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ConfigSlurper

ConfigSlurper is a utility class within Groovy for writing properties file like scripts for performing configuration. Unlike regular Java properties files ConfigSlurper scripts support native Java types and are structured like a tree.

Below is an example of how you could configure Log4j with a ConfigSlurper script:

log4j.appender.stdout = "org.apache.log4j.ConsoleAppender"
log4j.appender."stdout.layout"="org.apache.log4j.PatternLayout"
log4j.rootLogger="error,stdout"
log4j.logger.org.springframework="info,stdout"
log4j.additivity.org.springframework=false

To load this into a readable config you can do:

def config = new ConfigSlurper().parse(new File('myconfig.groovy').toURL())

assert "info,stdout" == config.log4j.logger.org.springframework
assert false == config.log4j.additivity.org.springframework

As you can see from the example above you can navigate the config using dot notation and the return values are Java types like strings and booleans.

You can also use scoping in config scripts to avoid repeating yourself. So the above config could also be written as:

log4j {
    appender.stdout = "org.apache.log4j.ConsoleAppender"
    appender."stdout.layout"="org.apache.log4j.PatternLayout"
    rootLogger="error,stdout"
    logger {
        org.springframework="info,stdout"
    }
    additivity {
        org.springframework=false
    }
}

Converting to and from Java properties files

You can convert ConfigSlurper configs to and from Java properties files. For example:

java.util.Properties props = // load from somewhere

def config = new ConfigSlurper().parse(props)

props = config.toProperties()

Merging configurations

You can merge config objects so if you have multiple config files and want to create one central config object you can do:

def config1 = new ConfigSlurper().parse(..)
def config2 = new ConfigSlurper().parse(..)

config1 = config1.merge(config2)

Serializing a configuration to disk

You can serialize a config object to disk. Each config object implements the groovy.lang.Writable interface that allows you to write out the config to any java.io.Writer:

def config = new ConfigSlurper().parse(..)

new File("..").withWriter { writer ->
     config.writeTo(writer)
}

Special "environments" Configuration

The ConfigSlurper class has a special constructor other than the default constructor that takes an "environment" parameter. This special constructor works in concert with a property setting called environments. This allows a default setting to exist in the property file that can be superceded by a setting in the appropriate environments closure. This allows multiple related configurations to be stored in the same file.

Given this groovy property file:

Sample.groovy
sample {
  foo = "default_foo"
  bar = "default_bar"
}

environments {
  development {
    sample {
      foo = "dev_foo"
    }
  }
  test {
    sample {
      bar = "test_bar"
    }
  }
}

Here is the demo code that exercises this configuration:

def config = new ConfigSlurper("development").parse(new File('Sample.groovy').toURL())

assert config.sample.foo == "dev_foo"
assert config.sample.bar == "default_bar"

config = new ConfigSlurper("test").parse(new File('Sample.groovy').toURL())

assert config.sample.foo == "default_foo"
assert config.sample.bar == "test_bar"

Note: the environments closure is not directly parsable. Without using the special environment constructor the closure is ignored.

The value of the environment constructor is also available in the configuration file, allowing you to build the configuration like this:

switch (environment) {
  case 'development':
    baseUrl = "devServer/"
    break
  case 'test':
    baseUrl = "testServer/"
    break
  default:
    baseUrl = "localhost/"
}

Further information

Using Groovy ConfigSlurper to Configure Spring Beans

 

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