How to read a bin file to a byte array?

Question

I have a bin file that I need to convert to a byte array. Can anyone tell me how to do this?

Here is what I have so far:

File f = new File("notification.bin");
is = new FileInputStream(f);

long length = f.length();

/*if (length > Integer.MAX_VALUE) {
    // File is too large
}*/

// Create the byte array to hold the data
byte[] bytes = new byte[(int)length];

// Read in the bytes
int offset = 0;
int numRead = 0;
while (offset < bytes.length && (numRead=is.read(bytes, offset, bytes.length-offset)) >= 0) {
    offset += numRead;
}

// Ensure all the bytes have been read in
if (offset < bytes.length) {
    throw new IOException("Could not completely read file "+f.getName());
}

But it's not working...

Kaddy

I fixed that for you. Please try to actually format questions you post so they are intelligent and legible. — i_am_jorf, Oct 02 '09 at 20:15
In what way is it not working? What is the File class you are using? Why not use the standard std::ifstream? — Clifford, Oct 02 '09 at 20:15
It certainly looks a heck of a lot more like Java than C#, anyway. I've edited the tags accordingly. — Jon Skeet, Oct 02 '09 at 20:23
It was tagged C++, but that seems to have been removed. I give up! — Clifford, Oct 02 '09 at 20:27
Yeah, and it was tagged C# when I commented. Oh well, my bad! :) — Sterno, Oct 02 '09 at 21:00

score 2 · Accepted Answer · answered Oct 02 '09 at 20:20

2

try using this

public byte[] readFromStream(InputStream inputStream) throws Exception
{
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    DataOutputStream dos = new DataOutputStream(baos);
    byte[] data = new byte[4096];
    int count = inputStream.read(data);
    while(count != -1)
    {
        dos.write(data, 0, count);
        count = inputStream.read(data);
    }

    return baos.toByteArray();
}

Btw, do you want a Java code or C++ code. Seeing the code in your question, I assumed it to be a java code and hence gave a java answer to it

answered Oct 02 '09 at 20:20

Prabhu R

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2

What's that `DataOutputStream` about? – Tom Hawtin - tackline Oct 02 '09 at 20:35
+1 That's a nice catch Tom, ByteArrayOutputStream would suffice in this case, where we just read bytes and write bytes. If we were to write primitive types in addition DataOutputStream might be needed – Prabhu R Oct 03 '09 at 06:13

score 1 · Answer 2 · edited May 23 '17 at 12:23

1

You're probably better off using a memory mapped file. See this question

edited May 23 '17 at 12:23

Community

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answered Oct 02 '09 at 20:17

Jherico

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score 0 · Answer 3 · answered Oct 02 '09 at 20:25

Unless you really need to do it just that way, maybe simplify what you're doing.

Doing everything in the for loop may seem like a very slick way of doing it, but it's shooting yourself in the foot when you need to debug and don't immediately see the solution.

Stephen C · Answer 4 · 2009-10-02T23:13:57.623

In Java, a simple solution is:

InputStream is = ...
ByteArrayOutputStream os = new ByteArrayOutputStream();
byte[] data = new byte[4096];  // A larger buffer size would probably help
int count; 
while ((count = is.read(data)) != -1) {
    os.write(data, 0, count);
}
byte[] result = os.toByteArray();

If the input is a file, we can preallocate a byte array of the right size:

File f = ...
long fileSize = f.length();
if (fileSize > Integer.MAX_VALUE) {
    // file too big
}
InputStream is = new FileInputStream(f);
byte[] data = new byte[fileSize];
if (is.read(data)) != data.length) {
    // file truncated while we were reading it???
}

However, there is probably a more efficient way to do this task using NIO.

score 0 · Answer 5 · edited May 23 '17 at 10:28

In this answer I read from an URL

You could modify it so the InputStream is from a File instead of a URLConnection.

Something like:

    FileInputStream inputStream = new FileInputStream("your.binary.file");

    ByteArrayOutputStream output = new ByteArrayOutputStream();
    byte [] buffer               = new byte[ 1024 ];

    int n = 0;
    while (-1 != (n = inputStream.read(buffer))) {
       output.write(buffer, 0, n);
    }
    inputStream.close();

etc

score 0 · Answer 6 · answered Oct 02 '09 at 23:17

0

Try open source library apache commons-io IOUtils.toByteArray(inputStream) You are not the first and not the last developer who needs to read a file, no need to reinvent it each time.

answered Oct 02 '09 at 23:17

Pavel Feldman

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How to read a bin file to a byte array?

6 Answers6