code: public EntityManager createEntityManager(String projectId, InputStream jsonCredentialsStream,
        String namespace) {
      ConnectionParameters parameters = new ConnectionParameters();
      parameters.setProjectId(projectId);
      parameters.setNamespace(namespace);
      parameters.setJsonCredentialsStream(jsonCredentialsStream);
      return createEntityManager(parameters);
    }
docs: Creates and return a new {@link EntityManager} using the provided JSON formatted credentials.
  
  @param projectId
  the project ID
  
  @param jsonCredentialsStream
  the JSON formatted credentials 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}