added method to check user existence

CHANGELOG.md

@@ -11,6 +11,8 @@ method add and remove admin on a VREFolder enabled also for admin role
 
 fixed bug on unsharing folder on user removal 
 
+added method exist user
+
 ## [v1.2.2] - [2020-06-20]
 
 method for description update added

src/main/java/org/gcube/data/access/storagehub/services/GroupManager.java

@@ -380,6 +380,9 @@ public class GroupManager {
 			Group group = (Group)usrManager.getAuthorizable(groupId);
 			User user = (User)usrManager.getAuthorizable(userId);
 
+			if (user==null)
+				throw new InvalidCallParameters("user "+userId+" not exists"); 
+			
 			if (group.isMember(user))
 				throw new InvalidCallParameters("user "+userId+" is already member of group "+groupId);
 

src/main/java/org/gcube/data/access/storagehub/services/UserManager.java

@@ -32,10 +32,11 @@ import org.apache.jackrabbit.api.security.user.QueryBuilder;
 import org.apache.jackrabbit.api.security.user.User;
 import org.apache.jackrabbit.core.security.principal.PrincipalImpl;
 import org.gcube.common.authorization.control.annotations.AuthorizationControl;
+import org.gcube.common.gxrest.response.outbound.ErrorCode;
 import org.gcube.common.gxrest.response.outbound.GXOutboundErrorResponse;
 import org.gcube.common.storagehub.model.Excludes;
 import org.gcube.common.storagehub.model.exceptions.BackendGenericError;
-import org.gcube.common.storagehub.model.exceptions.InvalidCallParameters;
+import org.gcube.common.storagehub.model.exceptions.IdNotFoundException;
 import org.gcube.common.storagehub.model.exceptions.StorageHubException;
 import org.gcube.common.storagehub.model.items.Item;
 import org.gcube.common.storagehub.model.types.NodeProperty;
@@ -104,6 +105,37 @@ public class UserManager {
 		return users;
 	}
 
+	@GET
+	@Path("{user}")
+	public String getUser(@PathParam("user") String user){
+		
+		InnerMethodName.instance.set("getUser");
+		
+		JackrabbitSession session = null;
+		try {
+			session = (JackrabbitSession) repository.getRepository().login(CredentialHandler.getAdminCredentials(context));
+
+			org.apache.jackrabbit.api.security.user.UserManager usrManager = session.getUserManager();
+			Authorizable authorizable = usrManager.getAuthorizable(user);
+			
+			if (authorizable != null && !authorizable.isGroup())
+				return authorizable.getPrincipal().getName();
+			
+			log.debug("user {} not found", user);
+			
+		}catch(Exception e) {
+			log.error("jcr error getting user", e);
+			GXOutboundErrorResponse.throwException(new BackendGenericError(e));
+		} finally {
+			if (session!=null)
+				session.logout();
+		}
+		
+		GXOutboundErrorResponse.throwException(new IdNotFoundException(user));
+		
+		return null;
+	}
+	
 	@POST
 	@Path("")
 	@Consumes(MediaType.APPLICATION_FORM_URLENCODED)