The controller reads inStockOnly from the query string and supplies products to Model. It no longer decides which stock values qualify.
findAll(false) returns every product. findAll(true) adds only products whose stock is greater than zero to the result list. That if condition is our business rule. @Service is a specialized component annotation that tells readers this class performs application operations.
Spring supplies ProductFileReader to ProductService and ProductService to ProductController. The browser never creates these Java objects. They are connected during application startup.
This project deliberately changes product 5 in products.txt to stock 0. All products therefore shows 30 rows; In-stock products shows 29. The original Stage 6 project is unchanged. The query ?inStockOnly=true selects the filtered operation.
findById returns Optional<Product>. Optional is a Java type for a value that may be absent, not a Spring annotation. The controller turns an absent product into a 404 response.
Use JDK 21+ and Maven 3.9+. Extract spring-products-service.zip and open a terminal in the spring-products-service folder containing pom.xml. Keep the source files in their supplied paths.
mvn spring-boot:runOpen http://localhost:8087/products. Keep the terminal open. Stop with Ctrl+C. If the port is occupied, change server.port in src/main/resources/application.properties, restart and use the new port in the browser.
# Choose another available port if this port is busy.
server.port=8087
Compare /products (30 rows) and /products?inStockOnly=true (29 rows). Product 5 still has a details page with stock 0. An unknown ID returns 404.
Every project file is reproduced below. Create each file at the indicated path if building manually.
/target/
<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>4.1.1</version>
<relativePath/>
</parent>
<groupId>com.edupoly</groupId>
<artifactId>spring-products-service</artifactId>
<version>1.0.0</version>
<properties>
<java.version>21</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-webmvc</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
package com.edupoly.products;
import java.math.BigDecimal;
public class Product {
private int id;
private String name;
private String category;
private BigDecimal price;
private String brand;
private int stock;
private String description;
private int warrantyMonths;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getCategory() {
return category;
}
public void setCategory(String category) {
this.category = category;
}
public BigDecimal getPrice() {
return price;
}
public void setPrice(BigDecimal price) {
this.price = price;
}
public String getBrand() {
return brand;
}
public void setBrand(String brand) {
this.brand = brand;
}
public int getStock() {
return stock;
}
public void setStock(int stock) {
this.stock = stock;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
public int getWarrantyMonths() {
return warrantyMonths;
}
public void setWarrantyMonths(int warrantyMonths) {
this.warrantyMonths = warrantyMonths;
}
}
package com.edupoly.products;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class ProductApplication {
public static void main(String[] args) {
SpringApplication.run(ProductApplication.class, args);
}
}
package com.edupoly.products;
import org.springframework.http.HttpStatus;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.server.ResponseStatusException;
@Controller
public class ProductController {
private final ProductService service;
public ProductController(ProductService service) {
this.service = service;
}
@GetMapping({"/", "/products"})
public String listProducts(
@RequestParam(name = "inStockOnly", defaultValue = "false") boolean inStockOnly,
Model model) {
model.addAttribute("products", service.findAll(inStockOnly));
return "products";
}
@GetMapping("/products/{id}")
public String productDetails(@PathVariable("id") int id, Model model) {
Product product = service.findById(id).orElseThrow(() ->
new ResponseStatusException(HttpStatus.NOT_FOUND, "Product not found"));
model.addAttribute("product", product);
return "product-details";
}
}
package com.edupoly.products;
import java.io.IOException;
import org.springframework.core.io.ClassPathResource;
import org.springframework.stereotype.Component;
import tools.jackson.databind.json.JsonMapper;
@Component
public class ProductFileReader {
private final Product[] products;
public ProductFileReader() throws IOException {
var resource = new ClassPathResource("data/products.txt");
try (var input = resource.getInputStream()) {
JsonMapper mapper = JsonMapper.builder().build();
products = mapper.readValue(input, Product[].class);
}
System.out.println("Created ProductFileReader");
}
public Product[] getProducts() {
return products;
}
}
package com.edupoly.products;
import java.util.ArrayList;
import java.util.List;
import java.util.Optional;
import org.springframework.stereotype.Service;
@Service
public class ProductService {
private final ProductFileReader reader;
public ProductService(ProductFileReader reader) {
this.reader = reader;
}
public List<Product> findAll(boolean inStockOnly) {
List<Product> selected = new ArrayList<>();
for (Product product : reader.getProducts()) {
if (!inStockOnly || product.getStock() > 0) {
selected.add(product);
}
}
return selected;
}
public Optional<Product> findById(int id) {
for (Product product : reader.getProducts()) {
if (product.getId() == id) {
return Optional.of(product);
}
}
return Optional.empty();
