JSOUP上的java获取索引不工作

Question

try {
    String url = "http://www.billboard.com/charts/artist-100";
    String urlFound;
    String closing = ")";
    String start = "h";
    Document doc = Jsoup.connect(url).get();
    Elements urls = doc.getElementsByClass("chart-row__image");
    for (Element u : urls) {
        urlFound = u.attr("style");
        String sub =  urlFound.substring(urlFound.indexOf(start), urlFound.indexOf(closing));
        System.out.println(sub);
        //Log.d("URLS,", attr.substring(attr.indexOf("http://"), attr.indexOf(")")));
    }
}
catch(IOException ex){
}

我试着调试了好几次，但是我一直得到错误，Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: -1我也不知道为什么会发生这种情况？有人能告诉我什么地方出了问题吗

Answer 1

您正在从所有的div class="chart-row__image元素中提取样式属性字符串，但是要知道，这个组中的许多元素都没有样式属性。在这种情况下，JSoup将返回一个空字符串，这将打乱您的程序。解决方案不是这样做，而是让jsoup只选择那些具有style属性的元素

例如，不是：

Elements urls = doc.getElementsByClass("chart-row__image");

而是：

Elements urls = doc.select(".chart-row__image[style]");

是的，不要忽略例外情况

所以

    String url = "http://www.billboard.com/charts/artist-100";
    String urlFound;
    String closing = ")";
    String start = "h";
    Document doc;
    try {
        doc = Jsoup.connect(url).get();
        // Elements urls = doc.getElementsByClass("chart-row__image");
        Elements urls = doc.select(".chart-row__image[style]");
        for (Element u : urls) {
            urlFound = u.attr("style");
            int startingIndex = urlFound.indexOf(start);
            int endingIndex = urlFound.indexOf(closing);
            if (startingIndex > 0 && endingIndex > 0) {
                String sub = urlFound.substring(startingIndex, endingIndex);
                System.out.println(sub);
            }
        }
    } catch (IOException e) {
        e.printStackTrace();
    }