Java NIO之五 通道数据传输、内存映射文件

通道数据传输 、 内存映射文件

1. 将 Buffer 中数据写入Channel
   如： inChannel.write(buf);

2. 从Channel读取数据到Buffer
   如：inChannel.read(buf);

3. transferFrom() : 将数据从源通道传输到其他Channel中：
   

4. transferTo() : 将数据从源通道传输到其他Channel中：
   

/*
 * 一、通道(Channel)：用于资源节点与目标节点的连接。
 * 在Java NIO 中负责缓冲中数据的传去。
 * Channel本身不存储数据，需要配合缓冲区进行传输。
 * 
 * 二、通道的主要实现类
 * 	java.nio.channels.Channel 接口：
 * 		|--FileChannel :
 * 		|--SokectChannel
 * 		|--SeverSocketChannel
 *		|--DatagramChannel
 *
 *三、获取通道
 *1. Java 针对支持通道的类提供了getChannel()方法
 *		本地IO操作
 *		FileInputStream/FileOutStream
 *		RandomAccessFile
 *
 *		网络IO：
 *		Socket
 *		ServerSocket
 *		DatagramSocket
 *		
 *2.在 JDK 1.7 中的NIO.2针对各个通道提供了一个静态方法open()
 *3.在 JDK 1.7 中的NIO.2的Files 工具类的newByteChannel()
 *
 *四、通道之间的数据传输
 *transferFrom()
 *transferTo()
 */
public class TestChannel {
	
	//通道之间的数据传输（直接缓冲区的方式）
	@Test
	public void test3() {

		long start = System.currentTimeMillis();
		
		FileChannel readChannel = null;
		FileChannel writeChannel = null;
		try {
			readChannel = FileChannel.open(Paths.get("1.jpg"), StandardOpenOption.READ);
			writeChannel = FileChannel.open(Paths.get("5.jpg"), StandardOpenOption.WRITE,StandardOpenOption.READ,StandardOpenOption.CREATE_NEW);
			
//			readChannel.transferTo(0, readChannel.size(), writeChannel);
			writeChannel.transferFrom(readChannel, 0, readChannel.size());
		} catch (IOException e) {
			e.printStackTrace();
		}finally {
			if(readChannel != null) {
				try {
					readChannel.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			if(writeChannel != null) {
				try {
					writeChannel.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			
			long end = System.currentTimeMillis();
			System.out.println(end - start);
		}
		
	}
	
	
	//2.使用直接缓冲区完成文件的复制（内存映射文件）：直接缓冲区只有ByteBuffer支持
	@Test
	public void test2(){
		
		long start = System.currentTimeMillis();
		
		FileChannel readChannel = null;
		FileChannel writeChannel = null;
		try {
			readChannel = FileChannel.open(Paths.get("1.jpg"), StandardOpenOption.READ);
			writeChannel = FileChannel.open(Paths.get("3.jpg"), StandardOpenOption.WRITE,StandardOpenOption.READ,StandardOpenOption.CREATE_NEW);
			
			//内存映射文件
			MappedByteBuffer inMappedBuf = readChannel.map(MapMode.READ_ONLY, 0, readChannel.size());
			MappedByteBuffer outMappedBuf =writeChannel.map(MapMode.READ_WRITE, 0, readChannel.size());


			//直接对缓冲区进行数据的读写操作
			byte [] dst = new byte [inMappedBuf.limit()];
			inMappedBuf.get(dst);
			outMappedBuf.put(dst);
		} catch (IOException e) {
			e.printStackTrace();
		}finally {
			if(readChannel != null) {
				try {
					readChannel.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			if(writeChannel != null) {
				try {
					writeChannel.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			
			long end = System.currentTimeMillis();
			System.out.println(end - start);
		}
		
	}
	
	//1. 利用通道完成文件的复制(非直接缓冲区)
	@Test
	public void test1()  {
		
		long start = System.currentTimeMillis();
		
		FileInputStream fis = null;
		FileOutputStream fos = null;
		
		FileChannel inChannel = null;
		FileChannel outChannel= null;
		try {
			fis = new FileInputStream("1.jpg");
			fos = new FileOutputStream("2.jpg");
			//①获取通道
			inChannel = fis.getChannel();
			outChannel = fos.getChannel();
			
			// ②分配指定大小的缓冲区
			ByteBuffer buf = ByteBuffer.allocate(1024);
			
			//③将通道中数据存入缓冲区
			while(inChannel.read(buf) != -1) {
				buf.flip();//切换成读取数据的模式
				//④将换缓冲区中的数据写入通道中
				outChannel.write(buf);
				buf.clear();//清空缓冲区
			}
		} catch (IOException e) {
			e.printStackTrace();
		}finally {
			if(outChannel  != null) {
				try {
					outChannel.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			if(inChannel  != null) {
				try {
					inChannel.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			if(fos  != null) {
				try {
					fos.close();
				} catch (IOException e) {
					e.printStackTrace();
				}		
			}
			if(fis  != null) {
				try {
					fis.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			long end = System.currentTimeMillis();
			System.out.println(end - start);
		}
	}
}