把12小时格式的时间字符串转换为24小时格式的字符串

 /**
     * 把12小时格式的时间字符串转换为24小时格式的字符串
     * input: 07:05:45PM
     * output: 19:05:45
     * input: 12:00:00PM
     * output:  00:00:00
     * @param lowFormatTimeStr
     * @return
     */
    public static String convertTimeFormate(String lowFormatTimeStr){
        if(lowFormatTimeStr==null){
            return null;
        }
        String trim = lowFormatTimeStr.trim();
        if (trim.isEmpty()){
            return null;
        }
        int length = trim.length();
        if (length!=10){
            return null;
        }
        String substring7 = trim.substring(0, 2);
        if (substring7.equals("00")){
            return null;
        }else {
            Integer i = Integer.valueOf(substring7);
            if (i>12){
                return null;
            }
        }
        String substring8 = trim.substring(3, 5);
        if (!(substring8.substring(0,1).equals("0"))){
            Integer i = Integer.valueOf(substring8);
            if (i>60){
                return null;
            }
        }
        String substring9 = trim.substring(6, 8);
        if (!(substring9.substring(0,1).equals("0"))){
            Integer i = Integer.valueOf("0");
            if (i>60){
                return null;
            }
        }
        for (int i = 0; i < trim.length(); i++) {
            char c = trim.charAt(i);
            if (trim.endsWith("PM")){
                continue;
            }else if(trim.endsWith("AM")){
                continue;
            }else {
                return null;
            }
        }
        String substring = trim.substring(0, 2);
        for (int i = 0; i < substring.length(); i++) {
            char c = substring.charAt(i);
            if (!Character.isDigit(c)){
                return null;
            }
        }
        String substring1 = trim.substring(2, 3);
        if (!substring1.equals(":")){
            return null;
        }
        String substring2 = trim.substring(3, 5);
        for (int i = 0; i < substring2.length(); i++) {
            char c = substring2.charAt(i);
            if(!Character.isDigit(c)){
                return null;
            }
        }
        String substring3 = trim.substring(5, 6);
        if(!substring3.equals(":")){
            return null;
        }
        String substring4 = trim.substring(6, 8);
        for (int i = 0; i < substring4.length(); i++) {
            char c = substring4.charAt(i);
            if (!Character.isDigit(c)){
                return null;
            }
        }
        String substring5 = trim.substring(0, 2);
        StringBuilder stringBuilder = new StringBuilder();
        if (trim.endsWith("PM")){
            String substring6 = substring5.substring(0, 1);
            Integer i=null;
            if (substring6.equals("0")){
                i = Integer.valueOf(substring5.substring(1));
            }else {
                i = Integer.valueOf(substring5);
            }
            if (i<12){
                i+=12;
            }else {
                i-=12;
            }
            if (i>=10){
                String s = String.valueOf(i);
                stringBuilder.append(s);
                stringBuilder.append(trim.substring(2,8));
            }else {
                StringBuilder stringBuilder1 = new StringBuilder();
                stringBuilder1.append(0);
                stringBuilder1.append(i);
                stringBuilder1.append(trim.substring(2,8));
                return stringBuilder1.toString();
            }
        }else {
            return trim.substring(0,8);
        }
        return stringBuilder.toString();
    }