BewareMyPower commented on issue #12087:
URL: https://github.com/apache/pulsar/issues/12087#issuecomment-922235898
There're something in addition to the implementation.
Before this proposal, I tried to add following method.
```java
/**
* Set the payload converter class.
*
* The class must implement
org.apache.pulsar.common.api.raw.PayloadConverter in pulsar-common module.
Otherwise,
* this method will fail silently. If this method was called
successfully, each time a message arrived, the raw
* payload will be replaced by a new payload returned by
PayloadConverter#convert(ByteBuf).
*
* @param clazz
* @return
*/
ConsumerBuilder<T> payloadConverterClass(Class<?> clazz);
```
It's simple but looks ugly. After discussing with @codelipenghui, I adopted
the current way to load converter at runtime. But there's something different.
@codelipenghui's original opinion was that no changes should be made for client
configs like `ConsumerBuilder`. However, there're some flaws for this solution.
Because reflection brings overhead when creating a consumer. Though the
overhead might not be significant, we should still avoid it for the regular
cases.
I've thought of another solution that all consumers share the same converter
so that the class loader could only be called once. But it might become
complicated if there're multiple entry formats. For example, assuming we've
enabled KoP, AoP, MoP for the same broker and there're three different entry
formats. With PIP 96, we can implement three converters like:
- org.apache.pulsar.client.converter.kop.KafkaPayloadConverter
- org.apache.pulsar.client.converter.aop.AmqpPayloadConverter
- org.apache.pulsar.client.converter.mop.MqttPayloadConverter
Then we can create three consumers using a common `PulsarClient`. It's also
why I configured the converter package at consumer level instead of client
level.
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