java nio通过ByteBuffer输出文件信息

Posted 2021-11-07 lishuaiqi

1.通过ByteBuffer的get()方法每次读取一个字节转换成char类型输出.

        fc = new FileInputStream("src/demo20/data.txt").getChannel();
        ByteBuffer buff = ByteBuffer.allocate(BSIZE);
        buff = ByteBuffer.allocateDirect(BSIZE);
        fc.read(buff);
        buff.flip();
        while (buff.hasRemaining()) {
            System.out.print((char)buff.get());
        }

2.使用系统字符集进行解码

FileChannel fc = new FileOutputStream("src/demo20/data2.txt").getChannel();
        fc.write(ByteBuffer.wrap("Some text".getBytes()));
buff.rewind();
String encoding = System.getProperty("file.encoding");//获取系统字符集
System.out.println("Decoded using "+ encoding + ":" + Charset.forName(encoding).decode(buff));//Decoded using GBK:Some text

System.getProperty可以获取系统字符集,可以用产生系统字符集的CharSet对象,来进行解码操作.

3.写入时进行编码

fc = new FileOutputStream("src/demo20/data2.txt").getChannel();
        fc.write(ByteBuffer.wrap("Some text".getBytes("UTF-16BE")));
        fc.close();
        fc = new FileInputStream("src/demo20/data2.txt").getChannel();
        buff.clear();
        fc.read(buff);
        buff.flip();
        System.out.println(buff.asCharBuffer());

ByteBuffer.wrap()方法将 ""UTF-16BE"编码的 byte 数组包装到缓冲区中,写入文件,转换成CharBuffer即可读取文件.

4.通过CharBuffer写入

fc = new FileOutputStream("src/demo20/data2.txt").getChannel();
        buff = ByteBuffer.allocate(24);
        buff.asCharBuffer().put("Some text");
        fc.write(buff);
        fc.close();
        fc = new FileInputStream("src/demo20/data2.txt").getChannel();
        buff.clear();
        fc.read(buff);
        buff.flip();
        System.out.println(buff.asCharBuffer());

buff分配了24个字节,能储存12个字符,写入Some text可以通过FileInputStream获取的通道读取.