Hadoop的OutputFormat和InputFormat
Hadoop用于数据的输入和输出，需要指定OutputFormat和InputFormat，这两个类的目的是为了指明读数据和写数据相关的包括格式等信息。InputFormat：
public abstract
List<InputSplit> getSplits(JobContext context
) throws IOException, InterruptedException;
public abstract
RecordReader<K,V> createRecordReader(InputSplit split,
TaskAttemptContext context
) throws IOException,
InterruptedException;
createRecordReader：指明具体的读操作
getSplits：获取要读的数据块
我们可以看到InputSplit的类：
public abstract long getLength() throws IOException, InterruptedException;
public abstract
String[] getLocations() throws IOException, InterruptedException;
具体的路径和长度
OutputFormat：
public abstract RecordWriter<K, V>
getRecordWriter(TaskAttemptContext context
) throws IOException, InterruptedException;
public abstract void checkOutputSpecs(JobContext context
) throws IOException,
InterruptedException;
public abstract
OutputCommitter getOutputCommitter(TaskAttemptContext context
) throws IOException, InterruptedException;
getRecordWriter：具体记录的写的方式
checkOutputSpecs：检测数据输出空间
getOutputCommitter：写flush操作
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