Image read/write in Java without imageio between local file systems

Question

I'm very new to Java and I'm recently making a program which reads image files(jpg) from one directory, and write(copy) them to another directory.

I can't use imageio or move/copy methods and I also have to check the time consuming caused by the R/W operation.

The problem is I wrote some codes below and it runs, but all of my output image files in the destination have 0 byte and have no contents at all. I can see only black screens which have no bytes when I open the result images.

public class image_io {

public static void main(String[] args)
{
    FileInputStream fis = null;
    FileOutputStream fos = null;
    BufferedInputStream bis = null;
    BufferedOutputStream bos = null;

    // getting path
    File directory = new File("C:\\src");
    File[] fList = directory.listFiles();
    String fileName, filePath, destPath;

    // date for time check
    Date d = new Date();

    int byt = 0;
    long start_t, end_t;

    for (File file : fList)
    {
        // making paths of source and destination
        fileName = file.getName();
        filePath = "C:\\src\\" + fileName;
        destPath = "C:\\dest\\" + fileName;

        // read the images and check reading time consuming
        try 
        {
        fis = new FileInputStream(filePath);
        bis = new BufferedInputStream(fis);

        do
        {
            start_t = d.getTime();
        }
        while ((byt = bis.read()) != -1);

        end_t = d.getTime();
        System.out.println(end_t - start_t);

        } catch (Exception e) {e.printStackTrace();}

        // write the images and check writing time consuming
        try
        {
            fos = new FileOutputStream(destPath);
            bos = new BufferedOutputStream(fos);

            int idx = byt;

            start_t = d.getTime();

            for (; idx == 0; idx--)
            {
                bos.write(byt);
            }

            end_t = d.getTime();
            System.out.println(end_t - start_t);

        } catch (Exception e) {e.printStackTrace();}
    }
}

}

Is FileInput/OutputStream doesn't support image files? Or is there some mistakes in my code?

Please, somebody help me..

Answer 1

There are multiple problems with your code:

With this loop

do
{
    start_t = d.getTime();
}
while ((byt = bis.read()) != -1);

you are trying to read the file. The problem with it is, that you always only remember a single byte and store it to byt. In the next iteration it gets overridden by the next byte in the file until you reach the end, in which case the read value is -1. So the net effect of this loop is byt being equal to -1. You need to read all bytes to some buffer, e.g. an array that is large enough to hold the whole file.

Another problem here is that you repeatedly set start_t. You probably want to do this only once before entering the loop. Note also that d.getTime() will always return the same value, the one it got when you did Date d = new Date();. You probably want to call System.currentTimeMillis() or something like that instead.

After you have fixed the issues above, you need to adjust the write loop accordingly.

You should also look into some Java coding guideline, as your code violates several common practices:

• Naming style of classes and variables (image_io => ImageIO, start_t => startTime…)
• Declaration of variables on first use instead of on top (e.g. your streams and idx)
• Some indention issues (e.g. first try block is not indented)
• You do not close your streams. If you have Java 7+ available, you should have a look at try-with-resources which closes your streams automatically.

When you have your program doing what you want you could post it on Code Review to get additional advices on what you could improve.