Acknowledgment (spring-kafka 2.9.1 API)

```
public interface Acknowledgment
```
Handle for acknowledging the processing of a ConsumerRecord. Recipients can store the reference in asynchronous scenarios, but the internal state should be assumed transient (i.e. it cannot be serialized and deserialized later)

Method Summary

All Methods Instance Methods Abstract Methods Default Methods
Modifier and Type	Method	Description
`void`	`acknowledge()`	Invoked when the record or batch for which the acknowledgment has been created has been processed.
`default void`	`nack(int index, long sleepMillis)`	Negatively acknowledge the record at an index in a batch - commit the offset(s) of records before the index and re-seek the partitions so that the record at the index and subsequent records will be redelivered after the sleep time (in milliseconds).
`default void`	`nack(long sleepMillis)`	Negatively acknowledge the current record - discard remaining records from the poll and re-seek all partitions so that this record will be redelivered after the sleep time (in milliseconds).

- Method Detail
  - acknowledge
```
void acknowledge()
```
    Invoked when the record or batch for which the acknowledgment has been created has been processed. Calling this method implies that all the previous messages in the partition have been processed already.
  - nack
```
default void nack(long sleepMillis)
```
    Negatively acknowledge the current record - discard remaining records from the poll and re-seek all partitions so that this record will be redelivered after the sleep time (in milliseconds). Must be called on the consumer thread.
    
    Parameters:
    
    sleepMillis - the time to sleep in milliseconds; the actual sleep time will be larger of this value and the container's maxPollInterval, which defaults to 5 seconds.
    
    Since:
    
    2.3
  - nack
```
default void nack(int index,
                  long sleepMillis)
```
    Negatively acknowledge the record at an index in a batch - commit the offset(s) of records before the index and re-seek the partitions so that the record at the index and subsequent records will be redelivered after the sleep time (in milliseconds). Must be called on the consumer thread.
    
    Parameters:
    
    index - the index of the failed record in the batch.
    
    sleepMillis - the time to sleep in milliseconds; the actual sleep time will be larger of this value and the container's maxPollInterval, which defaults to 5 seconds.
    
    Since:
    
    2.3