（Scala編程P.173）打開某個資源，對它進(jìn)行操作，然后關(guān)閉這個資源宫静。可以用類似如下的方法券时，將這個模式捕獲成一個控制抽象孤里，withPrintWriter打開某個資源并將這個資源“貸出”給函數(shù)op

def withPrintWriter(file: File, op: PrintWriter => Unit): Unit = {
  val writer = new PrintWriter(file)
  try {
    op(writer)
  } finally {
    writer.close()
  }
}

withPrintWriter(
  new File("date.txt"),
  writer => writer.println(new java.util.Date)
)

實踐：

讀取配置文件，都是打開文件橘洞，讀取配置文件內(nèi)容捌袜，可以考慮貸出模式

ReadConfigFile.scala

import com.typesafe.config.{Config, ConfigFactory}

import scala.reflect.ClassTag

class ReadConfigFile[T:ClassTag](clz: Class[T]){
  def read(fileName: String)(fromConfig: Config => T): T = {  //柯里化
    val file = new File(fileName)
    if (!file.exists())  clz.newInstance()//不能直接new T(),scala不能識別，需要通過ClassTag,增加Class[T]入?yún)⒂谜ㄔ妫琻ewInstance來構(gòu)造一個新的對象虏等，而且這個對象不能帶入?yún)ⅰ?    else {
      println(s"path = $fileName")
      try {
        val conf:Config = ConfigFactory.parseFile(file).withFallback(ConfigFactory.load())
        fromConfig(conf)
      } catch {
        case ex: Exception => clz.newInstance()
      }
    }
  }
}

這里用到了泛型類，可以傳入對于任何需要讀取配置參數(shù)類适肠，將讀取文件的方法通過fromConfig函數(shù)值傳進(jìn)來

PersonConfig.scala

class PersonConfig{
  var name: String = ""
  var age: Int = 0

  override def toString: String = {
    "name=" + name + " age=" + age
  }
}

object PersonConfig{
  def createPersonConfig(config: Config): PersonConfig= {
    val PersonConfig= new PersonConfig
    PersonConfig.name = config.getString("name ")
    PersonConfig.age= config.getInt("age")
    PersonConfig
  }
}

ITDepartmentConfig.scala

class ITDepartmentConfigextends ReadConfigFile(classOf[PersonConfig]){
  private val personConfig: PersonConfig= {
    read("person.conf") { config =>
      PersonConfig.createServerConfig(config.getConfig("person_config"))
    }//傳入讀取文件的方法并生成相關(guān)的對象
  }

  def person: PersonConfig= personConfig
}

**Test.scala**
object Test {
  def main(args: Array[String]): Unit = {
    val itDepartmentConfig= new ITDepartmentConfig
    println(itDepartmentConfig.person.toString)
  }
}

上這里提到了不能直接new T()的問題霍衫，可以通過多加一個傳名參數(shù)來解決，就不需要使用ClassTag，使用ClassTag導(dǎo)致構(gòu)造函數(shù)中不可以帶入?yún)ⅰ７椒ㄈ缦拢?/p>

class ReadConfigFile[T]{
  def read(fileName: String)(fromConfig: Config => T)(emptyObject: => T): T = {
    val file = new File(fileName)
    if (!file.exists())  emptyObject
    else {
      println(s" path = $fileName ")
      try {
        val conf:Config = ConfigFactory.parseFile(file).withFallback(ConfigFactory.load())
        fromConfig(conf)
      } catch {
        case ex: Exception => emptyObject
      }
    }
  }
}

調(diào)用時

class RESTServerConfig extends ReadConfigFile[ServerConfig] with Subject {
  private val serverConfig: ServerConfig = {
    read(FileUtil.getConfigPath + "rest-server.conf") { config =>
      ServerConfig.createServerConfig(config.getConfig("rest_server_config"))
    }(new ServerConfig())
  }

  def server: ServerConfig = serverConfig
}