- The example CorDapp
- Downloading the example CorDapp
- Opening the example CorDapp in IntelliJ
- Running the example CorDapp
- Interacting with the example CorDapp
- Via HTTP
- Via the interactive shell (terminal only)
- Via the h2 web console
- Using the example RPC client
- Running nodes across machines
- Testing your CorDapp
- Debugging your CorDapp
The example CorDapp allows nodes to agree IOUs with each other, as long as they obey the following contract rules:
- The IOU’s value is strictly positive
- A node is not trying to issue an IOU to itself
We will deploy and run the CorDapp on four test nodes:
- Notary, which hosts a validating notary service
Because data is only propagated on a need-to-know basis, any IOUs agreed between PartyA and PartyB become “shared facts” between PartyA and PartyB only. PartyC won’t be aware of these IOUs.
Start by downloading the example CorDapp from GitHub:
Let’s open the example CorDapp in IntelliJ IDEA:
- Open IntelliJ
- A splash screen will appear. Click
open, navigate to the folder where you cloned the
cordapp-example, and click
- Once the project is open, click
Project Structure. Under
Project SDK:, set the project SDK by clicking
JDK, and navigating to
XXXis the latest minor version number). Click
- Again under
Project Structure, select
Import Module, then select the
cordapp-examplefolder and click
Open. Choose to
Import module from external model, select
Finish(leaving the defaults) and
- Gradle will now download all the project dependencies and perform some indexing. This usually takes a minute or so
The example CorDapp has the following structure:
. ├── config │ ├── dev │ │ └── log4j2.xml │ └── test │ └── log4j2.xml ├── doc │ └── example_flow.plantuml ├── gradle │ └── wrapper │ ├── gradle-wrapper.jar │ └── gradle-wrapper.properties ├── lib │ ├── README.txt │ └── quasar.jar ├── java-source │ └── ... ├── kotlin-source │ ├── build.gradle │ └── src │ ├── main │ │ ├── kotlin │ │ │ └── com │ │ │ └── example │ │ │ ├── api │ │ │ │ └── ExampleApi.kt │ │ │ ├── client │ │ │ │ └── ExampleClientRPC.kt │ │ │ ├── contract │ │ │ │ └── IOUContract.kt │ │ │ ├── flow │ │ │ │ └── ExampleFlow.kt │ │ │ ├── model │ │ │ │ └── IOU.kt │ │ │ ├── plugin │ │ │ │ └── ExamplePlugin.kt │ │ │ ├── schema │ │ │ │ └── IOUSchema.kt │ │ │ └── state │ │ │ └── IOUState.kt │ │ └── resources │ │ ├── META-INF │ │ │ └── services │ │ │ └── net.corda.webserver.services.WebServerPluginRegistry │ │ ├── certificates │ │ │ ├── readme.txt │ │ │ ├── sslkeystore.jks │ │ │ └── truststore.jks │ │ └── exampleWeb │ │ ├── index.html │ │ └── js │ │ └── angular-module.js │ └── test │ └── kotlin │ └── com │ └── example │ ├── Main.kt │ ├── contract │ │ └── IOUContractTests.kt │ └── flow │ └── IOUFlowTests.kt ├── .gitignore ├── LICENCE ├── README.md ├── TRADEMARK ├── build.gradle ├── gradle.properties ├── gradlew ├── gradlew.bat └── settings.gradle
The key files and directories are as follows:
- The root directory contains some gradle files, a README and a LICENSE
- config contains log4j configs
- gradle contains the gradle wrapper, which allows the use of Gradle without installing it yourself and worrying about which version is required
- lib contains the Quasar jar which rewrites our CorDapp’s flows to be checkpointable
- kotlin-source contains the source code for the example CorDapp written in Kotlin
- kotlin-source/src/main/kotlin contains the source code for the example CorDapp
- kotlin-source/src/main/resources contains the certificate store, some static web content to be served by the nodes and the WebServerPluginRegistry file
- kotlin-source/src/test/kotlin contains unit tests for the contracts and flows, and the driver to run the nodes via IntelliJ
- java-source contains the same source code, but written in Java. CorDapps can be developed in any language targeting the JVM
There are two ways to run the example CorDapp:
- Via the terminal
- Via IntelliJ
Both approaches will create a set of test nodes, install the CorDapp on these nodes, and then run the nodes. You can read more about how we generate nodes here.
