Create @nAmed bindings for properties in a typesafe Config.

ConfigBinder.scala

/**
 * Copyright (c) 2012, Vast
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met: 
 * 
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer. 
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution. 
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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 */
package com.vast.common.config

import java.lang.{Boolean => JBoolean}
import scala.collection.JavaConversions._
import com.typesafe.config._
import com.google.inject.name.Names
import com.google.inject.{Key, Binder}

/**
 * Bind the properties from a config. Each binding key is the
 * name of the property prefixed by "config.".
 *
 * For example if you have
 *
 * a-root {
 *   a: 10
 *   b: "Goodbye"
 *   c: true
 *   nested: {
 *     a: "X"
 *   }
 *   aList: [
 *     "h"
 *     {
 *       b: "Y"
 *     }
 *    ]
 * }
 *
 * b-root {
 *   x: "Hello World"
 * }
 *
 * and you call bind(config, "a-root") you'll get properties including
 * "config.a-root.a", "config.a-root.nested.a", and "config.a-root.aList.1.b".
 * Not only the individual properties are bound but the intermediate configs,
 * for example "config.a-root.nested".
 *
 * To ensure the correct order of creation you must create your config and
 * ConfigBinder inside one of the configure methods in your modules. For example
 *
 * def configure() {
 *    var config = ConfigFactory.parseResources("com/vast/common/config/configBinder-test.conf")
 *    new ConfigBinder(binder()).bind(config, "a-root")
 *    bind(classOf[Config]).toInstance(config)
 *  }
 *
 * In addition the module that creates the config must be the last one
 * listed in the Guice.createInjector call. For example, in the call below
 * it is ConfigModuleOne that creates the Config instance and calls ConfigBinder.bind
 *
 * Guice.createInjector(Stage.PRODUCTION, new ConfigModuleTwo, new ConfigModuleOne)
 *
 * @author Alex Moffat (alex.moffat@vast.com)
 */

class ConfigBinder(binder: Binder) {

  def bind(config: Config, root: String) {
    bind(config.getObject(root), "config." + root)
  }

  private def bind(obj: ConfigValue, bindingPath: String) {
    obj.valueType() match {
      case ConfigValueType.OBJECT => {
        val configObj =  obj.asInstanceOf[ConfigObject]
        // Bind the config from the object.
        binder
          .bind(Key.get(classOf[Config], Names.named(bindingPath)))
          .toInstance(configObj.toConfig)
        // Bind any nested values.
        configObj.entrySet().foreach(me => {
          val key = me.getKey
          bind(me.getValue,
            bindingPath + "." + key)
        })
      }
      case ConfigValueType.LIST => {
        val values = obj.asInstanceOf[ConfigList]
        for (i <- 0 until values.size()) {
          bind(values(i),
            bindingPath + "." + i.toString)
        }
      }
      case ConfigValueType.NUMBER => {
        // Bind as string and rely on guice's conversion code when the value is used.
        binder
          .bindConstant()
          .annotatedWith(Names.named(bindingPath))
          .to(obj.unwrapped()
          .asInstanceOf[Number].toString)
      }
      case ConfigValueType.BOOLEAN => {
        binder
          .bindConstant()
          .annotatedWith(Names.named(bindingPath))
          .to(obj.unwrapped()
          .asInstanceOf[JBoolean])
      }
      case ConfigValueType.NULL => {
        // NULL values are ignored.
      }
      case ConfigValueType.STRING => {
        binder
          .bindConstant()
          .annotatedWith(Names.named(bindingPath))
          .to(obj.unwrapped()
          .asInstanceOf[String])
      }
    }
  }
}