Question

In Java,

Create a program that can change any file (The file will be given by the user) given to a byte array. Examples are: an image, audio file, etc (Can not be a text file!).

Answer 1

Java: convert a file to a byte array, then convert byte array to a file.

In this post, I will show you how to convert a file to a byte array and then convert a byte array to a file.

To convert a file to byte array, ByteArrayOutputStream class is used. This class implements an output stream in which the data is written into a byte array. The buffer automatically grows as data is written to it. The data can be retrieved using toByteArray() and toString().

To convert byte array back to the original file, FileOutputStream class is used. A file output stream is an output stream for writing data to a File or to a FileDescriptor.

The following code has been fully tested.

import java.io.ByteArrayOutputStream; import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import java.util.logging.Level; import java.util.logging.Logger; public class genFile { public static void main(String[] args) throws FileNotFoundException, IOException { File file = new File("java.pdf"); FileInputStream fis = new FileInputStream(file); //System.out.println(file.exists() + "!!"); //InputStream in = resource.openStream(); ByteArrayOutputStream bos = new ByteArrayOutputStream(); byte[] buf = new byte[1024]; try { for (int readNum; (readNum = fis.read(buf)) != -1;) { bos.write(buf, 0, readNum); //no doubt here is 0 //Writes len bytes from the specified byte array starting at offset off to this byte array output stream. System.out.println("read " + readNum + " bytes,"); } } catch (IOException ex) { Logger.getLogger(genJpeg.class.getName()).log(Level.SEVERE, null, ex); } byte[] bytes = bos.toByteArray(); //below is the different part File someFile = new File("java2.pdf"); FileOutputStream fos = new FileOutputStream(someFile); fos.write(bytes); fos.flush(); fos.close(); } }