日期计算方法中的Java日期转换问题

Question

我曾尝试用Java创建一个方法，它将获取当前日期或存储的日期，并在之前或之后获取x天

//28 days ago
java.util.Date thresholdPast28Date  = BasicUtils.setTimeInDays(sqlTodayDate, -28);

//56 days ago
java.util.Date thresholdPast56Date  = BasicUtils.setTimeInDays(sqlTodayDate, -56);

函数如下所示

public static Date setTimeInDays(Date startingTime, Integer days){
    Calendar c = Calendar.getInstance(); 
    c.setTime(startingTime); 
    c.add(Calendar.DATE, days);//a day in the future or past
    return c.getTime();
}

虽然我试图把今天的日期推到这个方法中，但还是会出错

java.util.Date cannot be cast to java.sql.Date

--今天就这样约会

//today date
Calendar today = Calendar.getInstance(); 
Date sqlTodayDate =  (Date) today.getTime();

Answer 1

这里的问题是，您试图在这一行中将java.util.Date转换为java.sql.Date

java.sql.Date sqlTodayDate = (java.sql.Date) today.getTime();

你应该简单地使用

java.util.Date sqlTodayDate = today.getTime();

最终的工作代码如下：

import java.util.Date;
import java.util.Calendar;

public class Test2 {
    public static void main(String[] args) {
        Calendar today = Calendar.getInstance();
        Date sqlTodayDate = today.getTime();

        //28 days ago
        java.util.Date thresholdPast28Date  = BasicUtils.setTimeInDays(sqlTodayDate, -28);

        System.out.println(thresholdPast28Date);

        //56 days ago
        java.util.Date thresholdPast56Date  = BasicUtils.setTimeInDays(sqlTodayDate, -56);

        System.out.println(thresholdPast56Date);
    }
}

class BasicUtils {
    public static Date setTimeInDays(Date startingTime, Integer days){
        Calendar c = Calendar.getInstance(); 
        c.setTime(startingTime); 
        c.add(Calendar.DATE, days);//a day in the future or past
        return c.getTime();
    }
}

注意：Calendar.getInstance()将需要一些时间来执行。 你可以直接使用java.util.Date sqlTodayDate = new java.util.Date()

如果你坚持使用java.sql.Date，以下内容对你有用

import java.sql.Date;
import java.util.Calendar;

public class Test2 {
    public static void main(String[] args) {
        Calendar today = Calendar.getInstance();
        Date sqlTodayDate = new Date(today.getTimeInMillis());

        //28 days ago
        java.util.Date thresholdPast28Date  = BasicUtils.setTimeInDays(sqlTodayDate, -28);

        System.out.println(thresholdPast28Date);

        //56 days ago
        java.util.Date thresholdPast56Date  = BasicUtils.setTimeInDays(sqlTodayDate, -56);

        System.out.println(thresholdPast56Date);
    }
}

class BasicUtils {
    public static java.util.Date setTimeInDays(Date startingTime, Integer days){
        Calendar c = Calendar.getInstance(); 
        c.setTime(startingTime); 
        c.add(Calendar.DATE, days);//a day in the future or past
        return c.getTime();
    }
}