如何通过JDBC将java.time等java.time类型插入到H2 Database Engine等sql数据库中？
使用PreparedStatement::setDate和ResultSet::getDate的旧方法适用于旧版java.sql.Date.我想避免使用这些麻烦的旧日期时间类.
通过JDBC driver发送java.time类型的现代方法是什么？
解决方法:
我们有两条通过JDBC交换java.time对象的路径：
>符合JDBC 4.2的驱动程序如果JDBC驱动程序符合JDBC 4.2 specification或更高版本,则可以直接处理java.time对象.
> JDBC之前的旧驱动程序4.2如果您的JDBC驱动程序尚未符合JDBC 4.2或更高版本,那么您可以将java.time对象简要地转换为其等效的java.sql类型,反之亦然.查看添加到旧类的新转换方法.
旧的日期时间类(如java.util.Date,java.util.Calendar)和相关的java.sql类(如java.sql.Date)非常混乱.它们采用设计糟糕的黑客攻击方式构建,已证明存在缺陷,麻烦和混乱.尽可能避免使用它们.现在取代了java.time类.
符合JDBC 4.2的驱动程序
H2的内置JDBC驱动程序(截至2017-03)似乎符合JDBC 4.2.
兼容的驱动程序现在知道java.time类型.但是,不是添加setLocalDate / getLocalDate方法,JDBC委员会添加了setObject/getObject方法.
要将数据发送到数据库,只需将java.time对象传递给PreparedStatement :: setobject即可.传递的参数的java类型由驱动程序检测并转换为适当的sql类型. Java LocalDate将转换为sql DATE类型.有关这些映射的列表,请参见JDBC Maintenance Release 4.2的PDF文档的第22节.
myPreparedStatement.setobject ( 1 , myLocalDate ); // Automatic detection and conversion of data type.
要从数据库中检索数据,请调用ResultSet :: getobject.我们可以传递一个额外的参数,即我们期望接收的数据类型的Class,而不是转换生成的Object对象.通过指定期望的类,我们通过IDE和编译器检查并验证type-safety.
LocalDate localDate = myResultSet.getobject ( "my_date_column_" , LocalDate.class );
这是一个完整的工作示例应用程序,显示如何在H2数据库中插入和选择LocalDate值.
package com.example.h2localdate;
import java.sql.*;
import java.time.LocalDate;
import java.time.ZoneId;
import java.util.UUID;
/**
* Hello World!
*/
public class App {
public static void main ( String[] args ) {
App app = new App ( );
app.doIt ( );
}
private void doIt ( ) {
try {
Class.forName ( "org.h2.Driver" );
} catch ( ClassNotFoundException e ) {
e.printstacktrace ( );
}
try (
Connection conn = DriverManager.getConnection ( "jdbc:h2:mem:trash_me_db_" ) ;
Statement stmt = conn.createStatement ( ) ;
) {
String tableName = "test_";
String sql = "CREATE TABLE " + tableName + " (\n" +
" id_ UUID DEFAULT random_uuid() PRIMARY KEY ,\n" +
" date_ DATE NOT NULL\n" +
");";
stmt.execute ( sql );
// Insert row.
sql = "INSERT INTO test_ ( date_ ) " + "VALUES (?) ;";
try ( PreparedStatement preparedStatement = conn.prepareStatement ( sql ) ; ) {
LocalDate today = LocalDate.Now ( ZoneId.of ( "America/Montreal" ) );
preparedStatement.setobject ( 1, today.minusDays ( 1 ) ); // Yesterday.
preparedStatement.executeUpdate ( );
preparedStatement.setobject ( 1, today ); // Today.
preparedStatement.executeUpdate ( );
preparedStatement.setobject ( 1, today.plusDays ( 1 ) ); // Tomorrow.
preparedStatement.executeUpdate ( );
}
// Query all.
sql = "SELECT * FROM test_";
try ( ResultSet rs = stmt.executeQuery ( sql ) ; ) {
while ( rs.next ( ) ) {
//Retrieve by column name
UUID id = rs.getobject ( "id_", UUID.class ); // Pass the class to be type-safe, rather than casting returned value.
LocalDate localDate = rs.getobject ( "date_", LocalDate.class ); // Ditto, pass class for type-safety.
//display values
System.out.println ( "id_: " + id + " | date_: " + localDate );
}
}
} catch ( sqlException e ) {
e.printstacktrace ( );
}
}
}
跑步时
id_: e856a305-41a1-45fa-ab69-cfa676285461 | date_: 2017-03-26
id_: a4474e79-3e1f-4395-bbba-044423b37b9f | date_: 2017-03-27
id_: 5d47bc3d-ebfa-43ab-bbc2-7bb2313b33b0 | date_: 2017-03-28
不合规的司机
对于H2,上面显示的代码是我建议你采取的道路.但是,对于其他不符合JDBC 4.2的数据库,我可以向您展示如何在java.time和java.sql类型之间进行简单转换.这种转换代码肯定会在H2上运行,如下所示,但这样做很愚蠢,因为我们现在有了更简单的方法.
要将数据发送到数据库,请使用添加到该旧类的新方法将LocalDate转换为java.sql.Date对象.
java.sql.Date MysqLDate = java.sql.Date.valueOf( myLocalDate );
然后传递给PreparedStatement :: setDate方法.
preparedStatement.setDate ( 1, MysqLDate );
要从数据库中检索,请调用ResultSet :: getDate以获取java.sql.Date对象.
java.sql.Date MysqLDate = myResultSet.getDate( 1 );
然后立即转换为LocalDate.您应该尽可能简短地处理java.sql对象.使用java.time类型完成所有业务逻辑和其他工作.
