File truncate operation in Java

Question

What is the best-practice way to truncate a file in Java? For example this dummy function, just as an example to clarify the intent:

void readAndTruncate(Fil         


        

Answer 1

Use Apache Commons IO API:

    org.apache.commons.io.FileUtils.write(new File(...), "", Charset.defaultCharset());

Answer 2

It depends on how you're going to write to the file, but the simplest way is to open a new FileOutputStream without specifying that you plan to append to the file (note: the base FileOuptutStream constructor will truncate the file, but if you want to make it clear that the file's being truncated, I recommend using the two-parameter variant).

Answer 3

One liner using Files.write()...

Files.write(outFile, new byte[0], StandardOpenOption.TRUNCATE_EXISTING);

Can use File.toPath() to convert from File to Path prior as well.

Also allows other StandardOpenOptions.

Answer 4

Use FileChannel.truncate:

try (FileChannel outChan = new FileOutputStream(f, true).getChannel()) {
  outChan.truncate(newSize);
}

Answer 5

RandomAccessFile.setLength() seems to be exactly what's prescribed in this case.

Answer 6

Use RandomAccessFile#read and push the bytes recorded in this way into a new File object.

RandomAccessFile raf = new RandomAccessFile(myFile,myMode);  
byte[] numberOfBytesToRead = new byte[truncatedFileSizeInBytes];  
raf.read(numberOfBytesToRead);    
FileOutputStream fos = new FileOutputStream(newFile);  
fos.write(numberOfBytesToRead);