Java-NIO（五）：通道（Channel）的数据传输与内存映射文件

  • 通道（Channel）的数据传输(采用非直接缓冲区)
 1     @Test
 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     }
  •  内存映射文件（采用直接缓冲区） 
 1     /**
 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     }
  • transferTo&transferFrom将数据从源通道传输到其他 Channel 中(采用直接缓存区)
 1     public void testTransfer() throws IOException {
 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     }

 

posted @ 2017-07-31 16:52  cctext  阅读(828)  评论(0)  编辑  收藏  举报