LocalDate myLocalDate = MysqLDate.toLocalDate();
这是一个完整的示例应用程序,显示了在H2数据库中使用java.time类型的java.sql类型.
package com.example.h2localdate;
import java.sql.*;
import java.time.LocalDate;
import java.time.ZoneId;
import java.util.UUID;
/**
* Hello World!
*/
public class App {
public static void main ( String[] args ) {
App app = new App ( );
app.doIt ( );
}
private void doIt ( ) {
try {
Class.forName ( "org.h2.Driver" );
} catch ( ClassNotFoundException e ) {
e.printstacktrace ( );
}
try (
Connection conn = DriverManager.getConnection ( "jdbc:h2:mem:trash_me_db_" ) ;
Statement stmt = conn.createStatement ( ) ;
) {
String tableName = "test_";
String sql = "CREATE TABLE " + tableName + " (\n" +
" id_ UUID DEFAULT random_uuid() PRIMARY KEY ,\n" +
" date_ DATE NOT NULL\n" +
");";
stmt.execute ( sql );
// Insert row.
sql = "INSERT INTO test_ ( date_ ) " + "VALUES (?) ;";
try ( PreparedStatement preparedStatement = conn.prepareStatement ( sql ) ; ) {
LocalDate today = LocalDate.Now ( ZoneId.of ( "America/Montreal" ) );
preparedStatement.setDate ( 1, java.sql.Date.valueOf ( today.minusDays ( 1 ) ) ); // Yesterday.
preparedStatement.executeUpdate ( );
preparedStatement.setDate ( 1, java.sql.Date.valueOf ( today ) ); // Today.
preparedStatement.executeUpdate ( );
preparedStatement.setDate ( 1, java.sql.Date.valueOf ( today.plusDays ( 1 ) ) ); // Tomorrow.
preparedStatement.executeUpdate ( );
}
// Query all.
sql = "SELECT * FROM test_";
try ( ResultSet rs = stmt.executeQuery ( sql ) ; ) {
while ( rs.next ( ) ) {
//Retrieve by column name
UUID id = ( UUID ) rs.getobject ( "id_" ); // Cast the `Object` object to UUID if your driver does not support JDBC 4.2 and its ability to pass the expected return type for type-safety.
java.sql.Date sqlDate = rs.getDate ( "date_" );
LocalDate localDate = sqlDate.toLocalDate (); // Immediately convert into java.time. Mimimize use of java.sql types.
//display values
System.out.println ( "id_: " + id + " | date_: " + localDate );
}
}
} catch ( sqlException e ) {
e.printstacktrace ( );
}
}
}
为了好玩,让我们尝试另一个.这次using a DataSource implementation从中获得连接.而这一次尝试LocalDate.MIN,这是大约10亿年前的常数,-999,999,999-01-01.
package work.basil.example;
import java.sql.*;
import java.time.LocalDate;
import java.time.ZoneId;
import java.util.UUID;
public class LocalDateMin
{
public static void main ( String[] args )
{
LocalDateMin app = new LocalDateMin();
app.doIt();
}
private void doIt ()
{
org.h2.jdbcx.JdbcDataSource ds = new org.h2.jdbcx.JdbcDataSource();
ds.setURL( "jdbc:h2:mem:localdate_min_example_db_;DB_CLOSE_DELAY=-1" );
ds.setUser( "scott" );
ds.setPassword( "tiger" );
try (
Connection conn = ds.getConnection() ;
Statement stmt = conn.createStatement() ;
)
{
String tableName = "test_";
String sql = "CREATE TABLE " + tableName + " (\n" +
" id_ UUID DEFAULT random_uuid() PRIMARY KEY ,\n" +
" date_ DATE NOT NULL\n" +
");";
stmt.execute( sql );
// Insert row.
sql = "INSERT INTO test_ ( date_ ) " + "VALUES (?) ;";
try ( PreparedStatement preparedStatement = conn.prepareStatement( sql ) ; )
{
LocalDate today = LocalDate.Now( ZoneId.of( "America/Montreal" ) );
preparedStatement.setobject( 1 , LocalDate.MIN ); // MIN =
preparedStatement.executeUpdate();
}
// Query all.
sql = "SELECT * FROM test_";
try ( ResultSet rs = stmt.executeQuery( sql ) ; )
{
while ( rs.next() )
{
//Retrieve by column name
UUID id = rs.getobject( "id_" , UUID.class ); // Pass the class to be type-safe, rather than casting returned value.
LocalDate localDate = rs.getobject( "date_" , LocalDate.class ); // Ditto, pass class for type-safety.
//display values
System.out.println( "id_: " + id + " | date_: " + localDate );
}
}
} catch ( sqlException e )
{
e.printstacktrace();
}
}
}
id_: 4b0ba138-d7ae-469b-854f-5cbe7430026f | date_: -999999999-01-01
关于java.time
java.time框架内置于Java 8及更高版本中.这些类取代了麻烦的旧legacy日期时间类,如java.util.Date,Calendar和& SimpleDateFormat.
Joda-Time项目现在是maintenance mode,建议迁移到java.time课程.
要了解更多信息,请参阅Oracle Tutorial.并搜索Stack Overflow以获取许多示例和说明.规格是JSR 310.
从哪里获取java.time类？
>内置.
>部分标准Java API,带有捆绑实现.
> Java 9增加了一些小功能和修复.
>大部分java.time功能都被反向移植到Java 6& 7月在ThreeTen-Backport.
> Android
> ThreeTenABP项目专门针对Android调整了ThreeTen-Backport(如上所述).
>见How to use ThreeTenABP….
ThreeTen-Extra项目使用其他类扩展了java.time.该项目是未来可能添加到java.time的试验场.您可以在这里找到一些有用的类,例如Interval,YearWeek,YearQuarter和more.
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