NIO之通道(Channel)的原理与获取以及数据传输与内存映射文件

  1 package com.expgiga.NIO;
  2 
  3 import java.io.FileInputStream;
  4 import java.io.FileOutputStream;
  5 import java.io.IOException;
  6 import java.nio.ByteBuffer;
  7 import java.nio.MappedByteBuffer;
  8 import java.nio.channels.FileChannel;
  9 import java.nio.file.Paths;
 10 import java.nio.file.StandardOpenOption;
 11 
 12 /**
 13  * 一、Channel:用于源节点与目标节点之间的连接。在Java NIO中，负责缓冲区中数据传输，Channel本身不存储数据，因此需要配合缓冲区进行传输。
 14  *
 15  * 二、Channel的实现类：
 16  *     java.nio.channels.Channel 接口：
 17  *     |-- FileChannel
 18  *     |-- SocketChannel
 19  *     |-- ServerSocketChannel
 20  *     |-- DatagramChannel
 21  *
 22  * 三、获取通道Channel
 23  * 1.Java针对支持通道的类提供了getChannel()方法
 24  *   本地IO
 25  *   FileInputStream/FileOutputStream
 26  *   RandomAccessFile
 27  *
 28  *   网络IO:
 29  *   Socket
 30  *   ServerSocket
 31  *   DatagramSocket
 32  *
 33  * 2.在jdk1.7中的NIO.2针对各个通道提供了静态方法open()
 34  *
 35  * 3.在jdk1.7中的NIO.2的Files工具类的newByteChannel()
 36  *
 37  * 四、通道之间的数据传输
 38  * transferFrom()
 39  * transferTo()
 40  *
 41  */
 42 public class TestChannel {
 43 
 44     public static void main(String[] args) throws IOException {
 45 
 46         /*
 47          * 1.利用通道完成文件的复制（非直接缓冲区）
 48          */
 49         FileInputStream fis = null;
 50         FileOutputStream fos = null;
 51 
 52         FileChannel inChannel = null;
 53         FileChannel outChannel = null;
 54 
 55         try {
 56             fis = new FileInputStream("1.jpg");
 57             fos = new FileOutputStream("2.jpg");
 58             //1.获取通道
 59             inChannel = fis.getChannel();
 60             outChannel = fos.getChannel();
 61 
 62             //2.分配指定大小的缓冲区
 63             ByteBuffer buffer = ByteBuffer.allocate(1024);
 64 
 65             //3.将通道中的数据缓冲区中
 66             while (inChannel.read(buffer) != -1) {
 67 
 68                 buffer.flip();//切换成都数据模式
 69 
 70                 //4.将缓冲区中的数据写入通道中
 71                 outChannel.write(buffer);
 72                 buffer.clear();//清空缓冲区
 73             }
 74         } catch (Exception e) {
 75             e.printStackTrace();
 76         } finally {
 77             if (outChannel != null) {
 78                 try {
 79                     outChannel.close();
 80                 } catch (IOException e) {
 81                     e.printStackTrace();
 82                 }
 83             }
 84 
 85             if (inChannel != null) {
 86                 try {
 87                     inChannel.close();
 88                 } catch (IOException e) {
 89                     e.printStackTrace();
 90                 }
 91             }
 92 
 93             if (fis != null) {
 94                 try {
 95                     fis.close();
 96                 } catch (IOException e) {
 97                     e.printStackTrace();
 98                 }
 99             }
100 
101             if (fos != null) {
102                 try {
103                     fos.close();
104                 } catch (IOException e) {
105                     e.printStackTrace();
106                 }
107             }
108         }
109 
110 
111         /*
112          * 2.利用（直接缓冲区）通道完成文件的复制(内存映射文件的方式)
113          */
114 
115         long start = System.currentTimeMillis();
116         FileChannel inChannel2 = FileChannel.open(Paths.get("1.jpg"), StandardOpenOption.READ);
117         FileChannel outChannel2 = FileChannel.open(Paths.get("3.jpg"), StandardOpenOption.WRITE, StandardOpenOption.READ, StandardOpenOption.CREATE);
118 
119         //内存映射文件
120         MappedByteBuffer inMappedBuf = inChannel2.map(FileChannel.MapMode.READ_ONLY, 0, inChannel.size());
121         MappedByteBuffer outMappedBuf = outChannel2.map(FileChannel.MapMode.READ_WRITE, 0, inChannel.size());
122 
123         //直接对缓冲区进行数据读写操作
124         byte[] dst = new byte[inMappedBuf.limit()];
125         inMappedBuf.get(dst);
126         outMappedBuf.put(dst);
127 
128         inChannel2.close();
129         outChannel2.close();
130 
131         long end = System.currentTimeMillis();
132         System.out.println("耗费的时间为：" + (end - start));
133 
134         /*
135          * 通道之间的数据传输（直接缓冲区）
136          */
137         FileChannel inChannel3 = FileChannel.open(Paths.get("1.jpg"), StandardOpenOption.READ);
138         FileChannel outChannel3 = FileChannel.open(Paths.get("3.jpg"), StandardOpenOption.WRITE, StandardOpenOption.READ, StandardOpenOption.CREATE);
139 
140         inChannel3.transferTo(0, inChannel3.size(), outChannel3);
141         //等价于
142 //        outChannel3.transferFrom(inChannel3, 0, inChannel3.size());
143 
144         inChannel3.close();
145         outChannel3.close();
146     }
147 }