数据库类型为TIMESTAMP而不是DATE，这意味着您存储了准确的时间.

The DB type is TIMESTAMP and not DATE, meaning you store exact times.

使用new GregorianCalendar(2012,12,5).getTime()时，您正在查询与给定日期00:00:00.000匹配且在数据库中不存在的时间戳

When using new GregorianCalendar(2012,12,5).getTime() you are quering timestamps that match the given date at 00:00:00.000 and that doesn't exist in your DB

您应该更改数据库以存储日期而不是时间戳，或更改查询.

You should either change the DB to store dates instead of timestamps or change your query.

JPA 2具有YEAR，MONTH和DAY功能，因此您可以

JPA 2 got YEAR, MONTH and DAY functions so you can

SELECT WHERE YEAR(yourdate) = YEAR(dbdate) AND MONTH(yourdate) = MONTH(dbdate) and DAY(yourdate) = DATE(dbdate)

在Criteria API中，您可以执行以下操作:

In Criteria API you can do something like this:

Expression<Integer> yourdateYear = cb.function("year", Integer.class, yourdate);
Expression<Integer> yourdateMonth = cb.function("month", Integer.class, yourdate);
Expression<Integer> yourdateDay = cb.function("day", Integer.class, yourdate);

然后将它们与AND表达式组合在一起，并对db中的date字段执行相同的操作并进行比较.

Then combine them with the AND expression and do the same for the date field in db and compare them.