java - 如何添加锁以从文件方法读取和写入

Question

我必须为学校的 readFromFile() 和 writeToFile() 方法添加锁。请查看下面的方法代码，并告诉我在代码中的什么位置放置锁？我会使用 ReentrantLock 还是 ReadWriteReentrantLock？我们必须使用锁。

谢谢。

读取方法

public static void readFromFile(List<Person> people)
{
   FileReader fr = new FileReader("names");
   Scanner sc = new Scanner(fr);
   while (sc.hasNext()) {
     String name = sc.nextLine();
     int age = Integer.parseInt(sc.nextLine());
     people.add(new Person(name, age));
   }
   sc.close();
}

写法

public static void writeToFile(List<Person> people)
{
  File outputFile = new File (List<Person> people)
  PrintWriter pw = new PrintWriter(outputFile);

  for (Person p: people) {
    pw.println(p.name); }

  pw.close();

}

Answer 1

只保护整个方法体

 static ReadWriteLock rwl = new ReentrantReadWriteLock();

  public static void readFromFile(List<Person> people) {
    rwl.readLock().lock();
    try {
...
      //method body is not changed
    } finally {
      rwl.readLock().unlock();
    }

  }

  public static void writeToFile(List<Person> people) {
    rwl.writeLock().lock();
    try {
...
      //method body is not changed
    } finally {
      rwl.writeLock().unlock();
    }
  }