How to Create a REST API With Helidon SE and Java?

Hello everyone, Today, we will show you how to create a simple REST API with Helidon SE 2.5.0 and Java 17.

Quick Overview:

  • Helidon SE is designed to be a microframework that fortifies the reactive programming model. Helidon SE features three core APIs to engender a microservice -- a web server, configuration, and security -- for building microservices-predicated applications. 
  • Helidon's web server is an asynchronous and reactive API that runs on top of Netty. The WebServer interface includes support for configuration, routing, error handling, and building metrics and health endpoints.
  • The Config loads and processes configuration properties(application.properties or application.yaml) in key/value format. 
  • The Security class provides support for authentication, sanction, and audit.
Let's begin,

Final Project Directory:



Maven [pom.xml]:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
https://maven.apache.org/xsd/maven-4.0.0.xsd">

<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>io.helidon.applications</groupId>
<artifactId>helidon-se</artifactId>
<version>2.5.0</version>
<relativePath>../../../applications/se/pom.xml
</relativePath>
</parent>

<groupId>com.knf.dev.demo</groupId>
<artifactId>helidon-se-rest-hello-world</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>helidon-se-rest-hello-world</name>
<description>Demo project for Helidon SE</description>

<properties>
<version.java>17</version.java>
<mainClass>com.knf.dev.demo.
helidonseresthelloworld.
HelidonSeRestHelloWorldApplication</mainClass>
</properties>
<dependencies>
<dependency>
<groupId>io.helidon.webserver</groupId>
<artifactId>helidon-webserver</artifactId>
</dependency>
<dependency>
<groupId>io.helidon.media</groupId>
<artifactId>helidon-media-jsonp</artifactId>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>

<configuration>
<source>${version.java}</source>
<target>${version.java}</target>
<release>${version.java}</release>
<forceJavacCompilerUse>true
</forceJavacCompilerUse>
</configuration>
</plugin>
</plugins>
</build>
</project>

HelloService.java

package com.knf.dev.demo.helidonseresthelloworld;

import java.util.Collections;
import java.util.concurrent.atomic.AtomicReference;
import javax.json.Json;
import javax.json.JsonBuilderFactory;
import io.helidon.config.Config;
import io.helidon.webserver.Routing.Rules;
import io.helidon.webserver.ServerRequest;
import io.helidon.webserver.ServerResponse;
import io.helidon.webserver.Service;

public class HelloService implements Service {

private static final JsonBuilderFactory JSON = Json.
createBuilderFactory(Collections.emptyMap());
private final AtomicReference<String> greeting =
new AtomicReference<>();

HelloService(Config config) {
greeting.set(config.get("app.message").
asString().orElse("Empty"));
}

@Override
public void update(Rules rules) {
rules.get("/", this::getDefaultMessageHandler);
}

private void getDefaultMessageHandler
(ServerRequest request, ServerResponse response) {
sendResponse(response, "Knowledgefactory");
}

private void sendResponse
(ServerResponse response, String name) {
var message = String.format("%s %s!",
greeting.get(), name);
var returnObject = JSON.
createObjectBuilder().
add("message", message).build();
response.send(returnObject);
}
}

application.properties:

server.port=9080
app.message=Greetings from

Main 

package com.knf.dev.demo.helidonseresthelloworld;

import java.util.logging.Logger;
import io.helidon.common.reactive.Single;
import io.helidon.config.Config;
import io.helidon.media.jsonp.JsonpSupport;
import io.helidon.webserver.Routing;
import io.helidon.webserver.WebServer;

public class HelidonSeRestHelloWorldApplication {

private static final Logger LOGGER = Logger.
getLogger(HelidonSeRestHelloWorldApplication.
class.getName());

public static void main(final String[] args) {
startServer();
}

private static Single<WebServer> startServer() {

// Load the default configuration using the
// reate() method.
var config = Config.create();

/*
* Helidon's web server is an asynchronous and
* reactive API that runs on top of
* Netty. The WebServer interface includes
* support for configuration, routing,
* error handling, and building metrics
* and health endpoints.
*/
var server = WebServer.
builder(createRouting(config)).
config(config.get("server"))
.addMediaSupport(JsonpSupport.create()).build();

// Start web server
var webserver = server.start();

webserver.thenAccept(ws -> {
LOGGER.info("Web server started! http://localhost:"
+ ws.port() + "/hello");
ws.whenShutdown().
thenRun(() -> LOGGER.info("Web server is down!"));
}).exceptionallyAccept(t -> {
LOGGER.severe("Web startup failed: "
+ t.getMessage());
});

return webserver;
}

private static Routing createRouting(Config config) {

var helloService = new HelloService(config);

return Routing.builder()

.register("/hello", helloService).build();
}
}

Local Setup and Run the application

Step1: Download or clone the source code to a local machine. - Click here


Step2: mvn clean install


Step3: Run the Main java application


INFO: Web server started! http://localhost:9080/hello

 Download the source code

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