Spring JDBC API + Azure Database for PostgreSQL - Build REST CRUD APIs

In this section, we will learn how to build REST CRUD APIs with Spring Boot, Spring JDBC API and Microsoft Azure Database for PostgreSQL Single Server.

A little bit of Background

Azure Database for PostgreSQL Single Server

Single Server is a fully managed database service with minimal requirements for customizations of the database. The single server platform is designed to handle most of the database management functions such as patching, backups, high availability, and security with minimal user configuration and control. The architecture is optimized to provide 99.99% availability on a single availability zone. It supports the community version of PostgreSQL 10 and 11. The service is generally available today in a wide variety of Azure regions.

More Info - Azure Database for PostgreSQL Single Server | Microsoft Learn

Spring Boot

Spring Boot makes it easy to create stand-alone, production-grade Spring-based Applications that you can "just run". 

More Info - Spring Boot

Spring JDBC API

The Spring Jdbc API is an adaptation of the standard JDBC API. It is very easy to get started using Spring Jdbc, and the API includes many useful methods that will map data to classes that Java developers use on a regular basis.

More Info - Spring JDBC Tutorial | Baeldung

After completing this tutorial what we will build? 

We will build REST APIs  CRUD features: 

Step 1: Sign in to Azure Portal and create a resource group

Sign in to Azure portal https://portal.azure.com/#home and find "Resource groups" like below.

Then, create a resource group like the one below.

Here the resource group name is "Knowledgefactory". Create a resource group by clicking the "Review + create " button.

Step 2: Create an Azure Database for PostgreSQL Single Server

Select "Azure Database for PostgreSQL servers",

You will be taken to a page like the below image, Then click on the "Create Azure Database for PostgreSQL Server" button.

You will be taken to a page like the below image,

Then click on the Single Server"Create" button.

You will be taken to a page like the below image,

Select/Enter necessary information like the above image and then, click on the "Review + create" button. 

Then click on the "Create" button.

Now, You can see "Deployment is in progress" like the below image.

Once deployment is completed you can see the "Your deployment is complete" page like the below image.

Click on the "Connection strings",

Copy the JDBC connection string and keep it safe for future purposes.

Whitelisting IP Address for Access to Azure PostgreSQL DB, like the below image.

Then click on the "Save" button,

Step 3: Creating a simple spring boot web application

First, open the Spring initializr https://start.spring.io/

Then, Provide the Group and Artifact name. We have provided Group name com.knf.dev.demo and Artifact spring-boot-azure-postgresql-crud. Here I selected the Maven project - language Java - Spring Boot 2.7.1 and add Spring web dependency, Spring Data JPA, and PostgreSQL Driver. 

Then, click on the Generate button. When we click on the Generate button, it starts packing the project in a .zip(spring-boot-azure-postgresql-crud.zip) file and downloads the project. 

Then, Extract the Zip file.

Import the project on your favourite IDE,

Final Project Directory:

Pom.xml

A Project Object Model or POM is the fundamental unit of work in Maven. It is an XML file that contains information about the project and configuration details utilized by Maven to build the project. 

<?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>2.7.3</version>
      <relativePath/> <!-- lookup parent from repository -->
   </parent>
   <groupId>com.knf.dev.demo</groupId>
   <artifactId>spring-jdbc-azure-postgres-crud</artifactId>
   <version>0.0.1-SNAPSHOT</version>
   <name>spring-jdbc-azure-postgres-crud</name>
   <description>Demo project for Spring Boot</description>
   <properties>
      <java.version>17</java.version>
   </properties>
   <dependencies>
      <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-jdbc</artifactId>
      </dependency>
      <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-web</artifactId>
      </dependency>

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

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

schema.sql: Creating a table for 'users'

Spring Boot can automatically create the schema (DDL scripts) of your DataSource and initialize it (DML scripts). It loads SQL from the standard root classpath locations: schema. sql and data. sql , respectively.

DROP TABLE IF EXISTS users;

CREATE TABLE users (
    id serial PRIMARY KEY,
    first_name VARCHAR ( 50 )  NOT NULL,
    last_name VARCHAR ( 50 ) NOT NULL,
    email VARCHAR ( 255 )  NOT NULL
);

application.properties

The following properties are needed to configure PostgresSQL with Spring Boot. 

