Example app
The Answer by Alex Miller is correct. I will add a complete example Java app as a demonstration.
Embedded mode
To clarify: "Embedded mode" means running the database engine within a Java app. If embedded, the database is not accessible from outside that app.
So the Comments on the Question about port numbers makes no sense for an embedded database. When embedded, no network is involved, and therefore no port numbers are involved. (If you want to make connections over the network from other apps, then run H2 in Server mode rather than Embedded mode.)
Embedded-mode database URL
Let’s analyze the embedded-mode database URL seen in code below: "jdbc:h2:mem:ExampleDb;DB_CLOSE_DELAY=-1".
- The first two parts say that we want to use JDBC to access an H2 Database Engine database.
- The third-part indicates we want an in-memory database named with the fourth part,
ExampleDb.
- By default, the in-memory database is closed and discarded after our database connection ends. If you want to keep the database intact for more connections, add the fifth part,
DB_CLOSE_DELAY=-1. By adding that fifth part, the in-memory database will continue to exist, until our app exits.
Persistent storage versus In-memory
If you want to persist your database to storage, rather than in-memory, drop the mem part. Use an embedded database URL as seen on the Cheat Sheet. For example, a database named InvoicesDb in the user’s Home folder would have an embedded database URL of "jdbc:h2:~/InvoicesDb".
java.sql.DataSource
Also notice the use of a DataSource implementation. Using that interface allows you to externalize the connection info outside your source code. Then a system administrator can make changes without you needing to edit your Java code and recompile the app.
Example code
package work.basil.example.jdbc;
import org.h2.jdbcx.JdbcDataSource;
import org.intellij.lang.annotations.Language;
import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.time.OffsetDateTime;
public class ExampleNow
{
public static void main ( String[] args )
{
ExampleNow app = new ExampleNow( );
app.demo( );
}
private void demo ( )
{
DataSource dataSource = this.obtainDataSource( );
// @Language ( "SQL" ) // Or comment: language=HTML — If using IntelliLang plugin in IntelliJ, for language injections. https://www.jetbrains.com/help/idea/using-language-injections.html
String sql = """
SELECT CURRENT_TIMESTAMP ;
""";
try
(
Connection connection = dataSource.getConnection( ) ;
PreparedStatement preparedStatement = connection.prepareStatement( sql ) ;
ResultSet resultSet = preparedStatement.executeQuery( );
)
{
if ( resultSet.next( ) )
{
OffsetDateTime offsetDateTime = resultSet.getObject( 1 , OffsetDateTime.class );
System.out.println( "offsetDateTime.toString() = " + offsetDateTime );
}
} catch ( SQLException e )
{
throw new RuntimeException( e );
}
}
private DataSource obtainDataSource ( )
{
org.h2.jdbcx.JdbcDataSource ds = new JdbcDataSource( ); // Implementation of `javax.sql.DataSource`, bundled with H2.
ds.setURL( "jdbc:h2:mem:ExampleDb;DB_CLOSE_DELAY=-1" ); // To not auto-close (and delete) the in-memory database, pass `DB_CLOSE_DELAY=-1`.
ds.setUser( "scott" );
ds.setPassword( "tiger" );
ds.setDescription( "An example database to capture the current moment." );
return ds;
}
}
Where run:
offsetDateTime.toString() = 2024-08-09T21:04:20.395959Z
