java - 如何从另一个线程返回一个字符串？

Question

我想从另一个线程返回一个字符串“finalurl”，如下所示:

public String getImageURL(String url) {

    final String finalUrl = url;

    Thread t1 = new Thread(new Runnable() {
        public void run() {
            Document doc = null;
            try {
                doc = Jsoup.connect(finalUrl).get();
            } catch (IOException e) {
                e.printStackTrace();
            }
            Element masthead = doc.select("div.post-image").select("img[src~=(?i)\\.(png|jpe?g)]").first();
            finalUrl = masthead.absUrl("src");
        }
    });

    t1.start();
    return finalUrl;
}

但是它不起作用。如何正确制作？

Answer 1

 return finalUrl;

此代码永远不会返回您想要的字符串。

您需要通过多种技术之一来修复您的逻辑。对您来说最简单的方法是使用处理程序。像这样:

private static final int URL_MESSAGE = 1;

private final Handler handler = new Handler(Looper.getMainLooper()) {

    @Override
    public void handleMessage(Message message) {
        super.handleMessage(message);
        if (message.arg1 == URL_MESSAGE) {
            final Object obj = message.obj;

            if (obj instanceof String) {
                String url = (String) obj;
            }
        }
    }
};

private final Runnable runnable = new Runnable() {
    public void run() {
        Document doc = null;
        try {
            doc = Jsoup.connect(finalUrl).get();
        } catch (IOException e) {
            e.printStackTrace();
        }
        Element masthead = doc.select("div.post-image").select("img[src~=(?i)\\.(png|jpe?g)]").first();
        String finalUrl = masthead.absUrl("src");

        Message message = new Message();
        message.arg1 = URL_MESSAGE;
        message.obj = finalUrl;
        handler.sendMessage(message);
    }
};

@Override
protected void onDestroy() {
    super.onDestroy();
    handler.removeCallbacks(runnable);
}

private void execute() {
    handler.post(runnable);
}