Streaming API

Redis can contain a huge set of data. Collections can burst your memory, when the amount of data is too massive for your heap. Lettuce can return your collection data either as List/Set/Map or can push the data on StreamingChannel interfaces.

StreamingChannels are similar to callback methods. Every method, which can return bulk data (except transactions/multi and some config methods) specifies beside a regular method with a collection return class also method which accepts a StreamingChannel. Lettuce interacts with a StreamingChannel as the data arrives so data can be processed while the command is running and is not yet completed.

There are 4 StreamingChannels accepting different data types:

• KeyStreamingChannel

• ValueStreamingChannel

• KeyValueStreamingChannel

• ScoredValueStreamingChannel

The result of the steaming methods is the count of keys/values/key-value pairs as long value.

Long count = redis.hgetall(new KeyValueStreamingChannel<String, String>()
    {
        @Override
        public void onKeyValue(String key, String value)
        {
            ...
        }
    }, key);

Streaming happens real-time to the redis responses. The method call (future) completes after the last call to the StreamingChannel.

Examples

ValueStreamingChannel using a list

redis.lpush("key", "one")
redis.lpush("key", "two")
redis.lpush("key", "three")

Long count = redis.lrange(new ValueStreamingChannel<String, String>()
    {
        @Override
        public void onValue(String value)
        {
            System.out.println("Value: " + value);
        }
    }, "key",  0, -1);

System.out.println("Count: " + count);

will produce following output:

Value: one
Value: two
Value: three
Count: 3