@Cacheable for read caching in Spring Boot - Performance & Optimization

Performance: @Cacheable for read caching

MEDIUM IMPACT

This affects the speed of serving repeated read requests by avoiding repeated method executions and database hits.

Improving read performance by caching method results

Spring Boot

@Cacheable("dataCache")
@GetMapping("/data")
public Data getData() {
    return database.queryData();
}

Caches the result on first call and serves cached data on subsequent calls, avoiding DB hits.

📈 Performance GainReduces response time to under 5ms after first call, improves LCP

Improving read performance by caching method results

Spring Boot

@GetMapping("/data")
public Data getData() {
    return database.queryData();
}

Every request triggers a database query causing slower response and higher load.

📉 Performance CostBlocks rendering for 50-200ms per request depending on DB speed

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
No caching, direct DB call	N/A	N/A	Higher due to slower server response	[X] Bad
@Cacheable caching method result	N/A	N/A	Lower due to faster server response	[OK] Good

Rendering Pipeline

When a cached method is called, Spring checks the cache before executing the method. If cached data exists, it returns immediately, skipping database access and heavy computation.

→Server Processing

→Network Transfer

→Browser Rendering

⚠️ BottleneckServer Processing (database query and method execution)

Core Web Vital Affected

LCP

This affects the speed of serving repeated read requests by avoiding repeated method executions and database hits.

Optimization Tips

1Use @Cacheable on methods that return data that does not change often.

2Avoid caching methods with side effects or frequently changing data.

3Monitor cache size and eviction policies to prevent stale data issues.

Performance Quiz - 3 Questions

What is the main performance benefit of using @Cacheable on a read method?

A It improves the browser's rendering speed directly.

B It reduces the size of the database.

C It avoids repeated database queries by returning cached results.

D It compresses the network response.

DevTools: Network

How to check: Open DevTools, go to Network tab, observe response times for repeated requests to the cached endpoint.

What to look for: Faster response times on repeated requests indicate effective caching.

Practice

1. What is the main purpose of using @Cacheable in a Spring Boot application?

easy

A. To store the result of a method call and reuse it for the same inputs to improve performance.

B. To delete data from the database automatically.

C. To make a method run asynchronously in a separate thread.

D. To validate user input before processing.

Solution

1. Step 1: Understand what @Cacheable does

   @Cacheable stores the output of a method so that if the method is called again with the same inputs, it returns the stored result instead of running the method again.

2. Step 2: Identify the main benefit

   This caching avoids repeated slow or expensive operations, improving performance.

3. Final Answer:

   To store the result of a method call and reuse it for the same inputs to improve performance. -> Option A

4. Quick Check:

   @Cacheable purpose = store and reuse results [OK]

Hint: Remember: @Cacheable speeds up repeated reads by caching results [OK]

Common Mistakes:

• Thinking @Cacheable deletes or modifies data
• Confusing caching with asynchronous execution
• Assuming it validates inputs automatically

2. Which of the following is the correct way to use @Cacheable on a method named getUserById with cache name "users"?

easy

A. @Cacheable(cacheNames = "users") public User getUserById(Long id) { ... }

B. @Cacheable(name = "users") public User getUserById(Long id) { ... }

C. @Cacheable(cache = "users") public User getUserById(Long id) { ... }

D. @Cacheable(cacheName = "users") public User getUserById(Long id) { ... }

Solution

1. Step 1: Recall the correct attribute name for cache name

   The correct attribute to specify cache names in @Cacheable is cacheNames.

2. Step 2: Match the syntax with the method

   @Cacheable(cacheNames = "users") public User getUserById(Long id) { ... } uses @Cacheable(cacheNames = "users") which is correct syntax for Spring Boot caching.

