java - Java线程从静态内部类访问外部类

这建立在我的previous question上。

我的ftp服务器有10个文件，例如test1.txt，test2.txt等。我希望能够同时下载多个文件（最多3个）。我正在呼叫downloadFilesByPattern(....)如果我不对downloadFile（）使用同步，那么仅下载了一部分文件，而不是全部下载。如果使用同步，则将下载所有文件，但我认为它们不是并行发生的。问题是因为实例变量传递给所有线程，并且所有线程都调用该实例上的方法。

public class FTPClientService implements IClient {

private String username;
private String password;
private String port;
private String host;
private String path;
FTPClient client = new FTPClient();

private static class DownloadTask implements Runnable {

    private String name;
    private String toPath;
    private IClient client;

    public DownloadTask(String name, String toPath, IClient client) {
        this.name = name;
        this.toPath = toPath;
        this.client = client;
    }

    @Override
    public void run() {
        System.out.println("download = " + name);
        client.downloadFile(name, toPath);
    }
}

public void downloadFilesByPattern(String fileNamePattern, final String outputFilePath) {

    if(!changeDirectory()){
        return;
    }

    try {
        //get a list of file names that match the pattern
        String[] names = client.listNames();

        ExecutorService pool = Executors.newFixedThreadPool(3);
        for (String name : names) {
            //check if the filename matches the pattern
            Pattern pattern =  Pattern.compile(fileNamePattern);
            Matcher matcher = pattern.matcher(name);
            if(matcher.find()){
                System.out.println("Match found = " + name);
                pool.submit(new DownloadTask(name, outputFilePath, this));
            }else{
                System.out.println("No match = " + name);
            }
        }
        pool.shutdown();
        try {
            pool.awaitTermination(Long.MAX_VALUE, TimeUnit.MILLISECONDS);
        } catch (InterruptedException ex) {
        }

    } catch (IOException ex) {
    }
}

public synchronized void downloadFile(String fileName, String outputFilePath) {

    FileOutputStream fos = null;
    try {
        fos = new FileOutputStream(outputFilePath+"/"+fileName);
        if(this.isFilePresent(fileName)){
            //look for fileName in the path and write it to
            client.retrieveFile(fileName, fos);
            System.out.println("Downloading file " + fileName + " ...");
        }else{
            System.out.println("Could not find file " + fileName);
        }
    } catch (IOException ex) {
    } finally {
        try {
            fos.close();
        } catch (IOException ex) {
        }
    }
}
}

最佳答案

这是因为它们都使用相同的实例

FTPClient client

您需要为每个下载/线程创建新的FTPClientService实例，或者为每个线程创建一个FTPClient实例。我个人更喜欢第二个变体，可以使用ThreadLocal轻松实现。