Hadoop中map()方法的接口和源代码以及操作示例是什么？

●   public void map(Text relPath,CopyListingFileStatus sourceFileStatus,           Context context) throws IOException,InterruptedException


从输入参数可以看出来，这其实就是对上面分析过的UniformSizeInputFormat类里分片后的数据里的每一行进行处理，每行里存放的就是“K-V”对，也就是fileList.seq文件每行的内容。Map方法体前半部分有一大堆代码内容，其实都是一些准备和判断工作，为后面的拷贝服务，最终的拷贝动作发生在copyFileWithRetry(description,sourceCurrStatus, target, context, action, fileAttributes)这个函数中，进入这个函数一直往里面读，就能看到数据最终通过常用的Java输入输出流的方式完成点对点拷贝，最后拷贝方法源码如下：

 




 
long copyBytes(FileStatus sourceFileStatus, long    sourceOffset,

      OutputStream    outStream, int bufferSize, Mapper.Context    context)

      throws    IOException {

    Path    source = sourceFileStatus.getPath();

    byte    buf[] = new byte[bufferSize];

    ThrottledInputStream    inStream = null;

    long    totalBytesRead = 0;

 

    try    {

      inStream    = getInputStream(source, context.getConfiguration());

      int    bytesRead = readBytes(inStream, buf, sourceOffset);

      while    (bytesRead >= 0) {

           totalBytesRead += bytesRead;

        if    (action == FileAction.APPEND) {

             sourceOffset += bytesRead;

        }

           outStream.write(buf, 0, bytesRead);

           updateContextStatus(totalBytesRead, context, sourceFileStatus);

           bytesRead = readBytes(inStream, buf, sourceOffset);

      }

         outStream.close();

         outStream = null;

    } finally    {

      IOUtils.cleanup(LOG,    outStream, inStream);

    }

    return    totalBytesRead;

}