Using System properties in Grails

Retrieving a few of system variables is inevitable in developing computer applications within any environment. In this post, we would show you system variables existing once the application is loaded and how to retrieve a specific variable to pass it to another routine.

To do so, the following statements will print out all the existing values of System variables.

System.properties.each { k, v ->
    println "$k = $v"
}

The result often looks like

java.vendor = Oracle Corporation
sun.java.launcher = SUN_STANDARD
catalina.base = C:\Users\tnguyen\EBI\Projects\jummp-biomodels\target\work\tomcat
sun.nio.ch.bugLevel = 
sun.management.compiler = HotSpot 64-Bit Tiered Compilers
catalina.useNaming = true
os.name = Windows 10
sun.boot.class.path = C:\Program Files\Java\jdk1.8.0_162\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_162\jre\lib\rt.jar;C:\Program Files\Java\jdk1.8.0_162\jre\lib\sunrsasign.jar;C:\Program Files\Java\jdk1.8.0_162\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_162\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_162\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_162\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_162\jre\classes
org.mortbay.xml.XmlParser.NotValidating = true
sun.desktop = windows
grails.env.default = true
java.vm.specification.vendor = Oracle Corporation
java.runtime.version = 1.8.0_162-b12
grails.env.initializing = false
grails.env = development
user.name = tnguyen
java.naming.factory.initial = org.apache.naming.java.javaURLContextFactory
user.language = en
jdk.reflect.allowGetCallerClass = true
sun.boot.library.path = C:\Program Files\Java\jdk1.8.0_162\jre\bin
javax.sql.DataSource.Factory = org.apache.commons.dbcp.BasicDataSourceFactory
java.version = 1.8.0_162
user.timezone = Europe/London
sun.arch.data.model = 64
jline.shutdownhook = false
java.endorsed.dirs = C:\Program Files\Java\jdk1.8.0_162\jre\lib\endorsed
sun.cpu.isalist = amd64
sun.jnu.encoding = Cp1252
file.encoding.pkg = sun.io
file.separator = \
java.specification.name = Java Platform API Specification
java.class.version = 52.0
grails.server.factory = org.grails.plugins.tomcat.TomcatServerFactory
user.country = GB
java.home = C:\Program Files\Java\jdk1.8.0_162\jre
grails.home = C:\Users\tnguyen\devtools\grails-2.5.5
java.vm.info = mixed mode
os.version = 10.0
grails.build.execution.context = C:\Users\tnguyen\AppData\Local\Temp\jummp-biomodels3048486709134205985grails-execution-context
grails.version = 2.5.5
path.separator = ;
java.vm.version = 25.162-b12
grails.disable.exit = true
user.variant = 
grails.env.set = true
grails.fork.active = true
java.awt.printerjob = sun.awt.windows.WPrinterJob
grails.shutdown.hook.installed = true
sun.io.unicode.encoding = UnicodeLittle
awt.toolkit = sun.awt.windows.WToolkit
jummp.basePath = C:\Users\tnguyen\EBI\Projects\jummp-biomodels\.
user.script = 
java.naming.factory.url.pkgs = org.apache.naming
user.home = C:\Users\tnguyen
java.specification.vendor = Oracle Corporation
springloaded = profile=grails;cacheDir=C:\Users\tnguyen/.grails/2.5.5/
java.library.path =...

Let’s give an example.

We often want to get the directory of the currently logged-in user to make other directories to store exported files or backup data, for instance. To do so, the snippet below may help.

String tmpDirPath = System.getProperty("java.io.tmpdir")
String userHomePath = System.getProperty("user.home")

// We also do like the following
def fileSeparator = System.properties.'file.separator'
def log4jFileName = System.properties.'catalina.base' + "${fileSeparator}logs${fileSeparator}${appName}.log"

Setting System property from the command line in grails

In one of my recent grails project, I have needed to set System property from the command line while running the grails application. Presumably, we want to set any property, say app.property=”propertyValue”, then the command to set the property in grails application would be:

grails -Dapp.property="propertyValue" run-app

Similarly to retrieve the value of System property, we use

String myPropertyValue= System.getProperty("app.property")

Another example could be liked this

log4jFileName = (System.properties.'catalina.base') + "/logs/${appName}.log"
file: "${config.log4jFileName}"

I found the post on the blog of the developer of Grails core’s ones which is discussing quite a lot of useful tips and tricks for retrieving the application’s properties. The copyright of the featured image comes from that blog.

Hope it helps you to solve your problem.