根据spring官网小栗子实现一个简单的spring-cloud-stream自定义binder

关于如何实现自定义binder，spring官网提供了一套方式，具体如下：

• Add the required dependencies
• Provide a ProvisioningProvider implementation
• Provide a MessageProducer implementation
• Provide a MessageHandler implementation
• Provide a Binder implementation
• Create a Binder Configuration
• Define your binder in META-INF/spring.binders

下面我们就根据这个步骤简单实现一个demo。

Add the required dependencies

<dependency>
  <groupId>org.springframework.cloudgroupId>
  <artifactId>spring-cloud-streamartifactId>
dependency>

当然为了测试，我们还会加上spring-boot-starter-web

<dependency>
  <groupId>org.springframework.bootgroupId>
  <artifactId>spring-boot-starter-webartifactId>
dependency>

Provide a ProvisioningProvider implementation

public class FileMessageBinderProvisioner implements ProvisioningProvider<ConsumerProperties, ProducerProperties> {

    @Override
    public ProducerDestination provisionProducerDestination(
            final String name,
            final ProducerProperties properties) {

        return new FileMessageDestination(name);
    }

    @Override
    public ConsumerDestination provisionConsumerDestination(
            final String name,
            final String group,
            final ConsumerProperties properties) {

        return new FileMessageDestination(name);
    }

    private class FileMessageDestination implements ProducerDestination, ConsumerDestination {

        private final String destination;

        private FileMessageDestination(final String destination) {
            this.destination = destination;
        }

        @Override
        public String getName() {
            return destination.trim();
        }

        @Override
        public String getNameForPartition(int partition) {
            throw new UnsupportedOperationException("Partitioning is not implemented for file messaging.");
        }

    }

}

Provide a MessageProducer implementation

public class FileMessageProducer extends MessageProducerSupport {

    public static final String ARCHIVE = "archive.txt";
    private final ConsumerDestination destination;
    private String previousPayload;

    public FileMessageProducer(ConsumerDestination destination) {
        this.destination = destination;
    }

    @Override
    public void doStart() {
        receive();
    }

    private void receive() {
        ScheduledExecutorService executorService = Executors.newScheduledThreadPool(1);

        executorService.scheduleWithFixedDelay(() -> {
            String payload = getPayload();

            if(payload != null) {
                Message<String> receivedMessage = MessageBuilder.withPayload(payload).build();
                archiveMessage(payload);
                sendMessage(receivedMessage);
            }

        }, 0, 50, MILLISECONDS);
    }

    private String getPayload() {
        try {
            List<String> allLines = Files.readAllLines(Paths.get(destination.getName()));
            String currentPayload = allLines.get(allLines.size() - 1);

            if(!currentPayload.equals(previousPayload)) {
                previousPayload = currentPayload;
                return currentPayload;
            }
        } catch (IOException e) {
            throw new RuntimeException(e);
        }

        return null;
    }

    private void archiveMessage(String payload) {
        try {
            Files.write(Paths.get(ARCHIVE), (payload + "\n").getBytes(), CREATE, APPEND);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

}

Provide a MessageHandler implementation

public class FileMessageHandler implements MessageHandler {

    private final ProducerDestination destination;

    public FileMessageHandler(ProducerDestination destination) {
        this.destination = destination;
    }

    @Override
    public void handleMessage(Message<?> message) throws MessagingException {
        //write message to file
        String fileName = destination.getName();
        String payload = new String((byte[])message.getPayload()) + "\n";

        try {
            Files.write(Paths.get(fileName), payload.getBytes(), CREATE, APPEND);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }


}

Provide a Binder implementation

public class FileMessageBinder extends AbstractMessageChannelBinder<ConsumerProperties, ProducerProperties, FileMessageBinderProvisioner> {

    public FileMessageBinder(
            String[] headersToEmbed,
            FileMessageBinderProvisioner provisioningProvider) {

        super(headersToEmbed, provisioningProvider);
    }

    @Override
    protected MessageHandler createProducerMessageHandler(
            final ProducerDestination destination,
            final ProducerProperties producerProperties,
            final MessageChannel errorChannel) throws Exception {
        return new FileMessageHandler(destination);
    }

