To get started creating Spring Cloud Stream applications, head over to start.spring.io and create a new project named GreetingSource.
Select the Spring Boot Version to be 1.3.4 (SNAPSHOT as of the time of this release) and tick the checkbox for Stream Kafka as we will be using Kafka for messaging.
Next create a new class GreetingSource in the same package as the class GreetingSourceApplication with the following code:
import org.springframework.cloud.stream.annotation.EnableBinding; import org.springframework.cloud.stream.messaging.Source; import org.springframework.integration.annotation.InboundChannelAdapter; @EnableBinding(Source.class) public class GreetingSource { @InboundChannelAdapter(Source.OUTPUT) public String greet() { return "hello world " + System.currentTimeMillis(); } }
The annotation @EnableBinding is what triggers the creation of Spring Integration infrastructure components.
Specifically, it will create a Kafka Connection Factory, Kafka Outbound Channel Adapter, and the Message Channel defined inside the Source interface.
public interface Source { String OUTPUT = "output"; @Output(Source.OUTPUT) MessageChannel output(); }
Furthermore, the auto configuration creates a default poller so that the greet method will be invoked once a second. The standard Spring Integration InboundChannelAdapter annotation sends a message to the source’s output channel using the return value as the payload of the message.
To test drive this setup run a Kafka Message Broker. An easy way to do this is using a docker image.
# on mac docker run -p 2181:2181 -p 9092:9092 --env ADVERTISED_HOST=`docker-machine ip \`docker-machine active\`` --env ADVERTISED_PORT=9092 spotify/kafka # on linux docker run -p 2181:2181 -p 9092:9092 --env ADVERTISED_HOST=localhost --env ADVERTISED_PORT=9092 spotify/kafka
Build the application using ./mvnw clean package
The consumer application is coded in a similar manner, go back to start.spring.io and create a new project named LoggerSink. Then create a new class LoggingSink in the same package as the class LoggingSinkApplication with the following code
import org.springframework.cloud.stream.annotation.EnableBinding; import org.springframework.cloud.stream.annotation.StreamListener; import org.springframework.cloud.stream.messaging.Sink; @EnableBinding(Sink.class) public class LoggingSink { @StreamListener(Sink.INPUT) public void log(String message) { System.out.println(message); } }
Build the application using ./mvnw clean package
To connect the Source application to the Sink application, each application needs to share the same destination name. Starting up both applications as shown below you will see the consumer application printing ‘hello world’ and the timestamp to the console.
cd GreetingSource java -jar target/GreetingSource-0.0.1-SNAPSHOT.jar --spring.cloud.stream.bindings.output.destination=mydest cd LoggingSink java -jar target/LoggingSink-0.0.1-SNAPSHOT.jar --server.port=8090 --spring.cloud.stream.bindings.input.destination=mydest
The different server port is avoid collisions of the http port used to service the boot actuator endpoints.
The output of the logging sink will look something like
[ main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 8090 (http)
[ main] com.example.LoggingSinkApplication : Started LoggingSinkApplication in 6.828 seconds (JVM running for 7.371)
hello world 1458595076731
hello world 1458595077732
hello world 1458595078733
hello world 1458595079734
hello world 1458595080735
= Appendices
[appendix]
[[building]]
== Building
:jdkversion: 1.7
=== Basic Compile and Test
To build the source you will need to install JDK {jdkversion}.
The build uses the Maven wrapper so you don't have to install a specific
version of Maven. To enable the tests for Redis, Rabbit, and Kafka bindings you
should have those servers running before building. See below for more
information on running the servers.
