Retrieving external config properties from JNDI, environment shell, and/or system properties.

I need to deploy multiple instances of the same WAR in a single Tomcat instance. I've been reading external config properties from System properties (e.g. System.getProperty('ext.xyz')). That won't work when deploying multiple WAR instances. So I whipped this up to read from JNDI as well as System properties (and I threw in reading from environment vars as well).

	import javax.naming.Context
	import javax.naming.InitialContext
	import javax.naming.NamingException
	class ExtConfig {
	public ExtConfig() {
	}
	public String find(String key) {
	String path = findJndiEnvVar(key)
	if(!path) {
	path = System.getenv(key)
	if(!path) {
	path = System.getProperty(key)
	}
	}
	return path
	}
	private String findJndiEnvVar(String key) {
	try {
	def ctx = (Context) new InitialContext().lookup('java:comp/env')
	return ctx.lookup(key)
	}
	catch(NamingException e) {
	// not found, carry on
	return null
	}
	}
	}

view raw ExtConfig.groovy hosted with ❤ by GitHub

Then in Config.groovy, I use it thus...

	def extConfigPath = new ExtConfig().find('pathToExtFile')
	if(extConfigPath) {
	external.file = new File(extConfigPath)
	if(external.file.exists()) {
	println "Loading external config at ${external.file.path}"
	grails.config.locations = [ "file:${external.file.path}" ]
	}
	else {
	println "External config defined at ${extConfigPath} doesn't exist (huh?)"
	}
	}
	else {
	println "No external config found"
	}

view raw gistfile1.txt hosted with ❤ by GitHub

This way my config file doesn't care where the external property comes from. In dev, I can define it as a system property. In prod, I can define it as a JNDI env var.

For completeness, here's how I'm defining the context xml in Tomcat.

	<Context>
	<Environment name="pathToExtFile" value="/path/to/external/file" type="java.lang.String" />
	</Context>

view raw myWebApp.xml hosted with ❤ by GitHub