Hello, world!

In this article, I will clearly guide you how to build java application with connection to database. Slightly different, because of Spring, one of the most popular Java framework as a main controller that will provide service and data connecting to/from database.

OK. Let us go!

Murez Nasution

Attention!
All of experiments in this article has been tested and run well on the Windows platform. Other platforms never already tested, and some functionality would not run properly. Thank you.

Requirements

1. Any current JDK.
2. MySQL Community version 5.6 or later.

   Attention!
   
   Source: https://spring.io/guides/gs/accessing-data-mysql/

3. Any text editor or IDE (recommended to use IntelliJ IDEA)
4. Your passion and free time.

Implementation

After all needs are met, here is a general steps that we will do.

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Overview

We will try to create a simple product management project, which the product consists of attributes: name, price and stock. And the available services are add new product, update the existing product and delete old product. Here is the general steps:

1. Settings up Database
   1.1. Create Database
   1.2. Grant User Access
2. Settings up Project
   2.1. Create New Project
   2.2. Build Gradle
   2.3 Application Properties
3. Create Entity Class
4. Create Controller
5. Create Auto-Repository Interface and Launcher

Make sure each of the following steps is done correctly, so that you can get the expected results.

1.1. Create Database

Open Command Prompt

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Directly access to directory MySQL/bin

MySQL Database Login

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Type: mysql -u root -p, and hit Enter. Then, enter your root password.

Create Database Sample

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Type: CREATE DATABASE Sample, and hit Enter.

1.2. Grant User Access

Create User of Tester

Type: CREATE User 'Tester'@'localhost' IDENTIFIED BY 'myPass123';, and hit Enter.

Gives All the Privileges to the Tester

Type: GRANT ALL ON Sample.* TO 'Tester'@'localhost';, and hit Enter.

2.1. Create New Project

Open IntelliJ IDEA

• After IDE is ready, Click File > New > Project...
• On the left side, choose Gradle project, as seen below
  
  Click Next.
• On field of ArtifactId type Sample, or any else you want to. You can make custom on version too. Click Next.
• Checked option of Use auto-import.
  
  That's all and then click Next, and Finish.

2.2. Build Gradle

• After building project has already done, edit file: build.gradle. And all of its contents will be as follows:

version '1.0-SNAPSHOT'
buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:1.5.9.RELEASE")
    }
}

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'idea'
apply plugin: 'org.springframework.boot'

jar {
    baseName = 'murez-db'
    version =  '0.1.0'
}

repositories {
    mavenCentral()
}

sourceCompatibility = 1.8
targetCompatibility = 1.8

dependencies {
   /*
     * Required on JDK 9
     * compile 'javax.xml.bind:jaxb-api:2.3.0'
     */
    compile("org.springframework.boot:spring-boot-starter-web")
    compile 'org.springframework.boot:spring-boot-starter-data-jpa'
    compile 'mysql:mysql-connector-java'
    testCompile('org.springframework.boot:spring-boot-starter-test')
}

Attention!
JDK 9 has done some changes for java.xml.bind and other Java EE modules. So, it has deprecated and removed from default classpath. And also javax.xml.bind is sub-package of java.xml.bind module and will not be available on classpath by default in JDK 9.
Solution:

• Add javax.xml.bind on classpath, we can add using following command:
  --add-modules java.xml.bind
• We can use Maven and Gradle to include javax.xml.bind in our project.

Maven

<dependency>
     <groupId>javax.xml.bind</groupId>
     <artifactId>jaxb-api</artifactId>
     <version>2.3.0</version>
</dependency> 

Gradle

compile 'javax.xml.bind:jaxb-api:2.3.0'

Source: https://docs.oracle.com/javase/9/docs/api/java.xml.bind-summary.html

2.3 Application Properties

Add a resource file in directory: src/main/resources/application.properties, type as follows:

spring.jpa.hibernate.ddl-auto=create
spring.datasource.url=jdbc:mysql://localhost:3306/sample
spring.datasource.username=Tester
spring.datasource.password=myPass123

