java中的拷贝文件FileChannel

以前用Java拷贝文件，只知道写byte数组循环拷贝，今天知道了可以用FileChannel进行拷贝，上代码：

下边是传统的byte数组拷贝方法

</pre><pre name="code" class="java">private void copyFilefromByte() throws IOException {
		long start = System.currentTimeMillis();
		MemorySee memorySee = new MemorySee();
		memorySee.begin();
		File name = new File("D:\\a\\hehe.zip");
		File n1 = new File("D:\\a\\a.zip");
		FileInputStream fileInputStream = new FileInputStream(name);
		n1.createNewFile();
		FileOutputStream fileOutputStream = new FileOutputStream(n1);
		byte[] bytes = new byte[1024000];
		int length = -1;
		while ((length = fileInputStream.read(bytes, 0, bytes.length)) != -1) {
			fileOutputStream.write(bytes, 0, length);
		}
		fileOutputStream.flush();
		fileOutputStream.close();
		fileInputStream.close();
		memorySee.end();
		memorySee.sayMemoryUse();
		long end = System.currentTimeMillis();
		System.out.println("run time:" + (end - start));
	}

下边是使用FileChannel拷贝文件的方法：

private void copyFileFromCannel() throws IOException {
		long start = System.currentTimeMillis();
		MemorySee memorySee = new MemorySee();
		memorySee.begin();
		File name = new File("D:\\a\\hehe.zip");
		File n1 = new File("D:\\a\\b.zip");
		FileInputStream fileInputStream = new FileInputStream(name);
		FileChannel fileChannel = fileInputStream.getChannel();
		n1.createNewFile();
		FileOutputStream fileOutputStream = new FileOutputStream(n1);
		FileChannel fileChannel2 = fileOutputStream.getChannel();
		int position = -1;
		long fileSize = name.length();
		int writeLength = 0;
		while (true) {

			writeLength += fileChannel2.transferFrom(fileChannel, writeLength,
					fileSize - writeLength);
			System.out.println("writeLength:"+writeLength);
			if (writeLength == fileSize) {
				break;
			}
		}
		fileChannel2.close();
		fileChannel.close();
		memorySee.end();
		memorySee.sayMemoryUse();
		long end = System.currentTimeMillis();
		System.out.println("run time:" + (end - start));
	}

还有一个辅助打印memory的类：

 class MemorySee{

		private long startM =0;
		private long endM =0;
		public void begin(){
			Runtime.getRuntime().gc();
			startM=Runtime.getRuntime().freeMemory();
		}

		public void end(){
			  endM=Runtime.getRuntime().freeMemory();
		}

		public void sayMemoryUse(){
			 System.out.println(startM-endM);
		}

	}

最后输出结果：

使用FileChannel拷贝的时间，要比byte节约大约1/2时间，或者更多，内存占用总比byte少，如果要提高byte的时间，那么就要提高byte的大小，这样就会消耗更多内存，总之，使用FileChannel既快速，又省内存。

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