Add stream (kafka, Rabbit) and Rsocket examples for Cloud Event
This commit is contained in:
Oleg Zhurakousky
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## Examples of Cloud Events with Spring
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## Examples of Cloud Events with Spring via HTTP
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### Introduction
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The current example uses spring-cloud-function framework as its core which allows users to only worry about functional aspects of
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their requirement while taking care-off non-functional aspects. For more information on Spring Cloud Function please visit
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our https://spring.io/projects/spring-cloud-function[project page].
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The example consists of a class https://github.com/spring-cloud/spring-cloud-function/blob/master/spring-cloud-function-samples/function-sample-cloudevent/src/main/java/io/spring/cloudevent/CloudeventDemoApplication.java[CloudeventDemoApplication]
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which contains a set of function beans of different type signatures which you can interact with following instructions below.
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It also provides necessary dependencies and instructions to demonstrate several distinct invocation models:
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- _Direct function invocation_
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- _Function as a REST endpoint_
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- _Function as message handler (e.g., Kafka, RabbitMQ etc)_
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- _Function invocation via RSocket_
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The POM file defines all the necessary dependency in a segregated way, so you can choose the one you're interested in by commenting in/out dependencies
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that fit your scenario (e.g., Streaming vs. REST, ect_
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### Direct function invocation
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By looking up user declared functions in `FunctionCatalog` you can interact (i.e., for testing purposes) with functions directly
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while enjoying all the features of _spring-cloud-function_ such as transparent type conversion, function composition and more.
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[source, java]
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----
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Message<String> binaryCloudEventMessage = MessageBuilder
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.withPayload("{\"releaseDate\":\"24-03-2004\", \"releaseName\":\"Spring Framework\", \"version\":\"1.0\"}")
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.setHeader("ce-specversion", "1.0")
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.setHeader("ce-type", "com.example.springevent")
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.setHeader("ce-source", "spring.io/spring-event")
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.setHeader("ce-id", "123-456-9876-09")
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.build();
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Function<Message<String>, String> asPojoMessage = catalog.lookup("asPOJOMessage");
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System.out.println(asPojoMessage.apply(binaryCloudEventMessage));
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----
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The test case link:src/test/java/io/spring/cloudevent/CloudeventDemoApplicationFunctionTests.java[CloudeventDemoApplicationFunctionTests]
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provides a good example on how to accomplish this.
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### Function as a REST endpoint
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The example consists of a Spring boot configuration class
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https://github.com/spring-cloud/spring-cloud-function/blob/master/spring-cloud-function-samples/function-sample-cloudevent/src/main/java/io/spring/cloudevent/DemoApplication.java[DemoApplication]
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which contains a sample function which you can interact with following via HTTP.
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Given that SCF allows function to be exposed as REST endpoints, you can post cloud event to any of the
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functions by using function name as path (e.g., `localhost:8080/<function_name>`).
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Just add this to your dependency (or in your case simply un-comment)
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[source, xml]
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----
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<!-- REST - only needed if you intend to invoke via HTTP -->
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-web</artifactId>
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</dependency>
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<dependency>
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<groupId>org.springframework.cloud</groupId>
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<artifactId>spring-cloud-function-web</artifactId>
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<version>3.1.0-SNAPSHOT</version>
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</dependency>
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<!-- end REST -->
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----
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Here is an example of curl command posting a cloud event in binary-mode:
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[source, text]
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----
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curl -w'\n' localhost:8080/asPOJO \
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curl -w'\n' localhost:8080/hire \
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-H "ce-id: 0001" \
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-H "ce-specversion: 1.0" \
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-H "ce-type: com.example.springevent" \
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-H "ce-type: hire" \
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-H "ce-source: spring.io/spring-event" \
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-H "Content-Type: application/json" \
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-H "ce-id: 0001" \
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-d '{"releaseDate":"24-03-2004", "releaseName":"Spring Framework", "version":"1.0"}'
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-d '{"firstName":"John", "lastName":"Doe"}' -i
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----
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And here is an example of curl command posting a cloud event in structured-mode:
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@@ -87,85 +39,9 @@ curl -w'\n' localhost:8080/asString \
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"id" : "A234-1234-1234",
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"datacontenttype" : "application/json",
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"data" : {
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"version" : "1.0",
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"releaseName" : "Spring Framework",
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"releaseDate" : "24-03-2004"
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"firstName" : "John",
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"lastName" : "Doe"
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}
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}'
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----
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Feel free to change the function you're invoking by changing URI path (e.g., `localhost:8080/asString` to `localhost:8080/consumeAndProduceCloudEventAsPojoToPojo`).
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### Function as message handler (e.g., Kafka, RabbitMQ etc)
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Streaming support for Apache Kafka and RabbitMQ is provided via https://spring.io/projects/spring-cloud-stream[Spring Cloud Stream] framework.
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In fact we're only mentioning Apache Kafka and RabbitMQ here as an example.
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Streaming support is automatically provided for any existing binders (e.g., Solace, Google PubSub, Amazon Kinesis and many more).
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Please see project page for for additional details on available binders.
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Binders are components of Spring Cloud Stream responsible to bind user code (e.g., java function) to message broker destinations, so execution
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is triggered by messages posted to the broker destination and results of execution are sent back to the broker destinations. Binders also provide
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support for _consumer groups_, _partitioning_ and many other features. For more information on Spring Cloud Stream, Binders and available features
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please visit our https://docs.spring.io/spring-cloud-stream/docs/3.1.0-SNAPSHOT/reference/html/[documentation page].
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*RabbitMQ*
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By simply declaring the following dependency
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[source, xml]
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----
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<dependency>
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<groupId>org.springframework.cloud</groupId>
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<artifactId>spring-cloud-stream-binder-rabbit</artifactId>
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<version>3.1.0-SNAPSHOT</version>
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</dependency>
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----
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. . . any function can now act as message handler bound to RabitMQ message broker. All you need to do is identify which function you intend to bind
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by identifying it via `spring.cloud.function.definition` property.
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[source, text]
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----
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--spring.cloud.function.definition=asPOJOMessage
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----
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See link:src/main/resources/application.properties[application.properties] for more details.
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Assuming RabbitMQ broker is running on localhost:default_port, start the application and navigate to
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http://localhost:15672/#/exchanges[RabbitMQ Dashboard]. Select `asPOJOMessage-in-0` exchange and:
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_...post a binary-mode message by filling all the required Cloud Events headers and posting `data` element as payload (see the screenshot below)._
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image::images\rabbit-send-binary.png[binary,700,700]
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_...post a structured-mode message by filling `contentType` header to the value of `application/cloudevents+json` while providing the
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entire structure of Cloud Event message as payload (see the screenshot below)._
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[source, json]
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----
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{
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"specversion" : "1.0",
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"type" : "org.springframework",
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"source" : "https://spring.io/",
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"id" : "A234-1234-1234",
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"datacontenttype" : "application/json",
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"data" : {
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"version" : "1.0",
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"releaseName" : "Spring Framework",
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"releaseDate" : "24-03-2004"
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}
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}
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----
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image::images\rabbit-send-structured.png[structured,700,700]
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You can follow similar approach with Apache Kafka or any other binder. All you need is bring a required binder dependency.
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For example for Apache Kafka
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[source, xml]
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----
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<dependency>
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<groupId>org.springframework.cloud</groupId>
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<artifactId>spring-cloud-stream-binder-kafka</artifactId>
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<version>3.1.0-SNAPSHOT</version>
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</dependency>
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----
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### Function invocation via RSocket
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TBD
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