Open a terminal window in the
Build the test nodes with our CorDapp using the following command:
- Unix/Mac OSX:
This will automatically build four nodes with our CorDapp already installed
- Unix/Mac OSX:
CorDapps can be written in any language targeting the JVM. In our case, we’ve provided the example source in
both Kotlin (
/kotlin-source/src) and Java (
/java-source/src). Since both sets of source files are
functionally identical, we will refer to the Kotlin version throughout the documentation.
After the build finishes, you will see the generated nodes in the
There will be a folder for each generated node, plus a
runnodesshell script (or batch file on Windows) to run all the nodes simultaneously
Each node in the
nodesfolder has the following structure:
. nodeName ├── corda.jar // The Corda node runtime. ├── corda-webserver.jar // The node development webserver. ├── node.conf // The node configuration file. └── cordapps // The node's CorDapps.
Start the nodes by running the following command from the root of the
- Unix/Mac OSX:
On Unix/Mac OSX, do not click/change focus until all seven additional terminal windows have opened, or some nodes may fail to start.
For each node, the
runnodes script creates a node tab/window:
______ __ / ____/ _________/ /___ _ / / __ / ___/ __ / __ `/ Top tip: never say "oops", instead / /___ /_/ / / / /_/ / /_/ / always say "Ah, Interesting!" \____/ /_/ \__,_/\__,_/ --- Corda Open Source corda-3.0 (4157c25) ----------------------------------------------- Logs can be found in : /Users/joeldudley/Desktop/cordapp-example/kotlin-source/build/nodes/PartyA/logs Database connection url is : jdbc:h2:tcp://localhost:59472/node Incoming connection address : localhost:10007 Listening on port : 10007 Loaded CorDapps : corda-finance-corda-3.0, cordapp-example-0.1, corda-core-corda-3.0 Node for "PartyA" started up and registered in 38.59 sec Welcome to the Corda interactive shell. Useful commands include 'help' to see what is available, and 'bye' to shut down the node. Fri Mar 02 17:34:02 GMT 2018>>>
For every node except the notary, the script also creates a webserver terminal tab/window:
Logs can be found in /Users/username/Desktop/cordapp-example/kotlin-source/build/nodes/PartyA/logs/web Starting as webserver: localhost:10009 Webserver started up in 42.02 sec
It usually takes around 60 seconds for the nodes to finish starting up. To ensure that all the nodes are running, you
can query the ‘status’ end-point located at
The nodes’ webservers run locally on the following ports:
These ports are defined in each node’s node.conf file under
Each node webserver exposes the following endpoints:
partyNamewhich is CN name of a node
There is also a web front-end served from
The content in
web/example is only available for demonstration purposes and does not implement
anti-XSS, anti-XSRF or other security techniques. Do not use this code in production.
An IOU can be created by sending a PUT request to the
api/example/create-iou endpoint directly, or by using the
the web form served from
To create an IOU between PartyA and PartyB, run the following command from the command line:
curl -X PUT 'http://localhost:10009/api/example/create-iou?iouValue=1&partyName=O=PartyB,L=New%20York,C=US'
Note that both PartyA’s port number (
10009) and PartyB are referenced in the PUT request path. This command
instructs PartyA to agree an IOU with PartyB. Once the process is complete, both nodes will have a signed, notarised
copy of the IOU. PartyC will not.
To create an IOU between PartyA and PartyB, navigate to
/web/example, click the “create IOU” button at the top-left
of the page, and enter the IOU details into the web-form. The IOU must have a positive value. For example:
Counterparty: Select from list Value (Int): 5
And click submit. Upon clicking submit, the modal dialogue will close, and the nodes will agree the IOU.
Assuming all went well, you can view the newly-created IOU by accessing the vault of PartyA or PartyB:
Via the HTTP API:
- PartyA’s vault: Navigate to http://localhost:10009/api/example/ious
- PartyB’s vault: Navigate to http://localhost:10012/api/example/ious
- PartyA: Navigate to http://localhost:10009/web/example and hit the “refresh” button
- PartyB: Navigate to http://localhost:10012/web/example and hit the “refresh” button
The vault and web front-end of PartyC (at
localhost:10015) will not display any IOUs. This is because PartyC was
not involved in this transaction.
