  We propose three independent methods to compute the hadron mass spectra of
gauge theories in the Hamiltonian formalism. The determination of hadron masses
is one of the key issues in QCD, which has been precisely calculated by the
Monte Carlo method in the Lagrangian formalism. We confirm that the mass of
hadrons can be calculated by examining correlation functions, the one-point
function, or the dispersion relation in Hamiltonian formalism. These methods
are suitable for quantum computation and tensor network approaches. The methods
are demonstrated with the tensor network (DMRG) in the 2-flavor Schwinger
model, which shares important properties with QCD. We show that the numerical
results are consistent with each other and with the analytic prediction of the
bosonization technique. We also discuss their efficiency and potential
applications to other models.
