support java.time.Instant serialization with gson

CHANGES.md

@@ -25,6 +25,7 @@ Apollo 2.4.0
 * [Feature: Add rate limiting function to ConsumerToken](https://github.com/apolloconfig/apollo/pull/5267)
 * [Feature: add JSON formatting function in apollo-portal](https://github.com/apolloconfig/apollo/pull/5287)
 * [Fix: add missing url patterns for AdminServiceAuthenticationFilter](https://github.com/apolloconfig/apollo/pull/5291)
+* [Fix: support java.time.Instant serialization with gson](https://github.com/apolloconfig/apollo/pull/5298)
 
 ------------------
 All issues and pull requests are [here](https://github.com/apolloconfig/apollo/milestone/15?closed=1)

apollo-common/src/main/java/com/ctrip/framework/apollo/common/controller/HttpMessageConverterConfiguration.java

@@ -19,6 +19,11 @@
 import com.google.common.collect.Lists;
 import com.google.gson.GsonBuilder;
 
+import com.google.gson.JsonDeserializer;
+import com.google.gson.JsonNull;
+import com.google.gson.JsonPrimitive;
+import com.google.gson.JsonSerializer;
+import java.time.Instant;
 import org.springframework.boot.autoconfigure.http.HttpMessageConverters;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
@@ -37,9 +42,23 @@
 public class HttpMessageConverterConfiguration {
   @Bean
   public HttpMessageConverters messageConverters() {
+    // Custom Gson TypeAdapter for Instant
+    JsonSerializer<Instant> instantJsonSerializer = (src, typeOfSrc, context) ->
+        src == null ? JsonNull.INSTANCE : new JsonPrimitive(src.toString()); // Serialize Instant as ISO-8601 string
+
+    JsonDeserializer<Instant> instantJsonDeserializer = (json, typeOfT, context) -> {
+      if (json == null || json.isJsonNull()) {
+        return null;
+      }
+      return Instant.parse(json.getAsString()); // Deserialize from ISO-8601 string
+    };
+
     GsonHttpMessageConverter gsonHttpMessageConverter = new GsonHttpMessageConverter();
     gsonHttpMessageConverter.setGson(
-            new GsonBuilder().setDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSZ").create());
+            new GsonBuilder().setDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSZ")
+                .registerTypeAdapter(Instant.class, instantJsonSerializer)
+                .registerTypeAdapter(Instant.class, instantJsonDeserializer)
+                .create());
     final List<HttpMessageConverter<?>> converters = Lists.newArrayList(
             new ByteArrayHttpMessageConverter(), new StringHttpMessageConverter(),
             new AllEncompassingFormHttpMessageConverter(), gsonHttpMessageConverter);