Question

我目前正在开发一个应用程序，该应用程序打印远程服务器目录中的文件列表，并能够单击指定的文件并下载它。

到目前为止，这就是我所拥有的：

public class MainActivity extends Activity {


    private String user = "username";
    private String pass = "password";
    private String host = "hostname";
    private int portNum = 22;

    private static final String SFTPWORKINGDIR = "/path/to/file";
    private String fileName;

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        final ListView list = (ListView)findViewById(R.id.choose_sound_listView);

        new AsyncTask<Void, Void, List<String>>() {
            @Override
            protected List<String> doInBackground(Void... params) {
                try {
                    return executeRemoteCommand(user, pass, host, portNum);
                } catch (Exception e) {
                    e.printStackTrace();
                }
                return null;
            }

            @Override
            public void onPostExecute(List<String> soundNames){
                ArrayAdapter<String> adapter = new ArrayAdapter<String>(MainActivity.this,android.R.layout.simple_expandable_list_item_1, android.R.id.text1, soundNames);
                list.setAdapter(adapter);

                list.setOnItemClickListener(new AdapterView.OnItemClickListener() {

                    @Override
                    public void onItemClick(AdapterView<?> arg0, View arg1,
                                            int position, long arg3) {

                        String  newFileName = (String) list.getItemAtPosition(position);

                        fileName = newFileName;

                        Downloader(fileName);

                        // Show Alert
                        Toast.makeText(getApplicationContext(),
                                "Downloaded " + fileName , Toast.LENGTH_LONG).show();
                    }
                });
            }
        }.execute();
    }

    public List<String> executeRemoteCommand(String username, String password, String hostname, int port) throws Exception {

        List<String> soundNames = new ArrayList<String>();

        JSch jsch = new JSch();
        Session session = jsch.getSession(username, hostname, port);
        session.setPassword(password);

        // Avoid asking for key confirmation
        Properties prop = new Properties();
        prop.put("StrictHostKeyChecking", "no");
        session.setConfig(prop);

        session.connect();

        String command = "ls -la | awk '{ print $9}'";

        Channel channel = session.openChannel("exec");
        ((ChannelExec) channel).setCommand(command);

        ((ChannelExec) channel).setErrStream(System.err);

        InputStream in = channel.getInputStream();

        System.out.println("Connect to session...");
        channel.connect();

        StringBuffer buffer = new StringBuffer();

        //This is the recommended way to read the output
        byte[] tmp = new byte[1024];
        while (true) {
            while (in.available() > 0) {
                int i = in.read(tmp, 0, 1024);
                if (i < 0) {
                    break;
                }
                buffer.append(new String(tmp, 0, i));
            }
            if (channel.isClosed()) {
                System.out.println("exit-status: " + channel.getExitStatus());
                break;
            }
            try {
                Thread.sleep(1000);
            } catch (Exception ee) {
            }
        }

        channel.disconnect();
        session.disconnect();

        Scanner scanner = new Scanner(buffer.toString());
        while (scanner.hasNextLine()){
            String line = scanner.nextLine();
            soundNames.add(line);

            Log.i("SSH", ": " + line);
        }

        return soundNames;
    }


    public void Downloader(String fileName) {

        JSch jsch = new JSch();
        Session session = null;
        Channel channel = null;
        ChannelSftp sftpChannel = null;

        try {

            session = jsch.getSession(user, host, portNum);
            session.setConfig("StrictHostKeyChecking", "no");
            session.setPassword(pass);
            session.connect();

            channel = session.openChannel("sftp");
            channel.connect();
            sftpChannel = (ChannelSftp) channel;
            sftpChannel.cd(SFTPWORKINGDIR); //cd to dir that contains file

            try {
                byte[] buffer = new byte[1024];
                BufferedInputStream bis = new BufferedInputStream(sftpChannel.get(fileName));

                File path = Environment.getExternalStoragePublicDirectory(
                        Environment.DIRECTORY_DOCUMENTS);
                File newFile = new File(path, "/" + fileName);

                Log.d("Dir" , " " + newFile);

                OutputStream os = new FileOutputStream(newFile);
                BufferedOutputStream bos = new BufferedOutputStream(os);
                int readCount;
                while( (readCount = bis.read(buffer)) > 0) {
                    Log.d("Downloading", " " + fileName );
                    bos.write(buffer, 0, readCount);
                }
                bis.close();
                bos.close();

            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }

            Log.d( "SUCCESS ", fileName + " has been downloaded!!!!");

            sftpChannel.exit();
            session.disconnect();

        } catch (JSchException e) {
            e.printStackTrace();
        } catch (SftpException e) {
            e.printStackTrace();
        }
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }
}

但是，当我点击listView中的文件时，我得到一个跟踪错误：

com.jcraft.jsch.JSchException：android.os.NetworkOnMainThreadException

编辑：使用AsyncTask在后台运行它似乎可以修复错误，但如果我这样做，应用程序就无法下载指定文件onClick，除非我硬编码文件名。

任何人都知道如何解决这个问题？

Answer 1

您正在主应用程序线程上进行网络I / O，如异常所示。如果查看堆栈跟踪，它将指出您在主应用程序线程上执行网络I / O的确切行。

最有可能的是，它来自您的Downloader()方法，因为您肯定在该方法中执行网络I / O，并且该方法是从onItemClick()调用的，该方法本身在主应用程序中调用线。请在后台主题上执行此下载。

Answer 2

您在Downloader(String fileName)执行onPostExecute(List<String> soundNames)。但onPostExecute()在主线程上执行。只有doInBackground()在单独的线程上执行。将Downloader(String fileName)的执行移至doInBackground()。

编辑：或创建一个单独的AsyncTask，在自己的Downloader(String fileName)

中执行doInBackground()

Answer 3

您应该将任何网络移动到doInBackground中，以便它在AsyncTask的线程中运行

使用onClick从远程服务器下载SFTP

3 个答案: