flink multiple output

Flink Multiple Output is a feature in Apache Flink that allows users to write data to multiple destinations from a single data stream. This feature is particularly useful when you need to write the same data to different sinks, for example, when you need to store data in multiple databases or send it to multiple messaging systems.

To use Flink Multiple Output, you need to define your sinks and the output tags that correspond to each sink. An output tag is a unique identifier that you associate with each sink. You can define your sinks and output tags using the OutputTag class.

Once you have defined your sinks and output tags, you can use the split() function to split your data stream into multiple streams based on some criteria. For example, you could split the stream based on the value of a certain field in the data. You can then use the sideOutput() function to write data to each sink using the corresponding output tag.

Here is an example of how to use Flink Multiple Output:

// Define your sinks and output tags
OutputTag<String> firstOutputTag = new OutputTag<String>("first-output"){};
OutputTag<String> secondOutputTag = new OutputTag<String>("second-output"){};

DataStream<String> stream = ... // your data stream

// Split the stream into two streams based on some criteria
SingleOutputStreamOperator<String> firstStream = stream
    .filter(data -> data.startsWith("A"))
    .map(data -> data.toUpperCase())
    .returns(Types.STRING)
    .name("First Stream")
    .tag(firstOutputTag);

SingleOutputStreamOperator<String> secondStream = stream
    .filter(data -> data.startsWith("B"))
    .map(data -> data.toLowerCase())
    .returns(Types.STRING)
    .name("Second Stream")
    .tag(secondOutputTag);

// Write data to each sink using the corresponding output tag
firstStream.getSideOutput(firstOutputTag).addSink(... // first sink);
secondStream.getSideOutput(secondOutputTag).addSink(... // second sink);

In this example, we define two output tags, `firstOutputTag` and `secondOutputTag`, and use them to split the data stream into two streams, `firstStream` and `secondStream`. We then use the `getSideOutput()` function to write data to each sink using the corresponding output tag.

Overall, Flink Multiple Output is a powerful feature that can help you write data to multiple sinks from a single data stream. It can simplify your code and improve your application's performance and scalability.