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.

Note

Don’t issue blocking calls (includes synchronous API calls to Lettuce) from inside of callbacks such as the streaming API as this would block the EventLoop. If you need to fetch data from Redis from inside a StreamingChannel callback, please use the asynchronous API or use the reactive API directly.

Example 1. Streaming results for HGETALL

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

Example 2. ValueStreamingChannel using a Redis 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 the following output:

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