Programs use byte streams to perform input and output of 8-bit bytes. All byte stream classes are descended from InputStream and OutputStream.

There are many byte stream classes. To demonstrate how byte streams work, we'll focus on the file I/O byte streams, FileInputStream and FileOutputStream.

Other kinds of byte streams are used in much the same way; they differ mainly in the way they are constructed.

Using Byte Streams

We'll explore FileInputStream and FileOutputStream by examining an example program named CopyBytes, which uses byte streams to copy xanadu.txt, one byte at a time.

package com.feng.learnjava; 
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
 
public class CopyBytes {
        public static void main(String[] args) throws IOException {
                FileInputStream in = null;
                FileOutputStream out = null;
 
             try {
                //必须把文件放在项目根目录，否则报 IO 异常
                    in = new FileInputStream("xanadu.txt");
                    out = new FileOutputStream("outagain.txt");
                    int c;
                 while ((c = in.read()) != -1) {
                        out.write(c);
                 }
                } finally {
                        if (in != null) {
                                in.close();
                        }
                        if (out != null) {
                                out.close();
                        }
                }
        }
}

• int java.io.FileInputStream.read() throws IOException
  Reads a byte of data from this input stream. This method blocks if no input is yet available.

• void java.io.FileOutputStream.write(int b) throws IOException
  Writes the specified byte to this file output stream. Implements the write method of OutputStream.

CopyBytes spends most of its time in a simple loop that reads the input stream and writes the output stream, one byte at a time, as shown in the following figure.