This version is still in development and is not considered stable yet. For the latest stable version, please use spring-cloud-stream 4.1.4!spring-doc.cn

Binder SPI

The Binder SPI consists of a number of interfaces, out-of-the box utility classes, and discovery strategies that provide a pluggable mechanism for connecting to external middleware.spring-doc.cn

The key point of the SPI is the Binder interface, which is a strategy for connecting inputs and outputs to external middleware. The following listing shows the definition of the Binder interface:spring-doc.cn

public interface Binder<T, C extends ConsumerProperties, P extends ProducerProperties> {
    Binding<T> bindConsumer(String bindingName, String group, T inboundBindTarget, C consumerProperties);

    Binding<T> bindProducer(String bindingName, T outboundBindTarget, P producerProperties);
}

The interface is parameterized, offering a number of extension points:spring-doc.cn

Input and output bind targets.spring-doc.cn
Extended consumer and producer properties, allowing specific Binder implementations to add supplemental properties that can be supported in a type-safe manner.spring-doc.cn

A typical binder implementation consists of the following:spring-doc.cn

A class that implements the Binder interface;spring-doc.cn
A Spring @Configuration class that creates a bean of type Binder along with the middleware connection infrastructure.spring-doc.cn
A META-INF/spring.binders file found on the classpath containing one or more binder definitions, as shown in the following example:spring-doc.cn
```
kafka:\
org.springframework.cloud.stream.binder.kafka.config.KafkaBinderConfiguration
```

As it was mentioned earlier Binder abstraction is also one of the extension points of the framework. So if you can’t find a suitable binder in the preceding list you can implement your own binder on top of Spring Cloud Stream. In the How to create a Spring Cloud Stream Binder from scratch post a community member documents in details, with an example, a set of steps necessary to implement a custom binder. The steps are also highlighted in the Implementing Custom Binders section.