}
}
# Choose another available port if this port is busy.
server.port=8087
[
{
"id": 1,
"name": "Wireless Mouse",
"category": "Electronics",
"price": 699,
"brand": "EduTech",
"stock": 12,
"description": "Wireless Mouse for everyday learning, study and work. Product 1 includes a simple user guide and protective packaging.",
"warrantyMonths": 12
},
{
"id": 2,
"name": "Mechanical Keyboard",
"category": "Electronics",
"price": 3499,
"brand": "EduTech",
"stock": 19,
"description": "Mechanical Keyboard for everyday learning, study and work. Product 2 includes a simple user guide and protective packaging.",
"warrantyMonths": 12
},
{
"id": 3,
"name": "USB-C Hub",
"category": "Electronics",
"price": 1599,
"brand": "EduTech",
"stock": 26,
"description": "USB-C Hub for everyday learning, study and work. Product 3 includes a simple user guide and protective packaging.",
"warrantyMonths": 12
},
{
"id": 4,
"name": "Laptop Stand",
"category": "Electronics",
"price": 1299,
"brand": "EduTech",
"stock": 33,
"description": "Laptop Stand for everyday learning, study and work. Product 4 includes a simple user guide and protective packaging.",
"warrantyMonths": 12
},
{
"id": 5,
"name": "Webcam",
"category": "Electronics",
"price": 2199,
"brand": "EduTech",
"stock": 0,
"description": "Webcam for everyday learning, study and work. Product 5 includes a simple user guide and protective packaging.",
"warrantyMonths": 12
},
{
"id": 6,
"name": "Bluetooth Speaker",
"category": "Electronics",
"price": 2499,
"brand": "EduTech",
"stock": 47,
"description": "Bluetooth Speaker for everyday learning, study and work. Product 6 includes a simple user guide and protective packaging.",
"warrantyMonths": 12
},
{
"id": 7,
"name": "Noise-Cancelling Headphones",
"category": "Electronics",
"price": 4999,
"brand": "EduTech",
"stock": 54,
"description": "Noise-Cancelling Headphones for everyday learning, study and work. Product 7 includes a simple user guide and protective packaging.",
"warrantyMonths": 12
},
{
"id": 8,
"name": "Portable SSD",
"category": "Electronics",
"price": 6499,
"brand": "EduTech",
"stock": 61,
"description": "Portable SSD for everyday learning, study and work. Product 8 includes a simple user guide and protective packaging.",
"warrantyMonths": 12
},
{
"id": 9,
"name": "USB Flash Drive",
"category": "Electronics",
"price": 599,
"brand": "EduTech",
"stock": 68,
"description": "USB Flash Drive for everyday learning, study and work. Product 9 includes a simple user guide and protective packaging.",
"warrantyMonths": 12
},
{
"id": 10,
"name": "Monitor",
"category": "Electronics",
"price": 12999,
"brand": "EduTech",
"stock": 15,
"description": "Monitor for everyday learning, study and work. Product 10 includes a simple user guide and protective packaging.",
"warrantyMonths": 12
},
{
"id": 11,
"name": "Desk Lamp",
"category": "Electronics",
"price": 899,
"brand": "EduTech",
"stock": 22,
"description": "Desk Lamp for everyday learning, study and work. Product 11 includes a simple user guide and protective packaging.",
"warrantyMonths": 12
},
{
"id": 12,
"name": "Power Bank",
"category": "Electronics",
"price": 1799,
"brand": "EduTech",
"stock": 29,
"description": "Power Bank for everyday learning, study and work. Product 12 includes a simple user guide and protective packaging.",
"warrantyMonths": 12
},
{
"id": 13,
"name": "Smartphone Stand",
"category": "Electronics",
"price": 399,
"brand": "EduTech",
"stock": 36,
"description": "Smartphone Stand for everyday learning, study and work. Product 13 includes a simple user guide and protective packaging.",
"warrantyMonths": 12
},
{
"id": 14,
"name": "HDMI Cable",
"category": "Electronics",
"price": 499,
"brand": "EduTech",
"stock": 43,
"description": "HDMI Cable for everyday learning, study and work. Product 14 includes a simple user guide and protective packaging.",
"warrantyMonths": 12
},
{
