Reading an ASCII File Using FileChannel and ByteArrays

Question

I have the following code:

        String inputFile = "somefile.txt";
        FileInputStream in = new FileInputStream(inputFile);
        FileChannel ch = in.getChannel();
        ByteBuffer buf = ByteBuffer.allocateDirect(BUFSIZE);  // BUFSIZE = 256

        /* read the file into a buffer, 256 bytes at a time */
        int rd;
        while ( (rd = ch.read( buf )) != -1 ) {
            buf.rewind();
            for ( int i = 0; i < rd/2; i++ ) {
                /* print each character */
                System.out.print(buf.getChar());
            }
            buf.clear();
        }

But the characters are displayed on ?. Is this related to Java using Unicode characters? How to fix it?

Answer 1

You should know what a file encoding is, and then decode a ByteBuffer into a CharBuffer using this encoding. Assume an ASCII file:

import java.util.*;
import java.io.*;
import java.nio.*;
import java.nio.channels.*;
import java.nio.charset.*;

public class Buffer
{
    public static void main(String args[]) throws Exception
    {
        String inputFile = "somefile";
        FileInputStream in = new FileInputStream(inputFile);
        FileChannel ch = in.getChannel();
        ByteBuffer buf = ByteBuffer.allocateDirect(BUFSIZE);  // BUFSIZE = 256

        Charset cs = Charset.forName("ASCII"); // Or whatever encoding you want

        /* read the file into a buffer, 256 bytes at a time */
        int rd;
        while ( (rd = ch.read( buf )) != -1 ) {
            buf.rewind();
            CharBuffer chbuf = cs.decode(buf);
            for ( int i = 0; i < chbuf.length(); i++ ) {
                /* print each character */
                System.out.print(chbuf.get());
            }
            buf.clear();
        }
    }
}

Answer 2

buf.getChar () expects 2 bytes per character, but you only save 1. Use:

 System.out.print((char) buf.get());

Answer 3

:

System.out.print((char)buf.get());

, .

Answer 4

somefile.txt . , .

, , . , . , - , ( ), , (, UTF-8).

Answer 5

- , , ?

ASCII , Reader.

:

File inputFile = new File("somefile.txt");
BufferedReader reader = new BufferedReader(new FileReader(inputFile));

readLine, !

Answer 6

, .

14 Chars , 7 '?'.

. .