Java中文件複製的一個彙總

Java文件複製（包括NIO）

我們首先定義一個拷貝接口：

public interface FileCopyRunner {
    void copyFile(File source, File target) throws IOException;
}

最原始的複製方法（不涉及到緩存）

FileCopyRunner noBufferStreamCopy = (source, target) -> {
            int r;
            InputStream fin = null;
            OutputStream fout = null;

            try {
                fin = new FileInputStream(source);
                fout = new FileOutputStream(target);
                while ((r = fin.read()) != -1){
                    fout.write(r);
                }
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }finally {
                close(fin);
                close(fout);
            }
        };

上面是直接從源文件中讀取出來，然後寫入目標文件中。

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基於緩存的文件複製方式

FileCopyRunner bufferedStreamCp = (source, target) -> {
            InputStream fin;
            OutputStream fout;
            fin = new BufferedInputStream(new FileInputStream(source));
            fout = new BufferedOutputStream(new FileOutputStream(target));
            byte[] buffer = new byte[1024];
            int r ;
            while((r = fin.read(buffer)) != -1){
                fout.write(buffer,0,r);
            }
            close(fin);
            close(fout);
        };

上面我們定義了一個1024字節的buffer，每次讀取這麼一個大小放入緩存中，然後一次性寫入文件中。

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NIO方式複製

FileCopyRunner nioBufferCopy = (source, target) -> {
            FileChannel fin;
            FileChannel fout;

            fin = new FileInputStream(source).getChannel();
            fout = new FileOutputStream(target).getChannel();

            ByteBuffer buffer = ByteBuffer.allocate(1024);
            while(fin.read(buffer) != -1){
                buffer.flip();
                while(buffer.hasRemaining()) fout.write(buffer);
                buffer.clear();
            }

            close(fin);
            close(fout);
        };

上面的似乎有些複雜，下面是簡化版。

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簡化版NIO

FileCopyRunner nioTransferCopy = (source, target) -> {
            FileChannel fin = null;
            FileChannel fout = null;
            fin = new FileInputStream(source).getChannel();
            fout = new FileOutputStream(target).getChannel();
            long len = 0L;
            while (len != fin.size()) {
                len += fin.transferTo(0,fin.size(),fout);
            }
            close(fin);
            close(fout);
        };

下面是關閉流close函數的一個定義：

public static void close(Closeable closeable) throws IOException {
        if(closeable != null) closeable.close();
    }