# Fission: Java and JVM Environment

This is the JVM environment for Fission.

It's a Docker image containing a OpenJDK8 runtime, along with a
dynamic loader.  A few dependencies are included in the
pom.xml file.

Looking for ready-to-run examples? See the [JVM examples directory](../../examples/jvm).

## Customizing this image

To add package dependencies, edit pom.xml to add what you
need, and rebuild this image (instructions below).

## Rebuilding and pushing the image

You'll need access to a Docker registry to push the image: you can
sign up for Docker hub at hub.docker.com, or use registries from
gcr.io, quay.io, etc.  Let's assume you're using a docker hub account
called USER.  Build and push the image to the the registry:

```
   docker build -t USER/jvm-env . && docker push USER/jvm-env
```

## Using the image in fission

You can add this customized image to fission with "fission env
create":

```
   fission env create --name jvm --image USER/jvm-env
```

Or, if you already have an environment, you can update its image:

```
   fission env update --name jvm --image USER/jvm-env   
```

After this, fission functions that have the env parameter set to the
same environment name as this command will use this environment.

## Web Server Framework

JVM environment uses Tomcat HTTP server by default as it is included in spring web. You can choose to use jetty or undertow by changing the dependency in pom.xml file as shown below.

```
<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-web</artifactId>
	<exclusions>
		<!-- Exclude the Tomcat dependency -->
		<exclusion>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-tomcat</artifactId>
		</exclusion>
	</exclusions>
</dependency>
<!-- Use Jetty instead -->
<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-jetty</artifactId>
</dependency>
```

## Java and JVM builder

JVM environment builder is based on OpenJDK8 and Maven 3.5.4 version. The default build command runs `mvn clean package` and uses the target/*with-dependencies.jar file for function. The default build command can be overridden as long as the uber jar file is copied to ${DEPLOY_PKG}.