The property spring.datasource.initialization-mode from Spring boot verion 2.7 and onwards is not any more depracated. It has been completely removed! So the change into the replacement property spring.sql.init.mode is a must do from now on.

Example: spring.sql.init.mode=always

spring.datasource.url= jdbc:postgresql://<servername>/postgres
spring.datasource.username= <username>
spring.datasource.password= <password>

spring.sql.init.mode=always

**Important note** Do not publish the fields directly for security. It would be a good choice to define these variables as environment variables or use the Azure Key Vault. 

Creating the Model User

package com.knf.dev.demo.springdatajdbcazurepostgrescrud.model;

public record User
        (Long id,
         String firstName,
         String lastName,
         String email) {
}

Creating the User Repository

package com.knf.dev.demo.springdatajdbcazurepostgrescrud.repository;

import com.knf.dev.demo.springdatajdbcazurepostgrescrud.model.User;
import java.util.List;

public interface UserRepository {

    public User findOne(Long id);

    public List<User> findAll();

    public void save(User user);

    public Long saveAndReturnId(User user);

    public void update(User user);

    public Boolean delete(Long id);

}

Creating the User Repository Implementation

package com.knf.dev.demo.springdatajdbcazurepostgrescrud.repository;

import com.knf.dev.demo.springdatajdbcazurepostgrescrud.exception.UserNotFound;
import com.knf.dev.demo.springdatajdbcazurepostgrescrud.model.User;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.dao.EmptyResultDataAccessException;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.jdbc.support.GeneratedKeyHolder;
import org.springframework.stereotype.Repository;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.List;

@Repository
public class UserRepositoryImpl implements UserRepository {

    private final JdbcTemplate jdbcTemplate;

    @Autowired
    public UserRepositoryImpl(JdbcTemplate jdbcTemplate) {
        this.jdbcTemplate = jdbcTemplate;
    }


    @Override
    public User findOne(Long id) {

        var sqlQuery = Query.FIND_ONE;

        try {

            return jdbcTemplate.
                    queryForObject(sqlQuery,
                            this::mapRowToUser, id);

        } catch (EmptyResultDataAccessException ex) {
            throw new UserNotFound("Invalid User Id");
        }
    }

    @Override
    public List<User> findAll() {

        var sqlQuery = Query.FIND_ALL;
        return jdbcTemplate.
                query(sqlQuery, this::mapRowToUser);
    }

    @Override
    public void save(User user) {

        var sqlQuery = Query.SAVE;
        jdbcTemplate.update(sqlQuery,
                user.firstName(),
                user.lastName(),
                user.email());
    }

    @Override
    public Long saveAndReturnId(User user) {

        var sqlQuery = Query.SAVE_AND_RETURN_ID;
        var keyHolder = new GeneratedKeyHolder();
        jdbcTemplate.update(connection -> {
            PreparedStatement stmt = connection.
                    prepareStatement(sqlQuery,
                            new String[] { "id" });

            stmt.setString(1, user.firstName());
            stmt.setString(2, user.lastName());
            stmt.setString(3, user.email());

            return stmt;

        }, keyHolder);

        return keyHolder.getKey().longValue();
    }

    @Override
    public void update(User user) {

        var sqlQuery = Query.UPDATE;
        jdbcTemplate.update(sqlQuery,
                user.firstName(),
                user.lastName(),
                user.email(),
                user.id());
    }

    @Override
    public Boolean delete(Long id) {

        var sqlQuery = Query.DELETE;
        return jdbcTemplate.update(sqlQuery, id) > 0;
    }

    private User mapRowToUser(ResultSet resultSet, int rowNum)
            throws SQLException {

        var user = new User(resultSet.getLong("id"),
                resultSet.getString("first_name"),
                resultSet.getString("last_name"),
                resultSet.getString("email"));

        return user;
    }
}

Query.java

package com.knf.dev.demo.springdatajdbcazurepostgrescrud.repository;

public class Query {

    public static final String FIND_ONE = 
            "select id, first_name, last_name,"
                + " email from users where id = ?";
    
    public static final String FIND_ALL =
            "select id, first_name,last_name,"
              + " email from users";
    
    public static final String SAVE =
            "insert into users(first_name, "
                + "last_name, email) "
                  + "values (?, ?, ?)";
    
    public static final String SAVE_AND_RETURN_ID =
            "insert into users" 
               + "(first_name, last_name, email) "
                   + "values (?, ?, ?)";
    public static final String UPDATE =
           "update users set " 
              + "first_name = ?, last_name = ?," 
                   + " email = ? " + "where id = ?";
    public static final String DELETE =
          "delete from users where id = ?";
}

