Java-NIO（五）：通道（Channel）的数据传输与内存映射文件

2     public void testChannel() throws IOException {
3         FileInputStream fileInputStream = new FileInputStream("Java NIO.pdf");
4         FileOutputStream fileOutputStream = new FileOutputStream("2.pdf");
5
6         // 1、获取通道
7         FileChannel inChannel = fileInputStream.getChannel();
8         FileChannel outChannel = fileOutputStream.getChannel();
9
10         // 2.分配指定大小的缓冲区
11         ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
12
13         // 3、将通道的数据读入缓冲区
14         while (inChannel.read(byteBuffer) != -1) {
15             byteBuffer.flip();// 切换缓冲区为读模式
16             // 4、把缓冲区的数据写入通道
17             outChannel.write(byteBuffer);
18             byteBuffer.clear();// 因为需要循环多次读，需要清空缓冲区。
19         }
20
21         byteBuffer.clear();
22         inChannel.close();
23         outChannel.close();
24         fileInputStream.close();
25         fileOutputStream.close();
26     }

2      * 内存映射文件
3      *
4      * @throws IOException
5      */
6     @Test
7     public void testMemoryMappingFile() throws IOException {
8         long start = System.currentTimeMillis();
9
10         FileChannel inChannel = FileChannel.open(Paths.get("D:\\nio.zip"), StandardOpenOption.READ);
11         // 注意：StandardOpenOption.CREATE
12         // 如果文件已经存在，直接覆盖，StandardOpenOption.CREATE_NEW,如果文件已经存在，就抛出异常。
13         FileChannel outChannel = FileChannel.open(Paths.get("E:\\nio.zip"), StandardOpenOption.READ,
14                 StandardOpenOption.WRITE, StandardOpenOption.CREATE);
15
16         // 获取内存映射文件
17         MappedByteBuffer inMappedByteBuffer = inChannel.map(MapMode.READ_ONLY, 0, inChannel.size());
18         MappedByteBuffer outMappedByteBuffer = outChannel.map(MapMode.READ_WRITE, 0, inChannel.size());
19
20         // 直接对数据进行读写
21         byte[] bytes = new byte[inMappedByteBuffer.limit()];
// 此时，如果数据读超出了一定返回会抛出异常。如果内存不足时，会抛出java.lang.OutOfMemoryError: Java heap space
22         inMappedByteBuffer.get(bytes);
23         outMappedByteBuffer.put(bytes);
24
25         inChannel.close();
26         outChannel.close();
27         long end = System.currentTimeMillis();
28
29         System.out.println((end - start));
30     }

2         FileChannel inChannel = FileChannel.open(Paths.get("D:\\nio.zip"), StandardOpenOption.READ);
3         // 注意：StandardOpenOption.CREATE
4         // 如果文件已经存在，直接覆盖，StandardOpenOption.CREATE_NEW,如果文件已经存在，就抛出异常。
5         FileChannel outChannel = FileChannel.open(Paths.get("E:\\nio.zip"), StandardOpenOption.READ,
6                 StandardOpenOption.WRITE, StandardOpenOption.CREATE);
7
8         //inChannel.transferTo(0, inChannel.size(), outChannel);
9         outChannel.transferFrom(inChannel, 0, inChannel.size());
10     }