Java 新I/O
Java新IO所使用的结构更接近于操作系统执行I/O的方式：通道和缓冲器。通过是包含煤层的矿藏，缓冲器则是派送到矿藏的卡车。唯一与通道交互的缓冲器是ByteBuffer。
旧I/O库中有三个类被修改了，用以产生FileChannel
public class GetChannel {public static void main(String[] args) throws IOException { FileChannel fc = new FileOutputStream("data").getChannel(); fc.write(ByteBuffer.wrap("some text ".getBytes())); fc.close(); fc = new RandomAccessFile("data", "rw").getChannel(); fc.position(fc.size()); fc.write(ByteBuffer.wrap("some more ".getBytes())); fc.close(); fc = new FileInputStream("data").getChannel(); ByteBuffer buf = ByteBuffer.allocate(1024); fc.read(buf); // 让ByteBuffer做好让别人读的准备 buf.flip(); while (buf.hasRemaining()) System.out.print((char) buf.get());}}
转换数据
public class BufferToText {public static void main(String[] args) throws IOException { //=======================第一次============================ FileChannel fc = new FileOutputStream("data").getChannel(); fc.write(ByteBuffer.wrap("some text ".getBytes())); fc.close(); fc = new FileInputStream("data").getChannel(); ByteBuffer buf = ByteBuffer.allocate(1024); fc.read(buf); buf.flip(); System.out.println(buf.asCharBuffer()); //乱码 // 返回到数据开始的地方 buf.rewind(); //=======================第二次============================ String encoding = System.getProperty("file.encoding"); System.out.println("system file encoding is " + encoding); fc = new FileOutputStream("data").getChannel(); // 进行decode fc.write(ByteBuffer.wrap("some text ".getBytes("UTF-16BE"))); fc.close(); fc = new FileInputStream("data").getChannel(); buf.clear(); fc.read(buf); buf.flip(); System.out.println(buf.asCharBuffer()); //=======================第三次============================ fc = new FileOutputStream("data").getChannel(); buf = ByteBuffer.allocate(24); // 进行encode buf.asCharBuffer().put("Some text"); fc.write(buf); fc.close(); fc = new FileInputStream("data").getChannel(); buf.clear(); fc.read(buf); buf.flip(); System.out.println(buf.asCharBuffer());}}
获得基本类型
public class GetData {public static void main(String[] args) { ByteBuffer bb = ByteBuffer.allocate(1024); int i = 0; // 分配ByteBuffer后，缓冲器其内容全部为0，共检测了1024个值 bb.limit()=1024 while (i++ < bb.limit()) if (bb.get() != 0) System.out.println("i = " + i); bb.rewind(); bb.asCharBuffer().put("howdy!"); char c; while ((c = bb.getChar()) != 0) System.out.print(c + " ");System.out.println(); bb.rewind(); bb.asIntBuffer().put(987654321); System.out.println(bb.getInt()); bb.rewind(); bb.asFloatBuffer().put(987654321); System.out.println(bb.getFloat()); bb.rewind();}}
视图缓冲器
可以让我们通过某个特定的基本数据类型的视窗，查看其底层的ByteBuffer，ByteBuffer依然是存储数据的地方，所以我们对视图的修改会映射成为对ByteBuffer的修改。
