Spring Cloud Task Application Starters provide you with predefined Spring Cloud Task applications that you can run independently or with Spring Cloud Data Flow. You can also use the starters as a basis for creating your own applications. They include commonly used tasks that can run as is or be modified to your needs.

As a user of Spring Cloud Task Application Starters you have access to two types of artifacts.

Starters are libraries that contain the complete configuration of a Spring Cloud Task application with a specific role (e.g. an JDBC HDFS that migrates data from a JDBC Repository via sql query to a file on hdfs). Starters are not executable applications, and are intended to be included in other Spring Boot applications.

Prebuilt applications are Spring Boot applications that include the starters. Prebuilt applications are uberjars and include minimal code required to execute standalone.

	Note
	Only starters are present in the source code of the project. Prebuilt applications are generated according to the Maven plugin configuration.

<dependency>
  <group>org.springframework.cloud.task.app</group>
  <artifactId>spring-cloud-starter-task-timestamp</artifactId>
  <version>1.0.0.BUILD-SNAPSHOT</version>
</dependency>

org.springframework.cloud.task.app:timestamp-task:1.0.0.BUILD-SNAPSHOT

./generate.sh

cd apps

mvn clean install

In this section we will describe how to create your own application.

<dependencies>
  <!- other dependencies -->
  <dependencies>
    <dependency>
      <groupId>org.springframework.cloud.task.app</groupId>
      <artifactId>spring-cloud-starter-task-timestamp</artifactId>
    </dependency>
</dependencies>

package org.springframework.cloud.task.app.timestamp;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Import;


@SpringBootApplication
@Import(org.springframework.cloud.task.app.timestamp.TimestampTaskConfiguration.class)
public class TimestampTaskApplication {

        public static void main(String[] args) {
                SpringApplication.run(TimestampTaskApplication.class, args);
        }
}

In this section, we will explain how to develop a custom task application and then generate maven and docker artifacts for it using the existing tooling provided by the spring cloud task app starter infrastructure. For explanation purposes, we will assume that we are creating a new task application for a technology named foobar.

Please look into the existing starters for how to design and structure a new one. Ensure that you name the main @Configuration class of your starter as FoobarTaskConfiguration as this is the default convention used by the app generation later. The default package for the class with @Configuration is org.springfamework.cloud.task.app.foobar. If you have a different class/package name, see below for how to override that in the app generator. The technology name for which the app starter is created can be a hyphenated stream of strings such as in spark-client This starter module for this needs to be spring-cloud-starter-task-spark-client.

The starters in spring-cloud-task-app-starters are slightly different from the other starters in spring-boot and spring-cloud in that here we don’t provide a way to auto configure any configuration through spring factories mechanism. Rather, we delegate this responsibility to the maven plugin that is generating the binder based apps. Therefore, you don’t have to provide a spring.factories file that lists all your configuration classes.

./mvnw clean install -pl :spring-cloud-starter-task-foobar

<dependencyManagement>
...
...
    <dependency>
        <groupId>org.springframework.cloud.task.app</groupId>
        <artifactId>spring-cloud-starter-task-foobar</artifactId>
        <version>1.0.0.BUILD-SNAPSHOT</version>
    </dependency>
...
...

./mvnw clean install -pl :spring-cloud-task-app-dependencies

The minimal configuration needed to generate the app is to add to plugin configuration in spring-cloud-task-app-generator/pom.xml. There are other plugin options that customize the generated applications which are described in the plugin documentation (github.com/spring-cloud/spring-cloud-stream-app-maven-plugin). A few plugin features are described below.

<generatedApps>
....
    <foobar-task />
....
</generatedApps>

More information about the maven plugin used above can be found here: github.com/spring-cloud/spring-cloud-stream-app-maven-plugin

If you did not follow the default convention expected by the plugin of where it is looking for the main configuration class, which is org.springfamework.cloud.task.app.foobar.FoobarTaskConfiguration, you can override that in the configuration for the plugin. For example, if your main configuration class is foo.bar.SpecialFooBarTaskConfiguration.class, this is how you can tell the plugin to override the default.

<foobar-task>
    <autoConfigClass>foo.bar.SpecialFooBarTaskConfiguration.class</autoConfigClass>
</foobar-task>

This will generate the foobar task app in a directory named apps at the root of the repository. If you want to change the location where the apps are generated, for instance /tmp/task-apps, you can do it in the configuration section of the plugin.

<configuration>
    ...
    <generatedProjectHome>/tmp/task-apps</generatedProjectHome>
    ...
</configuration

If you have an artifact that is only available through a private internal maven repository (may be an enterprise wide Nexus repo that you use globally across teams), and you need that for your app, you can define that as part of the maven plugin configuration.

For example,

<configuration>
...
    <extraRepositories>
        <repository>
            <id>private-internal-nexus</id>
            <url>.../</url>
            <name>...</name>
            <snapshotEnabled>...</snapshotEnabled>
        </repository>
    </extraRepositories>
</configuration>

Then you can define this as part of your app tag:

<foobar-task>
    <extraRepositories>
        <private-internal-nexus />
    </extraRepositories>
</foobar-task>

Here you will see foobar-task along with all the other out of the box apps that is generated.

If you only care about the foobar-task apps and nothing else, you can cd into that directory and import it directly into your IDE of choice. Each of them is a self contained spring boot application project. For all the generated apps, the parent is spring-boot-starter-parent as is required by Spring Initializr, the library used under the hood to generate the apps.

You can cd into these custom foobar-task directories and do the following to build the apps:

cd foobar-task

mvn clean install

This would install the foobar-task into your local maven cache (~/.m2 by default).

The app generation phase adds an integration test to the app project that ensures all the spring components and contexts are loaded properly. However, these tests are not run by default when you do a mvn install. You can force the running of these tests by doing the following:

mvn clean install -DskipTests=false

java -jar foobar-task.jar

It should start the application up.

mvn clean package docker:build

This creates the docker image under the target/docker/springcloudtask directory. Please ensure that the Docker container is up and running and DOCKER_HOST environment variable is properly set before you try docker:build.

All the generated apps from the repository are uploaded to Docker Hub

However, for a custom app that you build, this won’t be uploaded to docker hub under springcloudtask repository. If you think that there is a general need for this app, you should contribute this starter to the main repository and upon review, this app then can be uploaded to the above location in docker hub.

If you still need to push this to docker hub under a different repository you can take the following steps.

Go to the pom.xml of the generated app [ example - foobar-task/pom.xml] Search for springcloudtask. Replace with your repository name.

Then do this:

mvn clean package docker:build docker:push -Ddocker.username=[provide your username] -Ddocker.password=[provide password]

This would upload the docker image to the docker hub in your custom repository.