Merge multiple files using java

Question

I have a file in parts. I have to merge them all to in file. I am merging them using RandomAccessFile and it's working fine but for larger files it is very slow.

Here is the code I am using for merging them:

    RandomAccessFile outFile = new RandomAccessFile(filename, "rw");

    long len = 0;

    //inFiles is a LinkedList<String> conatining all file part names

    for (String inFileName : inFiles) {

        RandomAccessFile inFile = new RandomAccessFile(inFileName, "r");
        int data;

        outFile.seek(len);

        while ((data = inFile.read()) != -1) {
            outFile.writeByte(data);
        }

        len += inFile.length();

        inFile.close();

    }


    outFile.close();

Is there any other way of merging the files that may be faster than this method?... Please help me optimize this code.

Answer 1

As Nemo_64 points out, you are using read() byte at a time which will be very slow on large files. As you are not really using RandomAccessFile for random access, just using sequential stream IO would be enough, something like:

try(OutputStream out = Files.newOutputStream(Paths.get(filename), StandardOpenOption.CREATE, StandardOpenOption.WRITE)) {
    for (String inFileName : inFiles) {
        Files.copy(Paths.get(inFileName), out);
    }
}