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();
}