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/*
* Copyright 2016-2019 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.kafka.annotation;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.context.annotation.Import;
/**
* Enable Kafka listener annotated endpoints that are created under the covers by a
* {@link org.springframework.kafka.config.AbstractKafkaListenerContainerFactory
* AbstractListenerContainerFactory}. To be used on
* {@link org.springframework.context.annotation.Configuration Configuration} classes as
* follows:
*
*
* @Configuration
* @EnableKafka
* public class AppConfig {
* @Bean
* public ConcurrentKafkaListenerContainerFactory myKafkaListenerContainerFactory() {
* ConcurrentKafkaListenerContainerFactory factory = new ConcurrentKafkaListenerContainerFactory();
* factory.setConsumerFactory(consumerFactory());
* factory.setConcurrency(4);
* return factory;
* }
* // other @Bean definitions
* }
*
*
* The {@code KafkaListenerContainerFactory} is responsible to create the listener
* container for a particular endpoint. Typical implementations, as the
* {@link org.springframework.kafka.config.ConcurrentKafkaListenerContainerFactory
* ConcurrentKafkaListenerContainerFactory} used in the sample above, provides the
* necessary configuration options that are supported by the underlying
* {@link org.springframework.kafka.listener.MessageListenerContainer
* MessageListenerContainer}.
*
*
* {@code @EnableKafka} enables detection of {@link KafkaListener} annotations on any
* Spring-managed bean in the container. For example, given a class {@code MyService}:
*
*
* package com.acme.foo;
*
* public class MyService {
* @KafkaListener(containerFactory = "myKafkaListenerContainerFactory", topics = "myTopic")
* public void process(String msg) {
* // process incoming message
* }
* }
*
*
* The container factory to use is identified by the
* {@link KafkaListener#containerFactory() containerFactory} attribute defining the name
* of the {@code KafkaListenerContainerFactory} bean to use. When none is set a
* {@code KafkaListenerContainerFactory} bean with name
* {@code kafkaListenerContainerFactory} is assumed to be present.
*
*
* the following configuration would ensure that every time a message is received from
* topic "myQueue", {@code MyService.process()} is called with the content of the message:
*
*
* @Configuration
* @EnableKafka
* public class AppConfig {
* @Bean
* public MyService myService() {
* return new MyService();
* }
*
* // Kafka infrastructure setup
* }
*
*
* Alternatively, if {@code MyService} were annotated with {@code @Component}, the
* following configuration would ensure that its {@code @KafkaListener} annotated method
* is invoked with a matching incoming message:
*
*
* @Configuration
* @EnableKafka
* @ComponentScan(basePackages = "com.acme.foo")
* public class AppConfig {
* }
*
*
* Note that the created containers are not registered with the application context but
* can be easily located for management purposes using the
* {@link org.springframework.kafka.config.KafkaListenerEndpointRegistry
* KafkaListenerEndpointRegistry}.
*
*
* Annotated methods can use a flexible signature; in particular, it is possible to use
* the {@link org.springframework.messaging.Message Message} abstraction and related
* annotations, see {@link KafkaListener} Javadoc for more details. For instance, the
* following would inject the content of the message and the kafka partition header:
*
*
* @KafkaListener(containerFactory = "myKafkaListenerContainerFactory", topics = "myTopic")
* public void process(String msg, @Header("kafka_partition") int partition) {
* // process incoming message
* }
*
*
* These features are abstracted by the
* {@link org.springframework.messaging.handler.annotation.support.MessageHandlerMethodFactory
* MessageHandlerMethodFactory} that is responsible to build the necessary invoker to
* process the annotated method. By default,
* {@link org.springframework.messaging.handler.annotation.support.DefaultMessageHandlerMethodFactory
* DefaultMessageHandlerMethodFactory} is used.
*
*
* When more control is desired, a {@code @Configuration} class may implement
* {@link KafkaListenerConfigurer}. This allows access to the underlying
* {@link org.springframework.kafka.config.KafkaListenerEndpointRegistrar
* KafkaListenerEndpointRegistrar} instance. The following example demonstrates how to
* specify an explicit default {@code KafkaListenerContainerFactory}
*
*
* @Configuration
* @EnableKafka
* public class AppConfig implements KafkaListenerConfigurer {
* @Override
* public void configureKafkaListeners(KafkaListenerEndpointRegistrar registrar) {
* registrar.setContainerFactory(myKafkaListenerContainerFactory());
* }
*
* @Bean
* public KafkaListenerContainerFactory<?, ?> myKafkaListenerContainerFactory() {
* // factory settings
* }
*
* @Bean
* public MyService myService() {
* return new MyService();
* }
* }
*
*
* It is also possible to specify a custom
* {@link org.springframework.kafka.config.KafkaListenerEndpointRegistry
* KafkaListenerEndpointRegistry} in case you need more control on the way the containers
* are created and managed. The example below also demonstrates how to customize the
* {@link org.springframework.messaging.handler.annotation.support.DefaultMessageHandlerMethodFactory}
* as well as how to supply a custom {@link org.springframework.validation.Validator
* Validator} so that payloads annotated with
* {@link org.springframework.validation.annotation.Validated Validated} are first
* validated against a custom {@code Validator}.
*
*
* @Configuration
* @EnableKafka
* public class AppConfig implements KafkaListenerConfigurer {
* @Override
* public void configureKafkaListeners(KafkaListenerEndpointRegistrar registrar) {
* registrar.setEndpointRegistry(myKafkaListenerEndpointRegistry());
* registrar.setMessageHandlerMethodFactory(myMessageHandlerMethodFactory);
* registrar.setValidator(new MyValidator());
* }
*
* @Bean
* public KafkaListenerEndpointRegistry myKafkaListenerEndpointRegistry() {
* // registry configuration
* }
*
* @Bean
* public MessageHandlerMethodFactory myMessageHandlerMethodFactory() {
* DefaultMessageHandlerMethodFactory factory = new DefaultMessageHandlerMethodFactory();
* // factory configuration
* return factory;
* }
*
* @Bean
* public MyService myService() {
* return new MyService();
* }
* }
*
*
* Implementing {@code KafkaListenerConfigurer} also allows for fine-grained control over
* endpoints registration via the {@code KafkaListenerEndpointRegistrar}. For example, the
* following configures an extra endpoint:
*
*
* @Configuration
* @EnableKafka
* public class AppConfig implements KafkaListenerConfigurer {
* @Override
* public void configureKafkaListeners(KafkaListenerEndpointRegistrar registrar) {
* SimpleKafkaListenerEndpoint myEndpoint = new SimpleKafkaListenerEndpoint();
* // ... configure the endpoint
* registrar.registerEndpoint(endpoint, anotherKafkaListenerContainerFactory());
* }
*
* @Bean
* public MyService myService() {
* return new MyService();
* }
*
* @Bean
* public KafkaListenerContainerFactory<?, ?> anotherKafkaListenerContainerFactory() {
* // ...
* }
*
* // Kafka infrastructure setup
* }
*
*
* Note that all beans implementing {@code KafkaListenerConfigurer} will be detected and
* invoked in a similar fashion. The example above can be translated in a regular bean
* definition registered in the context in case you use the XML configuration.
*
* @author Stephane Nicoll
* @author Gary Russell
* @author Artem Bilan
*
* @see KafkaListener
* @see KafkaListenerAnnotationBeanPostProcessor
* @see org.springframework.kafka.config.KafkaListenerEndpointRegistrar
* @see org.springframework.kafka.config.KafkaListenerEndpointRegistry
*/
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(KafkaListenerConfigurationSelector.class)
public @interface EnableKafka {
}
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