reuse ModelMapper instance

Author: Vladimir Kotal

opengrok-web/src/main/java/org/opengrok/web/api/v1/controller/RepositoriesController.java

@@ -25,7 +25,7 @@
 import org.opengrok.indexer.configuration.RuntimeEnvironment;
 import org.opengrok.indexer.history.RepositoryInfo;
 import org.opengrok.indexer.util.ClassUtil;
-import org.opengrok.web.util.DTO;
+import org.opengrok.web.util.DTOUtil;
 
 import javax.ws.rs.GET;
 import javax.ws.rs.Path;
@@ -45,7 +45,7 @@ public class RepositoriesController {
     private Object getRepositoryInfoData(String repositoryPath) {
         for (RepositoryInfo ri : env.getRepositories()) {
             if (ri.getDirectoryNameRelative().equals(repositoryPath)) {
-                return DTO.createDTO(ri);
+                return DTOUtil.createDTO(ri);
             }
         }
 

opengrok-web/src/main/java/org/opengrok/web/util/DTO.java renamed to opengrok-web/src/main/java/org/opengrok/web/util/DTOUtil.java

@@ -28,11 +28,15 @@
 
 import java.lang.reflect.Field;
 
-public class DTO {
-    private DTO() {
+public class DTOUtil {
+    private DTOUtil() {
         // private to ensure static
     }
 
+    // ModelMapper is thread-safe and we only need to convert different object types for now
+    // so it should be safe to reuse its instance.
+    private static final ModelMapper modelMapper = new ModelMapper();
+
     /**
      * Generate Data Transfer Object from an object. Any field in the input object
      * that is annotated with <code>DTOElement</code> will be brought along.
@@ -49,7 +53,6 @@ public static Object createDTO(Object object) {
         }
         Object bean = beanGenerator.create();
 
-        ModelMapper modelMapper = new ModelMapper();
         return modelMapper.map(object, bean.getClass());
     }
 }