Mapper类如何将SequenceFile标识为hadoop中的输入文件？(How does Mapper class identify the SequenceFile as inputfile in hadoop?)

 在我的一个MapReduce任务中，我将BytesWritable重写为KeyBytesWritable，并将ByteWritable重写为ValueBytesWritable。 然后我使用SequenceFileOutputFormat输出结果。 
 
 我的问题是当我开始下一个MapReduce任务时，我想使用这个SequenceFile作为输入文件。 那么我怎样才能设置工作类，以及Mapper类如何识别我之前被覆盖的SequenceFile中的键和值？ 
 
 我明白我可以使用SequenceFile.Reader来读取关键字和值。 
 
Configuration config = new Configuration();
Path path = new Path(PATH_TO_YOUR_FILE);
SequenceFile.Reader reader = new SequenceFile.Reader(FileSystem.get(config), path, config);
WritableComparable key = (WritableComparable) reader.getKeyClass().newInstance();
Writable value = (Writable) reader.getValueClass().newInstance();
while (reader.next(key, value))
 
 但是我不知道如何使用这个Reader将键和值作为参数传递给Mapper类。 我怎样才能将Conf.setInputFormat设置为SequenceFileInputFormat，然后让Mapper获得关键字和值？ 
 
 谢谢 

In my one MapReduce task, I override the BytesWritable as KeyBytesWritable, and override the ByteWritable as ValueBytesWritable. Then I output the result using SequenceFileOutputFormat.
 
My question is when I start the next MapReduce task, I want to use this SequenceFile as inputfile. So how could I set the jobclass, and how the Mapper class could identify the key and value in the SequenceFile which I overrided before?
 
I understand that I could SequenceFile.Reader to read the key and value.
 
Configuration config = new Configuration();
Path path = new Path(PATH_TO_YOUR_FILE);
SequenceFile.Reader reader = new SequenceFile.Reader(FileSystem.get(config), path, config);
WritableComparable key = (WritableComparable) reader.getKeyClass().newInstance();
Writable value = (Writable) reader.getValueClass().newInstance();
while (reader.next(key, value))
 
But I don't know how to use this Reader to pass the key and value into Mapper class as Parameters. How could I set conf.setInputFormat to SequenceFileInputFormat and then let Mapper get the key and values?
 
Thanks 

原文：https://stackoverflow.com/questions/15179456