code: public EntityManager createEntityManager(String projectId, File jsonCredentialsFile,
        String namespace) {
      try {
        return createEntityManager(projectId, new FileInputStream(jsonCredentialsFile), namespace);
      } catch (Exception exp) {
        throw new EntityManagerFactoryException(exp);
      }
    }
docs: Creates and return a new {@link EntityManager} using the provided JSON formatted credentials.
  
  @param projectId
  the project ID
  
  @param jsonCredentialsFile
  the JSON formatted credentials file for the target Cloud project.
  @param namespace
  the namespace (for multi-tenant datastore) to use. If <code>null</code>, default
  namespace is used.
  @return a new {@link EntityManager}