java.sql.Date,java.sql.Time和java.sql.Timestamp

java.sql.Date,java.sql.Time和java.sql.Timestamp三个都是java.util.Date的子类（包装类）。
但是为什么java.sql.Date类型的值插入到数据库中Date字段中会发生数据截取呢？
java.sql.Date是为了配合SQL DATE而设置的数据类型。“规范化”的java.sql.Date只包含年月日信息，时分秒毫秒都会清零。格式类似：YYYY-MM-DD
当我们调用ResultSet的getDate()方法来获得返回值时，java程序会参照"规范"的java.sql.Date来格式化数据库中的数值。因此，如果
数据库中存在的非规范化部分的信息将会被劫取。在sun提供的ResultSet.java中这样对getDate进行注释的：
Retrieves the value of the designated column in the current row of this <code>ResultSet</code> object as a “java.sql.Date” object in the Java programming language.
同理。如果我们把一个java.sql.Date值通过PrepareStatement的setDate方法存入数据库时，java程序会对传入的java.sql.Date规范化
，非规范化的部分将会被劫取。
然而，我们java.sql.Date一般由java.util.Date转换过来，如：java.sql.Date sqlDate=new java.sql.Date(new java.util.Date().getTime()).
显然，这样转换过来的java.sql.Date往往不是一个规范的java.sql.Date.

以上摘自:http://www.blogjava.net/huabingl/archive/2006/07/06/56977.aspx

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java.sql.Date stores only date information, not times. Simply converting a java.util.Date into a java.sql.Date will silently set the time to midnight. So, to store date/times to be manipulated as java.util.Date objects, don’t do this:

// BUG: loses time of day
preparedStatement.setDate(1, new java.sql.Date(date.getTime()));
do this instead:

preparedStatement.setTimestamp(1, new java.sql.Timestamp(date.getTime()));
java.sql.Timestamp is not a date java.sql.Timestamp extends java.util.Date, but it should not be used as a Date. In JDK 1.3.1, Timestamp.getTime() (inherited from Date) returns the time to the nearest second only, but JDK 1.4.2 and JDK 1.5 it returns the time to the nearest millisecond as expected. So in JDK 1.3, when reading a timestamp from a ResultSet, don’t do this:

// Java 1.3j
ava.util.Date d = resultSet.getTimestamp(1);
long millis = d.getTime(); // BUG: loses fractional seconds
in JDK 1.3To get the full date including milliseconds, you have to do this:

java.sql.Timestamp timestamp = resultSet.getTimestamp(1);
java.util.Date d = new java.util.Date(timestamp.getTime() +           timestamp.getNanos() / 1000000);
In JDK 1.4.2 and JDK 1.5, you can just do this, depending on what you’re going to do with the Date:

// Java 1.4+
java.util.Date d = resultSet.getTimestamp(1);
But this might be safer since it avoids any other potential Timestamp problems:

// Java 1.4+java.util.Date d = new java.util.Date(resultSet.getTimestamp(1).getTime());
If your code needs to run on JDK 1.3 and later, you’ll have to do this:

java.sql.Timestamp timestamp = resultSet.getTimestamp(1);long millis = (timestamp.getTime() / 1000) * 1000 + timestamp.getNanos() / 1000000;以上摘自：http://www.thunderguy.com/semicolon/2003/08/14/java-sql-date-is-not-a-real-date/java.util.Date d = new java.util.Date(millis);