Scala中的PrintWriter没有写入文件？ [英] PrintWriter in Scala not writing to file?

问题描述

  val file = new PrintWriter（new FileWriter（new File（TMP_DIR ，fileName），true））
 file.write（getFirstRow（tableName））
  

一些奇怪的原因，它不是写给我的文件，而是每次创建它。 getFirstRow方法返回一个我想追加到文件的字符串。出了什么问题？ 您不是 flush 关闭 文件（或者 PrintWriter ，也可以这样做） / p>

这是一个常见的错误，使用贷款模式：
$ b $ pre $ def $ withPrintWriter（dir：String，name：String）（f： （PrintWriter）=> Any）{
val file = new File（dir，name）
val writer = new FileWriter（file）$ b $ val printWriter = new PrintWriter（writer）
试试{
f（printWriter）
}
finally {
printWriter.close（）
}




$ p
$ b $ pre> withPrintWriter（/ tmp，myFile）{printWriter =>
printWriter.write（all good）
}


I have the following file creation/writing code:

val file =  new PrintWriter(new FileWriter(new File(TMP_DIR, fileName), true))
    file.write(getFirstRow(tableName))

For some weird reason, it's not writing to my file, but it creates it everytime. The getFirstRow method returns a string that I want to append to the file. What is going wrong?

解决方案

You are neither flushing nor closeing the File (or the PrintWriter, which would also do that).

This is such a common mistake that it's a fantastic opportunity to use an example of the Loan Pattern:

def withPrintWriter(dir:String, name:String)(f: (PrintWriter) => Any) {
  val file = new File(dir, name)
  val writer = new FileWriter(file)
  val printWriter = new PrintWriter(writer)
  try {
    f(printWriter)
  }
  finally {
    printWriter.close()
  }

}

Which you use like this:

withPrintWriter("/tmp", "myFile") { printWriter =>
  printWriter.write("all good")
}

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