java-IO操作性能对比
在软件系统中，IO速度比内存速度慢，IO读写在很多情况下会是系统的瓶颈。
在java标准IO操作中，InputStream和OutputStream提供基于流的IO操作，以字节为处理单位；Reader和Writer实现了Buffered缓存，以字符为处理单位。
从Java1.4开始，增加NIO（New IO），增加缓存Buffer和通道Channel，以块为处理单位，是双向通道（可读可写，类似RandomAccessFile），支持锁和内存映射文件访问接口，大大提升了IO速度。
以下例子简单测试常见IO操作的性能速度。 /** * 测试不同io操作速度 * * @author peter_wang * @create-time 2014-6-4 下午12:52:48 */ public class SpeedTest { private static final String INPUT_FILE_PATH = "io_speed.txt"; private static final String OUTPUT_FILE_PATH = "io_speed_copy.txt"; /** * @param args */ public static void main(String[] args) { long ioStreamTime1 = ioStreamCopy(); System.out.println("io stream copy:" + ioStreamTime1); long ioStreamTime2 = bufferedStreamCopy(); System.out.println("buffered stream copy:" + ioStreamTime2); long ioStreamTime3 = nioStreamCopy(); System.out.println("nio stream copy:" + ioStreamTime3); long ioStreamTime4 = nioMemoryStreamCopy(); System.out.println("nio memory stream copy:" + ioStreamTime4); } /** * 普通文件流读写 * * @return 操作的时间 */ private static long ioStreamCopy() { long costTime = -1; FileInputStream is = null; FileOutputStream os = null; try { long startTime = System.currentTimeMillis(); is = new FileInputStream(INPUT_FILE_PATH); os = new FileOutputStream(OUTPUT_FILE_PATH); int read = is.read(); while (read != -1) { os.write(read); read = is.read(); } long endTime = System.currentTimeMillis(); costTime = endTime - startTime; } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { try { if (is != null) { is.close(); } if (os != null) { os.close(); } } catch (IOException e) { e.printStackTrace(); } } return costTime; } /** * 加入缓存的文件流读写， Reader默认实现缓存，只能读取字符文件，无法准确读取字节文件如图片视频等 * * @return 操作的时间 */ private static long bufferedStreamCopy() { long costTime = -1; FileReader reader = null; FileWriter writer = null; try { long startTime = System.currentTimeMillis(); reader = new FileReader(INPUT_FILE_PATH); writer = new FileWriter(OUTPUT_FILE_PATH); int read = -1; while ((read = reader.read()) != -1) { writer.write(read); } writer.flush(); long endTime = System.currentTimeMillis(); costTime = endTime - startTime; } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { try { if (reader != null) { reader.close(); } if (writer != null) { writer.close(); } } catch (IOException e) { e.printStackTrace(); } } return costTime; } /** * nio操作数据流 * * @return 操作的时间 */ private static long nioStreamCopy() { long costTime = -1; FileInputStream is = null; FileOutputStream os = null; FileChannel fi = null; FileChannel fo = null; try { long startTime = System.currentTimeMillis(); is = new FileInputStream(INPUT_FILE_PATH); os = new FileOutputStream(OUTPUT_FILE_PATH); fi = is.getChannel(); fo = os.getChannel(); ByteBuffer buffer = ByteBuffer.allocate(1024); while (true) { buffer.clear(); int read = fi.read(buffer); if (read == -1) { break; } buffer.flip(); fo.write(buffer); } long endTime = System.currentTimeMillis(); costTime = endTime - startTime; } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { try { if (fi != null) { fi.close(); } if (fo != null) { fo.close(); } if (is != null) { is.close(); } if (os != null) { os.close(); } } catch (IOException e) { e.printStackTrace(); } } return costTime; } /** * nio内存映射操作数据流 * * @return 操作的时间 */ private static long nioMemoryStreamCopy() { long costTime = -1; FileInputStream is = null; //映射文件输出必须用RandomAccessFile RandomAccessFile os = null; FileChannel fi = null; FileChannel fo = null; try { long startTime = System.currentTimeMillis(); is = new FileInputStream(INPUT_FILE_PATH); os = new RandomAccessFile(OUTPUT_FILE_PATH, "rw"); fi = is.getChannel(); fo = os.getChannel(); IntBuffer iIb=fi.map(FileChannel.MapMode.READ_ONLY, 0, fi.size()).asIntBuffer(); IntBuffer oIb = fo.map(FileChannel.MapMode.READ_WRITE, 0, fo.size()).asIntBuffer(); while(iIb.hasRemaining()){ int read = iIb.get(); oIb.put(read); } long endTime = System.currentTimeMillis(); costTime = endTime - startTime; } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { try { if (fi != null) { fi.close(); } if (fo != null) { fo.close(); } if (is != null) { is.close(); } if (os != null) { os.close(); } } catch (IOException e) { e.printStackTrace(); } } return costTime; } } 运行结果： io stream copy:384 buffered stream copy:125 nio stream copy:12 nio memory stream copy:10
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