"id": 15,
"name": "Ethernet Adapter",
"category": "Electronics",
"price": 999,
"brand": "EduTech",
"stock": 50,
"description": "Ethernet Adapter for everyday learning, study and work. Product 15 includes a simple user guide and protective packaging.",
"warrantyMonths": 12
},
{
"id": 16,
"name": "Graphics Tablet",
"category": "Electronics",
"price": 3999,
"brand": "EduTech",
"stock": 57,
"description": "Graphics Tablet for everyday learning, study and work. Product 16 includes a simple user guide and protective packaging.",
"warrantyMonths": 12
},
{
"id": 17,
"name": "Microphone",
"category": "Electronics",
"price": 2999,
"brand": "EduTech",
"stock": 64,
"description": "Microphone for everyday learning, study and work. Product 17 includes a simple user guide and protective packaging.",
"warrantyMonths": 12
},
{
"id": 18,
"name": "Laptop Backpack",
"category": "Electronics",
"price": 1499,
"brand": "EduTech",
"stock": 71,
"description": "Laptop Backpack for everyday learning, study and work. Product 18 includes a simple user guide and protective packaging.",
"warrantyMonths": 12
},
{
"id": 19,
"name": "Screen Cleaner",
"category": "Electronics",
"price": 249,
"brand": "EduTech",
"stock": 18,
"description": "Screen Cleaner for everyday learning, study and work. Product 19 includes a simple user guide and protective packaging.",
"warrantyMonths": 12
},
{
"id": 20,
"name": "Mouse Pad",
"category": "Electronics",
"price": 299,
"brand": "EduTech",
"stock": 25,
"description": "Mouse Pad for everyday learning, study and work. Product 20 includes a simple user guide and protective packaging.",
"warrantyMonths": 12
},
{
"id": 21,
"name": "Notebook",
"category": "Study Essentials",
"price": 149,
"brand": "StudyWorks",
"stock": 32,
"description": "Notebook for everyday learning, study and work. Product 21 includes a simple user guide and protective packaging.",
"warrantyMonths": 6
},
{
"id": 22,
"name": "Ballpoint Pen Set",
"category": "Study Essentials",
"price": 199,
"brand": "StudyWorks",
"stock": 39,
"description": "Ballpoint Pen Set for everyday learning, study and work. Product 22 includes a simple user guide and protective packaging.",
"warrantyMonths": 6
},
{
"id": 23,
"name": "Water Bottle",
"category": "Study Essentials",
"price": 599,
"brand": "StudyWorks",
"stock": 46,
"description": "Water Bottle for everyday learning, study and work. Product 23 includes a simple user guide and protective packaging.",
"warrantyMonths": 6
},
{
"id": 24,
"name": "Desk Organizer",
"category": "Study Essentials",
"price": 449,
"brand": "StudyWorks",
"stock": 53,
"description": "Desk Organizer for everyday learning, study and work. Product 24 includes a simple user guide and protective packaging.",
"warrantyMonths": 6
},
{
"id": 25,
"name": "Reading Light",
"category": "Study Essentials",
"price": 699,
"brand": "StudyWorks",
"stock": 60,
"description": "Reading Light for everyday learning, study and work. Product 25 includes a simple user guide and protective packaging.",
"warrantyMonths": 6
},
{
"id": 26,
"name": "Calculator",
"category": "Study Essentials",
"price": 499,
"brand": "StudyWorks",
"stock": 67,
"description": "Calculator for everyday learning, study and work. Product 26 includes a simple user guide and protective packaging.",
"warrantyMonths": 6
},
{
"id": 27,
"name": "Whiteboard",
"category": "Study Essentials",
"price": 1299,
"brand": "StudyWorks",
"stock": 14,
"description": "Whiteboard for everyday learning, study and work. Product 27 includes a simple user guide and protective packaging.",
"warrantyMonths": 6
},
{
"id": 28,
"name": "Marker Set",
"category": "Study Essentials",
"price": 299,
"brand": "StudyWorks",
"stock": 21,
"description": "Marker Set for everyday learning, study and work. Product 28 includes a simple user guide and protective packaging.",
"warrantyMonths": 6
},
{
"id": 29,
"name": "Book Stand",
