Why caching matters for performance in Spring Boot - See It in Action

Why caching matters for performance

📖 Scenario: You are building a simple Spring Boot application that fetches user data from a slow database. To improve performance, you want to add caching so repeated requests for the same user do not hit the database every time.

🎯 Goal: Build a Spring Boot service that caches user data after the first fetch to speed up subsequent requests.

📋 What You'll Learn

Create a Map<Integer, String> to simulate a slow database with user IDs and names

Add a boolean variable cacheEnabled to control caching

Implement a method getUserName(int userId) that uses caching when cacheEnabled is true

Add a cache Map<Integer, String> to store fetched user names

💡 Why This Matters

🌍 Real World

Caching is used in real applications to speed up data access and reduce load on databases or external services.

💼 Career

Understanding caching is important for backend developers to build efficient, scalable applications.

1

DATA SETUP: Create a simulated database

Create a Map<Integer, String> called userDatabase with these exact entries: 1: "Alice", 2: "Bob", 3: "Charlie".

Spring Boot

// Your code here

Need a hint?

Use Map.of() to create the userDatabase with the exact user IDs and names.

2

CONFIGURATION: Add a cache control variable

Add a boolean variable called cacheEnabled and set it to true inside the UserService class.

Spring Boot

import java.util.Map;
import java.util.HashMap;

public class UserService {
    private Map userDatabase = Map.of(
        1, "Alice",
        2, "Bob",
        3, "Charlie"
    );
    // Your code here
}

Need a hint?

Declare cacheEnabled as a private boolean and set it to true.

3

CORE LOGIC: Implement caching in the user fetch method

Add a private Map<Integer, String> called userCache initialized as an empty HashMap. Then create a public method getUserName(int userId) that returns the user name. If cacheEnabled is true, first check userCache for the user name. If not found, get it from userDatabase, store it in userCache, and return it. If cacheEnabled is false, return directly from userDatabase.

Spring Boot

import java.util.Map;
import java.util.HashMap;

public class UserService {
    private Map userDatabase = Map.of(
        1, "Alice",
        2, "Bob",
        3, "Charlie"
    );
    private boolean cacheEnabled = true;

    // Your code here
}

Need a hint?

Use userCache.containsKey(userId) to check cache, and userCache.put(userId, userName) to store new entries.

4

COMPLETION: Add a method to clear the cache

Add a public method called clearCache() that clears all entries from userCache.

Spring Boot

import java.util.Map;
import java.util.HashMap;

public class UserService {
    private Map userDatabase = Map.of(
        1, "Alice",
        2, "Bob",
        3, "Charlie"
    );
    private boolean cacheEnabled = true;
    private Map userCache = new HashMap();

    public String getUserName(int userId) {
        if (cacheEnabled) {
            if (userCache.containsKey(userId)) {
                return userCache.get(userId);
            } else {
                String userName = userDatabase.get(userId);
                userCache.put(userId, userName);
                return userName;
            }
        } else {
            return userDatabase.get(userId);
        }
    }

    // Your code here
}

Need a hint?

Use userCache.clear() inside the clearCache() method to empty the cache.