Java NIO Channel to Channel Transfers通道傳輸接口

在Java NIO中如果一個channel是FileChannel類型的，那麼他可以直接把資料傳輸到另一個channel。這個特性得益于FileChannel包含的transferTo和transferFrom兩個方法。

transferFrom()

FileChannel.transferFrom方法把資料從通道源傳輸到FileChannel：

RandomAccessFile fromFile = new RandomAccessFile("fromFile.txt", "rw");
FileChannel      fromChannel = fromFile.getChannel();

RandomAccessFile toFile = new RandomAccessFile("toFile.txt", "rw");
FileChannel      toChannel = toFile.getChannel();

long position = 0;
long count    = fromChannel.size();

toChannel.transferFrom(fromChannel, position, count);      

transferFrom的參數position和count表示目标檔案的寫入位置和最多寫入的資料量。如果通道源的資料小于count那麼就傳實際有的資料量。 另外，有些SocketChannel的實作在傳輸時隻會傳輸那些處于就緒狀态的資料，即使SocketChannel後續會有更多可用資料。是以，這個傳輸過程可能不會傳輸整個的資料。

transferTo()

RandomAccessFile fromFile = new RandomAccessFile("fromFile.txt", "rw");
FileChannel      fromChannel = fromFile.getChannel();

RandomAccessFile toFile = new RandomAccessFile("toFile.txt", "rw");
FileChannel      toChannel = toFile.getChannel();

long position = 0;
long count    = fromChannel.size();

fromChannel.transferTo(position, count, toChannel);