====== Setting up a simple Java Jetty Server  ======

Java web programming includes a servlet architecture for making server applications in java and having the nitty gritty of managing the web server part of the application to a web server that functions as a servlet container. One popular embedded server for Java projects is [[https://www.eclipse.org/jetty/ |Jetty]].

You can create a java server project that embeds Jetty and run it on [[metaarray|the MetaArray]] on your [[meta_port_allocation|assigned port]]. Below is a very simple example on how to get started with that. It doesn't use any IDE, so it's a bit manual. You can find more detailed directions at the external project links below.

There are lots of different java web frameworks that center around using the [[https://www.eclipse.org/jetty/ |Jetty]] server, including a few microframeworks. This page is going to go through an example using [[https://javalin.io | Javalin]], which is a microframework that has a lighter footprint and is easier to configure than Spring Boot and other more mainline frameworks.  It has a simple tutorial that was used and modified a bit here to show you how to set up a Java Jetty server. To make things quick to set up, we'll use Maven (''mvn'').

===== Create Project Space =====

First, let's create your maven-style project folder.
  - Go to an appropriate project folder that you want to work in
  - make the java source folder in the maven style
    * ''mkdir -p src/main/java/myproject''

===== Create Project Object Model =====

Next, let's set up the POM file, which maven will use to pull all the dependencies for our framework and let us build it.

  - Create a new file in “myproject”, call it ''pom.xml''
    * ''nano pom.xml''
  - Paste in the following: <code>
<project>
    <!-- model version - always 4.0.0 for Maven 2.x POMs -->
   <modelVersion>4.0.0</modelVersion>

  <!-- project coordinates - values which uniquely identify this project -->
 <groupId>myproject.helloWorld</groupId>
<artifactId>helloWorld</artifactId>
    <version>1.0.0-SNAPSHOT</version>
<properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.target>1.8</maven.compiler.target>
</properties>
   <!-- library dependencies -->
  <dependencies>
<dependency>
  <groupId>io.javalin</groupId>
    <artifactId>javalin</artifactId>
 <version>4.3.0</version>
    </dependency>
    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-simple</artifactId>
      <version>1.7.31</version>
     </dependency>
   </dependencies>
     <build>
    <plugins>
      <plugin>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.6.0</version>
        <configuration>
          <source>1.8</source>
          <target>1.8</target>
          <showDeprecation/>
          <showWarnings/>
          <compilerArgs>
            <arg>-Xlint:unchecked</arg>
            <arg>-Xlint:all</arg>
            <arg>-Xlint:-serial</arg>
          </compilerArgs>
        </configuration>
      </plugin>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-surefire-plugin</artifactId>
        <version>2.19.1</version>
        <configuration>
          <systemPropertyVariables>
            <java.util.logging.config.file>src/main/resources/logging.properties</java.util.logging.config.file>
          </systemPropertyVariables>
        </configuration>
      </plugin>
      <plugin>
        <!-- Exec plugin lets us run app directly from maven and not deal with classpaths -->
       <groupId>org.codehaus.mojo</groupId>
         <artifactId>exec-maven-plugin</artifactId>
         <version>3.0.0</version>
         <executions>
           <execution>
             <goals>
               <goal>java</goal>
             </goals>
           </execution>
         </executions>
         <configuration>
           <!-- This is what exec will run as project main, *CHANGE THIS IF YOU ARE USING A DIFFERENT MAIN CLASS-->
           <mainClass>myproject.helloWorld</mainClass>
         </configuration>
       </plugin>
      </plugins>
    </build>
</project>

</code>
  - Save the file

===== Add Your Java Code =====

  - Using an editor again, create your hello world class file, in its proper folder for maven:
    - ''nano src/main/java/myproject/helloWorld.java''
    - paste in the following: <code java>
package myproject;

import io.javalin.Javalin;

public class helloWorld {
    private static int MY_JETTY_PORT= 8388;  //replace 8388 with your port as explained in the wiki
    
    public static void main(String[] args){
        Javalin app = Javalin.create().start(MY_JETTY_PORT);
        app.get("/", ctx -> ctx.result("Hello World, this is my Java App on Jetty!"));
    }
}
</code>
  - move the cursor up and change the value of MY_JETTY_PORT to be your [[meta_port_allocation|Port on the MetaArray]] (that is, replace 8388 with your UID number).
  - save the file

===== Build Your Project =====

Here we go. Back at the command line, type
  mvn package
 
You will see a bunch of log info scroll by, but at the end, you should see something like this:

  [INFO] ------------------------------------------------------------------------
  [INFO] BUILD SUCCESS
  [INFO] ------------------------------------------------------------------------
  [INFO] Total time:  3.537 s
  [INFO] Finished at: 2022-01-20T21:04:04Z
  [INFO] ------------------------------------------------------------------------

===== Run Your Server =====

Now, let's run the server. We've set up an “exec goal” in the POM so we can run the resulting project from maven, like so:

  mvn exec:java
  
You should see something like this (hopefully any warnings you get are ignorable):

  WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
  WARNING: All illegal access operations will be denied in a future release
  [INFO] Scanning for projects...
  [INFO] 
  [INFO] ------------------< myproject.helloWorld:helloWorld >-------------------
  [INFO] Building helloWorld 1.0.0-SNAPSHOT
  [INFO] --------------------------------[ jar ]---------------------------------
  [INFO] 
  [INFO] --- exec-maven-plugin:3.0.0:java (default-cli) @ helloWorld ---
  [myproject.helloWorld.main()] INFO io.javalin.Javalin -  
         __                      __ _            __ __
        / /____ _ _   __ ____ _ / /(_)____      / // /
   __  / // __ `/| | / // __ `// // // __ \    / // /_
  / /_/ // /_/ / | |/ // /_/ // // // / / /   /__  __/
  \____/ \__,_/  |___/ \__,_//_//_//_/ /_/      /_/  
  
          https://javalin.io/documentation
  
  [myproject.helloWorld.main()] INFO org.eclipse.jetty.util.log - Logging initialized @2496ms to org.eclipse.jetty.util.log.Slf4jLog
  [myproject.helloWorld.main()] INFO io.javalin.Javalin - Starting Javalin ...
  [myproject.helloWorld.main()] INFO io.javalin.Javalin - You are running Javalin 4.3.0 (released January 13, 2022).
  [myproject.helloWorld.main()] INFO io.javalin.Javalin - Listening on http://localhost:32056/
  [myproject.helloWorld.main()] INFO io.javalin.Javalin - Javalin started in 263ms \o/
  
If you get here, then your server is running! Now try it out: point your web browser to //http://yourusername.yourSDFmetarraydomain.org:yourMetaArrayPort // and see it if works!

Press ''ctl-c'' to stop the server. 

The rest is up to your imagination!