Mixing JdbcTemplate and raw JDBC - spring

Question

I am experiencing some strange behaviour which I can't easily explain. The following code runs fine:
try (Connection connection = dataSource.getConnection();
Statement statement = connection.createStatement()) {
statement.executeUpdate("DELETE FROM product");
} catch (Exception ex) {
throw new RuntimeException(ex);
}
try (Connection connection = dataSource.getConnection();
Statement statement = connection.createStatement()) {
statement.executeUpdate("INSERT INTO product ...");
} catch (SQLException ex) {
throw new RuntimeException(ex);
}
However this code causes a deadlock:
jdbcTemplate.update("DELETE FROM product");
try (Connection connection = dataSource.getConnection();
Statement statement = connection.createStatement()) {
statement.executeUpdate("INSERT INTO product ...");
} catch (SQLException ex) {
throw new RuntimeException(ex);
}
The exception is
java.sql.SQLException: Lock wait timeout exceeded; try restarting transaction
Both jdbcTemplate and dataSource are created by Spring boot and autowired
#Autowired
private DataSource dataSource;
#Autowired
private JdbcTemplate jdbcTemplate;
The statements form part of a method in a service (with the #Transactional annotation)
Can anyone explain why this happens?

Answer 1

If you want to use your own JDBC code that plays nice with the connections managed by Spring's transaction management you should use DataSourceUtils to obtain the connection -- see http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/jdbc/datasource/DataSourceUtils.html#getConnection-javax.sql.DataSource-
In your example, depending on the transaction configuration, the first statement using the JdbcTemplate might not be committed yet, so it would block the next JDBC statement from a different connection. Using the DataSourceUtils, both statements would be using the same connection.