PR ebean-orm#3149 - FIX: TypeManager initialization fails, if Jackson is not on class path

Author: rPraml

ebean-core/src/main/java/io/ebeaninternal/server/type/DefaultTypeManager.java

@@ -97,8 +97,7 @@ public DefaultTypeManager(DatabaseConfig config, BootupClasses bootupClasses) {
     this.offlineMigrationGeneration = DbOffline.isGenerateMigration();
     this.defaultEnumType = config.getDefaultEnumType();
 
-    ServiceLoader<ScalarJsonMapper> mappers = ServiceLoader.load(ScalarJsonMapper.class);
-    jsonMapper = mappers.findFirst().orElse(null);
+    jsonMapper = findJsonMapper();
 
     initialiseStandard(config);
     initialiseJavaTimeTypes(config);
@@ -112,6 +111,28 @@ public DefaultTypeManager(DatabaseConfig config, BootupClasses bootupClasses) {
     }
   }
 
+  /**
+   * Searches the JsonMapper and checks if markerAnnotation is on class path.
+   */
+  private static ScalarJsonMapper findJsonMapper() {
+    ServiceLoader<ScalarJsonMapper> mappers = ServiceLoader.load(ScalarJsonMapper.class);
+    ScalarJsonMapper mapper = mappers.findFirst().orElse(null);
+    if (mapper != null) {
+      try {
+        if (mapper.markerAnnotation() != null) {
+          return mapper;
+        } else {
+          log.log(System.Logger.Level.WARNING, "Not using {0}, because no marker annotation was provided. " +
+            "Please check, if there is a supported json library (e.g. jackson) on your classpath", mapper.getClass().getName());
+        }
+      } catch (NoClassDefFoundError e) {
+        log.log(System.Logger.Level.WARNING, "Can not use {0}. An error occured: {1}. " +
+          "Please check, if there is a supported json library (e.g. jackson) on your classpath", mapper.getClass().getName(), e.getMessage());
+      }
+    }
+    return null;
+  }
+
   private void loadGeoTypeBinder(DatabaseConfig config) {
     GeoTypeProvider provider = config.getServiceObject(GeoTypeProvider.class);
     if (provider == null) {