@Cacheable for read caching in Spring Boot - Step-by-Step Execution

Concept Flow - @Cacheable for read caching

Method call with key

↓

Check cache for key

↓

Return cached

↓

Return value

↓

Return value

When a method annotated with @Cacheable is called, Spring checks if the result is in cache. If yes, it returns cached data. If no, it runs the method, caches the result, then returns it.

Execution Sample

Spring Boot

@Cacheable("books")
public Book findBookById(Long id) {
  // simulate slow DB call
  return bookRepository.findById(id).orElse(null);
}

This method caches the book found by id. On first call, it fetches from DB and caches. Next calls with same id return cached book.

Execution Table

Step	Method Call	Cache Check	Cache Hit?	Action	Returned Value
1	findBookById(1)	Check cache for key=1	No	Call method, fetch from DB	Book{id=1, title='Java Basics'}
2	Store result in cache with key=1	-	-	Cache updated	-
3	findBookById(1)	Check cache for key=1	Yes	Return cached value	Book{id=1, title='Java Basics'}
4	findBookById(2)	Check cache for key=2	No	Call method, fetch from DB	Book{id=2, title='Spring Guide'}
5	Store result in cache with key=2	-	-	Cache updated	-
6	findBookById(2)	Check cache for key=2	Yes	Return cached value	Book{id=2, title='Spring Guide'}

💡 Method calls end when all requested keys are served either from cache or DB.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 4	After Step 5	Final
cache	empty	empty	{1: Book{id=1}}	{1: Book{id=1}}	{1: Book{id=1}, 2: Book{id=2}}	{1: Book{id=1}, 2: Book{id=2}}

Key Moments - 2 Insights

Why does the method not run on the second call with the same id?

Because the cache already has the result for that id (see execution_table step 3), so Spring returns cached data without running the method.

What happens if the cache does not have the key?

The method runs normally to get fresh data, then the result is stored in cache (see steps 1 and 2).

Visual Quiz - 3 Questions

Look at the execution_table, what is returned at step 3?

A Cached Book{id=1, title='Java Basics'}

B New DB call result

C Null

D Error

💡 Hint

Check the 'Returned Value' column at step 3 in execution_table.

At which step does the cache first get updated with key=2?

A Step 6

B Step 4

C Step 5

D Step 3

💡 Hint

Look for 'Store result in cache with key=2' in execution_table.

If the cache was empty initially, what would happen at step 1?

A Cache returns stale data

B Method runs and caches result

C Method returns null

D Method throws exception

💡 Hint

See execution_table step 1 and 2 for cache miss behavior.

Concept Snapshot

@Cacheable annotation caches method results by key.
On method call, cache is checked first.
If hit, cached value is returned immediately.
If miss, method runs and result is cached.
Improves performance by avoiding repeated DB calls.

Full Transcript

The @Cacheable annotation in Spring Boot helps store method results in a cache. When a method with @Cacheable is called, Spring checks if the result for the given key is already cached. If yes, it returns the cached result without running the method again. If no, it runs the method, stores the result in the cache, and then returns it. This saves time by avoiding repeated slow operations like database calls. For example, calling findBookById(1) first time fetches from DB and caches the book. The next call with id 1 returns the cached book instantly. The execution table shows each step: checking cache, method execution, caching, and returning values. The variable tracker shows how the cache grows as new keys are added. This caching pattern is useful for read-heavy methods where data changes infrequently.