JdbcTemplate
Internal
Overview
Basic persistence with JDBC is supported by the Spring Framework with JdbcTemplate. JdbcTemplate provides the means by which developers can perform SQL operations against a relational database without the need to retort to verbose JDBC low-level API. With JdbcTemplate, the interaction with the database is reduced to specifying the query and how to map the result of the query to the domain model object.
Spring Persistence Concepts
Spring Boot Support
To add support for JdbcTemplate to a Spring Boot project, add the following starter dependency:
dependencies {
implementation('org.springframework.boot:spring-boot-starter-jdbc')
}
JdbcTemplate needs a database to work with. This is how to add H2 support:
dependencies {
runtimeOnly('com.h2database:h2')
}
JdbcTemplate API
JdbcTemplate-Based Repositories
This is a JdbcTemplate-based concrete repository implementation that conceals from the application low-level data access details while exposing a domain model-typed API, represented by the example "IngredientRepository" interface.
@Repository
public class JdbcIngredientRepository implements IngredientRepository {
private JdbcTemplate jdbcTemplate;
@Autowired
public JdbcIngredientRepository(JdbcTemplate jdbcTemplate) {
this.jdbcTemplate = jdbcTemplate;
}
// Reading data ...
// Writing data ...
}
Reading Data
@Override
public Ingredient findOne(String id) {
return jdbcTemplate.queryForObject(
"SELECT id, name, type from INGREDIENT WHERE id=?",
this::mapRowToIngredient, id);
}
@Override
public Iterable<Ingredient> findAll() {
return jdbcTemplate.query(
"SELECT id, name, type from INGREDIENT",
this::mapRowToIngredient);
}
private Ingredient mapRowToIngredient(ResultSet rs, int rowNumber) throws SQLException {
return new Ingredient(
rs.getString("id"),
rs.getString("name"),
Ingredient.Type.valueOf(rs.getString("type")));
}
Writing Data
Writing Data with update()
No Data Returned
This form performs the update and does not return anything.
@Override
public Ingredient save(Ingredient ingredient) {
jdbcTemplate.update(
"INSERT INTO INGREDIENT (id, name, type) VALUES (?, ?, ?)",
ingredient.getId(),
ingredient.getName(),
ingredient.getType().toString());
return ingredient;
}
Primary Key Returned
There are situations, however, when inserting a row in the database triggers the generation of an ID by the database, and we may need to get a hold of that ID. For situations like these, use the update() version that accepts a PreparedStatementCreator and a KeyHolder:
PreparedStatementCreatorFactory factory = new PreparedStatementCreatorFactory(
"INSERT INTO TACO (name, createdAd) VALUES (?, ?)", Types.VARCHAR, Types.TIMESTAMP);
PreparedStatementCreator c =
factory.newPreparedStatementCreator(Arrays.asList("....", new Timestamp(...)));
KeyHolder keyHolder = new GeneratedKeyHolder();
jdbcTemplate.update(c, keyHolder);
// the ID will be returned by keyHolder:
Long id = keyHolder.getKey().longValue();
Writing Data with SimpleJdbcInsert
SimpleJdbcInsert has two useful methods for executing the insert: execute() and executeAndReturnKey(). Both accept Map<String, Object>, where the map keys correspond to the column names in the table to insert data into. The map values are inserted inn those columns.