Oracle10g驱动关于date类型问题一般的数据库中，DATE字段仅仅表示日期，不包括日期信息，而Oracle数据库中的D
Oracle10g驱动关于date类型问题
一般的数据库中，DATE字段仅仅表示日期，不包括日期信息，而Oracle数据库中的DATE数据类型是包括日期、时间的，对于不同的Oracle jdbc驱动版本，对于该问题的处理都有些区别。
最近使用 ORACLE 10G，时间字段因需求，设为了DATE类型，发现hibernate用native SQL 查询，显示不了时分秒，原来是JDBC驱动自动把date映射为 java.sql.date，故截断了时分秒信息，如果你使用9i或者11g 的驱动程序，就没有该问题，但是Oracle10g的JDBC驱动，你会发现没有时分秒 ，在Oracle9.2之后，引入了内置数据类型TIMESTAMP。之所以引入它，是因为内置数据类型DATE的最小单位为秒；DATE的主要问题是它粒度不能足够区别出两个事件哪个先发生。9.2版本后ORACLE在DATE数据类型上扩展出来了TIMESTAMP数据类型，它包括了所有DATE数据类型的年月日时分秒的信息，而且包括了小数秒(纳秒Nanoseconds级的)的信息。如果你想把DATE类型转换成TIMESTAMP类型，就使用CAST函数。 也正是从oracle 9.2开始，内置数据类型DATE和TIMESTAMP在使用9i的JDBC驱动做查询时，DATE被映射为java.sql.Date,TIMESTAMP被映射为java.sql.Timestamp。 从Oracle11开始，其JDBC驱动程序又重新开始回归为将内置类型DATE映射为java.sql.Timestamp(正如9.2之前的那样)。
所以，时分秒精度的丢失与hibernate无关，是oracle jdbc驱动的问题。最好的解决办法就是：换驱动。经测试，将最开始使用的10g的驱动ojdbc14.jar换为11g的驱动ojdbc5.jar后；
引用
Simple Data Types
What is going on with DATE and TIMESTAMP?
This section is on simple data types. :-)
Prior to 9.2, the Oracle JDBC drivers mapped the DATE SQL type to java.sql.Timestamp. This made a certain amount of sense because the Oracle DATE SQL type contains both date and time information as does java.sql.Timestamp. The more obvious mapping to java.sql.Date was somewhat problematic as java.sql.Date does not include time information. It was also the case that the RDBMS did not support the TIMESTAMP SQL type, so there was no problem with mapping DATE to Timestamp.
In 9.2 TIMESTAMP support was added to the RDBMS. The difference between DATE and TIMESTAMP is that TIMESTAMP includes nanoseconds and DATE does not. So, beginning in 9.2, DATE is mapped to Date and TIMESTAMP is mapped to Timestamp. Unfortunately if you were relying on DATE values to contain time information, there is a problem.
There are several ways to address this problem in the 9.2 through 10.2 drivers:
Alter your tables to use TIMESTAMP instead of DATE. This is probably rarely possible, but it is the best solution when it is.
Alter your application to use defineColumnType to define the columns as TIMESTAMP rather than DATE. There are problems with this because you really don't want to use defineColumnType unless you have to (see What is defineColumnType and when should I use it?).
Alter you application to use getTimestamp rather than getObject. This is a good solution when possible, however many applications contain generic code that relies on getObject, so it isn't always possible.
Set the V8Compatible connection property. This tells the JDBC drivers to use the old mapping rather than the new one. You can set this flag either as a connection property or a system property. You set the connection property by adding it to the java.util.Properties object passed to DriverManager.getConnection or to OracleDataSource.setConnectionProperties. You set the system property by including a -D option in your java command line.
java -Doracle.jdbc.V8Compatible="true" MyApp
Oracle JDBC 11.1 fixes this problem. Beginning with this release the driver maps SQL DATE columns to java.sql.Timestamp by default. There is no need to set V8Compatible to get the correct mapping. V8Compatible is strongly deprecated. You should not use it at all. If you do set it to true it won't hurt anything, but you should stop using it.
Although it was rarely used that way, V8Compatible existed not to fix the DATE to Date issue but to support compatibility with 8i databases. 8i (and older) databases did not support the TIMESTAMP type. Setting V8Compatible not only caused SQL DATE to be mapped to Timestamp when read from the database, it also caused all Timestamps to be converted to SQL DATE when written to the database. Since 8i is desupported, the 11.1 JDBC drivers do not support this compatibility mode. For this reason V8Compatible is desupported.
As mentioned above, the 11.1 drivers by default convert SQL DATE to Timestamp when reading from the database. This always was the right thing to do and the change in 9i was a mistake. The 11.1 drivers have reverted to the correct behavior. Even if you didn't set V8Compatible in your application you shouldn't see any difference in behavior in most cases. You may notice a difference if you use getObject to read a DATE column. The result will be a Timestamp rather than a Date. Since Timestamp is a subclass of Date this generally isn't a problem. Where you might notice a difference is if you relied on the conversion from DATE to Date to truncate the time component or if you do toString on the value. Otherwise the change should be transparent.
If for some reason your app is very sensitive to this change and you simply must have the 9i-10g behavior, there is a connection property you can set. Set mapDateToTimestamp to false and the driver will revert to the default 9i-10g behavior and map DATE to Date.
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