用FileChannel和ByteArrays读取ASCII文件 [英] Reading an ASCII file with FileChannel and ByteArrays

问题描述

我有以下代码：

  String inputFile =somefile.txt; 
 FileInputStream in = new FileInputStream（inputFile）; 
 FileChannel ch = in.getChannel（）; 
 ByteBuffer buf = ByteBuffer.allocateDirect（BUFSIZE）; // BUFSIZE = 256 
 
 / *将文件读入一个缓冲区，一次256字节* / 
 int rd; （（rd = ch.read（buf））！= -1）{
 buf.rewind（）; 
 for（int i = 0; i< rd / 2; i ++）{
 / *打印每个字符* / 
 System.out.print（buf.getChar（））; 
} 
 buf.clear（）; 
} 
  

但是角色会显示在？这是否与使用Unicode字符的Java有关？如何解决这个问题？解决方案

你必须知道文件的编码是什么，然后将ByteBuffer解码为CharBuffer使用该编码。假设文件是​​ASCII：

  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）; //或者你想要的任何编码
 
 / *将文件读入一个缓冲区，一次256字节* / 
 int rd; （（rd = ch.read（buf））！= -1）{
 buf.rewind（）; 
 CharBuffer chbuf = cs.decode（buf）; 
 for（int i = 0; i< chbuf.length（）; i ++）{
 / *打印每个字符* / 
 System.out.print（chbuf.get（）） ; 
} 
 buf.clear（）; 
} 
} 
} 
  

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 get displayed at ?'s. Does this have something to do with Java using Unicode characters? How do I correct this?

解决方案

You have to know what the encoding of the file is, and then decode the ByteBuffer into a CharBuffer using that encoding. Assuming the file is ASCII:

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();
        }
    }
}

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