@CachePut for updating cache in Spring Boot - Mini Project: Build & Apply

Using @CachePut to Update Cache in Spring Boot

📖 Scenario: You are building a simple Spring Boot service that manages product prices. You want to cache product prices to improve performance. When a product price is updated, you want to update the cache immediately to keep it fresh.

🎯 Goal: Build a Spring Boot service with a method that updates a product price and uses @CachePut to update the cache with the new price.

📋 What You'll Learn

Create a Map<String, Double> called productPrices with initial product prices

Create a String variable called cacheName with value "prices"

Create a method updatePrice that takes String product and Double price and updates productPrices

Annotate updatePrice with @CachePut to update the cache named prices

💡 Why This Matters

🌍 Real World

Caching updated data in services is common to improve performance and keep data fresh in web applications.

💼 Career

Understanding @CachePut is important for backend developers working with Spring Boot to manage cache updates efficiently.

1

Create initial product prices map

Create a Map<String, Double> called productPrices with these exact entries: "apple" with 1.0, "banana" with 0.5, and "orange" with 0.8.

Spring Boot

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

public class PriceService {
    // Your code here
}

Hint

Use new HashMap<>() and add entries with put.

2

Add cache name variable

Add a String variable called cacheName and set it to the exact value "prices".

Spring Boot

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

public class PriceService {
    Map productPrices = new HashMap() {{
        put("apple", 1.0);
        put("banana", 0.5);
        put("orange", 0.8);
    }};
    // Your code here
}

Hint

Declare a String variable and assign the value "prices".

3

Create updatePrice method with cache update

Create a public method updatePrice that takes String product and Double price. Inside, update productPrices by putting the new price for the product. Annotate this method with @CachePut(cacheNames = "prices", key = "#product") to update the cache entry for the product.

Spring Boot

import java.util.Map;
import java.util.HashMap;
import org.springframework.cache.annotation.CachePut;

public class PriceService {
    Map productPrices = new HashMap() {{
        put("apple", 1.0);
        put("banana", 0.5);
        put("orange", 0.8);
    }};
    String cacheName = "prices";

    // Your code here
}

Hint

Use @CachePut with cacheNames = "prices" and key = "#product". Return the updated price.

4

Add class-level annotation and complete service

Add the @Service annotation to the PriceService class to make it a Spring service component.

Spring Boot

import java.util.Map;
import java.util.HashMap;
import org.springframework.cache.annotation.CachePut;
import org.springframework.stereotype.Service;

// Your code here
public class PriceService {
    Map productPrices = new HashMap() {{
        put("apple", 1.0);
        put("banana", 0.5);
        put("orange", 0.8);
    }};
    String cacheName = "prices";

    @CachePut(cacheNames = "prices", key = "#product")
    public Double updatePrice(String product, Double price) {
        productPrices.put(product, price);
        return price;
    }
}

Hint

Import and add @Service annotation above the class declaration.

Practice

1. What is the primary purpose of the @CachePut annotation in Spring Boot?

easy

A. To update the cache with the method's return value after execution

B. To clear all entries in the cache before method execution

C. To cache the method result only if it is not already cached

D. To disable caching for the annotated method

Solution

1. Step 1: Understand the role of @CachePut

   @CachePut is used to update the cache with fresh data after the method runs, unlike @Cacheable which caches only if data is absent.

2. Step 2: Compare options with @CachePut behavior

   Only To update the cache with the method's return value after execution correctly describes updating the cache after method execution. Others describe different caching behaviors.

3. Final Answer:

   To update the cache with the method's return value after execution -> Option A

4. Quick Check:

   @CachePut updates cache after method runs [OK]

Hint: Remember: @CachePut always updates cache after method runs [OK]

Common Mistakes:

• Confusing @CachePut with @Cacheable
• Thinking @CachePut clears cache
• Assuming it caches only if absent

2. Which of the following is the correct syntax to use @CachePut to update a cache named "users" with a key based on the method parameter id?

easy

A. @CachePut(cacheName = "users", key = "id")

B. @CachePut(value = "users", key = "#id")

C. @CachePut(name = "users", key = "id")

D. @CachePut(cache = "users", key = "#id")

Solution

1. Step 1: Recall correct attribute names for @CachePut

   The correct attribute for cache name is 'value' or 'cacheNames', and SpEL expressions for keys use '#'.

2. Step 2: Analyze each option's syntax

   @CachePut(value = "users", key = "#id") uses 'value' and '#id' correctly. Others use incorrect attribute names or miss the '#' for SpEL.

