问密码的doFinal()不写入字节

EN

import static java.nio.file.StandardOpenOption.READ;
import static java.nio.file.StandardOpenOption.TRUNCATE_EXISTING;
import static java.nio.file.StandardOpenOption.WRITE;

import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.security.MessageDigest;
import java.security.SecureRandom;
import javax.crypto.Cipher;
import javax.crypto.ShortBufferException;
import javax.crypto.spec.GCMParameterSpec;
import javax.crypto.spec.SecretKeySpec;

public class Test {

    public static void main(String[] args) throws Exception {
        encrypt();
        decrypt();
    }

    void encrypt() throws Exception {
        Path file = Paths.get("path/to/file");
        Path backupFile = file.getParent().resolve(file.getFileName().toString() + ".bak");
        Files.deleteIfExists(backupFile);
        Files.copy(file, backupFile);

        SecureRandom secureRandom = new SecureRandom();
        byte[] initializeVector = new byte[96 / Byte.SIZE];
        secureRandom.nextBytes(initializeVector);

        Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
        GCMParameterSpec p = new GCMParameterSpec(128, initializeVector);

        try (FileChannel src = FileChannel.open(backupFile, READ);
             FileChannel dest = FileChannel.open(file, WRITE, TRUNCATE_EXISTING)) {

            SecretKeySpec secretKeySpec =
                new SecretKeySpec(MessageDigest.getInstance("MD5").digest(new byte[]{0x00}), "AES");

            cipher.init(Cipher.ENCRYPT_MODE, secretKeySpec, p);

            ByteBuffer ivBuffer = ByteBuffer.allocate(Integer.BYTES + cipher.getIV().length);
            ivBuffer.putInt(cipher.getIV().length);
            ivBuffer.put(cipher.getIV());
            ivBuffer.flip();
            dest.write(ivBuffer);

            ByteBuffer readBuf = ByteBuffer.allocateDirect(8192);
            ByteBuffer writeBuf = ByteBuffer.allocateDirect(cipher.getOutputSize(8192));
            while (src.read(readBuf) >= 0) {
                if (cipher.getOutputSize(8192) > writeBuf.capacity()) {
                    writeBuf = ByteBuffer.allocateDirect(cipher.getOutputSize(8192));
                }
                readBuf.flip();

                cipher.update(readBuf, writeBuf);
                writeBuf.flip();
                dest.write(writeBuf);

                readBuf.clear();
                writeBuf.clear();
            }

            if (cipher.getOutputSize(0) > writeBuf.capacity()) {
                writeBuf = ByteBuffer.allocateDirect(cipher.getOutputSize(0));
            }

            cipher.doFinal(ByteBuffer.allocate(0), writeBuf);

            writeBuf.flip();
            dest.write(writeBuf);

            Files.delete(backupFile);
        } catch (ShortBufferException e) {
            //Should not happen!
            throw new RuntimeException(e);
        }
    }

    void decrypt() throws Exception {
        Path file = Paths.get("path/to/file");
        Path backupFile = file.getParent().resolve(file.getFileName().toString() + ".bak");
        Files.deleteIfExists(backupFile);
        Files.copy(file, backupFile);

        try (FileChannel src = FileChannel.open(backupFile, READ);
             FileChannel dest = FileChannel.open(file, WRITE, TRUNCATE_EXISTING)) {

            ByteBuffer ivLengthBuffer = ByteBuffer.allocate(Integer.BYTES);
            src.read(ivLengthBuffer);
            ivLengthBuffer.flip();
            int ivLength = ivLengthBuffer.getInt();

            ByteBuffer ivBuffer = ByteBuffer.allocate(ivLength);
            src.read(ivBuffer);
            ivBuffer.flip();
            byte[] iv = new byte[ivBuffer.limit()];
            ivBuffer.get(iv);

            Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
            GCMParameterSpec p = new GCMParameterSpec(128, iv);

            SecretKeySpec secretKeySpec =
                new SecretKeySpec(MessageDigest.getInstance("MD5").digest(new byte[]{0x00}), "AES");

            cipher.init(Cipher.DECRYPT_MODE, secretKeySpec, p);

            ByteBuffer readBuf = ByteBuffer.allocateDirect(8192);
            ByteBuffer writeBuf = ByteBuffer.allocateDirect(cipher.getOutputSize(8192));
            while (src.read(readBuf) >= 0) {
                if (cipher.getOutputSize(8192) > writeBuf.capacity()) {
                    writeBuf = ByteBuffer.allocateDirect(cipher.getOutputSize(8192));
                }
                readBuf.flip();
                cipher.update(readBuf, writeBuf);

                writeBuf.flip();
                dest.write(writeBuf);

                readBuf.clear();
                writeBuf.clear();
            }

            if (cipher.getOutputSize(0) > writeBuf.capacity()) {
                writeBuf = ByteBuffer.allocateDirect(cipher.getOutputSize(0));
            }
            cipher.doFinal(ByteBuffer.allocate(0), writeBuf);
            writeBuf.flip();
            dest.write(writeBuf);

            Files.deleteIfExists(backupFile);
        }
    }

}