ThinkJava-新IO

package com.java.io;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

public class GetChannel {
      private static final int BSIZE = 1024;
      
      @SuppressWarnings("resource")
      public static void main(String[] args) throws Exception {
              // 获取通道，该通道允许写操作
            FileChannel fc = new FileOutputStream("data.txt").getChannel();
            // 将字节数组包装到缓冲区中
            fc.write(ByteBuffer.wrap("Some text ".getBytes()));
            // 关闭通道
            fc.close();
            
            // 随机读写文件流创建的管道
            fc = new RandomAccessFile("data.txt", "rw").getChannel();
            // fc.position()计算从文件的开始到当前位置之间的字节数
            // 设置此通道的文件位置,fc.size()此通道的文件的当前大小,该条语句执行后，通道位置处于文件的末尾
            fc.position(fc.size()); // Move to the end
            fc.write(ByteBuffer.wrap("Some more".getBytes()));
            fc.close();
            
            // Read the file:
            fc = new FileInputStream("data.txt").getChannel();
            ByteBuffer buff = ByteBuffer.allocate(BSIZE);
            // 将文件内容读到指定的缓冲区中
            fc.read(buff);
            //buffer.flip();一定得有，如果没有，就是从文件最后开始读取的，当然读出来的都是byte=0时候的字符。
            //通过buffer.flip();这个语句，就能把buffer的当前位置更改为buffer缓冲区的第一个位置。
            buff.flip();
            while(buff.hasRemaining()){
                System.out.print((char)buff.get());
            }
      }
}

package com.java.io;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.Charset;

public class BufferToText {
    private static final int BSIZE = 1024;
    
    @SuppressWarnings("resource")
    public static void main(String[] args) throws Exception {
        FileChannel fc = new FileOutputStream("data2.txt").getChannel();
        fc.write(ByteBuffer.wrap("Some text".getBytes()));
        fc.close();
        fc = new FileInputStream("data2.txt").getChannel();
        ByteBuffer buff = ByteBuffer.allocate(BSIZE);
        fc.read(buff);
        buff.flip();
        // Doesn‘t work:
        System.out.println(buff.asCharBuffer());
        
        // Decode using this system‘s default Charset:
        buff.rewind();
        String encoding = System.getProperty("file.encoding");
        System.out.println("Decoded using " + encoding + ": " + Charset.forName(encoding).decode(buff));
        
        // Or, we could encode with something that will print:
        fc = new FileOutputStream("data2.txt").getChannel();
        fc.write(ByteBuffer.wrap("Some text".getBytes("UTF-16BE")));
        fc.close();
        // Now try reading again:
        fc = new FileInputStream("data2.txt").getChannel();
        buff.clear();
        fc.read(buff);
        buff.flip();
        System.out.println(buff.asCharBuffer());
        
        // Use a CharBuffer to write through:
        fc = new FileOutputStream("data2.txt").getChannel();
        buff = ByteBuffer.allocate(24); // More than needed
        buff.asCharBuffer().put("Some text");
        fc.write(buff);
        fc.close();
        
        // Read and display:
        fc = new FileInputStream("data2.txt").getChannel();
        buff.clear();
        fc.read(buff);
        buff.flip();
        System.out.println(buff.asCharBuffer());
    }
}