Transactional Kafka Producer per thread (#882)

* Update documentation

* Add code snippets

src/main/docs/guide/kafkaClient/kafkaClientTx.adoc

@@ -1,5 +1,9 @@
 Transaction processing can be enabled by defining `transactionalId` on `@KafkaClient`, which will initialize the producer for transactional usage and wrap any send operation with a transaction demarcation.
 
+.Transactional Client
+
+snippet::io.micronaut.kafka.docs.producer.config.TransactionalClient[tags = 'clazz']
+
 .Alternative Kafka producer transactional code
 [source,java]
 ----
@@ -11,4 +15,13 @@ try {
 } catch (Exception e) {
     producer.abortTransaction();
 }
-----
+----
+
+[NOTE]
+====
+`@KafkaClient` beans are by default singleton. When using multiple threads, you must either synchronize access to the individual instance or declare the bean as `@Prototype`. Additionally, you can use link:https://docs.micronaut.io/latest/guide/#_using_random_properties[random properties] to your advantage so that each instance of your producer gets a different transactional ID.
+
+.Random transactional ID
+
+snippet::io.micronaut.kafka.docs.producer.config.RandomTransactionalIdClient[tags = 'clazz']
+====

test-suite-groovy/src/test/groovy/io/micronaut/kafka/docs/producer/config/RandomTransactionalIdClient.groovy

@@ -0,0 +1,14 @@
+package io.micronaut.kafka.docs.producer.config
+
+import io.micronaut.configuration.kafka.annotation.KafkaClient
+import io.micronaut.context.annotation.Prototype
+import io.micronaut.context.annotation.Requires
+
+@Requires(property = "spec.name", value = "RandomTransactionalIdClientTest")
+// tag::clazz[]
+@Prototype
+@KafkaClient(id = "my-client", transactionalId = 'my-tx-id-${random.uuid}')
+interface RandomTransactionalIdClient {
+    // define client API
+}
+// end::clazz[]

test-suite-groovy/src/test/groovy/io/micronaut/kafka/docs/producer/config/TransactionalClient.groovy

@@ -0,0 +1,12 @@
+package io.micronaut.kafka.docs.producer.config
+
+import io.micronaut.configuration.kafka.annotation.KafkaClient
+import io.micronaut.context.annotation.Requires
+
+@Requires(property = "spec.name", value = "TransactionalClientTest")
+// tag::clazz[]
+@KafkaClient(id = "my-client", transactionalId = "my-tx-id")
+interface TransactionalClient {
+    // define client API
+}
+// end::clazz[]

test-suite-kotlin/src/test/kotlin/io/micronaut/kafka/docs/producer/config/RandomTransactionalIdClient.kt

@@ -0,0 +1,14 @@
+package io.micronaut.kafka.docs.producer.config
+
+import io.micronaut.configuration.kafka.annotation.KafkaClient
+import io.micronaut.context.annotation.Prototype
+import io.micronaut.context.annotation.Requires
+
+@Requires(property = "spec.name", value = "RandomTransactionalIdClientTest")
+// tag::clazz[]
+@Prototype
+@KafkaClient(id = "my-client", transactionalId = "my-tx-id-\${random.uuid}")
+interface RandomTransactionalIdClient {
+    // define client API
+}
+// end::clazz[]

test-suite-kotlin/src/test/kotlin/io/micronaut/kafka/docs/producer/config/TransactionalClient.kt

@@ -0,0 +1,12 @@
+package io.micronaut.kafka.docs.producer.config
+
+import io.micronaut.configuration.kafka.annotation.KafkaClient
+import io.micronaut.context.annotation.Requires
+
+@Requires(property = "spec.name", value = "TransactionalClientTest")
+// tag::clazz[]
+@KafkaClient(id = "my-client", transactionalId = "my-tx-id")
+interface TransactionalClient {
+    // define client API
+}
+// end::clazz[]

test-suite/src/test/java/io/micronaut/kafka/docs/producer/config/RandomTransactionalIdClient.java

@@ -0,0 +1,14 @@
+package io.micronaut.kafka.docs.producer.config;
+
+import io.micronaut.configuration.kafka.annotation.KafkaClient;
+import io.micronaut.context.annotation.Prototype;
+import io.micronaut.context.annotation.Requires;
+
+@Requires(property = "spec.name", value = "RandomTransactionalIdClientTest")
+// tag::clazz[]
+@Prototype
+@KafkaClient(id = "my-client", transactionalId = "my-tx-id-${random.uuid}")
+public interface RandomTransactionalIdClient {
+    // define client API
+}
+// end::clazz[]

test-suite/src/test/java/io/micronaut/kafka/docs/producer/config/TransactionalClient.java

@@ -0,0 +1,12 @@
+package io.micronaut.kafka.docs.producer.config;
+
+import io.micronaut.configuration.kafka.annotation.KafkaClient;
+import io.micronaut.context.annotation.Requires;
+
+@Requires(property = "spec.name", value = "TransactionalClientTest")
+// tag::clazz[]
+@KafkaClient(id = "my-client", transactionalId = "my-tx-id")
+public interface TransactionalClient {
+    // define client API
+}
+// end::clazz[]