signatures.java

progressTracker.setCurrentStep(SIGS_GATHERING);

// The list of parties who need to sign a transaction is dictated
// by the transaction's commands. Once we've signed a transaction
// ourselves, we can automatically gather the signatures of the
// other required signers using ``CollectSignaturesFlow``.
// The responder flow will need to call ``SignTransactionFlow``.
SignedTransaction fullySignedTx = subFlow(new CollectSignaturesFlow(twiceSignedTx, emptySet(), SIGS_GATHERING.childProgressTracker()));

progressTracker.setCurrentStep(VERIFYING_SIGS);

try {

    // We can verify that a transaction has all the required
    // signatures, and that they're all valid, by running:
    fullySignedTx.verifyRequiredSignatures();

    // If the transaction is only partially signed, we have to pass in
    // a vararg of the public keys corresponding to the missing
    // signatures, explicitly telling the system not to check them.
    onceSignedTx.verifySignaturesExcept(counterpartyPubKey);

    // There is also an overload of ``verifySignaturesExcept`` which accepts
    // a ``Collection`` of the public keys corresponding to the missing
    // signatures. In the example below, we could also use
    // ``Arrays.asList(counterpartyPubKey)`` instead of
    // ``Collections.singletonList(counterpartyPubKey)``.
    onceSignedTx.verifySignaturesExcept(singletonList(counterpartyPubKey));

    // We can also choose to only check the signatures that are
    // present. BE VERY CAREFUL - this function provides no guarantees
    // that the signatures are correct, or that none are missing.
    twiceSignedTx.checkSignaturesAreValid();

} catch (GeneralSecurityException e) {
    // Handle this as required.
}