3. Final Answer:

   @CachePut(value = "users", key = "#id") -> Option B

4. Quick Check:

   Use 'value' and '#param' for key in @CachePut [OK]

Hint: Use 'value' for cache name and '#' before param in key [OK]

Common Mistakes:

• Using wrong attribute names like cacheName or cache
• Missing '#' in key expression
• Using plain string instead of SpEL for key

3. Given the following method in a Spring Boot service:

@CachePut(value = "products", key = "#product.id")
public Product updateProduct(Product product) {
    product.setPrice(product.getPrice() + 10);
    return product;
}

What will be the effect on the cache when this method is called with a product having id=5 and price=100?

medium

A. The cache is not affected because @CachePut only caches if absent

B. The cache entry with key 5 is removed from the cache

C. The cache entry with key 5 is updated with the product having price 110

D. A new cache entry with key 110 is added

Solution

1. Step 1: Understand @CachePut behavior on method call

   @CachePut updates the cache entry with the key specified after the method returns the updated object.

2. Step 2: Analyze the method logic and cache key

   The method increases price by 10 and returns the product. The key is product.id which is 5, so cache key 5 is updated with product price 110.

3. Final Answer:

   The cache entry with key 5 is updated with the product having price 110 -> Option C

4. Quick Check:

   @CachePut updates cache key with returned value [OK]

Hint: Returned value updates cache at key specified [OK]

Common Mistakes:

• Thinking cache key changes to price
• Assuming cache entry is removed
• Confusing @CachePut with @Cacheable

4. Consider this method annotated with @CachePut:

@CachePut(value = "orders", key = "#order.id")
public Order updateOrder(Order order) {
    // missing return statement
}

What is the problem with this code?

medium

A. The method should be annotated with @Cacheable instead

B. The key expression is invalid and causes a syntax error

C. The cache name 'orders' is not allowed in @CachePut

D. The method does not return a value, so cache cannot be updated

Solution

1. Step 1: Check method return requirement for @CachePut

   @CachePut requires the method to return a value to update the cache with that value.

2. Step 2: Identify missing return statement issue

   The method lacks a return statement, so no value is returned to update the cache, causing runtime issues.

3. Final Answer:

   The method does not return a value, so cache cannot be updated -> Option D

4. Quick Check:

   @CachePut needs method return to update cache [OK]

Hint: Always return updated value when using @CachePut [OK]

Common Mistakes:

• Forgetting to return the updated object
• Confusing cache name attribute
• Using @Cacheable instead of @CachePut incorrectly

5. You have a method that updates a user's email and you want to ensure the cache entry for that user is updated immediately after the change. Which approach correctly uses @CachePut to achieve this, assuming the method signature is public User updateEmail(Long userId, String newEmail)?

hard

A. @CachePut(value = "users", key = "#userId")
public User updateEmail(Long userId, String newEmail) {
User user = userRepository.findById(userId);
user.setEmail(newEmail);
userRepository.save(user);
return user;
}

B. @CachePut(value = "users", key = "#newEmail")
public User updateEmail(Long userId, String newEmail) {
User user = userRepository.findById(userId);
user.setEmail(newEmail);
userRepository.save(user);
return user;
}

C. @CachePut(value = "users")
public void updateEmail(Long userId, String newEmail) {
User user = userRepository.findById(userId);
user.setEmail(newEmail);
userRepository.save(user);
}

D. @CachePut(key = "#userId")
public User updateEmail(Long userId, String newEmail) {
User user = userRepository.findById(userId);
user.setEmail(newEmail);
userRepository.save(user);
return user;
}

Solution

1. Step 1: Verify correct cache name and key usage

   @CachePut(value = "users", key = "#userId") public User updateEmail(Long userId, String newEmail) { User user = userRepository.findById(userId); user.setEmail(newEmail); userRepository.save(user); return user; } uses 'value = "users"' and key '#userId', correctly identifying the cache and key.

2. Step 2: Check method return and update logic

   @CachePut(value = "users", key = "#userId") public User updateEmail(Long userId, String newEmail) { User user = userRepository.findById(userId); user.setEmail(newEmail); userRepository.save(user); return user; } returns the updated User object, which is necessary for @CachePut to update the cache. Other options either use wrong key, no return, or missing cache name.

3. Final Answer:

   @CachePut(value = "users", key = "#userId") public User updateEmail(Long userId, String newEmail) { User user = userRepository.findById(userId); user.setEmail(newEmail); userRepository.save(user); return user; } -> Option A

4. Quick Check:

   Return updated object and use correct cache name and key [OK]

Hint: Return updated object and use correct cache name and key [OK]

Common Mistakes:

• Using wrong key expression
• Not returning updated object
• Omitting cache name in annotation