Spring Boot — Rest API

Spring Boot — REST

Discover the intricacies of crafting a robust RESTful API with Spring Boot in this comprehensive guide. From tool setup using Eclipse IDE and Postman for testing to database integration via Aiven’s MySQL service, each step is meticulously detailed. Explore the layered architecture, including the Presentation, Service, and DAO/Repository Layers, with clear instructions on endpoint creation, entity modeling, and CRUD operation implementation. This resource is a must-read for developers aiming to master API development using Spring Boot, concluding with expert tips on testing the API within Eclipse and validating it with Postman.

Server

Accepts request from client example: mobile, chrome

How Server works?

1. Presentation Layer { Controllers } [ Accepts Request ]
2. Service Layer { Checks for what s service to provide }
3. Dao/Repository Layer { Share and add Data to database and Service layer }
4. Databases { Store Data }

mobile, chrome → presentation layer ↔ service layer ↔ Dao/Repository Layer ↔ Database

API URL’s

Method API URL’s Operation

GET /users -> Get user

GET /users/{userId} -> Get single user

POST /user -> Add new user

PUT /user -> Update the user

DELETE /user/{userId} -> Delete the user

Requirements :

1. IDE → Eclipse
2. Postman
3. Database → Aiven [ MySQL ]

spring initializr

1. Spring web
2. Spring data JPA
3. Spring MySQL Driver

File System

1. src/main/java
   Packages
   Controllers
   Service
2. src/main/resources
   Application Setup
   Database connectivity
3. pom.xml
   All dependencies are here

Procedure

Aiven Database Connection

Goto Aiven → register → services → MySQL → get User Data [ Free Services are provided here ]

Add database information with aiven data to application.properties

spring.jpa.hibernate.ddl-auto=update 
spring.datasource.url=jdbc:mysql://{Host}:{Port}/{Database_Name} 
spring.datasource.username={UserName} 
spring.datasource.password={Password} 
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver

Create interface for providing repository from database JpaRepository of database so we can make CRUD onto it

package com.springrest.springrest.repository;

import org.springframework.data.jpa.repository.JpaRepository;  
import com.springrest.springrest.entity.Users;
  
public interface UserDao extends JpaRepository<Users, Long>{  
}

Create MyController class [ Main part to receive api request ] src.main.springrest.controller

Add Representational State Controller Mark

@RestController 
public class MyController {  

}

Create method and use getmapping, also checking if it’s working properly

@RestController
public class MyController {
 
 @GetMapping("/test")
 public String home() {
  return "this is test page";
 }
}

It’s working! Now Create model entity eg. Users inside src.main.springrest.springrest.entity

private long id;
private String name;
private int age;

// Generate Constructors using fields
// Generate Constructors using super
// Generate getters and setters for all
// Generate toString method for all

package com.springrest.springrest.entity;

import jakarta.persistence.Entity;
import jakarta.persistence.Id;

@Entity
public class Users {
 @Id
 private long id;
 private String name;
 private int age;
 
 public Users(long id, String name, int age) {
  super();
  this.id = id;
  this.name = name;
  this.age = age;
 }
 
 public Users() {
  super();
  // TODO Auto-generated constructor stub
 }
 
 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 getAge() {
  return age;
 }
 public void setAge(int age) {
  this.age = age;
 }
 
 @Override
 public String toString() {
  return "Users [id=" + id + ", name=" + name + ", age=" + age + "]";
 }
}

Create controller mapping for all users in MyController

// get all users
 @GetMapping("/users")
 public List<Users> getUsers(){
  
 }

Now, to get all users we need to have connector to database and here we use ‘services’

Create Services interface name UserService withing src.main.springrest.springrest.services

public interface UserServices {
  public List<Users> getUser();
}

create UserImpl class where you will create main service and that will be connected to database repository and couple it with UserService using implements method

@Service
public class UserImpl implements UserServices {
 
 @Autowired
 private UserDao userDao;
 
 public UserImpl() {
  
 }

@Override
 public List<Users> getUser() {
  // TODO Auto-generated method stub
  return userDao.findAll();
 }
}

Now use this in MyController to pass data

@Autowired
 private UserServices userServices;
 
 // get all users
 @GetMapping("/users")
 public List<Users> getUsers(){
  return this.userServices.getUser();
 }

Do similar for others too

MyController

package com.springrest.springrest.controller;

import java.util.List;
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.springrest.springrest.entity.Users;
import com.springrest.springrest.services.UserServices;
@RestController
public class MyController {
 
 @Autowired
 private UserServices userServices;
 
 // get all users
 @GetMapping("/user")
 public List<Users> getUsers(){
  return this.userServices.getUser();
 }
 
 // single user
 @GetMapping("/user/{userId}")
 public Users getUsers(@PathVariable String userId) {
  return this.userServices.getUser(Long.parseLong(userId));
 }
 
 // create user
 @PostMapping(path="/add", consumes="application/json")
 public Users addUser(@RequestBody Users user) {
  return this.userServices.addUser(user);
 }
 
 // Update the users
 @PutMapping("/update")
 public Users updateUser(@RequestBody Users user) {
  return this.userServices.updateUser(user);
 }
 
 
 
 // delete user
 @DeleteMapping("/delete/{userId}")
 public Users deleteUser(@PathVariable String userId) {
  return this.userServices.deleteUser(Long.parseLong(userId));
 }
 
 
}

UserService

package com.springrest.springrest.services;

import java.util.List;
import com.springrest.springrest.entity.Users;
public interface UserServices {
 public List<Users> getUser();
 
 public Users getUser(long userId);
 public Users addUser(Users user);
 public Users deleteUser(long userId);
 public Users updateUser(Users user);
}

UserImpl

package com.springrest.springrest.services;

import java.util.ArrayList;
import java.util.List;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import com.springrest.springrest.entity.Users;
import com.springrest.springrest.repository.UserDao;
@Service
public class UserImpl implements UserServices {
 
// List<Users> list;
 
 @Autowired
 private UserDao userDao;
 
 public UserImpl() {
  
 }
 @Override
 public List<Users> getUser() {
  // TODO Auto-generated method stub
  return userDao.findAll();
 }
 @Override
 public Users getUser(long userId) {
  // TODO Auto-generated method stub
  return userDao.findById(userId).orElse(null);
 }
 @Override
 public Users addUser(Users user) {
  // TODO Auto-generated method stub
  userDao.save(user);
  return user;
 }
 @Override
 public Users updateUser(Users user) {
  // TODO Auto-generated method stub
  userDao.save(user);
  return user;
 }
 @Override
 public Users deleteUser(long userId) {
  // TODO Auto-generated method stub
  Users user = userDao.findById(userId).orElse(null);
  userDao.delete(user);
  return user;
 }
}

Now test it run on Eclipse and test it on postman