Create a JSON REST service

If you are looking to create a JSON based REST service with Piranha then consider Piranha Core Profile. It features a runtime ideally suited for REST, JSON and micro services.

In 7 steps you will learn how to create the JSON REST service. They are:

Create the Maven POM file
Add the application class
Add the POJO class
Add the endpoint
Add an integration test
Test the application
Deploy the application

Create the Maven POM file

Create an empty directory to store your Maven project. Inside of that directory create the pom.xml file with the content as below.

<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>cloud.piranha.guides.coreprofile</groupId>
    <artifactId>json</artifactId>
    <version>1-SNAPSHOT</version>
    <packaging>war</packaging>
    <name>Temperature JSON service</name>
    <properties>
        <jakarta.jakartaee-core-api.version>10.0.0</jakarta.jakartaee-core-api.version>
        <junit.version>5.9.0</junit.version>
        <piranha-maven-plugin.version>22.10.0</piranha-maven-plugin.version>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>
    <dependencies>
        <dependency>
            <groupId>jakarta.platform</groupId>
            <artifactId>jakarta.jakartaee-core-api</artifactId>
            <version>${jakarta.jakartaee-core-api.version}</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-api</artifactId>
            <version>${junit.version}</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-engine</artifactId>
            <version>${junit.version}</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-params</artifactId>
            <version>${junit.version}</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <build>
        <finalName>temperature</finalName>
        <plugins>
            <plugin>
                <groupId>cloud.piranha.maven.plugins</groupId>
                <artifactId>piranha-maven-plugin</artifactId>
                <version>${piranha-maven-plugin.version}</version>
                <executions>
                    <execution>
                        <id>pre-integration-test</id>
                        <phase>pre-integration-test</phase>
                        <goals>
                            <goal>start</goal>
                        </goals>
                    </execution>
                    <execution>
                        <id>post-integration-test</id>
                        <phase>post-integration-test</phase>
                        <goals>
                            <goal>stop</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.10.1</version>
                <configuration>
                    <release>17</release>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-failsafe-plugin</artifactId>
                <version>3.0.0-M7</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>integration-test</goal>
                            <goal>verify</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>3.3.2</version>
                <configuration>
                    <failOnMissingWebXml>false</failOnMissingWebXml>
                </configuration>
            </plugin>
        </plugins>
    </build>
    <repositories>
        <repository>
            <id>jakarta-staging</id>
            <url>https://jakarta.oss.sonatype.org/content/repositories/staging/</url>
        </repository>
    </repositories>
</project>

Add the application class

Add the Application class in the src/main/java directory, which allows you to set the application path using the @ApplicationPath annotation.

package temperature;

import jakarta.ws.rs.ApplicationPath;
import jakarta.ws.rs.core.Application;

@ApplicationPath("")
public class TemperatureApplication extends Application {
}

Add the POJO

As we are going to be returning JSON in the endpoint we need a POJO to represent the model. Add the POJO class in the src/main/java directory.

package temperature;

public class Temperature {

    public enum TemperatureScale {
        CELSIUS,
        FAHRENHEIT
    }

    private TemperatureScale scale;

    private double temperature;

    public TemperatureScale getScale() {
        return scale;
    }

    public double getTemperature() {
        return temperature;
    }

    public void setScale(TemperatureScale scale) {
        this.scale = scale;
    }

    public void setTemperature(double temperature) {
        this.temperature = temperature;
    }
}

Add the endpoint

And the next step is creating the class with the celsius and fahrenheit endpoints.

package temperature;

import jakarta.enterprise.context.RequestScoped;
import jakarta.ws.rs.GET;
import jakarta.ws.rs.Path;
import jakarta.ws.rs.PathParam;
import jakarta.ws.rs.Produces;
import static jakarta.ws.rs.core.MediaType.APPLICATION_JSON;
import static temperature.Temperature.TemperatureScale.CELSIUS;
import static temperature.Temperature.TemperatureScale.FAHRENHEIT;

@RequestScoped
@Path("")
public class TemperatureBean {

    @GET
    @Produces(APPLICATION_JSON)
    @Path("/celsius/{celsius}")
    public Temperature celsius(@PathParam("celsius") double celsius) {
        Temperature temp = new Temperature();
        temp.setScale(CELSIUS);
        temp.setTemperature(celsius);
        return temp;
    }
    
    @GET
    @Produces("application/json")
    @Path("/fahrenheit/{fahrenheit}")
    public Temperature fahrenheit(@PathParam("fahrenheit") double fahrenheit) {
        Temperature temp = new Temperature();
        temp.setScale(FAHRENHEIT);
        temp.setTemperature(fahrenheit);
        return temp;
    }
}

Add an integration test

As we want to make sure the application gets tested before we release 2 integration tests are added which will be executed as part of the build.

We’ll add the 2 integration tests to the src/test/java directory.

package temperature;

import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.net.http.HttpResponse.BodyHandlers;
import static org.junit.jupiter.api.Assertions.assertEquals;
import org.junit.jupiter.api.Test;

class TemperatureIT {
 
    @Test
    void testCelsius() throws Exception {
        HttpClient client = HttpClient.newHttpClient();
        HttpRequest request = HttpRequest
                .newBuilder(new URI("http://localhost:8080/temperature/celsius/18.5"))
                .build();
        HttpResponse<String> response = client.send(request, BodyHandlers.ofString());
        assertEquals("{\"scale\":\"CELSIUS\",\"temperature\":18.5}", response.body());
    }
 
    @Test
    void testFahrenheit() throws Exception {
        HttpClient client = HttpClient.newHttpClient();
        HttpRequest request = HttpRequest
                .newBuilder(new URI("http://localhost:8080/temperature/fahrenheit/68.0"))
                .build();
        HttpResponse<String> response = client.send(request, BodyHandlers.ofString());
        assertEquals("{\"scale\":\"FAHRENHEIT\",\"temperature\":68.0}", response.body());
    }
}

Test the application

The application is setup to use JUnit to do integration testing using the Piranha Maven plugin so when you are building the application it will also execute an integration test validating the endpoint works.

To build and test the application execute the following command:

  mvn install

Deploy the application

To deploy your application you will need 2 pieces.

The Piranha Core Profile runtime JAR.
The WAR file you just produced.

For the WAR file see the target directory. For the Piranha Core Profile distribution go to Maven Central. And then the following command line will deploy your application:

  java -jar piranha-dist-coreprofile.jar --war-file json.war

Conclusion

As illustrated, creating a JSON based REST service with Piranha Core Profile is pretty straightforward because of the libaries available to you as part of the Jakarta EE Core Profile.

References

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