This example shows how PowerSync can be used in a Java 8+ application.

Notes on the important moving parts of this example client application:

• com.example.Main: The entrypoint setting up PowerSync, waiting for a sync to complete and running a simple query.
• ExampleBackendConnector.java: A Java implementation of a backend connector. The connector is responsible for obtaining a JWT token by implementing the fetchCredentials() method. There is also a uploadData() method which connects to a backend to forward local changes that need to be applied to the source backend database (i.e. MongoDB). For more details on the role of the backend connector, see Integrate with your Backend in the PowerSync docs.
  • Make sure to update the following in the ExampleBackendConnector.java class:
    • BACKEND_URL - This is the URL of the backend API that should receive changes from the client and apply them to the source backend database (i.e. MongoDB)
    • POWERSYNC_URL - This is the URL of the PowerSync instance that the client should connect to. It's required as part of the PowerSyncCredentials class returned by the fetchCredentials() method.
• PowerSync.java: A class which instantiates the PowerSyncJavaWrapper and takes in an instance of the ExampleBackendConnector.
• AppSchema.java: A class which defines the client-side schema for the local SQLite database. Update this class to define the tables that will be populated in the local SQLite database based on the configured Sync Rules.
• com.example.interfaces and com.example.wrappers: This is used to provide a minimal Java interface to the asynchronous Kotlin code as part of the PowerSync client SDK. These wrappers are part of this demo and create a bridge between the PowerSync Kotlin client SDK and the plain Java example client, but we intend to refactor this in the future and move it into our Kotlin SDK.

For the example client app to start successfully, it requires that a PowerSync Service instance is up and running. Once the PowerSync Service instance has started and available, simply navigate to this directory and run:

./gradlew run

When the example all starts, it will attempt to connect to the PowerSync Service instance to retrieve the JWT and then the sync will start.