Java Back-End Basics: Start Your Development Tutorial

Setting Up Your Java Development Environment

Installing the Java Development Kit (JDK)

To develop in Java, install a JDK. Refer to Oracle for official downloads and guidance: oracle.com. JDK 17 and JDK 21 are common choices; JDK 21 includes virtual threads (Project Loom) and newer language features. After installation, verify with:

java -version

Set JAVA_HOME in your OS environment variables to the JDK install path (required by many build tools and IDEs).

Configuring Your Integrated Development Environment (IDE)

Popular IDEs: IntelliJ IDEA (recommended for Java), Eclipse, Visual Studio Code. Install Java-specific plugins (e.g., Java support, Spring tools). After installation, create a simple project to confirm the toolchain:

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

Run the program from your IDE or via javac and java on the command line to validate compilation and runtime.

Exploring Java Frameworks for Back-End Applications

Frameworks and libraries to know

• Spring Boot (e.g., Spring Boot 3.2.1) — web, data, security, and microservices support
• Hibernate (JPA provider) — ORM for relational databases
• Spring Data JPA — repository abstractions for JPA
• Apache Kafka — event streaming and messaging
• HikariCP — high-performance JDBC connection pool

Spring Boot combines starters (spring-boot-starter-web, spring-boot-starter-data-jpa) to reduce boilerplate and embeds a servlet container (Tomcat/Jetty) for local runs. For official Spring resources, see the root Spring site: spring.io.

Building Your First Java Back-End Application

Overview: full lifecycle example (Maven + Spring Boot + PostgreSQL)

This section provides a minimal, complete Spring Boot application demonstrating the entity → repository → service → controller flow, plus configuration and Docker packaging. The example uses:

• Spring Boot 3.2.1
• spring-boot-starter-web, spring-boot-starter-data-jpa
• PostgreSQL JDBC driver
• HikariCP (default in Spring Boot 3)
• Build with Maven (pom.xml shown) and alternative Gradle notes in the next section

pom.xml (essential parts)

<project xmlns="http://maven.apache.org/POM/4.0.0" ...>
  <modelVersion>4.0.0</modelVersion>
  <parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>3.2.1</version>
    <relativePath/>
  </parent>

  <groupId>com.example</groupId>
  <artifactId>product-api</artifactId>
  <version>0.0.1-SNAPSHOT</version>

  <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>org.postgresql</groupId>
      <artifactId>postgresql</artifactId>
      <scope>runtime</scope>
    </dependency>
  </dependencies>

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

Entity (Product.java)

package com.example.productapi.model;

import jakarta.persistence.*;

@Entity
public class Product {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;
    private String description;
    private double price;

    // Constructors
    public Product() {}

    public Product(String name, String description, double price) {
        this.name = name;
        this.description = description;
        this.price = price;
    }

    // Getters and setters (encapsulation)
    public Long getId() { return id; }
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public String getDescription() { return description; }
    public void setDescription(String description) { this.description = description; }
    public double getPrice() { return price; }
    public void setPrice(double price) { this.price = price; }
}

Repository (ProductRepository.java)

package com.example.productapi.repository;

import com.example.productapi.model.Product;
import org.springframework.data.jpa.repository.JpaRepository;

public interface ProductRepository extends JpaRepository { }

Service (ProductService.java)

package com.example.productapi.service;

import com.example.productapi.model.Product;
import com.example.productapi.repository.ProductRepository;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class ProductService {
    private final ProductRepository repo;

    public ProductService(ProductRepository repo) {
        this.repo = repo;
    }

    public List findAll() { return repo.findAll(); }
    public Product save(Product p) { return repo.save(p); }
}

Controller (ProductController.java)

package com.example.productapi.controller;

import com.example.productapi.model.Product;
import com.example.productapi.service.ProductService;
import org.springframework.web.bind.annotation.*;

import java.util.List;

@RestController
@RequestMapping("/api/products")
public class ProductController {
    private final ProductService service;

    public ProductController(ProductService service) { this.service = service; }

    @GetMapping
    public List all() { return service.findAll(); }

    @PostMapping
    public Product create(@RequestBody Product p) { return service.save(p); }
}

application.properties (local dev)

spring.datasource.url=jdbc:postgresql://localhost:5432/productdb
spring.datasource.username=${DB_USER:postgres}
spring.datasource.password=${DB_PASS:password}
spring.jpa.hibernate.ddl-auto=update
server.port=8080

Note: use environment variables (or externalized configuration) for credentials and avoid committing secrets to version control.

