Banuprakash C

Full Stack Architect,

Co-founder Lucida Technologies Pvt Ltd.,

Corporate Trainer,

Email: [email protected]; [email protected]

https://www.linkedin.com/in/banu-prakash-50416019/

Softwares Required:

1. Java 8+
2. Eclipse for Enterprise edition / IntelliJ for Enterprise
3. MySQL / h2 memory database
4. Docker for Desktop [ Redis, Promethus] ==> docker-compose will be good =============================================

Spring Framework ==> Lightweight framework for building enterprise applications ==> Core Modules of Spring Framework supports Dependecy Injection [ Inversion Of Control] and Life cycle management

SOLID Design Principles ==> D ==> Dependency Injection

What is DI?

======================================================

Metadata XML:

public interface ProductDao{
	void addProduct(Product p);
}

public class ProductDaoJpaImpl implements ProductDao {
	public void addProduct(Product p) {
			JPA code
	}	
}

public class ProductDaoMongoDbImpl implements ProductDao {
	public void addProduct(Product p) {
			db.collections.insert(p); ...
	}	
}

public class AppService {
	private ProductDao productDao;

	public void setProductDao(ProductDao pd) {
		this.productDao = pd;
	}
	..
}

app.xml
<bean id="pjpa" class = "pkg.ProductDaoJpaImpl" />
<bean id="pmongo" class = "pkg.ProductDaoMongoDbImpl" />
<bean id="service" class = "pkg.AppService">
	<property name="productDao" ref="pmongo" />
</bean>

========================================= MetaData: Annotations

public interface ProductDao{
	void addProduct(Product p);
}
@Repository
public class ProductDaoJpaImpl implements ProductDao { // productDaoJpaImpl
	public void addProduct(Product p) {
			JPA code
	}	
}

@Service 
public class AppService { // appService
	@Autowired
	private ProductDao productDao;
}

Spring instantiates objects of classes which has one of these annoations:
1) @Component
2) @Repository
3) @Service
4) @Configuration
5) @Controller
6) @RestController


Depenency Injection with annoations will be done using @Autowired or @Inject [ JEE Specification javax.inject libraries]
@Autowired uses ==> Byte Code Instrumentation libraries like CGLIB or JavaAssist 

================================================================================================ Spring Boot? ==> Framework ==> a layer on Spring Framework ==> Simplifies Development

Highly opniated and configures lots of classes out of the box

For Example ==> JPA == > ORM
	==> configures Hikari dataSource [ pool of database connection]
	==> configures Hibernate as ORM provider
	==> ans instantiates most of the required stuff for ORM

For Web based ==> DispatcherServlet ==> Tomcat / Netty

==> Cloudier

==================================================================

Help ==> Eclipse Market place ==> Search for STS [ Spring tools suite 4.x] and install

@SpringBootApplication public class DemoApplication {

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

Dockerfile

FROM openjdk:8-jdk-alpine ARG JAR_FILE=target/*.jar COPY ${JAR_FILE} app.jar ENTRYPOINT ["java","-jar","/app.jar"]

@SpringBootApplication ==> @ComponentScan scans for classes with sterotype annotations on classes from "com.example.demo" package onwards and creates instances ==> @EnableAutoConfiguration scans for "jar" files in build path and creates instances of classes managed by spring container like Connection Pool; DispatcherServlet; HibernateJPaVendor; ... ==> @Configuration

to resolve "Field employeeDao in com.example.demo.service.AppService required a single bean, but 2 were found"

@Repository @Primary public class EmployeeDaoMongoImpl implements EmployeeDao {

@Override
public void addEmployee() {
	System.out.println("mongo store !!!");
}

application.properties spring.profiles.active=prod

or

Command line arguments: --spring.profiles.active=dev

@Repository @Profile("prod") public class EmployeeDaoJpaImpl implements EmployeeDao {

@Override
public void addEmployee() {
	System.out.println("stored in MySQL!!!");
}

}

@Repository @Profile("dev") public class EmployeeDaoMongoImpl implements EmployeeDao {

@Override
public void addEmployee() {
	System.out.println("mongo store !!!");
}

}

=============== Single object within a container: @Scope("singleton")

for every DI different object: @Scope("prototype")

When client makes a request this object is created and destroyed on response being commited @Scope("request") @ConditionalOnBean("hikariConnectionCP")

request.setAttribute("employeeDaoMongoImpl", new EmployeeDaoMongoImpl());

@Autowired @Qualifier("mongo") private EmployeeDao employeeDaoMongo;

@Autowired @Qualifier("mysql") private EmployeeDao employeeDaoMySQL;

@Configuration public class DBUtil {

@Bean
public DataSource getDataSource() {
	ComboPooledDataSource cpds = new ComboPooledDataSource();
	cpds.setDriverClass( "org.postgresql.Driver" ); //loads the jdbc driver            
	cpds.setJdbcUrl( "jdbc:postgresql://localhost/testdb" );
	cpds.setUser("dbuser");                                  
	cpds.setPassword("dbpassword"); 

	return cpds;
}

sample.properties url=192.168.12.34 userName=root port=1234

@Configuration @ConfigurationProperties("sample") public class SampleConfiguration {

@Value(${url})
private String url;

@Value(${userName})
private String userName;

@Value(${port})
private int port;

suppose we want different configurations based on profiles

--spring.profiles.active=prod

application.properties

application_prod.properties url=

application_dev.properties url=

Command Line ==> System properties ==> application.properties ==> application_profilename.properties

=====================================================================

RESTful and integrate with JPA Hibernate