3. Create Entity Class

Right click on src/main/java directory. And on pop-up dialog, type: com.murez.branch.test.entity.Product.
Next, type this code:

package com.murez.branch.test.entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@javax.persistence.Entity
public class Product {
    @Id @GeneratedValue(strategy = GenerationType.AUTO)
    private long _ID;
    private String name;
    private float price;
    private int stock;

    public Product() { }

   @Override
    public String toString() {
        return String.format("Customer{ ID: %d, name: '%s', price: '%f', stock: '%d' }", _ID, name, price, stock);
    }

    public Product setName(String name) {
        if(name != null && name.length() > 0) {
            this.name = name;
            return this;
        }
        else throw new IllegalArgumentException();
    }

    public Product setPrice(float price) {
        if(price > 0) {
            this.price = price;
            return this;
        }
        else throw new IllegalArgumentException();
    }

    public Product setStock(int stock) {
        if(stock > 0) {
            this.stock = stock;
            return this;
        }
        else throw new IllegalArgumentException();
    }

    public void setID(long ID) { this._ID = ID; }

    public final String getName() { return name; }

    public final float getPrice() { return price; }

    public final int getStock() { return stock; }

    public final long getID() { return _ID; }
}

4. Create Controller

Do as previous step, but the package and class is: com.murez.branch.test.MainController

package com.murez.branch.test;
import com.murez.branch.test.entity.Product;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;

@Controller
@RequestMapping(path = "/demo")
public class MainController {
    @org.springframework.beans.factory.annotation.Autowired
    private ProductRepository repo;

    @GetMapping(path = "/add")
    public @ResponseBody String add(
        @RequestParam String name,
        @RequestParam float price,
        @RequestParam int stock) {
            Product p = repo.save(new Product()
                .setName(name)
                .setPrice(price)
                .setStock(stock));
            return "{ 'code': 200, 'ID': " + p.getID() + " }";
    }

    @GetMapping(path = "/drop")
    public @ResponseBody String drop(@RequestParam String _ID) {
        try {
            repo.delete(Long.parseLong(_ID));
            return "{ 'code': 200 }";
        }
        catch(Exception e) {
            return "{ 'code': 500, reason: '" + e.getMessage() + "' }";
        }
    }

    @GetMapping(path = "/update")
    public @ResponseBody String update(
        @RequestParam String _ID,
        @RequestParam String name,
        @RequestParam String price,
        @RequestParam String stock) {
            if(name == null || name.length() < 1)
                return "{ 'code': 500, 'reason': 'Invalid name' }";
            try {
                Product p = repo.findOne(Long.parseLong(_ID))
                    .setName(name)
                    .setPrice(Float.parseFloat(price))
                    .setStock(Integer.parseInt(stock));
                repo.save(p);
                return "{ 'code': 200 }";
            } catch(Exception e) {
                return "{ 'code': 500, 'reason': '" + e.getMessage() + "' }";
            }
    }

    @GetMapping(path = "/all")
    public @ResponseBody Iterable<Product> getProducts() {
        return repo.findAll();
    }
}

5. Create Auto-Repository Interface and Launcher

• Auto-Repository Interface

Create class com.murez.branch.test.ProductRepository

package com.murez.branch.test;
import com.murez.branch.test.entity.Product;
import org.springframework.data.repository.CrudRepository;

public interface ProductRepository extends CrudRepository<Product, Long> { }

This class will be automatically implemented by Spring in a bean.

• Main Function

Create class com.murez.branch.test.App

package com.murez.branch.test;
@org.springframework.boot.autoconfigure.SpringBootApplication
public class App {
    public static void main(String[] args) {
        org.springframework.boot.SpringApplication.run(App.class, args);
    }
}

Deployment

1. Using ./gradlew bootRun
   Open Command Prompt, and access to project directory. Then hit gradlew bootRun. The result as seen below,
   

2. Using JAR File

   • Open Command Prompt, and access to project directory. Then hit gradlew build. The result as seen below,
     
   • Then, hit java -jar build/libs/murez-db-0.1.0.jar. The result as the same as seen before.
     

Test

Open your browser and hit several URL as follows:

• Add New Product

  • http://localhost:8080/demo/add?name=Baby Shampoo&price=24&stock=367
  • http://localhost:8080/demo/add?name=Potato Snack&price=13&stock=127

  Result

  <sup>Response
  
  Records</sup>
  

2. Update an Existing Product

http://localhost:8080/demo/update?name=Baby%20Shampoo&price=24&stock=13&_ID=1
Records

3. Drop Old Product

http://localhost:8080/demo/drop?_ID=1
Records

Thank you!

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