javaNIO中ByteBuffer用法

ByteBuffer类是在javaNIO中常常使用的一个缓冲区类，使用ByteBuffer可以进行高效的IO操作 下来我们看一下ByteBuffer类的常用方法： ByteBuffer.allocate();或者ByteBuffer.wrap();创建ByteBuffer

public static ByteBuffer allocate(int capacity) { if (capacity < 0) throw new IllegalArgumentException(); return new HeapByteBuffer(capacity, capacity); } public static ByteBuffer wrap(byte[] array, int offset, int length) { try { return new HeapByteBuffer(array, offset, length); } catch (IllegalArgumentException x) { throw new IndexOutOfBoundsException(); } }

读写的方法就read()、write(),在这之中我们看一下ByteBuffer内部字段 position：当前读取的位置 mark：为某一读过的位置做标记，便于有时候回退到该位置 capacity：初始化时候的容量 limit：读写的上限，limit <= capacity flip()方法写完数据需要开始读的时候，将position复位到0，并将limit设为当前position

public final Buffer flip() { limit = position; position = 0; mark = -1; return this; }

clear()方法是将position置为0，并不清除buffer内容

public final Buffer clear() { position = 0; limit = capacity; mark = -1; return this; }

*mark()方法是标记，reset()方法是回到标记

public final Buffer mark() { mark = position; return this; } public final Buffer reset() { int m = mark; if (m < 0) throw new InvalidMarkException(); position = m; return this; }

下来看一个例子

public void test() throws IOException { ByteBuffer buff = ByteBuffer.allocate(256); FileChannel in = null; FileChannel out = null; try { in = new FileInputStream("filein").getChannel(); out = new FileOutputStream("fileout").getChannel(); while(fin.read(buff) != -1) { buff.flip(); fout.write(buff); buff.clear(); } } catch (FileNotFoundException e) { throw e; } finally { try { if(in != null) { in.close(); } if(fout != null) { out.close(); } } catch(IOException e) { throw e; } } }