Java|Java NIO(一)-Channel和Buffer JavaNIO(一)-Channel和Buffer

Channel
Channel类似于流，但和流不同，流是单向的只能读或写，Channel是既可以读又可以写。Channel常见的实现类有FileChannel、DatagramChannel、SocketChannel、ServerSocketChannel。BIO中的FileInputStream、FileOutputStream和RandomAccessFile能通过getChannel方法得到FileChannel对象
Buffer
Buffer是唯一能与Channel交互的对象，它的常见实现有ByteBuffer、ShortBuffer、IntBuffer、LongBuffer、DoubleBuffer、FloatBuffer、CharBuffer。Buffer有四个属性position、limit、capacity和mark，Buffer初始化的时候需要指定容量capacity，Buffer它的底层实现是一个数组,如下图，以ByteBuffer为例，position表示数组中下一个要读或写的位置，当向Buffer写完后(不一定写满)，调用flip()方法，将Buffer的读写模式翻转，limit赋值为position，position赋值为0。mark是标记位置，可以通过reset()方法，将position值变为mark值。

public abstract class ByteBuffer extends Buffer implements Comparable { final byte[] hb; // Non-null only for heap buffers final int offset; boolean isReadOnly; // Valid only for heap buffers }

直接看看ByteBuffer的简单使用：

public class ByteBufferTest { public static void main(String[] args) { try { FileInputStream is = new FileInputStream("/home/reda/Documents/test/1.txt"); FileOutputStream fos = new FileOutputStream("/home/reda/Documents/test/1.txt"); FileOutputStream os = new FileOutputStream("/home/reda/Documents/test/2.txt"); FileChannel inChannel = is.getChannel(); FileChannel fosChannel = fos.getChannel(); FileChannel outChannel = os.getChannel(); //特殊情况，直接在channel传输 //inChannel.transferTo(0,inChannel.size(),outChannel); //outChannel.transferFrom(inChannel,0,inChannel.size()); ByteBuffer buffer = ByteBuffer.allocate(16); //写入内容 fosChannel.write(ByteBuffer.wrap("1234QAQ".getBytes("UTF-8"))); //while(inChannel.read(buffer) != -1) { //buffer.flip(); //outChannel.write(buffer); ////必须clear不然除了第一次，后面将读不进内容到Buffer //buffer.clear(); //}buffer.clear(); fosChannel.close(); inChannel.read(buffer); buffer.flip(); //将positon的位置标记在起始位置，将ByteBuffer中每个字节转为字符 buffer.mark(); while (buffer.hasRemaining()) { System.out.print((char)buffer.get()); } System.out.println(); //将positon的位置重置 buffer.reset(); CharBuffer charBuffer = buffer.asCharBuffer(); //打印乱码,ByteBuffer直接转成CharBuffer不行 System.out.println(charBuffer.toString()); //将ByteBuffer解码成utf8后，则能重新正确打印 CharBuffer charBuffer2 = Charset.forName("UTF-8").decode(buffer); System.out.println(charBuffer2.toString()); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } }

【Java|Java NIO(一)-Channel和Buffer】ByteBuffer类有方法能转换成其他类型的Buffer

文章图片
Buffer类型转换

public class BufferTest { public static void main(String[] args) { ByteBuffer buffer = ByteBuffer.wrap(new byte[]{0,0,0,0,0,0,0,'a'}); //byteBUffer result:0 0 0 0 0 0 0 97 while (buffer.hasRemaining()) System.out.print(buffer.get() + " "); //CharBuffer result:a CharBuffer charBuffer = ((ByteBuffer)buffer.rewind()).asCharBuffer(); while (charBuffer.hasRemaining()) System.out.print(charBuffer.get() + " "); //FloatBuffer result: 0.0 1.36E-43 FloatBuffer floatBuffer = ((ByteBuffer)buffer.rewind()).asFloatBuffer(); while (floatBuffer.hasRemaining()) System.out.print(floatBuffer.get() + " "); //IntBuffer result:0 97 IntBuffer intBuffer = ((ByteBuffer)buffer.rewind()).asIntBuffer(); while (intBuffer.hasRemaining()) System.out.print(intBuffer.get() + " "); //ShortBuffer result:0 0 0 97 ShortBuffer shortBuffer = ((ByteBuffer)buffer.rewind()).asShortBuffer(); while (shortBuffer.hasRemaining()) System.out.print(shortBuffer.get() + " "); //LongBuffer result:97 LongBuffer longBuffer = ((ByteBuffer)buffer.rewind()).asLongBuffer(); while (longBuffer.hasRemaining()) System.out.print(longBuffer.get() + " "); //DoubleBuffer result：4.8E-322 DoubleBuffer doubleBuffer = ((ByteBuffer)buffer.rewind()).asDoubleBuffer(); while (doubleBuffer.hasRemaining()) System.out.print(doubleBuffer.get() + " "); } }

一字节：byte boolean
二字节： char short
四字节：int float
八字节：long double
ByteBuffer包装了一个8字节的数组,byteBuffer每个值有一个字节所以有8个值，同理char、short4个值(char的前三个值为空，没显示)，int、float2个值，long和double一个值。