Identity Mapper: Identity Mapper is referred to as the default Mapper class which is provided by Hadoop. When there is no other Mapper class defined, identity mapper will be executed. It is only capable of writing the input data into output and does not perform any calculations and computations on the input data. The class name is org.apache.hadoop.mapred.lib.IdentityMapper.
Chain Mapper: Chain Mapper is referred to as the implementation of a simple Mapper class through which the chain operations across a set of Mapper classes, within a single map task. In the chain mapper, the output from the first mapper will become the input for the second mapper, and the output of the second mapper will be the input for the third mapper and so on till the last mapper. The class name is org.apache.hadoop.MapReduce.lib.ChainMapper.
