Groovy：如何从两个文件中读取/比较行，而不将一个或两个文件加载到内存中

Question

我需要使用groovy合并两个非常大（大于可用内存）的文件。

为了做到这一点，我提出了以下伪代码，我可以实现，除了来自FileA＆＃34;＆＃34;读取lineA。

// Pseudo Code:
open fileA for Input
open fileB for Input
open fileOut for Output

read lineA from fileA
read lineB from fileB

notDone = true

while (notDone) {
  if (lineA == lineB) {
    write lineA to fileOut;
    read lineA from fileA
    read lineB from fileB
  }
  elseif (lineA > lineB) {
    write lineB to fileOut;
    read lineB from file B
  }
  else { // lineA < lineB
    write lineA to fileOut;
    read lineA from fileA
  }
  if (lineA == null || lineB == null) {
    notDone= false
  }
}

上面的伪代码使用＆lt;，＆gt;和==来比较线条，现实世界的例子更复杂。

Answer 1

一位朋友帮我写了这个：

// ---------------------------------------------------------------------------------
BufferedReader bufferedReader_A = new BufferedReader(new FileReader("view-connections_6.txt"));
BufferedReader bufferedReader_B = new BufferedReader(new FileReader("view-connections_7.txt"));
BufferedWriter bufferedWriter   = new BufferedWriter(new FileWriter("OUTPUT.txt"));
// ---------------------------------------------------------------------------------
String lineA = bufferedReader_A.readLine()
String lineB = bufferedReader_B.readLine()
// ---------------------------------------------------------------------------------
Boolean notDone = true;
while(notDone) {
  if (lineA==lineB) {
    bufferedWriter.writeLine(lineA);
    lineA = bufferedReader_A.readLine()
    lineB = bufferedReader_B.readLine()
  }
  // ---------------------------------------------------------------------------------
  else if (lineA > lineB) {
    bufferedWriter.writeLine(lineB);
    lineB = bufferedReader_B.readLine()
  }
  // ---------------------------------------------------------------------------------
  else {
    bufferedWriter.writeLine(lineA);
    lineA = bufferedReader_A.readLine()
  }
  if (lineA == null || lineB == null) {
    notDone=false;
  }
}