Spring Boot receipt API project: build, test and inspect the limits

Last updated: 30 Sept 20264 min read

tutorial

The receipt API project assembles a Boot web application with validated commands, protected endpoints and a separate JDBC transaction fixture.

Download Spring source kit

This lesson uses the downloadable source kit: Java 21, Spring Boot 4.0.8 and its managed Spring Framework 7 dependencies. The version is pinned for repeatable builds.

Build the supplied application

The kit includes its Maven build, source files, properties and tests. Run mvn test and mvn package with JDK 21, then start the executable jar locally. ReceiptApplication is the selected entrypoint; the standalone teaching programs are separate runnable classes.

The API uses ReceiptStore, an in-memory synchronized map that loses receipts when the process stops. JdbcReceiptLedger is a separate transaction lesson and is not silently wired as durable API storage. Replacing the repository needs a migration, repository integration tests and explicit transaction ownership.

Inspect the actual promises

GET health is public. Other requests need the fixture identity, and mutation also needs CSRF protection. The tests check valid and invalid commands, missing receipts, bounded pages, CORS and rollback. None of this implements real payment settlement, tenant accounts or a production identity provider.

The next extension is durable repository ownership and an idempotency contract for retries. A retry after a lost response can otherwise create another receipt. Do not call this learning project production-ready before persistence, identity, request limits and operational recovery have been tested.

Checked source

package in.aitrove.learning;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
@SpringBootApplication
@EnableConfigurationProperties(ImportConfiguration.class)
public class ReceiptApplication {
    public static void main(String[] args) { SpringApplication.run(ReceiptApplication.class, args); }
}

Test the boundary

Run mvn test in the source-kit directory. All source-kit Maven tests checks the behavior described here. Java excerpts belong to the named source-kit classes; they are not independent source files unless the complete class is shown.

Costs and boundaries

The application starts a servlet server and H2 datasource, while API state remains in the in-memory store. Its source and tests expose those boundaries rather than implying a distributed service or a deployed backend.