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About Marcin Grzejszczak

Marcin Grzejszczak
Senior Java Developer with team building and managing skills. Enthusiast of JVM languages (Groovy, Scala) and clean coding

Spring Cloud Contract 3.0.0 released

With the release of the Spring Cloud 2020.0.0 (aka Ilford) release train we’re more than happy to announce the general availability of Spring Cloud Contract 3.0.0. In this blog post I’ll describe the most notable released features (in order of their release dates).

Incremental Test Generation for Maven

With the Incremental Test Generation for Maven we’re generating tests, stubs and stubs jar only if the contracts have changed. The feature is opt-out (enabled by default).

Resolves Credentials from settings.xml

With the support to resolve credentials from settings.xml when using Aether based solution to fetch the contracts / stubs, we will reuse your settings.xml credentials for the given server id (via the stubrunner.server-id property).

Rewrite Groovy to Java

It was fantastic to see so many people take part in rewriting the Spring Cloud Contract’s codebase from Groovy to Java. You can check this issue for more information.

Allow to Extend Contract & Stubs

With this issue and this pull request we’ve added an option to provide metadata to your contracts. Since we didn’t want to map all WireMock properties to the core of our Contract definition, we’ve allowed passing of metadata under the wiremock key. The passed value can be an actual WireMock definition. We will map that part to the generated stub.

Example of adding delays:

Contract.make {
		request {
			method GET()
			url '/drunks'
		response {
			status OK()
				count: 100
			headers {
		metadata([wiremock: '''\
		"response" : {
			"delayDistribution": {
                    "type": "lognormal",
                    "median": 80,
                    "sigma": 0.4

That also means that you can provide your own metadata. You can read more about this in the documentation

New [Custom] Mode of Test Generation

With this pr we’ve introduced a new custom mode of test generation. You’re able to pass your own implementation of an HTTP client (you can reuse our OkHttpHttpVerifier), thanks to which you can e.g. use HTTP/2. This was a prerequisite for the GRPC task. Thanks to the Spring Cloud Contract Workshops and the following refactoring of Spring Cloud Contract it was quite easy to add this feature, so thanks everyone involved then!

You can read more about this in the documentation.

Experimental GRPC Support

With the custom mode in place we could add the experimental GRPC support. Why experimental? Due to GRPC’s tweaking of the HTTP/2 Header frames, it’s impossible to assert the grpc-status header. You can read more about the feature, the issue and workarounds in the documentation.

Here you can find an example of GRPC producer and of a GRPC consumer.

GraphQL Support

With this PR we’ve added GraphQL support. Since GraphQL is essentially POST to and endpoint with specific body, you can create such a contract and set the proper metadata. You can read more about this in the documentation.

Here you can find an example of GraphQL producer and of a GraphQL consumer.

Stub Runner Boot Thin JAR

With this issue we’ve migrated the Stub Runner Boot application to be a thin jar based application. Not only have we managed to lower the size of the produced artifact, but also we’re able via properties turn on profiles (e.g. kafka or rabbit profiles) that would fetch additional dependencies at runtime.

Messaging Polyglot Support

Pre-built kafka and amqp support

With the thin jar rewrite and this PR and this issue we’re adding support for Kafka and AMQP based solutions with the Docker images.

You’ll have to have the following prerequisites met:

  • Middleware (e.g. RabbitMQ or Kafka) must be running before generating tests
  • Your contract needs to call a method triggerMessage(...) with a String parameter that is equal to the contract’s label.
  • Your application needs to have a HTTP endpoint via which we can trigger a message
  • That endpoint should not be available on production (could be enabled via an environment variable)

Your contract can leverage the kafka and amqp metadata sections like below:

description: 'Send a pong message in response to a ping message'
label: 'ping_pong'
    # You have to provide the `triggerMessage` method with the `label`
    # as a String parameter of the method
    triggeredBy: 'triggerMessage("ping_pong")'
    sentTo: 'output'
        message: 'pong'
                declareQueueWithName: "queue"
				receivedRoutingKey: '#'

Standalone mode

There is legitimate reason to run your contract tests against existing middleware. Some testing frameworks might give you false positive results – the test within your build passes whereas on production the communication fails.

In Spring Cloud Contract docker images we give an option to connect to existing middleware. As presented in previous subsections we do support Kafka and RabbitMQ out of the box. However, via Apache Camel Components we can support other middleware too. Let’s take a look at the following examples of usage.

Example of a contract connecting to a real RabbitMQ instance:

description: 'Send a pong message in response to a ping message'
label: 'standalone_ping_pong'
  triggeredBy: 'triggerMessage("ping_pong")'
  sentTo: 'rabbitmq:output'
    message: 'pong'
      options: rabbitmq:output?queue=output&routingKey=#
	  additionalOptions: routingKey=#&queue=output

You can read more about setting this up in this PR under the Documentation of the feature with standalone mode (aka with running middleware) section.

Messaging with Existing Middleware

Since it’s extremely easy to start a docker image with a broker via Testcontainers, we’re suggesting to slowly migrate your messaging tests to such an approach. From the perspective of Spring Cloud Contract it’s also better since we won’t need to replicate in our code the special cases of how frameworks behave when calling a real broker. Here you can find an example of how you can connect to a JMS broker on the producer side and here how you can consume it.

Gradle Plugin rewrite

This one is fully done by the one and only shanman190. The whole work on the Gradle plugin was done by him so you should buy him a beer once you get to see him :) Anyways, there are various changes to the Gradle plugin that you can check out.

Published on Java Code Geeks with permission by Marcin Grzejszczak, partner at our JCG program. See the original article here: Spring Cloud Contract 3.0.0 released

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