将string字符串转成LocalDateTime工具类

```
public class LocalDateTimeUtil {
/**
 * 将Long类型的时间戳转换成String 类型的时间格式，时间格式为：yyyy-MM-dd HH:mm:ss
 */
public static String convertTimeToString(Long time){
    if (StringUtils.isEmpty(time)){
        return null;
    }
    DateTimeFormatter ftf = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
    return ftf.format(LocalDateTime.ofInstant(Instant.ofEpochMilli(time), ZoneId.systemDefault()));
}

/**
 * 将Long类型的时间戳转换成String 类型的时间格式，时间格式为：yyyy-MM-dd
 */
public static String convertTimeToStringYMD(Long time){
    if (StringUtils.isEmpty(time)){
        return null;
    }
    DateTimeFormatter ftf = DateTimeFormatter.ofPattern("yyyy-MM-dd");
    return ftf.format(LocalDateTime.ofInstant(Instant.ofEpochMilli(time), ZoneId.systemDefault()));
}


/**
 * 将字符串转日期成Long类型的时间戳，格式为：yyyy-MM-dd HH:mm:ss
 */
public static Long convertTimeToLong(String time) {
    if (StringUtils.isEmpty(time)){
        throw new IllegalArgumentException("时间参数异常！");
    }
    DateTimeFormatter ftf = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
    LocalDateTime parse = LocalDateTime.parse(time, ftf);
    return LocalDateTime.from(parse).atZone(ZoneId.systemDefault()).toInstant().toEpochMilli();
}

/**
 * 将字符串转日期成Long类型的时间戳，格式为：yyyy-MM-dd
 */
public static Long convertTimeToLongYMD(String time) {
    if (StringUtils.isEmpty(time)){
        throw new IllegalArgumentException("时间参数异常！");
    }
    DateTimeFormatter ftf = DateTimeFormatter.ofPattern("yyyy-MM-dd");
    LocalDateTime parse = LocalDateTime.parse(time, ftf);
    return LocalDateTime.from(parse).atZone(ZoneId.systemDefault()).toInstant().toEpochMilli();
}

/**
 * 将日期转换为字符串，格式为：yyyy-MM-dd HH:mm:ss
 * @param localDateTime
 * @return
 */
public static  String convertDateToString(LocalDateTime localDateTime){
    DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
    String dateTime = dtf.format(localDateTime);
    return dateTime;
}

/**
 * 将日期转换为字符串，格式为：yyyy-MM-dd
 * @param localDateTime
 * @return
 */
public static  String convertDateToStringYMD(LocalDateTime localDateTime){
    DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd");
    String dateTime = dtf.format(localDateTime);
    return dateTime;
}

/**
 * 将字符串转换为日期，格式为：yyyy-MM-dd HH:mm:ss
 * @param time
 * @return
 */
public static LocalDateTime convertStringToDate(String time){
    DateTimeFormatter dft = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
    LocalDateTime dateTime = LocalDateTime.parse(time, dft);
    return dateTime;
}

/**
 * 将字符串转换为日期，格式为：yyyy-MM-dd
 * @param time
 * @return
 */
public static LocalDateTime convertStringToDateYMD(String time){
    DateTimeFormatter dft = DateTimeFormatter.ofPattern("yyyy-MM-dd");
    LocalDateTime dateTime = LocalDateTime.parse(time, dft);
    return dateTime;
}

/**
 * 取本月第一天
 */
public static LocalDate firstDayOfThisMonth() {
    LocalDate today = LocalDate.now();
    return today.with(TemporalAdjusters.firstDayOfMonth());
}

/**
 * 取本月第N天
 */
public static LocalDate dayOfThisMonth(int n) {
    LocalDate today = LocalDate.now();
    return today.withDayOfMonth(n);
}

/**
 * 取本月最后一天
 */
public static LocalDate lastDayOfThisMonth() {
    LocalDate today = LocalDate.now();
    return today.with(TemporalAdjusters.lastDayOfMonth());
}

/**
 * 取本月第一天的开始时间
 */
public static LocalDateTime startOfThisMonth() {
    return LocalDateTime.of(firstDayOfThisMonth(), LocalTime.MIN);
}


/**
 * 取本月最后一天的结束时间
 */
public static LocalDateTime endOfThisMonth() {
    return LocalDateTime.of(lastDayOfThisMonth(), LocalTime.MAX);
}
```