[[jdbc-advanced-jdbc]]
= JDBC Batch Operations

Most JDBC drivers provide improved performance if you batch multiple calls to the same
prepared statement. By grouping updates into batches, you limit the number of round trips
to the database.


[[jdbc-batch-classic]]
== Basic Batch Operations with `JdbcTemplate`

You accomplish `JdbcTemplate` batch processing by implementing two methods of a special interface,
`BatchPreparedStatementSetter`, and passing that implementation in as the second parameter
in your `batchUpdate` method call. You can use the `getBatchSize` method to provide the size of
the current batch. You can use the `setValues` method to set the values for the parameters of
the prepared statement. This method is called the number of times that you specified in the
`getBatchSize` call. The following example updates the `t_actor` table based on entries in a list,
and the entire list is used as the batch:

[tabs]
======
Java::
+
[source,java,indent=0,subs="verbatim,quotes"]
----
	public class JdbcActorDao implements ActorDao {

		private JdbcTemplate jdbcTemplate;

		public void setDataSource(DataSource dataSource) {
			this.jdbcTemplate = new JdbcTemplate(dataSource);
		}

		public int[] batchUpdate(final List<Actor> actors) {
			return this.jdbcTemplate.batchUpdate(
					"update t_actor set first_name = ?, last_name = ? where id = ?",
					new BatchPreparedStatementSetter() {
						public void setValues(PreparedStatement ps, int i) throws SQLException {
							Actor actor = actors.get(i);
							ps.setString(1, actor.getFirstName());
							ps.setString(2, actor.getLastName());
							ps.setLong(3, actor.getId().longValue());
						}
						public int getBatchSize() {
							return actors.size();
						}
					});
		}

		// ... additional methods
	}
----

Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes"]
----
	class JdbcActorDao(dataSource: DataSource) : ActorDao {

		private val jdbcTemplate = JdbcTemplate(dataSource)

		fun batchUpdate(actors: List<Actor>): IntArray {
			return jdbcTemplate.batchUpdate(
					"update t_actor set first_name = ?, last_name = ? where id = ?",
					object: BatchPreparedStatementSetter {
						override fun setValues(ps: PreparedStatement, i: Int) {
							ps.setString(1, actors[i].firstName)
							ps.setString(2, actors[i].lastName)
							ps.setLong(3, actors[i].id)
						}

						override fun getBatchSize() = actors.size
					})
		}

		// ... additional methods
	}
----
======

If you process a stream of updates or reading from a file, you might have a
preferred batch size, but the last batch might not have that number of entries. In this
case, you can use the `InterruptibleBatchPreparedStatementSetter` interface, which lets
you interrupt a batch once the input source is exhausted. The `isBatchExhausted` method
lets you signal the end of the batch.


[[jdbc-batch-list]]
== Batch Operations with a List of Objects

Both the `JdbcTemplate` and the `NamedParameterJdbcTemplate` provides an alternate way
of providing the batch update. Instead of implementing a special batch interface, you
provide all parameter values in the call as a list. The framework loops over these
values and uses an internal prepared statement setter. The API varies, depending on
whether you use named parameters. For the named parameters, you provide an array of
`SqlParameterSource`, one entry for each member of the batch. You can use the
`SqlParameterSourceUtils.createBatch` convenience methods to create this array, passing
in an array of bean-style objects (with getter methods corresponding to parameters),
`String`-keyed `Map` instances (containing the corresponding parameters as values), or a mix of both.

The following example shows a batch update using named parameters:

[tabs]
======
Java::
+
[source,java,indent=0,subs="verbatim,quotes"]
----
	public class JdbcActorDao implements ActorDao {

		private NamedParameterTemplate namedParameterJdbcTemplate;

		public void setDataSource(DataSource dataSource) {
			this.namedParameterJdbcTemplate = new NamedParameterJdbcTemplate(dataSource);
		}

		public int[] batchUpdate(List<Actor> actors) {
			return this.namedParameterJdbcTemplate.batchUpdate(
					"update t_actor set first_name = :firstName, last_name = :lastName where id = :id",
					SqlParameterSourceUtils.createBatch(actors));
		}

		// ... additional methods
	}
----

Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes"]
----
	class JdbcActorDao(dataSource: DataSource) : ActorDao {

		private val namedParameterJdbcTemplate = NamedParameterJdbcTemplate(dataSource)

		fun batchUpdate(actors: List<Actor>): IntArray {
			return this.namedParameterJdbcTemplate.batchUpdate(
					"update t_actor set first_name = :firstName, last_name = :lastName where id = :id",
					SqlParameterSourceUtils.createBatch(actors));
		}

			// ... additional methods
	}
----
======

For an SQL statement that uses the classic `?` placeholders, you pass in a list
containing an object array with the update values. This object array must have one entry
for each placeholder in the SQL statement, and they must be in the same order as they are
defined in the SQL statement.

