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.micro</groupId>
    <artifactId>helloworld</artifactId>
    <version>24.11.0-SNAPSHOT</version>
    <packaging>war</packaging>
    <name>Piranha Micro - Create a Hello World application</name>
    <properties>
        <!-- dependencies -->
        <jakarta.jakartaee-web-api.version>11.0.0-M4</jakarta.jakartaee-web-api.version>
        <junit.version>5.9.1</junit.version>
        <!-- other -->
        <java.version>21</java.version>
        <piranha.distribution>micro</piranha.distribution>
        <piranha.version>24.9.0</piranha.version>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <!-- plugins -->
        <maven-compiler-plugin.version>3.10.1</maven-compiler-plugin.version>
        <maven-failsafe-plugin.version>3.0.0-M7</maven-failsafe-plugin.version>
        <maven-war-plugin.version>3.3.2</maven-war-plugin.version>
    </properties>
    <build>
        <finalName>piranha-micro-helloworld</finalName>
        <plugins>
            <plugin>
                <groupId>cloud.piranha.maven</groupId>
                <artifactId>piranha-maven-plugin</artifactId>
                <version>${piranha.version}</version>
                <executions>
                    <execution>
                        <id>pre-integration-test</id>
                        <phase>pre-integration-test</phase>
                        <goals>
                            <goal>start</goal>
                        </goals>
                    </execution>
                    <execution>
                        <id>post-integration-test</id>
                        <phase>post-integration-test</phase>
                        <goals>
                            <goal>stop</goal>
                        </goals>
                    </execution>
                </executions>
                <configuration>
                    <distribution>${piranha.distribution}</distribution>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>${maven-compiler-plugin.version}</version>
                <configuration>
                    <release>${java.version}</release>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-failsafe-plugin</artifactId>
                <version>${maven-failsafe-plugin.version}</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>integration-test</goal>
                            <goal>verify</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>${maven-war-plugin.version}</version>
                <configuration>
                    <failOnMissingWebXml>false</failOnMissingWebXml>
                </configuration>
            </plugin>
        </plugins>
    </build>
    <dependencies>
        <dependency>
            <groupId>jakarta.platform</groupId>
            <artifactId>jakarta.jakartaee-web-api</artifactId>
            <version>${jakarta.jakartaee-web-api.version}</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter</artifactId>
            <version>${junit.version}</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
</project>

Add the Hello Servlet

Add the HelloWorldServlet.java file in the src/main/java/helloworld directory.

package helloworld;

import java.io.IOException;
import java.io.PrintWriter;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

public class HelloWorldServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, 
            HttpServletResponse response) throws IOException, ServletException {
        try (PrintWriter writer = response.getWriter()) {
            response.setContentType("text/plain");
            writer.println("Hello World!");
            writer.flush();
        }
    }
}

Add the web.xml file

Add the web.xml file to the src/main/webapp/WEB-INF directory.

<?xml version="1.0" encoding="UTF-8"?>

<web-app version="4.0" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd">
    <servlet>
        <servlet-name>HelloWorldServlet</servlet-name>
        <servlet-class>helloworld.HelloWorldServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>HelloWorldServlet</servlet-name>
        <url-pattern>/index.html</url-pattern>
    </servlet-mapping>
    <session-config>
        <session-timeout>30</session-timeout>
    </session-config>
</web-app>

Add an integration test

As we want to make sure the application gets tested before we release an integration test is added which will be executed as part of the build.

We'll add the integration test to the src/test/java directory.

package helloworld;

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.assertTrue;
import org.junit.jupiter.api.Test;

class HelloWorldIT {
 
    @Test
    void testHelloWorldHtml() throws Exception {
        HttpClient client = HttpClient.newHttpClient();
        HttpRequest request = HttpRequest
                .newBuilder(new URI("http://localhost:8080/helloworld/helloworld.html"))
                .build();
        HttpResponse<String> response = client.send(request, BodyHandlers.ofString());
        assertTrue(response.body().contains("Hello World!"));
    }
}

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 web application 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.

1. The Piranha Micro runtime JAR.
2. The WAR file you just produced.

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

  java -jar piranha-dist-micro.jar --war-file helloworld.war

Conclusion

As you can see getting started with Piranha Micro is straightforward!