Although the framework currently allows one HBase table as input to a MapReduce job, other HBase tables can be accessed as lookup tables, etc., in a MapReduce job via creating an HTable instance in the setup method of the Mapper.

public class MyMapper extends TableMapper<Text, LongWritable> {
  private HTable myOtherTable;

  public void setup(Context context) {
    myOtherTable = new HTable("myOtherTable");
  }

  public void map(ImmutableBytesWritable row, Result value, Context context) throws IOException, InterruptedException {
	// process Result...
	// use 'myOtherTable' for lookups
  }