Java拆分和文件合并

参考 https://blog.youkuaiyun.com/u013632755/article/details/80467324

上面的实现可能针对作者的个人需求，我做了精简将拆分和合并写在一起，直接上代码

class FileSplitMerge {
    //拆分文件
    public static void splitFile(String filePath, int fileCount) throws IOException {
        FileInputStream fis = new FileInputStream(filePath);
        FileChannel inputChannel = fis.getChannel();
        final long fileSize = inputChannel.size();
        long average = fileSize / fileCount;//平均值
        long startPosition = 0; //子文件开始位置
        long endPosition = average;//子文件结束位置

        for (int i = 0; i < fileCount; i++) {
            if (i + 1 == fileCount) {//不是最后一个文件
                endPosition = fileSize; //最后一个文件直接指向文件末尾
            }

            //写文件
            FileOutputStream fos = new FileOutputStream(filePath + (i + 1));
            FileChannel outputChannel = fos.getChannel();
            inputChannel.transferTo(startPosition, endPosition - startPosition, outputChannel);//通道传输文件数据
            outputChannel.close();
            fos.close();
            startPosition = endPosition;//这边不需要+1
            endPosition += average;
        }
        inputChannel.close();
        fis.close();
    }

    /**
     * 合并文件
     */
    public static void mergeFile(String subfileName, String endfileName, int num) throws Exception {
        FileOutputStream fos = new FileOutputStream(endfileName);
        FileChannel ofc = fos.getChannel();
        for (int i = 0; i< num ; i++) {
            FileInputStream fio = new FileInputStream(subfileName + (i+1));
            FileChannel cfio = fio.getChannel();
            long tnum = cfio.transferTo(0,cfio.size(), ofc);//直接使用transferTo，使用通道直接传输，快的很
//            System.out.println(tnum + "::" + cfio.size());//可能不一定能读到cfio.size()个bytes的数据，具体查看这个方法的说明
            cfio.close();
        }
        ofc.close();
    }

    public static void main(String[] args) throws Exception {
//        Scanner 从终端格式化读取数据
//        Scanner scanner = new Scanner(System.in);
//        scanner.nextLine();
        long startTime = System.currentTimeMillis();
        splitFile("/Users/dingmac/Downloads/java_reader_uml.png", 5);
        long endTime = System.currentTimeMillis();
        System.out.println("split 耗费时间： " + (endTime - startTime) + " ms");

        startTime = System.currentTimeMillis();
        mergeFile("/Users/dingmac/Downloads/java_reader_uml.png","/Users/dingmac/Downloads/java_reader_uml_merge.png",  5);
        endTime = System.currentTimeMillis();
        System.out.println("merge 耗费时间： " + (endTime - startTime) + " ms");
//        scanner.nextLine();
    }
}

运行结果

split 耗费时间： 36 ms
merge 耗费时间： 1 ms

 

如有问题请指正~