Spring Boot + Database example - Data retrieval

 1.Create springboot project using https://start.spring.io/ 

2.Add dependency , Spring Web, Mysql Driver, Spring JPA

 

 

3. Generate the code and , import as existing maven project

4.Since this is simple database sample add DBconnection details to the application.properties file

spring.datasource.url=jdbc:mysql://db_ip:3306/db_name?useSSL=false&serverTimezone=UTC
spring.datasource.username=user_name
spring.datasource.password=password

5.Next we create 3 layers virtually for easy understand and development

1.Control Layer

2.Service Layer

3.Repository Layer

6.Create Entity class for relevant table to be used,name City

import java.util.Objects;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name = "cities_test") // Mapping table with DB
public class City {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    private String name;
    private int population;

    public City() {
    }

    public City(Long id, String name, int population) {
        this.id = id;
        this.name = name;
        this.population = population;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getPopulation() {
        return population;
    }

    public void setPopulation(int population) {
        this.population = population;
    }
}

7.Extend CrudRepository and create CityRepository interface for doing db related transactions

Make sure to add @Repository annotation to the class

import org.springframework.data.repository.CrudRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface CityRepository extends CrudRepository<City, Long>{

}
 

8.Then create and CityService interface for doing transaction with Repository

also add signature for retrieve data from db layer  

import java.util.List;

import lk.inova.example.all_demo.repository.City;

public interface CityService {
  List<City> findAllCities();
}

 

9.Then Create impl class by implementing above CityService interface method, also Autowired the CityRepository interface to service Impl class, make sure to set @Service annotation

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import lk.inova.example.all_demo.repository.City;
import lk.inova.example.all_demo.repository.CityRepository;
import lk.inova.example.all_demo.service.CityService;

@Service
public class CityServiceImpl implements CityService {
    @Autowired
    CityRepository repository;
    
    @Override
    public List<City> findAllCities() {
        return (List<City>) repository.findAll();
         
    }

}

10.Then create class MyCityConroller for any transaction about cities - Get Cities, Update, Delete..etc

makesure to add annotation @RestController,...Also Add request mapping and GetMapping to relevant method. also Autowired CityServiceImple class. 

@RestController
import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import lk.inova.example.all_demo.repository.City;
import lk.inova.example.all_demo.service.impl.CityServiceImpl;

@RestController
@RequestMapping("/db")
public class MyCityController {
    @Autowired
    CityServiceImpl cityServiceImpl;
    
    @GetMapping("/cities")
    public List<City> getAllCities(){
        return cityServiceImpl.findAllCities();
    }

}

11.Now you can see the all cities 

http://localhost:8080/db/cities

note : 

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.5.4</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>lk.inova.example</groupId>
    <artifactId>all_demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>all_demo</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>11</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>