How can I integrate wallet.dat from an old wallet(java) into a new one?
There is only the import of the private key which I do not know.
Same process as other full node wallets. You can either drop your wallet.dat into a fresh full node install (place wallet.dat into the Zelcash data directory) or you can use the web wallet at my.zel.cash and import your wallet.dat to transfer funds to a new lightweight address.