Building a CorDapp

Cordapps run on the Corda platform and integrate with it and each other. This article explains how to build CorDapps. To learn what a CorDapp is, please read What is a CorDapp?.

CorDapp format

A CorDapp is a semi-fat JAR that contains all of the CorDapp’s dependencies except the Corda core libraries and any other CorDapps it depends on.

For example, if a Cordapp depends on corda-core, your-other-cordapp and apache-commons, then the Cordapp JAR will contain:

  • All classes and resources from the apache-commons JAR and its dependencies
  • Nothing from the other two JARs

Build tools

In the instructions that follow, we assume you are using gradle and the cordformation plugin to build your CorDapp. You can find examples of building a CorDapp using these tools in the build.gradle file of the Kotlin CorDapp Template and the Java CorDapp Template.

Setting your dependencies

Choosing your Corda, Quasar and Kotlin versions

Several ext variables are used in a CorDapp’s build.gradle file to define which versions are used to build your CorDapp:

  • ext.corda_release_version defines the version of Corda
  • ext.corda_gradle_plugins_version defines the version of the Corda Gradle Plugins
  • ext.quasar_version defines the version of Quasar
  • ext.kotlin_version defines the version of Kotlin (if using Kotlin to write your CorDapp)

corda_gradle_plugins_versions are given in the form major.minor.patch. You should use the same major and minor versions as the Corda version you are using, and the latest patch version. A list of all the available versions can be found here: https://bintray.com/r3/corda/cordapp. If in doubt, you should base yourself on the version numbers used in the build.gradle file of the Kotlin CorDapp Template and the Java CorDapp Template.

For example, to use version 3.0 of Corda, version 3.0.8 of the Corda gradle plugins, version 0.7.9 of Quasar, and version 1.1.60 of Kotlin, you’d write:

ext.corda_release_version = 'corda-3.0'
ext.corda_gradle_plugins_version = '3.0.8'
ext.quasar_version = '0.7.9'
ext.kotlin_version = '1.1.60'

In certain cases, you may also wish to build against the unstable Master branch. See Building against Master.

Corda dependencies

The cordformation and cordapp plugins add two new gradle configurations:

  • cordaCompile, which extends compile
  • cordaRuntime, which extends runtime

cordaCompile and cordaRuntime indicate dependencies that should not be included in the CorDapp JAR. These configurations should be used for any Corda dependency (e.g. corda-core, corda-node) in order to prevent a dependency from being included twice (once in the CorDapp JAR and once in the Corda JARs).

To build against Corda, you must add the following to your build.gradle file:

The Cordapp plugin should be applied to any project that will be building a cordapp, and the cordformation plugin should be applied to projects that wish to create small testing networks locally.

After doing this, ensure that: net.corda:corda:$corda_release_version is defined as a cordaRuntime dependency and all other net.corda compile dependencies (eg net.corda:corda-core:$corda_release_version) are set as a cordaCompile dependency

You may also want to add:

  • net.corda:corda-test-utils:$corda_release_version as a testCompile dependency, in order to use Corda’s test frameworks
  • net.corda:corda-webserver:$corda_release_version as a cordaRuntime dependency, in order to use Corda’s built-in development webserver

Warning

Never include corda-test-utils as a compile or cordaCompile dependency.

Dependencies on other CorDapps

You CorDapp may also depend on classes defined in another CorDapp, such as states, contracts and flows. There are two ways to add another CorDapp as a dependency in your CorDapp’s build.gradle file:

  • cordapp project(":another-cordapp") (use this if the other CorDapp is defined in a module in the same project)
  • cordapp "net.corda:another-cordapp:1.0" (use this otherwise)

The cordapp gradle configuration serves two purposes:

  • When using the cordformation Gradle plugin, the cordapp configuration indicates that this JAR should be included on your node as a CorDapp
  • When using the cordapp Gradle plugin, the cordapp configuration prevents the dependency from being included in the CorDapp JAR

Note that the cordformation and cordapp Gradle plugins can be used together.

Other dependencies

If your CorDapps have any additional external dependencies, they can be specified like normal Kotlin/Java dependencies in Gradle. See the example below, specifically the apache-commons include.

For further information about managing dependencies, see the Gradle docs.

Example

Below is a sample of what a CorDapp’s Gradle dependencies block might look like. When building your own CorDapp, you should base yourself on the build.gradle file of the Kotlin CorDapp Template and the Java CorDapp Template.

dependencies {
    // Corda integration dependencies
    cordaCompile "net.corda:corda-core:$corda_release_version"
    cordaCompile "net.corda:corda-finance:$corda_release_version"
    cordaCompile "net.corda:corda-jackson:$corda_release_version"
    cordaCompile "net.corda:corda-rpc:$corda_release_version"
    cordaCompile "net.corda:corda-node-api:$corda_release_version"
    cordaCompile "net.corda:corda-webserver-impl:$corda_release_version"
    cordaRuntime "net.corda:corda:$corda_release_version"
    cordaRuntime "net.corda:corda-webserver:$corda_release_version"
    testCompile "net.corda:corda-test-utils:$corda_release_version"

    // Corda Plugins: dependent flows and services
    // Identifying a CorDapp by its module in the same project.
    cordapp project(":cordapp-contracts-states")
    // Identifying a CorDapp by its fully-qualified name.
    cordapp "net.corda:bank-of-corda-demo:1.0"

    // Some other dependencies
    compile "org.jetbrains.kotlin:kotlin-stdlib-jre8:$kotlin_version"
    testCompile "org.jetbrains.kotlin:kotlin-test:$kotlin_version"
    testCompile "junit:junit:$junit_version"

    compile "org.apache.commons:commons-lang3:3.6"
}

Creating the CorDapp JAR

Once your dependencies are set correctly, you can build your CorDapp JAR using the gradle jar task:

  • Unix/Mac OSX: ./gradlew jar
  • Windows: gradlew.bat jar

The CorDapp JAR will be output to the build/libs folder.

Warning

The hash of the generated CorDapp JAR is not deterministic, as it depends on variables such as the timestamp at creation. Nodes running the same CorDapp must therefore ensure they are using the exact same CorDapp JAR, and not different versions of the JAR created from identical sources.

The filename of the JAR must include a unique identifier to deduplicate it from other releases of the same CorDapp. This is typically done by appending the version string to the CorDapp’s name. This unique identifier should not change once the JAR has been deployed on a node. If it does, make sure no one is relying on FlowContext.appName in their flows (see Versioning).

Installing the CorDapp JAR

Note

Before installing a CorDapp, you must create one or more nodes to install it on. For instructions, please see Creating nodes locally.

At runtime, nodes will load any CorDapps present in their cordapps folder. Therefore in order to install a CorDapp on a node, the CorDapp JAR must be added to the <node_dir>/cordapps/ folder, where node_dir is the folder in which the node’s JAR and configuration files are stored.