How to output binary data to a file in Java?

Question

I'm trying to write data to a file in binary format for compression. The data consists entirely of floating points so I decided to quantize the data to an intergers between 0 and 65535 so the data can be written as two bit unsigned integers and ultimately save space. However, I need to output that quantized data to a file in binary instead of human-readable Ascii.

At the moment this is what I'm doing

@param outputFile the file containing the already quantized data as strings in a .txt file

public void generateBinaryRioFile(String materialLibrary,
        String outputFile, String group, String mtlAux) {

    try {

        // Create file
        FileWriter fileStream = new FileWriter(outputFile);
        try {

            BufferedReader br = new BufferedReader(new FileReader(new File(
                    "idx.txt")));

            while ((line = br.readLine()) != null) {
                writer.write(line + "\n");
            }
            try {
                br.close();

            } catch (FileNotFoundException e) {
                e.getMessage();
            } catch (IOException e) {
                e.printStackTrace();
            }           BufferedWriter writer = new BufferedWriter(fileStream);

However that writes to the file as a human readable string. I need it to be written as binary data. How does one go about doing this in Java?

Show some code that what have you done so far so I can help you on it — Talha Ahmed Khan, Aug 08 '11 at 11:43
@ Kit Ho I was told by my boss the motivation behind it is to save file space so instead of writing multiple ascii characters to a file which increases the filesize, it can be written in binary to save space. The file will be sent over the internet and the data used to generate a 3d model in webgl. We want the model to load as fast as possible — Zeeno, Aug 08 '11 at 11:48
I guess you got your answers please tell me if that is not you want — Talha Ahmed Khan, Aug 08 '11 at 11:59
Please make sure of one thing You are using `FileWriter` which will write the TEXT, You have to use `DataOutputStream` and `FileOutputStream` instead. They will write binary date. — Talha Ahmed Khan, Aug 08 '11 at 12:04

score 39 · Accepted Answer · edited Aug 08 '11 at 11:58

39

Maybe this fragment will help.

 int i = 42;
 DataOutputStream os = new DataOutputStream(new FileOutputStream("C:\\binout.dat"));
 os.writeInt(i);
 os.close();

edited Aug 08 '11 at 11:58

Talha Ahmed Khan

15,043
10
42
49

answered Aug 08 '11 at 11:47

rajah9

11,645
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4

if you only want to write 2 byte use `writeShort()` – ratchet freak Aug 08 '11 at 12:01
3

@Ratchet freak The Java short ranges from -32,768 to 32,767 (according to http://download.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html). If the OP uses Java short (which is a great idea, thank you) he should subtract 32,768 before writing and add 32,768 after reading. – rajah9 Aug 08 '11 at 13:13
@rajah9 thanks! Such great ideas! This will reduce a decent amount of filesize. Thanks guys, I appreciate all the help :-) – Zeeno Aug 08 '11 at 14:46
2

Thumbs up for the number 42 :) – Dexter Apr 25 '16 at 10:50

oliholz · Answer 2 · 2011-08-08T12:01:34.493

What about the DataOutputStream. You can write int which contains 2 of your data integers.

DataOutputStream dos = new DataOutputStream(new FileOutputStream(<path>));
ArrayList<Integer> list = new ArrayList<Integer>();
int sum;
for( int i = 0; i < list.size(); i++ ) {
    if(i%2!=0){
        sum |= list.get( i ).intValue()<<16;
        dos.writeInt( sum );
    } else {
        sum = list.get( i ).intValue();
    }
}

How to output binary data to a file in Java?

2 Answers2

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