Public Key derivation from address for ed25519 and secp256k1

gistfile1.java

//For ed25519 (Solana):
import org.bitcoinj.core.Base58;

String solAddress = "5Fh..."; // base58
byte[] ed25519PubKey = Base58.decode(solAddress); // 32 bytes

//For secp256k1 (EVM):
import org.web3j.crypto.Sign;
import org.web3j.crypto.Keys;
import org.web3j.utils.Numeric;
import java.math.BigInteger;

String message = "get-pubkey";
// signature is 65-byte hex from personal_sign (0x...): r(32) + s(32) + v(1)
String sigHex = "0x...";
byte[] sig = Numeric.hexStringToByteArray(sigHex);
byte v = sig[64];
if (v < 27) v += 27;

byte[] r = java.util.Arrays.copyOfRange(sig, 0, 32);
byte[] s = java.util.Arrays.copyOfRange(sig, 32, 64);
Sign.SignatureData sd = new Sign.SignatureData(v, r, s);

// Ethereum Signed Message hash
byte[] msgHash = Sign.getEthereumMessageHash(message.getBytes(java.nio.charset.StandardCharsets.UTF_8));

BigInteger pubKeyBI = Sign.signedPrefixedMessageToKey(message.getBytes(java.nio.charset.StandardCharsets.UTF_8), sd);
// Or: BigInteger pubKeyBI = Sign.signedMessageToKey(msgHash, sd);

String uncompressedPubKeyHex = "0x" + Keys.getPublicKey(pubKeyBI); // 64-byte hex (no 0x04)
// If you need 65-byte uncompressed (0x04 + X + Y):
String uncompressed65 = "0x04" + Keys.getPublicKey(pubKeyBI);