Enable external configuration in Grails 3

external_configuration_in_grails_3.md

External configuration in Grails 3

---

Working on Grails 3 I realized that I no longer can specify external configuration using the standard grails.config.locations property in Config.groovy file.

Reason is obvious! There is no Config.groovy now in Grails 3. Instead we now use application.yml to configure the properties. However, you can't specify the external configuration using this file too!

What the hack?

Now Grails 3 uses Spring's property source concept. To enable external config file to work we need to do something extra now.

Suppose I want to override some properties in application.yml file with my external configuration file.

E.g., from this:

 dataSource:
    username: sa
    password:
    driverClassName: "org.h2.Driver"

To this:

dataSource:
    username: root
    password: mysql
    driverClassName: "com.mysql.jdbc.Driver"

First I need to place this file in application's root. E.g., I've following structure of my Grails 3 application with external configuration file app-config.yml in place:

[human@machine tmp]$ tree -L 1 myapp
myapp
├── app-config.yml // <---- external configuration file!
├── build.gradle
├── gradle
├── gradle.properties
├── gradlew
├── gradlew.bat
├── grails-app
└── src
[human@machine tmp]$ 

Now, to enable reading this file just add following:

• To your build.gradle file

bootRun {
    // local.config.location is just a random name. You can use yours.
    jvmArgs = ['-Dlocal.config.location=app-config.yml']
}

• To your Application.groovy file

package com.mycompany

import grails.boot.GrailsApp
import grails.boot.config.GrailsAutoConfiguration
import org.springframework.beans.factory.config.YamlPropertiesFactoryBean
import org.springframework.context.EnvironmentAware
import org.springframework.core.env.Environment
import org.springframework.core.env.PropertiesPropertySource
import org.springframework.core.io.FileSystemResource
import org.springframework.core.io.Resource

class Application extends GrailsAutoConfiguration implements EnvironmentAware {
    static void main(String[] args) {
        GrailsApp.run(Application, args)
    }

    @Override
    void setEnvironment(Environment environment) {
        String configPath = System.properties["local.config.location"]
        Resource resourceConfig = new FileSystemResource(configPath)
        YamlPropertiesFactoryBean ypfb = new YamlPropertiesFactoryBean()
        ypfb.setResources([resourceConfig] as Resource[])
        ypfb.afterPropertiesSet()
        Properties properties = ypfb.getObject()
        environment.propertySources.addFirst(new PropertiesPropertySource("local.config.location", properties))
    }
}

Notice that Application class implements EnvironmentAware Interface and overrides its setEnvironment(Environment environment):void method.

Now this is all what you need to re-enable external config file in Grails 3 application.

Code and guidance is taken from following links with little modification:

1. http://grails.1312388.n4.nabble.com/Grails-3-External-config-td4658823.html
2. https://groups.google.com/forum/#!topic/grails-dev-discuss/_5VtFz4SpDY

Cheers!!!