java - 只读取大文件的一行以避免内存问题的最佳方法是什么？

Question

我不想将文件保存在内存中以及诸如此类的东西。是否可以只读取 CSV 的第一行而不将整个文件加载到内存中？也许使用扫描仪方法？

这只是 header 检查!

Answer 1

BufferedReader 有一个只能读取一行的 API。在引擎盖下，它的缓冲稍微多一些，但一般来说，您不需要担心它。这是我经常使用的习语:

String fileName = "..."; // use an actual file name :)
try (final FileReader fileReader = new FileReader(fileName);
            final BufferedReader bufferedReader = new BufferedReader(fileReader)) {
    // try-with-resources idiom for auto-closing the readers
    String line = null;
    while ((line = bufferedReader.readLine()) != null) {
        // Here you can deal with the line
        // Caveat: the line breaks are stripped.
        // So now you don't know if it was \r, '\n or both.
        System.out.println("--> read a line: " + line);
    }
} catch (IOException e) {
    // You might throw it too, or use a logger. Just don't hide it silently
    // because that makes debugging difficult.
    e.printStackTrace();
}