SpringBoot : Working with JdbcTemplate

Spring provides a nice abstraction on top of JDBC API using JdbcTemplate and also provides great transaction management capabilities using annotation based approach.

First let’s take a quick look at how we generally use Spring’s JdbcTemplate (without SpringBoot) by registering DataSource, TransactionManager and JdbcTemplate beans and optionally we can register DataSourceInitializer bean to initialize our database.

@Configuration
@ComponentScan
@EnableTransactionManagement
@PropertySource(value = { "classpath:application.properties" })
public class AppConfig 
{
    @Autowired
    private Environment env;

    @Value("${init-db:false}")
    private String initDatabase;
    
    @Bean
    public static PropertySourcesPlaceholderConfigurer placeHolderConfigurer()
    {
        return new PropertySourcesPlaceholderConfigurer();
    }    

    @Bean
    public JdbcTemplate jdbcTemplate(DataSource dataSource)
    {
        return new JdbcTemplate(dataSource);
    }

    @Bean
    public PlatformTransactionManager transactionManager(DataSource dataSource)
    {
        return new DataSourceTransactionManager(dataSource);
    }

    @Bean
    public DataSource dataSource()
    {
        BasicDataSource dataSource = new BasicDataSource();
        dataSource.setDriverClassName(env.getProperty("jdbc.driverClassName"));
        dataSource.setUrl(env.getProperty("jdbc.url"));
        dataSource.setUsername(env.getProperty("jdbc.username"));
        dataSource.setPassword(env.getProperty("jdbc.password"));
        return dataSource;
    }

    @Bean
    public DataSourceInitializer dataSourceInitializer(DataSource dataSource)
    {
        DataSourceInitializer dataSourceInitializer = new DataSourceInitializer();    
        dataSourceInitializer.setDataSource(dataSource);
        ResourceDatabasePopulator databasePopulator = new ResourceDatabasePopulator();
        databasePopulator.addScript(new ClassPathResource("data.sql"));
        dataSourceInitializer.setDatabasePopulator(databasePopulator);
        dataSourceInitializer.setEnabled(Boolean.parseBoolean(initDatabase));
        return dataSourceInitializer;
    }
}

With this configuration in place, we can inject JdbcTemplate into Data Access components to interact with databases.

public class User
{
    private Integer id;
    private String name;
    private String email;

    // setters & getters
}

@Repository
public class UserRepository
{
    @Autowired
    private JdbcTemplate jdbcTemplate;

    @Transactional(readOnly=true)
    public List<User> findAll() {
        return jdbcTemplate.query("select * from users", new UserRowMapper());
    }
}

class UserRowMapper implements RowMapper<User>
{
    @Override
    public User mapRow(ResultSet rs, int rowNum) throws SQLException 
    {
        User user = new User();
        user.setId(rs.getInt("id"));
        user.setName(rs.getString("name"));
        user.setEmail(rs.getString("email"));

        return user;
    }
}

You might have observed that most of the times we use this similar kind of configuration in our applications.

Now let us see how to use JdbcTemplate without requiring to configure all these beans manually by using SpringBoot.

Using JdbcTemplate with SpringBoot

By using SpringBoot we can take advantage of auto configuration feature and eliminate the need to configure beans by ourselves.

Create a SpringBoot maven based project and add spring-boot-starter-jdbc module.

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-jdbc</artifactId>
</dependency>

By adding spring-boot-starter-jdbc module, we get the following auto configuration:

• The spring-boot-starter-jdbc module transitively pulls tomcat-jdbc-{version}.jar which is used to configure the DataSource bean.
• If you have not defined any DataSource bean explicitly and if you have any embedded database driver in classpath such as H2, HSQL or Derby then SpringBoot will automatically registers DataSource bean using in-memory database settings.
• If you haven’t registered any of the following type beans then SpringBoot will register them automatically.
  • PlatformTransactionManager (DataSourceTransactionManager)
  • JdbcTemplate
  • NamedParameterJdbcTemplate 
• We can have schema.sql and data.sql files in root classpath which SpringBoot will automatically use to initialize database.In addition to schema.sql and data.sql, Spring Boot will load schema-${platform}.sql and data-${platform}.sql files if they are available in root classpath. Here platform value is the value of the property spring.datasource.platform which can be hsqldb, h2, oracle, mysql, postgresql etc.You can customize the default names of the scripts using the following properties:
  • spring.datasource.schema=create-db.sql
  • spring.datasource.data=seed-data.sql
     
    SpringBoot uses spring.datasource.initialize property value, which is true by default, to determine whether to initialize database or not. If you want to turn off the database initialization you can set spring.datasource.initialize=false

    If there are any errors in executing the scripts then application will fail to start. If you want to continue then you can set spring.datasource.continueOnError=true.

Let us add H2 database driver to our pom.xml.

<dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
</dependency>

Create schema.sql in src/main/resources as follows:

CREATE TABLE users
(
    id int(11) NOT NULL AUTO_INCREMENT,
    name varchar(100) NOT NULL,
    email varchar(100) DEFAULT NULL,
    PRIMARY KEY (id)
);

Create data.sql in src/main/resources as follows:

insert into users(id, name, email) values(1,'Siva','siva@gmail.com');
insert into users(id, name, email) values(2,'Prasad','prasad@gmail.com');
insert into users(id, name, email) values(3,'Reddy','reddy@gmail.com');

Now you can inject JdbcTemplate into UserRepository as follows:

@Repository
public class UserRepository
{
    @Autowired
    private JdbcTemplate jdbcTemplate;

    @Transactional(readOnly=true)
    public List<User> findAll() {
        return jdbcTemplate.query("select * from users", 
                new UserRowMapper());
    }

    @Transactional(readOnly=true)
    public User findUserById(int id) {
        return jdbcTemplate.queryForObject(
            "select * from users where id=?",
            new Object[]{id}, new UserRowMapper());
    }

    public User create(final User user) 
    {
        final String sql = "insert into users(name,email) values(?,?)";

        KeyHolder holder = new GeneratedKeyHolder();
        jdbcTemplate.update(new PreparedStatementCreator() {
            @Override
            public PreparedStatement createPreparedStatement(Connection connection) throws SQLException {
                PreparedStatement ps = connection.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS);
                ps.setString(1, user.getName());
                ps.setString(2, user.getEmail());
                return ps;
            }
        }, holder);

        int newUserId = holder.getKey().intValue();
        user.setId(newUserId);
        return user;
    }
}

class UserRowMapper implements RowMapper<User>
{
    @Override
    public User mapRow(ResultSet rs, int rowNum) throws SQLException {
        User user = new User();
        user.setId(rs.getInt("id"));
        user.setName(rs.getString("name"));
        user.setEmail(rs.getString("email"));
        return user;
    }
}

Create the entry point SpringbootJdbcDemoApplication.java.

@SpringBootApplication
public class SpringbootJdbcDemoApplication
{
    public static void main(String[] args)
    {
        SpringApplication.run(SpringbootJdbcDemoApplication.class, args);
    }
}

Let us create a JUnit Test class to test our UserRepository methods.

@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(SpringbootJdbcDemoApplication.class)
public class SpringbootJdbcDemoApplicationTests
{
    @Autowired
    private UserRepository userRepository;

    @Test
    public void findAllUsers() {
        List<User> users = userRepository.findAll();
        assertNotNull(users);
        assertTrue(!users.isEmpty());
    }

    @Test
    public void findUserById() {
        User user = userRepository.findUserById(1);
        assertNotNull(user);
    }

    @Test
    public void createUser() {
        User user = new User(0, "John", "john@gmail.com");
        User savedUser = userRepository.create(user);
        User newUser = userRepository.findUserById(savedUser.getId());
        assertNotNull(newUser);
        assertEquals("John", newUser.getName());
        assertEquals("john@gmail.com", newUser.getEmail());
    }
}

By default SpringBoot features such as external properties, logging etc are available in the ApplicationContext only if you use SpringApplication. So, SpringBoot provides @SpringApplicationConfiguration annotation to configure the ApplicationContext for tests which uses SpringApplication behind the scenes.

We have learned how to get started quickly with Embedded database. What if we want to use Non-Embedded databases like MySQL, Oracle or PostgreSQL etc?.

We can configure the database properties in application.properties file so that SpringBoot will use those jdbc parameters to configure DataSource bean.

spring.datasource.driver-class-name=com.mysql.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost:3306/test
spring.datasource.username=root
spring.datasource.password=admin

For any reason if you want to have more control and configure DataSource bean by yourself then you can configure DataSource bean in a Configuration class. If you register DataSource bean then SpringBoot will not configure DataSource automatically using AutoConfiguration. What if you want to use another Connection Pooling library?

SpringBoot by default pulls in tomcat-jdbc-{version}.jar and uses org.apache.tomcat.jdbc.pool.DataSource to configure DataSource bean.

SpringBoot checks the availability of the following classes and uses the first one that is available in classpath.

• org.apache.tomcat.jdbc.pool.DataSource
• com.zaxxer.hikari.HikariDataSource
• org.apache.commons.dbcp.BasicDataSource
• org.apache.commons.dbcp2.BasicDataSource

For example, If you want to use HikariDataSource then you can exclude tomcat-jdbc and add HikariCP dependency as follows:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-jdbc</artifactId>
    <exclusions>
        <exclusion>
        <groupId>org.apache.tomcat</groupId>
        <artifactId>tomcat-jdbc</artifactId>
        </exclusion>
    </exclusions>
</dependency>

<dependency>
    <groupId>com.zaxxer</groupId>
    <artifactId>HikariCP</artifactId>
</dependency>

With this dependency configuration SpringBoot will use HikariCP to configure DataSource bean.

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