partitionKey property
Determines which shard in the stream the data record is assigned to. Partition keys are Unicode strings with a maximum length limit of 256 characters for each key. Amazon Kinesis Data Streams uses the partition key as input to a hash function that maps the partition key and associated data to a specific shard. Specifically, an MD5 hash function is used to map partition keys to 128-bit integer values and to map associated data records to shards. As a result of this hashing mechanism, all data records with the same partition key map to the same shard within the stream.
Implementation
final String partitionKey;