Java: Spring Boot

Create microservices

import java.util.Arrays;
import java.util.List;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.annotation.GetMapping;

public class Course {
    private long id;
    private String name;
    private String author;

    public Course(long id, String name, String author){
        super();
        this.id = id;
        this.name = name;
        this.author = author;
    }

    public String toString() {
        return "Course [id=" + id + ", name= " + name + ", author=" + author + " ]";
    }

    public long getId() {
        return id;
    }
    public String getName() {
        return name;
    }
    public String getAuthor() {
        return author;
    }
}


@RestController
public class CourseController {
    @GetMapping("/courses")
    public List<Course> getAllCourses(){
    return Arrays.asList(new Course(1, "Learn microservices", "in28minutes"));
    }
}

Spring Boot Starter Projects

Found at Spring Initializr Under dependencies

Web Application: Spring Boot Starter Web

REST API: Spring Boot Starter Web

Talk to database using JPA: Spring Boot Starter Data JPA

Talk to database using JDBC: Spring Boot Starter Data JDBC

Secure your web application or REST API: Spring Boot Starter Security

Spring Boot Actuator

Monitor and manage your application

• beans: Complete list of Spring beans in your app
• health: Application health information
• metrics: Application metrics
• mappings: Details around Requests Mappings

To enable Spring Boot actuator at pom.xml:

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

http://127.0.0.1:8080/actuator

http://127.0.0.1:8080/actuator/health

http://127.0.0.1:8080/actuator/health/{*path}

http://127.0.0.1:8080/actuator/info

You can enable more endpoints of actuator at application.properties:

# anagement.endpoints.web.exposure.include=*
# anagement.endpoints.web.exposure.include=health,metrics

Dev Tools

Add at pom.xml

....
    <dependencies>
        ....
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-devtools</artifactId>
            <scope>runtime</scope>
        </dependency>
        ....
    </dependencies>
....

<scope>runtime</scope> --> runs only at development

Provides:

• Develop server reloading on changes (pom.xml changes are not detected)

Example: Spring Boot with Data JPA and in memory database H2

/pom.xml

....
    <dependencies>
        ....
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-devtools</artifactId>
            <scope>runtime</scope>
        </dependency>
        ....
    </dependencies>
....

/src/main/resources/application.properties

h2 Database

spring.datasource.url=jdbc:h2:mem:testdb

# If using Spring Boot >=2.5.0 the following line is also required
spring.jpa.defer-datasource-initialization=true

database will be accessible via http://localhost:8080/h2-console

Docker MySQL

#spring.datasource.url=jdbc:h2:mem:testdb
 
spring.jpa.hibernate.ddl-auto=update
spring.datasource.url=jdbc:mysql://localhost:3306/courses
spring.datasource.username=courses-user
spring.datasource.password=dummycourses
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQL57Dialect
 
#courses-user@localhost:3306

Start MySQL Docker container

docker run --detach --env MYSQL_ROOT_PASSWORD=dummypassword --env MYSQL_USER=courses-user --env MYSQL_PASSWORD=dummycourses --env MYSQL_DATABASE=courses --name mysql --publish 3306:3306 mysql:5.7

mysqlsh commands

mysqlsh
\connect courses-user@localhost:3306
\sql
use courses
select * from course;
\quit

# Stop MySQL container
docker container ls
docker container stop ID

/src/main/java/com/in28minutes/learnspringboot/courses/bean/Course.java

package com.in28minutes.learnspringboot.courses.bean;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.GeneratedValue;
// import javax.persistence.Column;

// @Entity(name="db_table_name")
@Entity
public class Course {
    @Id
    @GeneratedValue
    private long id;

    // @Column(name="db_column_name")
    private String name;
    private String author;

    public Course(){}  // Entities must have a default constructor

    public Course(long id, String name, String author){
        super();
        this.id = id;
        this.name = name;
        this.author = author;
    }

    public String toString() {
        return "Course [id=" + id + ", name= " + name + ", author=" + author + " ]";
    }

    public long getId() {
        return id;
    }
    public String getName() {
        return name;
    }
    public String getAuthor() {
        return author;
    }
}

src/main/resources/data.sql

querys in this file will be executed at startup automatically

insert into COURSE(ID, AUTHOR, NAME)
values(100001, 'in28minutes', 'Learn Microservices');
insert into COURSE(ID, AUTHOR, NAME)
values(100002, 'in28minutes', 'Learn FullStack with React and Angular');
insert into COURSE(ID, AUTHOR, NAME)
values(100003, 'in28minutes', 'Learn AWS, GCP and Azure');

/src/main/java/com/in28minutes/learnspringboot/courses/repository/CourseRepository.java

package com.in28minutes.learnspringboot.courses.repository;

import org.springframework.data.jpa.repository.JpaRepository;
import com.in28minutes.learnspringboot.courses.bean.Course;

public interface CourseRepository extends JpaRepository<Course, Long> {}

---

/src/main/java/com/in28minutes/learnspringboot/courses/controller/CourseController.java

package com.in28minutes.learnspringboot.courses.controller;

import java.util.List;
import java.util.Optional;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.DeleteMapping;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.PutMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;

import com.in28minutes.learnspringboot.courses.bean.Course;
import com.in28minutes.learnspringboot.courses.repository.CourseRepository;

@RestController
public class CourseController {
	
	@Autowired
	private CourseRepository repository;
	
	// http://localhost:8080/courses
	@GetMapping("/courses")
	public List<Course> getAllCourses() {		
		return repository.findAll();
	}
	
	//// http://localhost:8080/courses/1
	@GetMapping("/courses/{id}")
	public Course getCourseDetails(@PathVariable long id) {
		
		Optional<Course> course = repository.findById(id);
		
		if(course.isEmpty()) {
			throw new RuntimeException("Course not found with id " + id);
		}
	
		return course.get();
	}
	
	/*
	POST http://localhost:8080/courses
	{
		  "name": "Learn DevOps",
		  "author": "in28minutes"
	}*/

	//POST - Create a new resource (/courses)
	@PostMapping("/courses")
	public void createCourse(@RequestBody Course course){
		repository.save(course);		
	}
	
	/*
	PUT - http://localhost:8080/courses/100001
	{
		 "id": 100001,
		 "name": "Learn Microservices 2",
		 "author": "in28minutes"
		}
	*/
	
	//PUT - Update/Replace a resource (/courses/1)
	@PutMapping("/courses/{id}")
	public void updateCourse(@PathVariable long id, @RequestBody Course course){
		repository.save(course);		
	}

	
	//DELETE - Delete a resource (/courses/1)
	@DeleteMapping("/courses/{id}")
	public void deleteCourse(@PathVariable long id){
		repository.deleteById(id);
	}
	

//	docker run --detach 
//	--env MYSQL_ROOT_PASSWORD=dummypassword 
//	--env MYSQL_USER=courses-user 
//	--env MYSQL_PASSWORD=dummycourses 
//	--env MYSQL_DATABASE=courses 
//	--name mysql
//	--publish 3306:3306 mysql:5.7
}

REST API

GET

Retrieve information

/courses, /courses/1

POST

Create a new resource

/courses

PUT

Update/Replace a resource

/courses/1

PATCH

Update a part of the resource

/courses/1

DELETE

Delete a resource

/courses/1

Build

Make JAR not WAR (JAR contains embeded server)