getExample();
 }

modules/swagger-core/src/main/java/io/swagger/v3/core/util/ObjectMapperFactory.java

@@ -14,6 +14,7 @@
 import com.fasterxml.jackson.dataformat.yaml.YAMLFactory;
 import com.fasterxml.jackson.dataformat.yaml.YAMLGenerator;
 import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
+import io.swagger.v3.core.jackson.MediaTypeSerializer;
 import io.swagger.v3.core.jackson.SchemaSerializer;
 import io.swagger.v3.core.jackson.mixin.ComponentsMixin;
 import io.swagger.v3.core.jackson.mixin.DateSchemaMixin;
@@ -89,6 +90,8 @@ public JsonSerializer<?> modifySerializer(
                             SerializationConfig config, BeanDescription desc, JsonSerializer<?> serializer) {
                         if (Schema.class.isAssignableFrom(desc.getBeanClass())) {
                             return new SchemaSerializer((JsonSerializer<Object>) serializer);
+                        } else if (MediaType.class.isAssignableFrom(desc.getBeanClass())) {
+                            return new MediaTypeSerializer((JsonSerializer<Object>) serializer);
                         }
                         return serializer;
                     }

modules/swagger-core/src/test/java/io/swagger/v3/core/serialization/JsonSerializationTest.java

@@ -1,6 +1,9 @@
 package io.swagger.v3.core.serialization;
 
+import io.swagger.v3.core.matchers.SerializationMatchers;
 import io.swagger.v3.core.util.Json;
+import io.swagger.v3.core.util.ResourceUtils;
+import io.swagger.v3.core.util.Yaml;
 import io.swagger.v3.oas.models.OpenAPI;
 import io.swagger.v3.oas.models.Operation;
 import io.swagger.v3.oas.models.PathItem;
@@ -67,4 +70,20 @@ public void testSerializeASpecWithResponseReferences() throws Exception {
         assertEquals(rebuilt.getPaths().get("/health").getGet().getResponses().get("200"), expectedResponse);
 
     }
+
+    @Test
+    public void testSerializeNullExample() throws Exception {
+        final String yaml = ResourceUtils.loadClassResource(getClass(), "specFiles/null-example.yaml");
+        OpenAPI deser = Yaml.mapper().readValue(yaml, OpenAPI.class);
+        SerializationMatchers.assertEqualsToYaml(deser, yaml);
+
+    }
+
+    @Test
+    public void testSerializeNullInSchemaExample() throws Exception {
+        final String yaml = ResourceUtils.loadClassResource(getClass(), "specFiles/null-in-schema-example.yaml");
+        OpenAPI deser = Yaml.mapper().readValue(yaml, OpenAPI.class);
+        SerializationMatchers.assertEqualsToYaml(deser, yaml);
+
+    }
 }