如何通过java.time插入和获取 LocalDate 类型(例如JDBC)到SQL数据库(例如H2 Database Engine)？
使用 PreparedStatement::setDate 和 ResultSet::getDate 的旧方法适用于旧版 java.sql.Date 类型。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？
最佳答案
我们有两种通过JDBC交换java.time对象的途径:
传统的日期时间类(例如
java.util.Date，java.util.Calendar)和相关的java.sql类(例如java.sql.Date)实在是一团糟。它们采用设计不当的黑客手段构建而成，被证明是有缺陷，麻烦且令人困惑的。尽可能避免使用它们。现在由java.time类取代。
符合JDBC 4.2的驱动程序
H2的内置JDBC驱动程序(自2017年3月起)似乎符合JDBC 4.2。
兼容的驱动程序现在知道java.time类型。但是，JDBC委员会没有添加
setLocalDate/getLocalDate各种方法，而是添加了 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。驱动程序检测到传递的参数的Java类型，并将其转换为适当的SQL类型。将Java LocalDate转换为SQL DATE类型。有关这些映射的列表，请参见JDBC Maintenance Release 4.2 PDF文档的第22节。myPreparedStatement.setObject ( 1 , myLocalDate ); // Automatic detection and conversion of data type.
ResultSet::getObject。除了传递最终的Object对象，我们还可以传递一个额外的参数，即我们希望接收的数据类型的 Class 。通过指定期望的类，我们获得了type-safety和编译器检查并验证的IDE。LocalDate localDate = myResultSet.getObject ( "my_date_column_" , LocalDate.class );
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 ( );
}
}
}
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
不合规的驱动程序
对于H2，我建议您使用上面显示的代码。但是，仅供引用，对于其他尚不符合JDBC 4.2的数据库，我可以向您展示如何在java.time和java.sql类型之间进行简要转换。如下所示，这种转换代码当然可以在H2上运行，但是现在有了上面显示的更简单的方法，这样做是很愚蠢的。
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 );
PreparedStatement::setDate方法。preparedStatement.setDate ( 1, mySqlDate );
ResultSet::getDate以获取java.sql.Date对象。java.sql.Date mySqlDate = myResultSet.getDate( 1 );
LocalDate。您应该尽可能简短地处理java.sql对象。仅使用java.time类型执行所有业务逻辑和其他工作。LocalDate myLocalDate = mySqlDate.toLocalDate();
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 ( );
}
}
}
DataSource implementation。这次尝试使用 LocalDate.MIN ，它在ISO 8601(-999999999-01-01)中是大约十亿年前的常数。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，例如
java.util.Date ， Calendar 和 SimpleDateFormat 。要了解更多信息，请参见Oracle Tutorial。并在Stack Overflow中搜索许多示例和说明。规范为JSR 310。
现在位于Joda-Time中的maintenance mode项目建议迁移到java.time类。
您可以直接与数据库交换java.time对象。使用兼容JDBC driver或更高版本的JDBC 4.2。不需要字符串，不需要
java.sql.*类。 Hibernate 5和JPA 2.2支持java.time。在哪里获取java.time类？
ThreeTen-Extra项目使用其他类扩展了java.time。该项目为将来可能在java.time中添加内容提供了一个试验场。您可能会在这里找到一些有用的类，例如
Interval ， YearWeek ， YearQuarter 和more。
关于java - 在SQL数据库(例如H2)中插入和获取java.time.LocalDate对象，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/43039614/