byte getting read wrong from file?

Question

So, I am trying to store 3 longs to a file, but it will a lot of data so I convert them to byte arrays and save them. My current method for saving them:

try (FileOutputStream output = new FileOutputStream(path, true)) {
                    //Put the data into my format
                    byte[] data = new byte[24];
                    main.getLogger().log(Level.INFO, "Saving most sig bits");
                    System.arraycopy(ByteUtils.longToBytes(uuid.getMostSignificantBits()), 0, data, 0, 8);
                    System.arraycopy(ByteUtils.longToBytes(uuid.getLeastSignificantBits()), 0, data, 8, 8);
                    System.arraycopy(ByteUtils.longToBytes(player.getTokens()), 0, data, 16, 8);
                    //Write data in the format
                    output.write(data);
                }

longToBytes method:

private static ByteBuffer buffer = ByteBuffer.allocate(8);

public static byte[] longToBytes(long x) {
    System.out.println(x);
    buffer.putLong(0, x);
    return buffer.array();
}

The byte array gets saved to the file, but the first byte gets truncated. the print statement in longToByes prints 8 three times.

The original longs are:

-9089798603852198353, -5339652910133477779, 5992

If I print the byte array I get:

-127, -38, -116, 84, 97, -116, 78, 47, -75, -27, -67, -8, 11, -100, -2, 109, 0, 0, 0, 0, 0, 0, 23, 104 (24 bytes)

But in the file I see: ÚŒTaŒN/µå½ø(VT symbol)œþm(nul)(nul)(nul)(nul)(nul)(nul)(etb)h which is 23 bytes (the first box doesn't show in notepad++)

but if I read it using

bytes = IOUtils.toByteArray(new FileReader(file));

I see:

64, -38, -116, 84, 97, -116, 78, 47, -75, -27, -67, -8, 11, -100, -2, 109, 0, 0, 0, 0, 0, 0, 23, 104 (24 bytes)

-127 is replaced with 64 somehow.

I concat the byte with "" to print it btw.

xiaofeng.li · Accepted Answer · 2019-05-17 01:46:20Z

5

Do not use FileReader to read raw bytes from file. Use FileInputStream instead.

The problem with FileReader is that it reads chars, not bytes, from the file, by trying to decode the bytes using some character encoding (the default one if none was given).

bytes = IOUtils.toByteArray(new FileInputStream(file));

Alternatively you can use DataOutputStream to write long directly to an output stream and use DataInputStream to read from an input stream.

try (DataOutputStream out = new DataOutputStream(new FileOutputStream(file))) {
    out.writeLong(uuid.getMostSignificantBits());
    out.writeLong(uuid.getLeastSignificantBits());
    out.writeLong(player.getTokens());
}

try (DataInputStream in = new DataInputStream(new FileInputStream(file))) {
    long uuidMSB = in.readLong();
    long uuidLSB = in.readLong();
    long tokens = in.readLong();
}

edited May 17, 2019 at 1:46

answered May 17, 2019 at 1:30

xiaofeng.li

8,6372 gold badges26 silver badges31 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Big_Bad_E Over a year ago

I totally forgot that this causes a problem, thanks!

Jochen Reinhardt Over a year ago

If you are going to write lot's of data, you should add a buffer to your streams to increase performance, e.g. DataOutputStream out = new DataOutputStream(new BufferedOutputStream(new FileOutputStream(file))) and DataInputStream in = new DataInputStream(new BufferedInputStream(new FileInputStream(file))) respectively. Then you do not need to handle a buffer like your data array in your code manually.

Big_Bad_E Over a year ago

The data is going to be written over time, like 150 longs at once, about 1-10 times an hour, is refactoring my code a ton worth the performance?

Big_Bad_E Over a year ago

Nevermind, I need to append in the middle of a file, so a DataOutputStream is off the table I think.

Collectives™ on Stack Overflow

byte getting read wrong from file?

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related