"category": "Study Essentials",
"price": 799,
"brand": "StudyWorks",
"stock": 28,
"description": "Book Stand for everyday learning, study and work. Product 29 includes a simple user guide and protective packaging.",
"warrantyMonths": 6
},
{
"id": 30,
"name": "Travel Mug",
"category": "Study Essentials",
"price": 649,
"brand": "StudyWorks",
"stock": 35,
"description": "Travel Mug for everyday learning, study and work. Product 30 includes a simple user guide and protective packaging.",
"warrantyMonths": 6
}
]
body{margin:0;padding:28px 16px;background:#f5f7fb;color:#17253d;font:16px/1.6 system-ui,sans-serif}main{max-width:1100px;margin:20px auto;padding:28px;background:#fff;border:1px solid #dbe2ec;border-radius:12px}h1{margin-top:0}a{color:#2457a6;text-underline-offset:3px}.table-scroll{overflow-x:auto}table{width:100%;border-collapse:collapse}th,td{text-align:left;padding:12px;border-bottom:1px solid #dbe2ec}th{background:#edf3fc}tbody tr:hover{background:#f8faff}.detail{max-width:760px}dl{display:grid;grid-template-columns:160px minmax(0,1fr);gap:12px 20px;margin:24px 0}dt{font-weight:650}dd{margin:0;overflow-wrap:anywhere}@media(max-width:500px){main{padding:16px}dl{grid-template-columns:1fr;gap:4px}dd{margin-bottom:12px}}
.catalog-nav{margin:20px 0}form{margin:18px 0}button{padding:9px 14px;cursor:pointer}input{padding:8px;max-width:140px}form button{margin-left:8px}
<!doctype html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title th:text="${product.name}">Product details</title>
<link rel="stylesheet" th:href="@{/style.css}">
</head>
<body>
<main class="detail">
<h1>Product details</h1>
<h2 th:text="${product.name}">Wireless Mouse</h2>
<dl>
<dt>ID</dt><dd th:text="${product.id}">1</dd>
<dt>Name</dt><dd th:text="${product.name}">Wireless Mouse</dd>
<dt>Category</dt><dd th:text="${product.category}">Electronics</dd>
<dt>Price (INR)</dt><dd th:text="${product.price}">699</dd>
<dt>Brand</dt><dd th:text="${product.brand}">EduTech</dd>
<dt>Stock</dt><dd th:text="${product.stock}">12</dd>
<dt>Description</dt><dd th:text="${product.description}">Product description</dd>
<dt>Warranty (months)</dt><dd th:text="${product.warrantyMonths}">12</dd>
</dl>
<a th:href="@{/products}">Back to products</a>
</main>
</body>
</html>
<!doctype html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Products</title>
<link rel="stylesheet" th:href="@{/style.css}">
</head>
<body>
<main>
<h1>Products</h1>
<p>Stage 9: Product rules in a service. Select More details for a product.</p>
<nav class="catalog-nav"><a th:href="@{/products}">All products</a> · <a th:href="@{/products(inStockOnly=true)}">In-stock products</a></nav>
<div class="table-scroll">
<table>
<thead>
<tr><th>ID</th><th>Name</th><th>Category</th><th>Price (INR)</th><th>Action</th></tr>
</thead>
<tbody>
<tr th:each="product : ${products}">
<td th:text="${product.id}">1</td>
<td th:text="${product.name}">Wireless Mouse</td>
<td th:text="${product.category}">Electronics</td>
<td th:text="${product.price}">699</td>
<td><a th:href="@{/products/{id}(id=${product.id})}">More details</a></td>
</tr>
</tbody>
</table>
</div>
</main>
</body>
</html>
Change the stock rule from greater than zero to at least 10. Predict the filtered count from products.txt before running.
References: Spring constructor injection, Spring Data MongoDB repositories.
| Term | Our concrete example | Its place in Spring |
|---|---|---|
| @Service | ProductService | A component with the role of performing application operations. |
| Business rule | product.getStock() > 0 | Our Java condition defines which products are in stock. Spring does not invent the rule. |
| Separation of responsibilities | Controller handles HTTP; service selects products | The structure makes each class’s job easier to find. |
One small check: Point to the class, constructor or annotation that demonstrates each term before continuing.