java之通過FileChannel實(shí)現(xiàn)文件復(fù)制

1、FileChanel介紹

Java NIO FileChannel是連接文件的通道，從文件中讀取數(shù)據(jù)和將數(shù)據(jù)寫入文件。Java NIO FileChannel類是NIO用于替代使用標(biāo)準(zhǔn)Java IO API讀取文件的方法。

FileInputStream的getChannel方法獲取的文件通道是只讀的，當(dāng)然通過FileOutputStream的getChannel的方法獲取的文件通道是可寫的

部分API

1）、truncate截?cái)辔募δ?br>
       /**
         * 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()強(qiáng)制在內(nèi)存中的數(shù)據(jù)刷新到硬盤中去

        /**
         * 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可以看出是拷貝從源的position位置的count 字節(jié)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、復(fù)制文件常用方法

1、通過普通輸入輸出流復(fù)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;
                //讀取到輸入流數(shù)據(jù)，然后寫入到輸出流中去，實(shí)現(xiàn)復(fù)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、通過 FileChannel復(fù)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();
            }
        }

 
3、總結(jié)

一般復(fù)制使用輸入輸出流進(jìn)行操作，用源文件創(chuàng)建出一個(gè)輸入流，用目標(biāo)文件創(chuàng)建出一個(gè)輸出流，把輸入流的數(shù)據(jù)讀取寫入到輸出流，用fileChannel，直接連接輸入輸出流的文件通道，將數(shù)據(jù)直接寫入到目標(biāo)文件中，效率很高，尤其是復(fù)制文件比較大的時(shí)候，我們一般采用fileChannel復(fù)制文件。




作者：chen.yu
深信服三年半工作經(jīng)驗(yàn)，目前就職游戲廠商，希望能和大家交流和學(xué)習(xí),
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