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Common contracts repo

This repo contains all contracts for apps in the system.

As a consumer

You are working offline in order to play around with the API of the producer. What you need to do is to have the producer’s stubs installed locally. To do that you have to (from the root of the repo)

cd src/main/resources/contracts/com/example/beer-api-producer-external/1.0.0
mvn clean install -DskipTests

Then if you do ls ./target you’ll see beer-api-producer-external-0.0.1-SNAPSHOT-stubs.jar. This jar will contain the stubs generated from your contracts. That way you can reference the com.example:server:+:stubs dependency in your consumer tests.

Don’t mind that there’s a version mismatch in the stubs and the folder structure. The version number is there in the folder name for tests related to dealing with non-Java friendly naming of packages.

As a producer

Assuming that the consumers have filed a PR with the proposed contract the producers can work offline to generate tests and stubs. To work offline, as a producer you just have to go to the root folder of the contracts and:

./mvnw clean install -DskipTests

Then if you do ls ./target you’ll see contracts-0.0.1-SNAPSHOT.jar. This file contains all DSL contracts, for all applications.

Now the producer can include the contracts-0.0.1-SNAPSHOT.jar from your local maven repository. You can achieve that by setting the proper flag in plugin properties.

Example for Maven

        <!-- url not required for working locally -->

and for Gradle:

contracts {
    contractsMode = "LOCAL"
    contractDependency {
        stringNotation = "com.example:beer-contracts"

Dependency Visualization

When keeping contracts in an external repository, and by following the stubs per consumer feature, we have the full knowledge of who is calling who within our system. That way we can sketch a graph of dependencies between applications.

As a reminder, the stubs per consumer feature is all about creating a consumer subfolder, in each producer’s folder. E.g. if consumer baz uses producer foo.bar then the folder structure would look like this foo/bar/baz/contracts/…​.

Let’s assume that we have such setup (…​ signifies contract definitions):

├── com
│   └── example
│       └── beer-api-producer-external
│           ├── 1.0.0
│           │   ├── beer-api-consumer
│           │   │   ├── messaging
│           │   │   │   ├── ...
│           │   │   └── rest
│           │   │       ├── ...
│           │   ├── mvnw
│           │   ├── pom.xml
│           └── 2.0.0
│               ├── anotherConsumerOnly
│               │   ├── ...
│               ├── barService
│               │   ├── ...
│               ├── foo.bar.bazService
│               │   ├── ...
│               ├── foo.bar.consumerOnly
│               │   ├── ...
│               ├── foo.bar.fooService.1_2_3
│               │   ├── ...
│               └── pom.xml
└── foo
    └── bar
        ├── barService
        │   ├── pom.xml
        │   └── yetAnotherConsumer
        │       ├── ...
        ├── bazService
        │   ├── bazConsumer1
        │   │   └── rest
        │   │       └── ...
        │   └── pom.xml
        ├── beer-api-consumer
        │   ├── messaging
        │   │   ├── ...
        │   ├── pom.xml
        │   └── rest
        │       ├── ...
        └── fooService
            └── 1.2.3
                ├── ...
                └── pom.xml

We can reason that:

  • com.example:beer-api-producer-external in version 2.0.0 is used by 5 consumers

    • foo.bar:bazService

    • foo.bar:barService

    • anotherConsumerOnly

    • foo.bar:fooService in version 1.2.3

    • foo.bar:consumerOnly

  • com.example:beer-api-producer-external in version 1.0.0 is used by 1 consumer

    • foo.bar:beer-api-consumer

  • foo.bar:bazService is used by 1 consumer

    • bazConsumer1

  • foo.bar:barService is used by 1 consumer

    • yetAnotherConsumer

This information gives as all data we need to sketch a graph of the dependencies.

Figure 1. Example of d3 graph
Figure 2. Example of Dracula graph

Storing data

It’s enough to execute the docs.GenerateGraphFromContractsTests.java. The test scans the contract structure and builds a graph of relationships between consumers and producers.

It will create a file called relationships.js that you can source in your HTML file. It will load to a var called relationships the JSON representing the relationships. The JSON consists of source, target pairs where source is the producer and target is the consumer.

There are two example HTML files relationships_d3.html that uses d3js and relationships_dracula.html that uses Graph Dracula to render the graph.


  • You have to use the stubs per consumer feature to sketch a precise graph (i.e. each consumer has its own subfolder in the producer’s directory)

  • If using the producer contract approach (you don’t know who your consumers are) you can create file .producer_contracts that will tell the test that generates data that the subfolders do not represent consumer names

  • The folder where the consumers of a given producer lay, needs to have the pom.xml or build.gradle file (you need it anyways to, as a consumer, install stubs of the producer)