    @Override
    protected MessageProducer createConsumerEndpoint(
            final ConsumerDestination destination,
            final String group,
            final ConsumerProperties properties) throws Exception {

        return new FileMessageProducer(destination);
    }

}

Create a Binder Configuration

@Configuration
public class FileMessageBinderConfiguration {

    @Bean
    @ConditionalOnMissingBean
    public FileMessageBinderProvisioner fileMessageBinderProvisioner() {
        return new FileMessageBinderProvisioner();
    }

    @Bean
    @ConditionalOnMissingBean
    public FileMessageBinder fileMessageBinder(FileMessageBinderProvisioner fileMessageBinderProvisioner) {
        return new FileMessageBinder(null, fileMessageBinderProvisioner);
    }

}

Define your binder in META-INF/spring.binders

file:\
com.gx.sc.springcloudstreamredisbinder.FileMessageBinderConfiguration

完成以上七步基本上就创建好了一个简单的binder，当然还有一个事情也需要做，就是配置文件：

#此处的file就是我们在META-INF/spring.binders中定义的file
#channel name is output，对应StreamProcessor中的OUTPUT
spring.cloud.stream.bindings.output.binder=file
#default content-type is application/json, optional
spring.cloud.stream.bindings.output.content-type=application/json
#topic name is topic1
spring.cloud.stream.bindings.output.destination=topic1
#topic group is group1，group可以在多节点时避免消息的重复消费
spring.cloud.stream.bindings.output.group=group1

#此处的file就是我们在META-INF/spring.binders中定义的file
#channel name is input，对应StreamProcessor中的INPUT
spring.cloud.stream.bindings.input.binder=file
#default content-type is application/json, optional
spring.cloud.stream.bindings.input.content-type=application/json
#topic name is topic1
spring.cloud.stream.bindings.input.destination=topic1
#topic group is group1，group可以在多节点时避免消息的重复消费
spring.cloud.stream.bindings.input.group=group1

下面我们来测试一下，该demo是用spring-boot搭建的，当然会有下面的启动类：

@SpringBootApplication
public class SpringCloudStreamRedisBinderApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringCloudStreamRedisBinderApplication.class, args);
    }

}

再创建一个TestController

@RequestMapping("/test")
@RestController
@EnableBinding(StreamProcessor.class)
public class TestController {

    @Autowired
    private StreamProcessor streamProcessor;

    @GetMapping("/send")
    public void send(@RequestParam String message) {
        streamProcessor.output().send(MessageBuilder.withPayload(message).build());
    }


}

其中的StreamProcessor是指定需要绑定的目标，具体代码如下：

public interface StreamProcessor {

    String INPUT = "input";

    String OUTPUT = "output";

    @Input(INPUT)
    SubscribableChannel input();

    @Output(OUTPUT)
    MessageChannel output();

}

可以简单看一下@Input源码，大概意思就是指定binding(可以看成channel，方便理解)目标名称，然后将该名称作为一个bean的名称，所以该名称要保证唯一，否则会冲突，还有就是如果没有指定destination(可以理解成topic)名称,则以该名称作为默认的destination名称

@Qualifier
@Target({ ElementType.FIELD, ElementType.METHOD, ElementType.ANNOTATION_TYPE,
		ElementType.PARAMETER })
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface Input {

	/**
	 * Specify the binding target name; used as a bean name for binding target and as a
	 * destination name by default.
	 * @return the binding target name
	 */
	String value() default "";

}

@Output源码大概也是这么个意思，和@Input的区别就是@Output是代表发送方，@Input代表接收方，默认可以参考Source(发送方)和Sink(接收方)接口，另外还有一个接口Processor，继承了Source和Sink，所以它具有两者的意义。

@Qualifier
@Target({ ElementType.FIELD, ElementType.METHOD, ElementType.ANNOTATION_TYPE,
		ElementType.PARAMETER })
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface Output {

	/**
	 * Specify the binding target name; used as a bean name for binding target and as a
	 * destination name by default.
	 * @return the binding target name
	 */
	String value() default "";

}

到这里代码部分已经全部完成，下面就启动应用，打开浏览器，输入如下地址：

http://localhost:8080/test/send?message=hello

此时项目根路径下面会多出两个文件，一个是topic1（发送内容）,一个是archive.txt（接收内容），里面都有一行hello；

可以继续修改message的值，每次修改然后请求之后，两个文件就会多出来一行。

以上就是根据官网提供的步骤简单实现的一个binder的demo。