Flink's sink: a preliminary study

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About sink

The following figure comes from Flink official , In the red box is sink, Visible real-time data from Source Start at , stay Transformation After the business logic is completed in sink end , therefore sink It can be used to process the calculation results , For example, console output or save database ：

About 《Flink Of sink actual combat 》 Series articles

This article is about 《Flink Of sink actual combat 》 The first chapter of , In order to have a preliminary understanding of sink, Through the basic API and addSink Method analysis and research , Lay a good foundation for the subsequent coding practice ;

Full series Links

1. 《Flink Of sink One of the real battles ： On 》
2. 《Flink Of sink The second part of the actual battle ：kafka》
3. 《Flink Of sink The third part of the actual battle ：cassandra3》
4. 《Flink Of sink The fourth part of the actual battle ： Customize 》

Start with an instance code

1. Here is a simple flink Application code , The red box print The way is sink operation ：
   
2. Here's the official sink The way , All are DataStream Class API, It can be directly called sink, Just in the code print It's one of them ：
   
3. Let's look at the picture above API Source code , First look at print Method , stay DataStream.java in , as follows , It's actually called addSink Method , Participation is PrintSinkFunction：
   
4. The other is often used API yes writeAsText, Source code is as follows , Called writeUsingOutputFormat Method ：
   
5. track writeUsingOutputFormat Discovery is also called addSink, Participation is OutputFormatSinkFunction：
   
6. print and writeAsText Behind the call addSink, So another common writeAsCsv Methods? ？ It's a call addSink？ Open it and see , and writeAsText Same call writeUsingOutputFormat, In this method, you are calling addSink：
   
7. in summary ,data sink The key is addSink Input , namely SinkFunction Interface implementation , Use class diagrams to visualize common sink How is ability realized ：

8. From the figure above, we can see the abstract class RichSinkFunction With all kinds of sink Ability is closely related , We should focus on it , Show method signature on class diagram , Here's the picture ：

9. As shown in the figure above ,RichSinkFunction There is no content in itself , But it does SinkFunction, Inherit AbstractRichFunction, yes RichFunction and SinkFunction The combination of these two characteristics ;
10. RichFunction The characteristics of are in front of 《Flink Of DataSource Trilogy 》 We already know , It's about resources open and close;
11. SinkFunction The characteristics of ？ It's obviously used to process the calculation results , The class diagram shows two invoke Method , Take a look at the official PrintSinkFunction.java：

12. writer.write(record) The source code is PrintSinkOutputWriter.java, As shown below ：

Summary

thus , We're right Flink Of sink With a basic understanding ：

1. Be responsible for the processing of real-time calculation results ( Like output or persistence );
2. The main implementation is to call DataStream.addSink Method ;
3. Various sink The realization of ability , The main way is to achieve addSink The interface defined by the input parameter of the method ;

Later chapters , Together with sink Let's practice the coding of the aspect , The direction of actual combat ： Experience the official sink Ability , Customize sink Ability to achieve ;

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