The main build command is$ ./mvnw clean install
You can also add '-DskipTests' if you like, to avoid running the tests. NOTE: You can also install Maven (>=3.3.3) yourself and run the `mvn` command in place of `./mvnw` in the examples below. If you do that you also might need to add `-P spring` if your local Maven settings do not contain repository declarations for spring pre-release artifacts. NOTE: Be aware that you might need to increase the amount of memory available to Maven by setting a `MAVEN_OPTS` environment variable with a value like `-Xmx512m -XX:MaxPermSize=128m`. We try to cover this in the `.mvn` configuration, so if you find you have to do it to make a build succeed, please raise a ticket to get the settings added to source control. The projects that require middleware generally include a `docker-compose.yml`, so consider using http://compose.docker.io/[Docker Compose] to run the middeware servers in Docker containers. See the README in the https://github.com/spring-cloud-samples/scripts[scripts demo repository] for specific instructions about the common cases of mongo, rabbit and redis. === Documentation There is a "full" profile that will generate documentation. === Working with the code If you don't have an IDE preference we would recommend that you use http://www.springsource.com/developer/sts[Spring Tools Suite] or http://eclipse.org[Eclipse] when working with the code. We use the http://eclipse.org/m2e/[m2eclipe] eclipse plugin for maven support. Other IDEs and tools should also work without issue. ==== Importing into eclipse with m2eclipse We recommend the http://eclipse.org/m2e/[m2eclipe] eclipse plugin when working with eclipse. If you don't already have m2eclipse installed it is available from the "eclipse marketplace". Unfortunately m2e does not yet support Maven 3.3, so once the projects are imported into Eclipse you will also need to tell m2eclipse to use the `.settings.xml` file for the projects. If you do not do this you may see many different errors related to the POMs in the projects. Open your Eclipse preferences, expand the Maven preferences, and select User Settings. In the User Settings field click Browse and navigate to the Spring Cloud project you imported selecting the `.settings.xml` file in that project. Click Apply and then OK to save the preference changes. NOTE: Alternatively you can copy the repository settings from https://github.com/spring-cloud/spring-cloud-build/blob/master/.settings.xml[`.settings.xml`] into your own `~/.m2/settings.xml`. ==== Importing into eclipse without m2eclipse If you prefer not to use m2eclipse you can generate eclipse project metadata using the following command: [indent=0]
$ ./mvnw eclipse:eclipse
The generated eclipse projects can be imported by selecting `import existing projects` from the `file` menu. [[contributing] == Contributing Spring Cloud is released under the non-restrictive Apache 2.0 license, and follows a very standard Github development process, using Github tracker for issues and merging pull requests into master. If you want to contribute even something trivial please do not hesitate, but follow the guidelines below. === Sign the Contributor License Agreement Before we accept a non-trivial patch or pull request we will need you to sign the https://support.springsource.com/spring_committer_signup[contributor's agreement]. Signing the contributor's agreement does not grant anyone commit rights to the main repository, but it does mean that we can accept your contributions, and you will get an author credit if we do. Active contributors might be asked to join the core team, and given the ability to merge pull requests. === Code Conventions and Housekeeping None of these is essential for a pull request, but they will all help. They can also be added after the original pull request but before a merge. * Use the Spring Framework code format conventions. If you use Eclipse you can import formatter settings using the `eclipse-code-formatter.xml` file from the https://github.com/spring-cloud/build/tree/master/eclipse-coding-conventions.xml[Spring Cloud Build] project. If using IntelliJ, you can use the http://plugins.jetbrains.com/plugin/6546[Eclipse Code Formatter Plugin] to import the same file. * Make sure all new `.java` files to have a simple Javadoc class comment with at least an `@author` tag identifying you, and preferably at least a paragraph on what the class is for. * Add the ASF license header comment to all new `.java` files (copy from existing files in the project) * Add yourself as an `@author` to the .java files that you modify substantially (more than cosmetic changes). * Add some Javadocs and, if you change the namespace, some XSD doc elements. * A few unit tests would help a lot as well -- someone has to do it. * If no-one else is using your branch, please rebase it against the current master (or other target branch in the main project). * When writing a commit message please follow http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html[these conventions], if you are fixing an existing issue please add `Fixes gh-XXXX` at the end of the commit message (where XXXX is the issue number). // ======================================================================================