I try to open the bitcoin-qt wallet with bitcoinj, I write this code:

private static final File WALLET_FILE = new File("C:\\Users\\Bapt\\AppData\\Roaming\\Bitcoin\\wallet.dat");

public static void main(String[] args) {
    NetworkParameters networkParameters = NetworkParameters.prodNet();

    Wallet wallet;
    try {
        wallet = Wallet.loadFromFile(WALLET_FILE);
    } catch (IOException e) {
        System.out.println("Couldn't open wallet: " + e);
        return;
    }

    System.out.println("Balance: " + wallet.getBalance());
}

But I have an error:

Couldn't open wallet: com.google.protobuf.InvalidProtocolBufferException: Protocol message contained an invalid tag (zero).

So I have two questions:

• Is is possible to do what I want ?
• If yes, what do you think could happen here ?

Thanks for your answer.