What is a CorDapp?
CorDapps (Corda Distributed Applications) are distributed applications that run on the Corda platform. The goal of a CorDapp is to allow nodes to reach agreement on updates to the ledger. They achieve this goal by defining flows that Corda node owners can invoke over RPC:
CorDapps take the form of a set of JAR files containing class definitions written in Java and/or Kotlin.
These class definitions will commonly include the following elements:
- Flows: Define a routine for the node to run, usually to update the ledger
Key Concepts - Flows). They subclass
- States: Define the facts over which agreement is reached (see
Key Concepts - States).
They implement the
- Contracts, defining what constitutes a valid ledger update (see
Key Concepts - Contracts). They implement the
- Services, providing long-lived utilities within the node. They subclass
- Serialisation whitelists, restricting what types your node will receive off the wire. They implement the
But the CorDapp JAR can also include other class definitions. These may include:
- APIs and static web content: These are served by Corda’s built-in webserver. This webserver is not production-ready, and should be used for testing purposes only
- Utility classes
Suppose a node owner wants their node to be able to trade bonds. They may choose to install a Bond Trading CorDapp with the following components:
BondState, used to represent bonds as shared facts on the ledger
BondContract, used to govern which ledger updates involving
BondStatestates are valid
IssueBondFlow, allowing new
BondStatestates to be issued onto the ledger
TradeBondFlow, allowing existing
BondStatestates to be bought and sold on the ledger
ExitBondFlow, allowing existing
BondStatestates to be exited from the ledger
After installing this CorDapp, the node owner will be able to use the flows defined by the CorDapp to agree ledger updates related to issuance, sale, purchase and exit of bonds.