java - 获取 JSOUP 上的索引不起作用

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){
}

我试过几次调试，但我一直收到错误，Exception in thread "main"java.lang.StringIndexOutOfBoundsException: String index out of range: -1 我不确定为什么这也发生了吗？谁能告诉我哪里出了问题？

Answer 1

您正在从所有 div class="chart-row__image 元素中提取样式属性字符串，但要了解该组中的许多元素没有样式属性。在这种情况下，JSoup正在返回一个空字符串，这会打乱您的程序。解决方案不是这样做，而是让 jsoup 仅选择那些具有样式属性的元素。

例如，不是:

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

而是:

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

是的，不要忽略异常。

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();
    }