The following example is the same as the preceding example, except that it uses classic
JDBC `?` placeholders:

[tabs]
======
Java::
+
[source,java,indent=0,subs="verbatim,quotes"]
----
	public class JdbcActorDao implements ActorDao {

		private JdbcTemplate jdbcTemplate;

		public void setDataSource(DataSource dataSource) {
			this.jdbcTemplate = new JdbcTemplate(dataSource);
		}

		public int[] batchUpdate(final List<Actor> actors) {
			List<Object[]> batch = new ArrayList<>();
			for (Actor actor : actors) {
				Object[] values = new Object[] {
						actor.getFirstName(), actor.getLastName(), actor.getId()};
				batch.add(values);
			}
			return this.jdbcTemplate.batchUpdate(
					"update t_actor set first_name = ?, last_name = ? where id = ?",
					batch);
		}

		// ... additional methods
	}
----

Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes"]
----
	class JdbcActorDao(dataSource: DataSource) : ActorDao {

		private val jdbcTemplate = JdbcTemplate(dataSource)

		fun batchUpdate(actors: List<Actor>): IntArray {
			val batch = mutableListOf<Array<Any>>()
			for (actor in actors) {
				batch.add(arrayOf(actor.firstName, actor.lastName, actor.id))
			}
			return jdbcTemplate.batchUpdate(
					"update t_actor set first_name = ?, last_name = ? where id = ?", batch)
		}

		// ... additional methods
	}
----
======

All of the batch update methods that we described earlier return an `int` array
containing the number of affected rows for each batch entry. This count is reported by
the JDBC driver. If the count is not available, the JDBC driver returns a value of `-2`.

[NOTE]
====
In such a scenario, with automatic setting of values on an underlying `PreparedStatement`,
the corresponding JDBC type for each value needs to be derived from the given Java type.
While this usually works well, there is a potential for issues (for example, with
Map-contained `null` values). Spring, by default, calls `ParameterMetaData.getParameterType`
in such a case, which can be expensive with your JDBC driver. You should use a recent driver
version and consider setting the `spring.jdbc.getParameterType.ignore` property to `true`
(as a JVM system property or via the
xref:appendix.adoc#appendix-spring-properties[`SpringProperties`] mechanism)
if you encounter a specific performance issue for your application.

As of 6.1.2, Spring bypasses the default `getParameterType` resolution on PostgreSQL and
MS SQL Server. This is a common optimization to avoid further roundtrips to the DBMS just
for parameter type resolution which is known to make a very significant difference on
PostgreSQL and MS SQL Server specifically, in particular for batch operations. If you
happen to see a side effect, for example, when setting a byte array to null without specific type
indication, you may explicitly set the `spring.jdbc.getParameterType.ignore=false` flag
as a system property (see above) to restore full `getParameterType` resolution.

Alternatively, you could consider specifying the corresponding JDBC types explicitly,
either through a `BatchPreparedStatementSetter` (as shown earlier), through an explicit
type array given to a `List<Object[]>` based call, through `registerSqlType` calls on a
custom `MapSqlParameterSource` instance, through a `BeanPropertySqlParameterSource`
that derives the SQL type from the Java-declared property type even for a null value, or
through providing individual `SqlParameterValue` instances instead of plain null values.
====


[[jdbc-batch-multi]]
== Batch Operations with Multiple Batches

The preceding example of a batch update deals with batches that are so large that you want to
break them up into several smaller batches. You can do this with the methods
mentioned earlier by making multiple calls to the `batchUpdate` method, but there is now a
more convenient method. This method takes, in addition to the SQL statement, a
`Collection` of objects that contain the parameters, the number of updates to make for each
batch, and a `ParameterizedPreparedStatementSetter` to set the values for the parameters
of the prepared statement. The framework loops over the provided values and breaks the
update calls into batches of the size specified.

The following example shows a batch update that uses a batch size of 100:

[tabs]
======
Java::
+
[source,java,indent=0,subs="verbatim,quotes"]
----
	public class JdbcActorDao implements ActorDao {

		private JdbcTemplate jdbcTemplate;

		public void setDataSource(DataSource dataSource) {
			this.jdbcTemplate = new JdbcTemplate(dataSource);
		}

		public int[][] batchUpdate(final Collection<Actor> actors) {
			int[][] updateCounts = jdbcTemplate.batchUpdate(
					"update t_actor set first_name = ?, last_name = ? where id = ?",
					actors,
					100,
					(PreparedStatement ps, Actor actor) -> {
						ps.setString(1, actor.getFirstName());
						ps.setString(2, actor.getLastName());
						ps.setLong(3, actor.getId().longValue());
					});
			return updateCounts;
		}

		// ... additional methods
	}
----

Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes"]
----
	class JdbcActorDao(dataSource: DataSource) : ActorDao {

		private val jdbcTemplate = JdbcTemplate(dataSource)

		fun batchUpdate(actors: List<Actor>): Array<IntArray> {
			return jdbcTemplate.batchUpdate(
						"update t_actor set first_name = ?, last_name = ? where id = ?",
						actors, 100) { ps, argument ->
				ps.setString(1, argument.firstName)
				ps.setString(2, argument.lastName)
				ps.setLong(3, argument.id)
			}
		}

		// ... additional methods
	}
----
======

The batch update method for this call returns an array of `int` arrays that contains an
array entry for each batch with an array of the number of affected rows for each update.
The top-level array's length indicates the number of batches run, and the second level
array's length indicates the number of updates in that batch. The number of updates in
each batch should be the batch size provided for all batches (except that the last one
that might be less), depending on the total number of update objects provided. The update
count for each update statement is the one reported by the JDBC driver. If the count is
not available, the JDBC driver returns a value of `-2`.



