從文件中讀取N行並將其保存到新文件中

Question

例如，如何從readFile或n行讀取20行並將其保存到另一個文件（ writeFile ）？

public class Test_read_file {
  public static List<String> readFile() throws IOException {
    try(BufferedReader br = new BufferedReader(new FileReader("C:\\\\\\\\Users\\\\\\\\Admin\\\\\\\\Desktop\\\\\\\\Work Files\\\\\\\\314-WO0000001133814\\\\\\\\Cards\\\\\\\\MBD10760_182.out"))){
        List<String> listOfData = new ArrayList<>();
        String d;
        while((d = br.readLine()) != null){
            listOfData.add(d);
        }
        return listOfData;
    }
}

public static void writeFile(List<String> listOfData) throws IOException{
    try(BufferedWriter bw = new BufferedWriter(new FileWriter("C:\\\\\\\\Users\\\\\\\\Admin\\\\\\\\Desktop\\\\\\\\Work Files\\\\\\\\314-WO0000001133814\\\\\\\\Cards\\\\\\\\MBD10760_187.out"))){
        for(String str: listOfData){
            bw.write(str);
            bw.newLine();
        }
    }
}

public static void main(String[] args) throws IOException {
    List<String> data = readFile();
    writeFile(data);
}
}

Answer 1

假設你的代碼工作正常：

public static List<String> readFile(int n) throws IOException {
    try(BufferedReader br = new BufferedReader(new 
FileReader("C:\\\\\\\\Users\\\\\\\\Admin\\\\\\\\Desktop\\\\\\\\Work Files\\\\\\\\314- 
WO0000001133814\\\\\\\\Cards\\\\\\\\MBD10760_182.out"))){
        List<String> listOfData = new ArrayList<>();
        String d;
        while((d = br.readLine()) != null && n>0){
            listOfData.add(d);
            n--;
        }
        return listOfData;
    }

只需要告訴循環它應該讀取多少行。 如果file少於n行，那么while循環的第一個語句將返回null並且它將打破循環。 否則，當它讀取n行時，由於while循環中的第二個語句，它將再次打破循環。

Answer 2

只需在檢查listOfData大小時添加：

 while( ((d = br.readLine()) != null) && listOfData.size()<20 ) {
            listOfData.add(d);
}

Answer 3

 public static void main(String[] args) throws IOException {
     Path pathFrom = Paths.get("C:\\Users\\Admin\\Desktop\\Work Files\\314-WO0000001133814\\Cards\\MBD10760_182.out\"");
     Path pathTo = Paths.get("C:\\Users\\Admin\\Desktop\\Work Files\\314-WO0000001133814\\Cards\\MBD10760_187.out\"");
     Files.write(pathTo, Files.lines(pathFrom).limit(20).collect(Collectors.toList()));
 }