Nodes started via the terminal will display an interactive shell:
Welcome to the Corda interactive shell. Useful commands include 'help' to see what is available, and 'bye' to shut down the node. Fri Jul 07 16:36:29 BST 2017>>>
flow list in the shell to see a list of the flows that your node can run. In our case, this will return the
com.example.flow.ExampleFlow$Initiator net.corda.core.flows.ContractUpgradeFlow$Initiator net.corda.core.flows.ContractUpgradeFlow$Initiator net.corda.finance.flows.CashExitFlow net.corda.finance.flows.CashIssueAndPaymentFlow net.corda.finance.flows.CashIssueFlow net.corda.finance.flows.CashPaymentFlow
We can create a new IOU using the
ExampleFlow$Initiator flow. For example, from the interactive shell of PartyA,
you can agree an IOU of 50 with PartyB by running
flow start ExampleFlow$Initiator iouValue: 50, otherParty: "O=PartyB,L=New York,C=US".
This will print out the following progress steps:
✅ Generating transaction based on new IOU. ✅ Verifying contract constraints. ✅ Signing transaction with our private key. ✅ Gathering the counterparty's signature. ✅ Collecting signatures from counterparties. ✅ Verifying collected signatures. ✅ Obtaining notary signature and recording transaction. ✅ Requesting signature by notary service Requesting signature by Notary service Validating response from Notary service ✅ Broadcasting transaction to participants ✅ Done
We can also issue RPC operations to the node via the interactive shell. Type
run to see the full list of available
You can see the newly-created IOU by running
run vaultQuery contractStateType: com.example.state.IOUState.
As before, the interactive shell of PartyC will not display any IOUs.
You can connect directly to your node’s database to see its stored states, transactions and attachments. To do so, please follow the instructions in Node database.
/src/main/kotlin-source/com/example/client/ExampleClientRPC.kt defines a simple RPC client that connects to a node,
logs any existing IOUs and listens for any future IOUs. If you haven’t created
any IOUs when you first connect to one of the nodes, the client will simply log any future IOUs that are agreed.
Run the ‘Run Example RPC Client’ run configuration. By default, this run configuration is configured to connect to PartyA. You can edit the run configuration to connect on a different port.
Run the following gradle task:
This will connect the RPC client to PartyA and log their past and future IOU activity.
You can close the application using
For more information on the client RPC interface and how to build an RPC client application, see:
The nodes can be configured to communicate as a network even when distributed across several machines:
Deploy the nodes as usual:
- Unix/Mac OSX:
- Unix/Mac OSX:
Navigate to the build folder (
For each node, open its
node.conffile and change
p2pAddressto the IP address of the machine where the node will be run (e.g.
These changes require new node-info files to be distributed amongst the nodes. Use the network bootstrapper tool (see Network Bootstrapper) to update the files and have them distributed locally:
java -jar network-bootstrapper.jar kotlin-source/build/nodes
Move the node folders to their individual machines (e.g. using a USB key). It is important that none of the nodes - including the notary - end up on more than one machine. Each computer should also have a copy of
For example, you may end up with the following layout:
- Machine 1:
- Machine 2:
- Machine 1:
After starting each node, the nodes will be able to see one another and agree IOUs among themselves
The bootstrapper must be run after the
node.conf files have been modified, but before the nodes
are distributed across machines. Otherwise, the nodes will not be able to communicate.
If you are using H2 and wish to use the same
h2port value for two or more nodes, you must only assign them that
value after the nodes have been moved to their individual machines. The initial bootstrapping process requires access to the
nodes’ databases and if two nodes share the same H2 port, the process will fail.
Corda provides several frameworks for writing unit and integration tests for CorDapps.
You can run the CorDapp’s contract tests by running the
Run Contract Tests - Kotlin run configuration.
You can run the CorDapp’s flow tests by running the
Run Flow Tests - Kotlin run configuration.