springboot-java8

A small Spring Boot REST service whose purpose is to demonstrate Java language features — originally the Java 8 feature set, which is still what the code shows off. The name stuck, but the project itself now builds and runs on Java 21 with Spring Boot 3.5.16.

The domain is deliberately trivial: an in-memory, hardcoded list of Topic objects that you can create, read, update and delete over HTTP, plus a few endpoints that exist purely to print the result of stream / string / file operations.

Java 8 features demonstrated

NIO.2 file APIs (Files.list, Files.find, Files.walk, Files.newBufferedReader)
String operations (String.join, String.chars)
Stream operations (filter, map, sorted, Collectors.joining)
IntStream (IntStream.range for index lookups)
Functional interfaces (CustomPredicate<T>)
Lambda expressions
Optional / OptionalInt
forEach loops
default and static methods on interfaces (TimeClient)
The java.time API (LocalDateTime, ZonedDateTime, ChronoUnit)
Pattern as a stream source and as a predicate (splitAsStream, asPredicate)
try-with-resources over streams of paths

Java 21 idioms in use

The application was migrated from Spring Boot 2.0.2 / Java 8 to Spring Boot 3.5.16 / Java 21, and the presentation layer has been rewritten to use the modern language features that replace what the old code did by hand:

Text blocks (Java 15) for the multi-part responses of /datetime, /topic/string/operation and /topic/file/operation, using \ line-continuation escapes so the responses stay on a single line.
String.formatted(...) (Java 15) instead of String.format(...) and + concatenation.
Label templates are private static final constants rather than mutable instance fields.

Requirements

JDK 21 (the build sets <java.version>21</java.version>)
Maven is not required — use the bundled Maven Wrapper (./mvnw, Maven 3.9.9)
curl, HTTPie or Postman to call the API

Getting started

git clone https://github.com/COG-GTM/springboot-java8.git
cd springboot-java8

# compile, run the test suite and package the jar
./mvnw clean verify

# run the application (listens on http://localhost:8080)
./mvnw spring-boot:run

You can also run the packaged jar directly:

java -jar target/gs-spring-boot-0.1.0.jar

The Gradle build has been removed; Maven is the only supported build.

Every push and pull request is built by GitHub Actions with ./mvnw -B clean verify on JDK 21 (see .github/workflows/ci.yml).

Expected startup noise

On startup the app creates an in-memory H2 customers table with JdbcTemplate and logs a few rows — this is part of the demo, not an error.
It also tries to fetch a random quote from gturnquist-quoters.cfapps.io, a demo service that no longer exists. The resulting WARN Could not fetch a quote from ... is expected and must never fail startup.

API

All endpoints are served from http://localhost:8080.

Method	Path	Description
`GET`	`/`	Greeting; accepts an optional `?name=` parameter (defaults to `World`)
`GET`	`/topic`	All topics
`GET`	`/topic/{id}`	A single topic by id
`POST`	`/topic`	Add a topic (JSON body)
`PUT`	`/topic/{id}`	Replace the topic with the given id
`DELETE`	`/topic/{id}`	Delete the topic with the given id
`GET`	`/topic/sort`	All topics sorted by id
`GET`	`/topic/minimum/length/{minLength}`	Topics whose id is longer than `minLength`
`GET`	`/topic/string/operation`	Plain-text dump of the string/stream/regex examples
`GET`	`/topic/file/operation`	Plain-text dump of the NIO.2 file examples
`GET`	`/datetime`	Plain-text dump of the `java.time` examples

The topic list lives in memory, so POST / PUT / DELETE changes are lost when the application restarts.

Examples

$ curl 'http://localhost:8080/?name=Devin'
{"id":1,"content":"Hello, Devin!"}

$ curl http://localhost:8080/topic
[{"id":"spring","subjectName":"Spring Framework","subjectDescription":"Spring Framework Description"}, ...]

$ curl -X POST http://localhost:8080/topic \
    -H 'Content-Type: application/json' \
    -d '{"id":"kotlin","subjectName":"Kotlin","subjectDescription":"Kotlin Description"}'

The /topic/file/operation endpoint resolves paths relative to the working directory the application was started from, so its output depends on where you run it.

Project layout

src/main/java/hello
├── Application.java          # entry point + CommandLineRunner (H2 seeding, quote fetch)
├── config/                   # RestTemplate bean
├── controller/               # GreetingController, TopicController, HelloController
├── declaration/              # CustomPredicate, TimeClient (default/static interface methods)
├── model/                    # Topic, Greeting, Customer, Quote, Value, SimpleTimeClient
└── service/                  # TopicService — where most of the Java 8 examples live