public class IntBufferDemo {public static void main(String[] args) { ByteBuffer bb = ByteBuffer.allocate(1024); IntBuffer ib = bb.asIntBuffer(); ib.put(new int[] { 11, 22, 33, 45, 68 }); System.out.println("index 3 is " + ib.get(3)); ib.put(3, 3344); ib.flip(); while (ib.hasRemaining()) System.out.print(ib.get() + " ");}}package nio;import java.nio.ByteBuffer;import java.nio.CharBuffer;import java.nio.DoubleBuffer;import java.nio.FloatBuffer;import java.nio.IntBuffer;import java.nio.LongBuffer;import java.nio.ShortBuffer;public class ViewBuffers {public static void main(String[] args) { ByteBuffer bb = ByteBuffer.wrap(new byte[] { 0, 0, 0, 0, 0, 0, 0, 'a' }); bb.rewind(); System.out.print("Byte Buffer "); while (bb.hasRemaining()) System.out.print(bb.position() + " -> " + bb.get() + ", "); CharBuffer cb = ((ByteBuffer) bb.rewind()).asCharBuffer(); System.out.print("\r\nChar Buffer "); while (cb.hasRemaining()) System.out.print(cb.position() + " -> " + cb.get() + ", "); FloatBuffer fb = ((ByteBuffer) bb.rewind()).asFloatBuffer(); System.out.print("\r\nFloat Buffer "); while (fb.hasRemaining()) System.out.print(fb.position() + " -> " + fb.get() + ", "); IntBuffer ib = ((ByteBuffer) bb.rewind()).asIntBuffer(); System.out.print("\r\nInt Buffer "); while (ib.hasRemaining()) System.out.print(ib.position() + " -> " + ib.get() + ", "); LongBuffer lb = ((ByteBuffer) bb.rewind()).asLongBuffer(); System.out.print("\r\nLong Buffer "); while (lb.hasRemaining()) System.out.print(lb.position() + " -> " + lb.get() + ", "); ShortBuffer sb = ((ByteBuffer) bb.rewind()).asShortBuffer(); System.out.print("\r\nShort Buffer "); while (sb.hasRemaining()) System.out.print(sb.position() + " -> " + sb.get() + ", "); DoubleBuffer db = ((ByteBuffer) bb.rewind()).asDoubleBuffer(); System.out.print("\r\nDouble Buffer "); while (db.hasRemaining()) System.out.print(db.position() + " -> " + db.get() + ", ");}}
ByteBuffer通过一个被“包装”过得8字节数组产生，然后通过各种不同的基本类型视图缓冲器显示出来
http://dl.iteye.com/upload/attachment/273937/2e2f4c7b-bd53-3613-83e5-a0bf9d1d2403.jpg
字节的存放次序
ByteBuffer一高位优先的形式存储数据
高位优先 big endian 将重要的字节存放在地址最低的存储器单元
低位有限 litter endian 将重要的字节存放在地址最高的存储器单元
public class Edians {public static void main(String[] args) { ByteBuffer bb = ByteBuffer.wrap(new byte); show(bb); bb.order(ByteOrder.BIG_ENDIAN); show(bb); bb.order(ByteOrder.LITTLE_ENDIAN); show(bb);}private static void show(ByteBuffer bb) { bb.asCharBuffer().put("abcdef"); System.out.println(Arrays.toString(bb.array())); bb.rewind();}}
用缓冲器操作数据
http://dl.iteye.com/upload/attachment/273940/06082bc4-29c9-3395-9f51-ae92ce25fbe0.jpg
Buffer有4个索引 mark:标记position:位置limit:界限capacity:容量
http://dl.iteye.com/upload/attachment/273943/9b4dbb91-2fbb-31a2-9a22-a696d66c3453.jpg
public class UsingBuffer {private static void scramble(CharBuffer buf) { while (buf.hasRemaining()) { buf.mark(); // get put 方法会向后移动position char c1 = buf.get(); char c2 = buf.get(); // reset 方法 将position的值设为mark的值 buf.reset(); buf.put(c2).put(c1); }}public static void main(String[] args) { char[] data = "UsingBUffers".toCharArray(); ByteBuffer bb = ByteBuffer.allocate(data.length * 2); CharBuffer cb = bb.asCharBuffer(); cb.put(data); // 只能打印出position和limit直接的字符 // rewind 方法把position设置到缓冲器的开始位置 System.out.println(cb.rewind()); scramble(cb); System.out.println(cb.rewind()); scramble(cb); System.out.println(cb.rewind());}}
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