Exception Handler with Controller Advice in Spring

Spring supports exception handling by a global Exception Handler (@ExceptionHandler) with Controller Advice (@ControllerAdvice). This enables a mechanism that makes ResponseEntity work with the type safety and flexibility of @ExceptionHandler:

package com.knf.dev.demo.springdatajdbcazurepostgrescrud.exception;

import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.context.request.WebRequest;
import java.util.Date;

@ControllerAdvice
public class GlobalExceptionHandler {

    @ExceptionHandler(UserNotFound.class)
    public ResponseEntity<ErrorMessage> 
    userNotFound(Exception ex, WebRequest request) {
        var errors =
         new ErrorMessage(404, new Date(), 
           ex.getMessage(), "User Not Found");

        return new ResponseEntity<>
            (errors, HttpStatus.NOT_FOUND);
    }
}

Custom Exception - UserNotFound

package com.knf.dev.demo.springdatajdbcazurepostgrescrud.exception;

public class UserNotFound extends RuntimeException {
    private static final long serialVersionUID = 1L;

    public UserNotFound(String msg) {
        super(msg);
    }
}

Error Message

package com.knf.dev.demo.springdatajdbcazurepostgrescrud.exception;

import java.util.Date;

public record ErrorMessage
(Integer statusCode, 
        Date timestamp, 
          String message,
            String description) {
}

User Rest Controller

The @RestController annotation was introduced in Spring 4.0 to simplify the engendering of RESTful web services. It's a convenience annotation that combines @Controller and @ResponseBody. @RequestMapping annotation maps HTTP requests to handler methods of MVC and REST controllers.

package com.knf.dev.demo.springdatajdbcazurepostgrescrud.controller;

import com.knf.dev.demo.springdatajdbcazurepostgrescrud.model.User;
import com.knf.dev.demo.springdatajdbcazurepostgrescrud.repository.UserRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;
import java.util.List;

@RestController
@RequestMapping("/api/v1/users")
public class UserController {

    @Autowired
    UserRepository userRepository;

    //Create user
    @PostMapping
    public ResponseEntity<String> save(@RequestBody User usr) {

            var userId = userRepository.saveAndReturnId(usr);

            return new ResponseEntity<String>
             ("User successfully created , Id =" 
                + userId, HttpStatus.CREATED);

    }

    //Get all users
    @GetMapping
    public ResponseEntity<List<User>> getAll() {

            return new ResponseEntity<List<User>>
              (userRepository.findAll(), HttpStatus.OK);

    }

    //Get user by id
    @GetMapping("/{id}")
    public ResponseEntity<User> getById
        (@PathVariable("id") Long id) {

        return new ResponseEntity<>
           (userRepository.findOne(id), HttpStatus.OK);

    }

    // Delete user
    @DeleteMapping("/{id}")
    public ResponseEntity<String> deleteUser
         (@PathVariable("id") Long id) {

        userRepository.delete(userRepository.findOne(id).id());

        return new ResponseEntity<>
           ("User removed successfully", HttpStatus.OK);

    }

    // Update user
    @PutMapping("/{id}")
    public ResponseEntity<String> updateUser
       (@PathVariable("id") Long id, @RequestBody User user) {

        var _user = userRepository.findOne(id);
        var _upUSer = new User(_user.id(),
                user.firstName(),user.lastName(),user.email());
        
        userRepository.update(_upUSer);
        return new ResponseEntity<>
           ("Updated successfully", HttpStatus.OK);

    }
}

Spring Boot main driver

package com.knf.dev.demo.springdatajdbcazurepostgrescrud;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class SpringDataJdbcAzurePostgresCrudApplication {

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

Step 4: Local Setup and Run the application

Step 1: Download or clone the source code from GitHub to the local machine - Click here

Step 2: mvn clean install

Step 3: Run the Spring Boot application - 

mvn spring-boot:run

Step 5: Test the APIs using postman

1. Add User:

2. Get User By Id:

3. Update User:

4. Get All Users:

5. Delete User:

Download the complete source code - click here