Simple java API rest hello-world-fwless

Infos

This project aims to showcase how to use Dekorate to generate the Kubernetes MANIFEST (YAML resources) to build a container image of an application designed without a framework but based on Java classes only and deploy it easily next Kubernetes/Openshift.

NOTE

The master branch contains just the code of the Java application exposing a REST endpoint. Depending on the container platform and image building tool that you would like to use, you will find different branches on this repository:

Container Platform	Image building tool	git branch
Kubernetes	Docker	dekorate-4-k8s-docker
Kubernetes	JIB	dekorate-4-k8s-jib
OpenShift	Docker	dekorate-4-ocp-docker
OpenShift	JIB	dekorate-4-ocp-jib

Coding the API rest

The following steps describe how to create a maven project, configure it and add the needed maven dependency to develop a pure java API rest.

1. Create a Maven project with an initial pom.xml file

mvn archetype:generate \
  -DgroupId=org.acme \
      -DartifactId=hello-world-fwless \
      -DarchetypeArtifactId=maven-archetype-quickstart \
      -DinteractiveMode=false

2. Add these properties to the pom.xml

    <properties>
     <java.version>11</java.version>
     <maven.compiler.source>${java.version}</maven.compiler.source>
     <maven.compiler.target>${java.version}</maven.compiler.target>
    </properties>

3. Include Jackson for JSON serialization

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.11.1</version>
</dependency>

4. Specify the main class used as entry point within the Java JAR archive to launch the application

    <build>
     <pluginManagement>
     <plugins>
       <plugin>
         <artifactId>maven-jar-plugin</artifactId>
         <version>3.2.0</version>
         <configuration>
           <archive>
             <manifest>
               <mainClass>org.acme.App</mainClass>
             </manifest>
           </archive>
         </configuration>
       </plugin>
     </plugins>
    </pluginManagement>
    </build>

5. Edit the main App java class and paste the code above. This code instantiates a HttpServer and will run it at the specified. The endpoint or URI path to call the service is define using a HttpContext object. The response to be populated when a HTTP request is receive is managed with an OutputStream and HttpExchange.

package org.acme;

import com.sun.net.httpserver.HttpServer;

import java.io.IOException;
import java.io.OutputStream;
import java.net.InetSocketAddress;

public class App 
{
    public static void main(String[] args) throws IOException {
        int serverPort = 8080;
        HttpServer server = HttpServer.create(new InetSocketAddress(serverPort), 0);
        server.createContext("/api/hello", (exchange -> {
            String respText = "Hello FrameWorkless world!";
            exchange.sendResponseHeaders(200, respText.getBytes().length);
            OutputStream output = exchange.getResponseBody();
            output.write(respText.getBytes());
            output.flush();
            exchange.close();
        }));
        server.setExecutor(null); // creates a default executor
        System.out.println("Listening on port "+serverPort);
        server.start();
    }

}

You can run the main method int App java class using your favorite IDE. You will see that a web server listening on port 8000 will be started and will expose an endpoint. If you use a curl request at the address localhost:8080/api/hello, or open a browser, then the following message Hello FrameWorkless world! will be printed.

6. Compile the application using the mvn clean package command.

7. Launch the application within a terminal by executing this command: java -jar target/hello-world-fwless-1.0-SNAPSHOT.jar.

8. Verify if the endpoint is able to reply to a curl localhost:8080/api/hello request.

Containerization

A Dockerfile is provided in order to build a container that runs the application.

If you have docker installed in your machine, within a terminal you can build the image with:

docker build -f Dockerfile -t $USER/hello-world-fwless .

Then, run the image using this command:

docker run -i --rm -p 8080:8080 $USER/hello-world-fwless

Check if the endpoint is responding with curl localhost:8080/api/hello or open a browser to http://localhost:8080/api/hello.