Dockerfile (simple)

FROM eclipse-temurin:17-jdk-jammy
VOLUME /tmp
ARG JAR_FILE=target/product-api-0.0.1-SNAPSHOT.jar
COPY ${JAR_FILE} app.jar
ENTRYPOINT ["java","-jar","/app.jar"]

Run locally and test

1. Start PostgreSQL (local or container).
2. mvn spring-boot:run
3. Test: curl -X GET http://localhost:8080/api/products

Troubleshooting tips

• Port in use: check process with lsof -i :8080 (or OS equivalent).
• Connection refused to DB: validate spring.datasource.url and network access (container linking or host mapping).
• Dependency conflicts: run mvn dependency:tree to inspect versions.

Data Encapsulation and Inheritance (Examples)

The introduction promised explicit coverage of encapsulation and inheritance. Here are concise, correct examples showing how they apply to back-end models and services.

Encapsulation

Encapsulation hides internal state and exposes behavior through methods. In the Product entity above, fields are private and accessed via getters/setters. This prevents external code from placing the entity into an invalid state without validation.

public class Account {
    private String accountId;
    private double balance;

    public String getAccountId() { return accountId; }

    // enforce invariant: balance cannot be negative
    public void deposit(double amount) {
        if (amount <= 0) throw new IllegalArgumentException("amount must be positive");
        this.balance += amount;
    }

    public double getBalance() { return balance; }
}

Inheritance

Inheritance enables shared behavior. Use it for domain hierarchies or DTO specialization, but avoid overusing it—prefer composition for flexibility.

public abstract class BaseEntity {
    private Long id;
    private Instant createdAt;

    public Long getId() { return id; }
    public Instant getCreatedAt() { return createdAt; }
}

@Entity
public class Product extends BaseEntity {
    private String name;
    // additional fields
}

Here, Product reuses common fields from BaseEntity. With JPA, annotate the base class correctly (e.g., @MappedSuperclass) when needed.

Maven & Gradle: Dependency Management

Dependency management is central to reproducible builds and transitive dependency control. Below are minimal setups and common tasks.

Maven basics

• pom.xml declares dependencies, plugins, and the parent (spring-boot-starter-parent).
• Common commands: mvn clean package, mvn spring-boot:run, and mvn dependency:tree.
• Use <dependencyManagement> or a BOM to lock versions across multiple modules.

Gradle basics (Kotlin DSL example)

plugins {
  id("org.springframework.boot") version "3.2.1"
  id("io.spring.dependency-management") version "1.1.0"
  kotlin("jvm") version "1.9.10" // if using Kotlin
}

dependencies {
  implementation("org.springframework.boot:spring-boot-starter-web")
  implementation("org.springframework.boot:spring-boot-starter-data-jpa")
  runtimeOnly("org.postgresql:postgresql")
}

Gradle is fast for iterative development; Maven is conventional for many enterprise shops. Choose based on team preference and CI compatibility.

Dependency security and supply chain

• Scan dependencies for known vulnerabilities (use tools like OWASP Dependency-Check or integrated solutions in CI).
• Pin or centrally manage versions to avoid unexpected transitive upgrades.
• Use repository managers (e.g., Nexus or Artifactory) in organizations to control external artifact access.

Best Practices and Resources for Java Developers

Effective Resource Management

Key techniques:

• Connection pooling (HikariCP is used by default in Spring Boot) to reuse DB connections and reduce latency.
• Caching (Spring Cache + Redis) for hot reads—profile cache hit rates and TTLs to avoid stale data issues.
• try-with-resources for I/O to avoid leaks.
• Profile and load-test (JMeter, Gatling) to find bottlenecks before production.

Security & Configuration

• Never store secrets in source control—use environment variables, cloud secret stores, or Vault.
• Enable TLS for production traffic, and validate CORS and authentication flows for public APIs.
• Use principle of least privilege for database users and service accounts.

Community & Learning Resources

Official and community resources (root domains):

• Oracle Java
• Spring
• GitHub