Fix metric export

Author: trask

core/src/main/java/com/microsoft/applicationinsights/TelemetryClient.java

@@ -40,6 +40,7 @@
 import com.microsoft.applicationinsights.internal.config.connection.EndpointProvider;
 import com.microsoft.applicationinsights.internal.config.connection.InvalidConnectionStringException;
 import com.microsoft.applicationinsights.internal.quickpulse.QuickPulseDataCollector;
+import com.microsoft.applicationinsights.internal.util.CollectionTypeJsonSerializer;
 import com.microsoft.applicationinsights.internal.util.PropertyHelper;
 import org.apache.commons.text.StringSubstitutor;
 import org.checkerframework.checker.nullness.qual.Nullable;
@@ -445,7 +446,7 @@ private JacksonJsonAdapter() {
 
             // Customize serializer to use NDJSON
             SimpleModule ndjsonModule = new SimpleModule("Ndjson List Serializer");
-            ndjsonModule.addSerializer(new NdJsonSerializer());
+            ndjsonModule.setSerializers(new CollectionTypeJsonSerializer());
             mapper.registerModule(ndjsonModule);
         }
 

core/src/main/java/com/microsoft/applicationinsights/internal/util/CollectionTypeJsonSerializer.java

@@ -0,0 +1,39 @@
+package com.microsoft.applicationinsights.internal.util;
+
+import com.azure.monitor.opentelemetry.exporter.implementation.NdJsonSerializer;
+import com.fasterxml.jackson.databind.BeanDescription;
+import com.fasterxml.jackson.databind.JavaType;
+import com.fasterxml.jackson.databind.JsonSerializer;
+import com.fasterxml.jackson.databind.SerializationConfig;
+import com.fasterxml.jackson.databind.jsontype.TypeSerializer;
+import com.fasterxml.jackson.databind.module.SimpleSerializers;
+import com.fasterxml.jackson.databind.type.CollectionType;
+import java.util.List;
+
+public class CollectionTypeJsonSerializer extends SimpleSerializers {
+
+    @Override
+    public JsonSerializer<?> findCollectionSerializer(SerializationConfig config,
+                                                      CollectionType type,
+                                                      BeanDescription beanDesc,
+                                                      TypeSerializer elementTypeSerializer,
+                                                      JsonSerializer<Object> elementValueSerializer) {
+
+        if (isJavaLangObjectListType(type)) {
+            return new NdJsonSerializer();
+        }
+        return super.findCollectionSerializer(config, type, beanDesc, elementTypeSerializer, elementValueSerializer);
+    }
+
+
+    private boolean isJavaLangObjectListType(CollectionType type) {
+        JavaType contentType = type.getContentType();
+        if (List.class.isAssignableFrom(type.getRawClass())) {
+            // this means it's a list
+            if(contentType.isJavaLangObject()) {
+                return true;
+            }
+        }
+        return false;
+    }
+}