深入浅出Apache Pulsar（3）：Pulsar Schema

Pulsar Schema

Pulsar schema enables you to use language-specific types of data when constructing and handling messages from simple types to more complex application-specific types.

• 类型安全(序列化和反序列化)
• Schema 帮助 Pulsar 保留了数据在其他系统中原有的含义

Schema类型(Schema type)

• Primitive type

Producer producer = client.newProducer(Schema.STRING).create();
producer.newMessage().value("Hello Pulsar!").send();
Consumer consumer = client.newConsumer(Schema.STRING).subscribe();
consumer.receive();

• Complex type

1. keyvalue key/value pair.

Schema> schema = Schema.KeyValue(
Schema.INT32,
Schema.STRING,
KeyValueEncodingType.SEPARATED
);
// Producer
Producer> producer = client.newProducer(schema)
    .topic(TOPIC)
    .create();
final int key = 100;
final String value = "value-100";
producer.newMessage().value(new KeyValue<>(key, value)).send();
// Consumer
Consumer> consumer = client.newConsumer(schema)
    .topic(TOPIC).subscriptionName(SubscriptionName).subscribe();
Message> msg = consumer.receive();

2.struct AVRO, JSON, and Protobuf.

Producer producer = client.newProducer(Schema.AVRO(User.class)).create();
producer.newMessage().value(User.builder().userName("pulsar-user").userId(1L).build()).send();
Consumer consumer = client.newConsumer(Schema.AVRO(User.class)).subscribe();
User user = consumer.receive();

Schema工作方式(How does schema work)

Producer

Consumer

Schema管理(Schema manual management)

查询Schema

$ $PULSAR_HOME/bin/pulsar-admin schemas \
get persistent://public/default/spirit-avro-topic
$ $PULSAR_HOME/bin/pulsar-admin schemas \
get persistent://public/default/spirit-avro-topic \
--version=2

更新Schema

$ $PULSAR_HOME/bin/pulsar-admin schemas upload \
persistent://public/default/test-topic \
--filename $PULSAR_HOME/connectors/json-schema.json

提取Schema

$ $PULSAR_HOME/bin/pulsar-admin schemas \
extract persistent://public/default/test-topic  \
--classname com.cloudwise.modal.Packet \
--jar ~/cloudwise-pulsar-1.0.0-RELEASE.jar \
--type json
public void schemaInfo() {
    System.out.println("AvroSchema:" + AvroSchema.of(SeedEvent.class).getSchemaInfo());
    System.out.println("Schema.AVRO:" + Schema.AVRO(SeedEvent.class).getSchemaInfo());
}

删除Schema

$ $PULSAR_HOME/bin/pulsar-admin schemas \
delete persistent://public/default/spirit-avro-topic

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系列阅读

深入浅出Apache Pulsar（1）：Pulsar vs Kafka
深入浅出Apache Pulsar（2）：Pulsar消息机制