3. Final Answer:

   @Cacheable(cacheNames = "users") public User getUserById(Long id) { ... } -> Option A

4. Quick Check:

   Correct attribute = cacheNames [OK]

Hint: Use cacheNames, not name or cache, in @Cacheable [OK]

Common Mistakes:

• Using wrong attribute like name or cache instead of cacheNames
• Missing parentheses or quotes around cache name
• Placing @Cacheable on class instead of method

3. Given the following code snippet, what will be printed when getData(5) is called twice?

@Cacheable(cacheNames = "dataCache")
public int getData(int id) {
    System.out.println("Fetching data for " + id);
    return id * 2;
}

medium

A. Fetching data for 5
Fetching data for 10

B. Fetching data for 5
Fetching data for 5

C. No output printed

D. Fetching data for 5

Solution

1. Step 1: Understand caching effect on method calls

   The first call to getData(5) runs the method and prints "Fetching data for 5". The result (10) is cached.

2. Step 2: Analyze the second call with same argument

   The second call with argument 5 returns cached result without running the method body, so no print happens.

3. Final Answer:

   Fetching data for 5 -> Option D

4. Quick Check:

   Cached call skips print = only one print [OK]

Hint: Cached calls skip method body, so no repeated prints [OK]

Common Mistakes:

• Assuming method runs every time and prints twice
• Thinking cache stores only values, not skips method
• Confusing argument values causing cache miss

4. Identify the error in the following code using @Cacheable:

@Cacheable(cacheNames = "items")
public Item getItem(Long id) {
    return itemRepository.findById(id).get();
}

// Usage
getItem(null);

medium

A. Calling getItem with null causes NullPointerException because cache key is null.

B. Cache name "items" is invalid and causes syntax error.

C. Missing @EnableCaching annotation causes caching to fail silently.

D. Method must be static to use @Cacheable.

Solution

1. Step 1: Check required configuration for caching

   @EnableCaching must be present on a @Configuration class to activate Spring's caching support. Without it, @Cacheable has no effect and caching fails silently.

2. Step 2: Rule out distractors

   Cache name "items" is valid. Null arguments are handled via NullValue.INSTANCE in the default key generator, no exception from cache key. Methods do not need to be static.

3. Final Answer:

   Missing @EnableCaching annotation causes caching to fail silently. -> Option C

4. Quick Check:

   @EnableCaching required for caching [OK]

Hint: Always add @EnableCaching to a @Configuration class [OK]

Common Mistakes:

• Assuming cache name "items" is invalid
• Thinking null causes NullPointerException due to cache key
• Believing method must be static for @Cacheable

5. You want to cache results of a method findProduct(String category, int id) but only cache when category is not null or empty. Which @Cacheable usage correctly implements this conditional caching?

hard

A. @Cacheable(cacheNames = "products", unless = "#category == null || #category == ''")
public Product findProduct(String category, int id) { ... }

B. @Cacheable(cacheNames = "products", condition = "#category != null && #category != ''")
public Product findProduct(String category, int id) { ... }

C. @Cacheable(cacheNames = "products", key = "#category + #id")
public Product findProduct(String category, int id) { ... }

D. @Cacheable(cacheNames = "products", condition = "#id > 0")
public Product findProduct(String category, int id) { ... }

Solution

1. Step 1: Understand conditional caching with condition

   The condition attribute controls when caching happens. It caches only if the condition is true.

2. Step 2: Analyze each option

   @Cacheable(cacheNames = "products", condition = "#category != null && #category != ''") public Product findProduct(String category, int id) { ... } caches only if category is not null and not empty, matching the requirement. @Cacheable(cacheNames = "products", unless = "#category == null || #category == ''") public Product findProduct(String category, int id) { ... } uses unless which caches unless the condition is true, so it inverts logic. @Cacheable(cacheNames = "products", key = "#category + #id") public Product findProduct(String category, int id) { ... } only sets key, no condition. @Cacheable(cacheNames = "products", condition = "#id > 0") public Product findProduct(String category, int id) { ... } caches based on id, not category.

3. Final Answer:

   @Cacheable(cacheNames = "products", condition = "#category != null && #category != ''") public Product findProduct(String category, int id) { ... } -> Option B

4. Quick Check:

   Use condition to cache only when category valid [OK]

Hint: Use condition attribute to control caching logic [OK]

Common Mistakes:

• Confusing condition and unless attributes
• Not checking for empty string in condition
• Using key attribute instead of condition for caching control