  Spacelike and timelike generalized parton distributions (GPDs) have been
investigated in charged-lepton scattering and electron-positron collisions via
deeply virtual Compton scattering and two-photon processes, respectively.
Furthermore, we expect that hadron-accelerator-facility measurements will be
performed in future. The GPDs will play a crucial role in clarifying the
origins of hadron spins and masses in terms of quarks and gluons. It is also
possible to probe internal pressure within hadrons for understanding their
stability. Gravitational form factors of hadrons used to be considered as a
purely academic subject because gravitational interactions are too weak to be
measured in microscopic systems. However, due to the development of
hadron-tomography field, it became possible to extract the gravitational form
factors from the actual GPD measurements without relying on direct
gravitational interactions. Neutrino reactions can also be used for GPD studies
in future, for example, by using the Long-Baseline Neutrino Facility at
Fermilab. The neutrino GPD measurements are valuable especially for finding the
flavor dependence of the GPDs in a complementary way to the charged-lepton
experiments. We give an overview of the GPDs and discuss possible neutrino GPD
measurements using the single-pion production processes $\nu + N \to \ell^- +
N' + \pi$ and $\bar\nu + N \to \ell^+ + N' + \pi$.
