Question

我对以下几段代码感到困惑：

@Component
public class DrawingFileExplorer {

    private final ExecutorService pool = Executors.newFixedThreadPool(10);

        public void explore(File drawingFolder) throws InterruptedException {       
            for(File each : drawingFolder.listFiles(DrawingFileFilter.getInstance())) {
                if(each.isDirectory()) {
                    explore(each);
                } else {
                    //pool.execute(new DrawingFileReviewer(each));
                }
            }
            System.out.println("THIS LINE OF CODE SHOULD BE INVOKED ONCE");

            pool.shutdown();
            pool.awaitTermination(Integer.MAX_VALUE, TimeUnit.SECONDS);
        }

}

// Trigger of DrawingFileExplorer
public class DrawingFileExplorerTest {

    private static File baseFolder = new File("C:\\Users\\Jake\\Desktop\\baseFolder\\02. Current Drawings");

    public static void main(String[] args) throws InterruptedException {
        ApplicationContext ctx = new ClassPathXmlApplicationContext("spring/applicationContext.xml");
        DrawingFileExplorer drawingFileExplorer = (DrawingFileExplorer) ctx.getBean("drawingFileExplorer");
        drawingFileExplorer.explore(baseFolder);
    }

}

据我所知，foreach之后的行System.out.println（..）应该只被调用一次。但是代码的输出正在跟随。

THIS LINE OF CODE SHOULD BE INVOKED ONCE
THIS LINE OF CODE SHOULD BE INVOKED ONCE

有人可以解释一下如何调用它两次吗？由于shutdown（），我的第一个输出和第二个输出行之间的线程没有被执行。

Answer 1

你的方法是递归的，那么为什么你不希望它被反复调用（每个目录一次）？

Answer 2

在检查each是否是目录之后有一个递归调用，即 -

 if(each.isDirectory()) {
   explore(each); // <-- HERE

因此，如果（并且仅当）存在子目录，您将获得多行。

Answer 3

您的explore是递归方法，可以根据目录数多次调用。

for(File each : drawingFolder.listFiles(DrawingFileFilter.getInstance())) {
                if(each.isDirectory()) {
                    explore(each);  // this call is inside for loop and will be invoke recursively.
                } else {
                    //pool.execute(new DrawingFileReviewer(each));
                }
            }

例如，给定的目录结构将打印该行5次，

DraginFolder

SubFolder1
  SubFolder2
SubFolder3

SubFolder4

Answer 4

你必须搬家

System.out.println("THIS LINE OF CODE SHOULD BE INVOKED ONCE");
pool.shutdown();
pool.awaitTermination(Integer.MAX_VALUE, TimeUnit.SECONDS);

在explore之外

当目录上执行的代码只包含文件时，将执行上述3行代码。并且因为您关闭了池，您将无法浏览所有文件。

Answer 5

@Component
public class DrawingFileExplorer {

    private final ExecutorService pool = Executors.newFixedThreadPool(10);

    public void explore(File drawingFolder) throws InterruptedException {   
        _explore(drawingFolder);

        pool.shutdown();
        pool.awaitTermination(Integer.MAX_VALUE, TimeUnit.SECONDS);
    }

    private void _explore(File drawingFolder) {
        for(File each : drawingFolder.listFiles(DrawingFileFilter.getInstance())) {
            if(each.isDirectory()) {
                _explore(each);
            } else {
                pool.execute(new DrawingFileReviewer(each));
            }
        }
    }

}

做了另一个_explorer（..）方法来解决它。谢谢。

java线程代码流程

5 个答案: