Apache Flink-如何实现实现DeserializationSchema的自定义Deserializer [英] Apache Flink - How to implement custom Deserializer implementing DeserializationSchema

问题描述

我正在使用Flink，并且正在使用Kafka连接器.我从flink收到的消息是用逗号分隔的项目列表."'a'，'b'，'c'，1,0.1 ....'12:01:00.000'''其中一个包含事件时间，我想将此事件时间用于每个分区的加水印(在kafka源代码中)，然后将该事件时间用于会话窗口.我的情况与通常情况有所不同，因为据我了解，人们通常使用"kafka Timestamps"和SimpleStringSchema().在我的情况下，我必须编写自己的反序列化器以实现DeserializationSchema并返回一个Tuple或Pojo.因此，基本上用我自己的函数替换SimpleStringSchema().Flink开箱即用地提供了一些反序列化器，但是我真的不理解如何创建自定义反序列化逻辑.

检查flink网站，我发现了这一点:

我已经举了一个例子(谢谢大卫！)，但是我仍然不知道如何实现我的例子.

解决方案

您应该像这样介绍POJO

 公共类事件实现了可序列化的{...私人长时间戳；} 

并实现与链接中类似的简单反序列化器-您可以解析该行，或者用逗号手动分割消息字符串，也可以使用现成的csv阅读器，例如 公共类EventDeserializationSchema实现DeserializationSchema< Event>.{私有静态最终长serialVersionUID = 1L;@Override公共ClickEvent解串(字节[]消息)引发IOException {字符串行=新字符串(message，StandardCharsets.UTF_8);String []部分= line.split(，");事件event = new Event();//TODO:此处的活动零件返回事件；}@Overridepublic boolean isEndOfStream(Event nextElement){返回false；}@Override公共TypeInformation< Event>getProducedType(){返回TypeInformation.of(Event.class);}}

I'm working with Flink and I'm using the Kafka Connector. The messages that I'm receiving from flink is a list of comma separated items. "'a','b','c',1,0.1 ....'12:01:00.000'" One of them contain the event time, I would like to use this event time for the per-partition watermarking (in the kafka source), then use this Event Time for session windowing. My case is a bit different from usual because from what i have understood people usually use "kafka Timestamps" and SimpleStringSchema(). On my case instead I have to write my own deserializer that implement DeserializationSchema and return a Tuple or Pojo. So basically substitute the SimpleStringSchema() with my own function. Flink offer out of the box some deserializers but I really don't understnd how i can create a custom deserialization logic.

Checking the flink website i have found this:

https://ci.apache.org/projects/flink/flink-docs-release-1.11/dev/connectors/kafka.html

I have been given an example (Thanks David!), but still i don't get how to implement mine.

https://github.com/apache/flink-playgrounds/blob/master/docker/ops-playground-image/java/flink-playground-clickcountjob/src/main/java/org/apache/flink/playgrounds/ops/clickcount/records/ClickEventDeserializationSchema.java

I would really need an example of how I can do it for a list. The one indicated above is for JSON so is giving me the theory, the concept but i got stuck there.

解决方案

You should introduce the POJO like

public class Event implements Serializable {
    ...
    private Long timestamp;
}

and implement the simple deserializer similar to the one from the link - you can parse the line either manually splitting by comma the message string, or you an out-of-box csv readers, like opencsv, to parse the line into your POJO:

public class EventDeserializationSchema implements DeserializationSchema<Event> {

    private static final long serialVersionUID = 1L;

    @Override
    public ClickEvent deserialize(byte[] message) throws IOException {
        String line = new String(message, StandardCharsets.UTF_8);
        String[] parts = line.split(",");
        
        Event event = new Event();
        // TODO: parts to event here
        return event;
    }

    @Override
    public boolean isEndOfStream(Event nextElement) {
        return false;
    }

    @Override
    public TypeInformation<Event> getProducedType() {
        return TypeInformation.of(Event.class);
    }
}

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