java之通过FileChannel实现文件复制

1、FileChanel介绍

Java NIO FileChannel是连接文件的通道，从文件中读取数据和将数据写入文件。Java NIO FileChannel类是NIO用于替代使用标准Java IO API读取文件的方法。

FileInputStream的getChannel方法获取的文件通道是只读的，当然通过FileOutputStream的getChannel的方法获取的文件通道是可写的

部分API

1）、truncate截断文件功能

   /*** Truncates the file underlying this channel to a given size. Any bytes* beyond the given size are removed from the file. If there are no bytes* beyond the given size then the file contents are unmodified.* <p>* If the file position is currently greater than the given size, then it is* set to the new size.** @param size*            the maximum size of the underlying file.* @throws IllegalArgumentException*             if the requested size is negative.* @throws ClosedChannelException*             if this channel is closed.* @throws NonWritableChannelException*             if the channel cannot be written to.* @throws IOException*             if another I/O error occurs.* @return this channel.*/public abstract FileChannel truncate(long size) throws IOException;

2）、force()强制在内存中的数据刷新到硬盘中去

    /*** Requests that all updates to this channel are committed to the storage* device.* <p>* When this method returns, all modifications made to the platform file* underlying this channel have been committed if the file resides on a* local storage device. If the file is not hosted locally, for example on a* networked file system, then applications cannot be certain that the* modifications have been committed.* <p>* There are no assurances given that changes made to the file using methods* defined elsewhere will be committed. For example, changes made via a* mapped byte buffer may not be committed.* <p>* The <code>metadata</code> parameter indicates whether the update should* include the file's metadata such as last modification time, last access* time, etc. Note that passing <code>true</code> may invoke an underlying* write to the operating system (if the platform is maintaining metadata* such as last access time), even if the channel is opened read-only.** @param metadata*            {@code true} if the file metadata should be flushed in*            addition to the file content, {@code false} otherwise.* @throws ClosedChannelException*             if this channel is already closed.* @throws IOException*             if another I/O error occurs.*/public abstract void force(boolean metadata) throws IOException;

3）、transferFrom可以看出是拷贝从源的position位置的count 字节大小

    /*** Reads up to {@code count} bytes from {@code src} and stores them in this* channel's file starting at {@code position}. No bytes are transferred if* {@code position} is larger than the size of this channel's file. Less* than {@code count} bytes are transferred if there are less bytes* remaining in the source channel or if the source channel is non-blocking* and has less than {@code count} bytes immediately available in its output* buffer.* <p>* Note that this channel's position is not modified.** @param src*            the source channel to read bytes from.* @param position*            the non-negative start position.* @param count*            the non-negative number of bytes to transfer.* @return the number of bytes that are transferred.* @throws IllegalArgumentException*             if the parameters are invalid.* @throws NonReadableChannelException*             if the source channel is not readable.* @throws NonWritableChannelException*             if this channel is not writable.* @throws ClosedChannelException*             if either channel has already been closed.* @throws AsynchronousCloseException*             if either channel is closed by other threads during this*             operation.* @throws ClosedByInterruptException*             if the thread is interrupted during this operation.* @throws IOException*             if any I/O error occurs.*/public abstract long transferFrom(ReadableByteChannel src, long position,long count) throws IOException;

2、复制文件常用方法

1、通过普通输入输出流复制文件

    public void copyFile(File srcFile, File dstFile) throws FileNotFoundException {InputStream inputStream = null;OutputStream outputStream = null;try {inputStream = new BufferedInputStream(new FileInputStream(srcFile));outputStream = new BufferedOutputStream(new FileOutputStream(dstFile));byte[] bytes = new byte[1024];int i;//读取到输入流数据，然后写入到输出流中去，实现复制while ((i = inputStream.read(bytes)) != -1) {outputStream.write(bytes, 0, i);}} catch (Exception e) {e.printStackTrace();} finally {try {if (inputStream != null)inputStream.close();if (outputStream != null)outputStream.close();} catch (IOException e) {e.printStackTrace();}}}

2、通过 FileChannel复制文件

	public void copyFile(File srcFile, File dstFile) throws IOException {if (srcFile == null || !srcFile.exists()) {return;}if (dstFile == null || !dstFile.exists()) {return;}FileInputStream fileIns = null;FileOutputStream fileOuts = null;FileChannel source = null;FileChannel destination = null;try {fileIns = new FileInputStream(srcFile);fileOuts = new FileOutputStream(dstFile);source = fileIns.getChannel();destination = fileOuts.getChannel();destination.transferFrom(source, 0, source.size());} catch (Exception e) {e.printStackTrace();} finally {if (fileIns != null)fileIns.close();if (fileOuts != null)fileOuts.close();if (source != null)source.close();if (destination != null)destination.close();}}