卡夫卡流序列化程序isKey始终为false

我编写了一个简单的卡夫卡序列化程序,以检查序列化程序-->configure方法可以告诉我当前的键是被序列化还是被赋值。 看看接口定义,应该是这样的,但是当我使用下面的代码时,isKey总是返回false。

有人能告诉我什么时候会触发配置方法吗?

我是否误解了isKey变量,它实际上表明了一些不同的东西?

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.ObjectNode;
import org.apache.kafka.common.errors.SerializationException;
import org.apache.kafka.common.header.Headers;
import org.apache.kafka.common.serialization.Serializer;
import org.apache.kafka.connect.data.Struct;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.Map;

public class KafkaSerializer<T> implements Serializer<T> {

    protected ObjectMapper objectMapper = new ObjectMapper();
    protected JsonSchemaUtils jsonSchema = new JsonSchemaUtils();

    private boolean isKey;

    @Override
    public void configure(Map<String, ?> configs, boolean isKey) {
        this.isKey = isKey;
        Serializer.super.configure(configs, isKey);
    }


    @Override
    public byte[] serialize(String topic, T data) {
        Struct value = (Struct) data;
        System.out.println("isKey: " + isKey);
        ObjectNode schemaNode = jsonSchema.envelopeSchema(value);
        ObjectNode payloadNode = jsonSchema.envelopePayload(value);

        ByteArrayOutputStream out = new ByteArrayOutputStream();
        ObjectNode result = jsonSchema.envelope(schemaNode, payloadNode);
        try {
            out.write(objectMapper.writeValueAsBytes(result));
            byte[] bytes = out.toByteArray();
            out.close();
            return bytes;
        } catch (JsonProcessingException e) {
            throw new SerializationException(e);
        } catch (IOException e) {
            e.printStackTrace();
        }
        return new byte[0];
    }

    @Override
    public byte[] serialize(String topic, Headers headers, T data) {
        return Serializer.super.serialize(topic, headers, data);
    }

    @Override
    public void close() {
        Serializer.super.close();
    }
}