java 8中LocalDateTime和字符串转换，应用的类包含：j ava.time.LocalDateTime、java.time.format.DateTimeFormatter 。

 import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;

public class DateTimeHelper {

    /**
     * @param datetime
     * @return
     */    public static String formatLocalDate(LocalDateTime datetime) {
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd");
        String strDate = dtf.format(datetime);
        return strDate;
    }

    /**
     * @param timeStr
     * @return
     */    public static LocalDateTime toLocalDate(String timeStr) {
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd");
        LocalDateTime datetime = LocalDateTime.parse(timeStr, dtf);
        return datetime;
    }

    /**
     * @param datetime
     * @return
     */    public static String formatLocalDateTime(LocalDateTime datetime) {
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
        String strDate = dtf.format(datetime);
        return strDate;
    }

    /**
     * @param timeStr
     * @return
     */    public static LocalDateTime toLocalDateTime(String timeStr) {
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
        LocalDateTime datetime = LocalDateTime.parse(timeStr, dtf);
        return datetime;
    }

    public static void main(String[] args) {
        LocalDateTime datetime = LocalDateTime.now();
        System.out.println(formatLocalDate(datetime));
        System.out.println(formatLocalDateTime(datetime));
    }

}