Migration from Google App Engine to Flexible Environment

Migration

Google App Engine is great since it's reliable and have tons of services free to use. Compared to a platform like Heruko, you get search, database, image and other services for free. But as a javaite, it's unfortunate that it only supports Java 7. The only way to move forward is to migrate to Flexible Environment. But be aware, not all services can migrate!

Start: App Engine

Let's start with a simple App Engine Maven project and then migrate it.

Prerequisites

Use the following guide to install Java 7 SDK and Maven.

https://cloud.google.com/appengine/docs/java/tools/maven 

Create Artifact

Use Maven to create the simple appengine skeleton artifact.

1. Run
   $ mvn archetype:generate -Dappengine-version=1.9.38 -Dapplication-id=whatever -Dfilter=com.google.appengine.archetypes:
2. Select "1"
   1: remote -> com.google.appengine.archetypes:appengine-skeleton-archetype (A skeleton application with Google App Engine)
3. Select "6"
   6: 2.1.0-1.9.38
4. Enter group id (same as your Java package name for the project)
   Define value for property 'groupId':
5. Enter your name for your project
   Define value for property 'artifactId': :
6. Enter first version
   Define value for property 'version':  1.0-SNAPSHOT:
7. Enter Java package (same as group id)
   Define value for property 'package':
8. Enter gcloud version (find latest here)
   Define value for property 'gcloud-version': 2.0.9.111.v20160527
9. Confirm your selection
    Y:

Maven have now created an App Engine project in a subfolder. Start it with $ mvn appengine:devserver

Notice the layout and the few files needed.

Simple layout with few files

Migration: Flexible Environment

Let's go for Flexible Environment and Java 8!

Prerequisites

• Install Java 8 SDK and never look back!
  Note: that App Engine uses Jetty which need Java 7 to work with JSP. If you install Java 8 it will be difficult for you to run your old App Engine projects.
• Install Google Cloud SDK. Make sure Python is on path after installation!
  https://cloud.google.com/sdk/
• Install the app-engine component to GCloud
  $ gcloud components install app-engine-java
  https://cloud.google.com/appengine/docs/flexible/java/maven

Migration

Follow the steps in the following guide.

https://cloud.google.com/appengine/docs/flexible/java/migrating-an-existing-app

1. Add the following line in appengine-web.xml
   

   <vm>true</vm>

2. Add the following two plugins in pom.xml.
1. The first one to be able to run with GCloud maven goals
2. And the second to set Java 8 compilation.

3. <plugin>
      <groupId>com.google.appengine</groupId>
      <artifactId>gcloud-maven-plugin</artifactId>
      <version>2.0.9.106.v20160420</version>
   </plugin>

4.       <plugin>
           <groupId>org.apache.maven.plugins</groupId>
           <version>3.3</version>
           <artifactId>maven-compiler-plugin</artifactId>
           <configuration>
             <source>1.8</source>
             <target>1.8</target>
           </configuration>
         </plugin>

5. Run with
6. $ mvn gcloud:run

Google Flexible Environment with Virtual Scala JS Compiler

Google Flexible Environment with Virtual Scala JS Compiler

After several months I managed to translate Scala JS Fiddle to Google Java Flexible Environment 

Goal

To create a project with Scala backend which generates JavaScript in a virtual compiler.

Live Demo

The live demo uses a Scala Servlet to generate HTML (Scala Tags) with a JavaScript. A second Scala Servlet is responding to "/javascript.js" and is using a virtual compiler to compile a String with simple Scala JS code to a JavaScript

https://scala-js-compiler.appspot.com/index.scala

Environment

It's a Maven project using Google Flexible "Compat" Environment which includes some App Engine features (not used) and Java 8 with Servlet API 3.1.

Source

Check out my Github

https://github.com/AIMMOTH/scala-js-compiler/tree/web-demo

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