url：String，拼接query：String

URLUtil.java

public static void main(String[] args) throws ParseException {
        String query = "hello=world";
        List<String> list = new ArrayList<>();
        String url;
        url = "http://www.baidu.com"; // no ?, no #
        list.add(url); url = "http://www.baidu.com?"; // has ?, no # : just ?
        list.add(url); url = "http://www.baidu.com?&"; // has ?, no # : ?&
        list.add(url); url = "http://www.baidu.com?query"; // has ?, no # : ?query
        list.add(url); url = "http://www.baidu.com?query&"; // has ?, no # : ?query&
        list.add(url); url = "http://www.baidu.com#e"; // no ?, has # : #e
        list.add(url); url = "http://www.baidu.com#?"; // has ?, has # : invalid url : just ?
        list.add(url); url = "http://www.baidu.com#?&"; // has ?, has # : invalid url : ?&
        list.add(url); url = "http://www.baidu.com#?query"; // has ?, has # : invalid url : ?query
        list.add(url); url = "http://www.baidu.com#?query&"; // has ?, has # : invalid url : ?query&
        list.add(url); url = "http://www.baidu.com?#e"; // has ?, has # : valid url : just ?
        list.add(url); url = "http://www.baidu.com?&#e"; // has ?, has # : valid url : ?&
        list.add(url); url = "http://www.baidu.com?query#e"; // has ?, has # : valid url : ?query
        list.add(url); url = "http://www.baidu.com?query&#e"; // has ?, has # : valid url : ?query&
        list.add(url);

        for (String str : list) {
            System.out.println(str);
            System.out.println(addQuery(str, query));
            System.out.println();
        }
    }

    private static String addQuery(String url, String query) {
        if (TextUtils.isEmpty(url)) {
            return query;
        }
            
        if (TextUtils.isEmpty(query)) {
            return url;
        }

        StringBuilder stringBuilder = new StringBuilder(url.length() + query.length() + 2);
        stringBuilder.append(url);

        final int schemeSeparatorIndex = url.indexOf(':');
        final int querySeparatorIndex = url.indexOf('?', schemeSeparatorIndex);
        int fragmentSeparatorIndex = url.indexOf('#', schemeSeparatorIndex);
        if (querySeparatorIndex != -1) { // has '?'
            if (fragmentSeparatorIndex != -1) { // has fragment
                if (fragmentSeparatorIndex < querySeparatorIndex) { // invalid url
                    // LogManager.w("addQuery", "invalid url: url=" + url + "; addQuery=" + query);
                    if (url.length() - 1 - querySeparatorIndex > 0) { // had old query
                        if (stringBuilder.charAt(stringBuilder.length() - 1) != '&') {
                            stringBuilder.append('&');
                        }
                        stringBuilder.append(query);
                    } else {
                        stringBuilder.append(query);
                    }
                } else { // insert query [query, fragment]
                    if (fragmentSeparatorIndex - querySeparatorIndex > 1) { // has old query
                        if (stringBuilder.charAt(fragmentSeparatorIndex - 1) != '&') {
                            stringBuilder.insert(fragmentSeparatorIndex, '&');
                            fragmentSeparatorIndex++;
                        }
                        stringBuilder.insert(fragmentSeparatorIndex, query);
                    } else { // dont has old query, just a '?'
                        stringBuilder.insert(querySeparatorIndex + 1, query);
                    }
                }
            } else { // has '?', dont has fragment
                if (stringBuilder.length() - 1 != querySeparatorIndex) { // has old query
                    if (stringBuilder.charAt(stringBuilder.length() - 1) != '&') {
                        stringBuilder.append('&');
                    }
                    stringBuilder.append(query);
                } else { // dont has old query, just '?'
                    stringBuilder.append(query);
                }
            }
        } else { // dont has '?'
            if (fragmentSeparatorIndex != -1) { // has fragment
                stringBuilder.insert(fragmentSeparatorIndex, '?');
                fragmentSeparatorIndex++;
                stringBuilder.insert(fragmentSeparatorIndex, query);
            } else {
                stringBuilder.append('?').append(query);
            }
        }
        return stringBuilder.toString();
    }