what is the difference db configuration in spring boot - spring-boot

Question

1)This is class level configuration (#configuration).why we need this boilerplate code
#Configuration
#EnableJpaRepositories(basePackages = {"xxx.xxx.xxx.core.dao"})
#EnableTransactionManagement
public class Repository {
#Bean
public DataSource dataSource() {
DriverManagerDataSource dataSource = new DriverManagerDataSource();
dataSource.setDriverClassName("com.mysql.jdbc.Driver");
dataSource.setUrl("jdbc:mysql://localhost:3306/xxxx");
dataSource.setUsername("xxxx");
dataSource.setPassword("xxxx");
return dataSource;
}
#Bean
public EntityManagerFactory entityManagerFactory() {
HibernateJpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();
vendorAdapter.setGenerateDdl(true);
LocalContainerEntityManagerFactoryBean factory = new LocalContainerEntityManagerFactoryBean();
factory.setJpaVendorAdapter(vendorAdapter);
factory.setPackagesToScan("xx.xxxx.xxxx.xxxx.domain");
factory.setDataSource(dataSource());
factory.afterPropertiesSet();
return factory.getObject();
}
#Bean
public PlatformTransactionManager transactionManager() {
JpaTransactionManager txManager = new JpaTransactionManager();
txManager.setEntityManagerFactory(entityManagerFactory());
return txManager;
}
2) This option also working fine.spring boot will take rest of the code and it will take application.property file for configuration
#Configuration
#EnableJpaRepositories(basePackages = {"xxx.xxx.xxx.core.dao"})
#EnableTransactionManagement
#SpringBootApplication
#EnableCaching
public class Application extends SpringBootServletInitializer {
#Override
protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
return application.sources(Application.class);
}
public static void main(String[] args) {
ConfigurableApplicationContext app = SpringApplication.run(Application.class, args);
}
}
which one is good practice and why we need to create one class for database configuration(option 1)and how spring will take care all configuration (option 2)

Answer 1

This is class level configuration (#configuration).why we need this
boilerplate code
It is not mandatory to have these boilerplate code. You do this only in specific cases. For example, if you don't want spring-boot to do Autoconfiguration for you(with default values or values from application.properties).
Another example is when you have multiple datasbases to connect to in your application. In such cases, springboot's autoconfiguration is not of much help, and hence you would do like this. Not once, but as many times as the number of databases you have.
which one is good practice and why we need to create one class for
database configuration(option 1)and how spring will take care all
configuration (option 2)
As you might be knowing, spring-boot is primarily opinionated. Which means, it assumes a lot of things based on the dependencies you add in your pom. Even if you don't add anything in your properties file, it still tries to connect to database on your localhost and some predefined port as soon as it encounters and database dependencies in your pom.
So the answer is "It Depends". It depends on many things, whether you have one or multiple datasources, and also do you want complete control of how database configuration needs to be done... etc