Handbooks / Spring Boot / Chapter 8

Caching, Async and Scheduling

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Spring BootPage 1

Caching, Async and Scheduling Mental Model

1. Proxy-Based AOP

Calleranother bean
Spring proxyintercepts call
Extra behaviourcache, thread, timer
Real methodyour code

Opt-in switches on a @Configuration class: @EnableCaching, @EnableAsync, @EnableScheduling
No switch = annotations silently ignored

2. When the Proxy Is Skipped

this.method() self-invocation: @Cacheable, @Async, @Transactional do nothing
private methods are not intercepted; use public
final class or method cannot be proxied
Object must be a Spring-managed bean, not new

java

public User first() {
    return this.get(1L); // no proxy
}
@Cacheable("users")
public User get(long id) { ... }

get() always runs; call it from another bean

3. Cache Facade

CacheManager hands out named Cache objects
Provider is swappable; annotated code stays unchanged

@Cacheableannotation
CacheManagerfacade
Cache usersnamed cache
Caffeine or Redisprovider

Go through the proxy

Call the annotated method from another bean. A call inside the same class is never intercepted.

Spring BootPage 2

Cacheable, CacheEvict and CachePut Workflow

1. The @Cacheable flow

Callthrough proxy
Lookupcache + key
Hitbody skipped
Missrun, then store

@Cacheable("users") checks the cache first
Default key = all arguments (SimpleKey if none)
Override with SpEL: key = "#id" or key = "#user.id"

2. Three annotations

Annotation	Method runs?	Cache effect
`@Cacheable`	only on a miss	reads, or fills
`@CachePut`

Spring BootPage 3

Cache Providers: Caffeine vs Redis

1. Two Providers

	Caffeine	Redis
Where	In-process	Out-of-process, shared
Speed	Fastest, no network hop	Network + serialization cost
Instances	Own copy each, entries drift	Consistent across instances
Restart	Cache lost	Survives

2. Configuration

Caffeine: one spec string sets size and expiry

Spring BootPage 4

Async Methods and Executors

1. What @Async Does

On a public bean method: returns immediately, body runs on an executor thread
Return void, Future or CompletableFuture<T>

Callercalls proxy
Proxysubmits task
Executor threadruns body

2. Executors

Setting	Value
Default bean	`applicationTaskExecutor` (ThreadPoolTaskExecutor)
Default sizing	core 8, queue unbounded
Named pool

Spring BootPage 5

Scheduled Tasks and Thread Pool Pitfalls

1. Triggers

Attribute	Timing
`fixedRate=5000`	every 5s, start to start
`fixedDelay=5000`	5s after the previous run finishes
`initialDelay`	postpones the first run

java

@Scheduled(cron = "0 0 2 * * *", zone = "Asia/Kolkata")

second minute hour day month weekday: daily 02:00 in that zone

2. Pool pitfalls

Default scheduler is single-threaded: one slow job delays all others
Fix: spring.task.scheduling.pool.size or a TaskScheduler bean

Spring BootPage 6

Spring Caching, Async and Scheduling Cheat Sheet

1. Switches and the proxy

@EnableCaching, @EnableAsync, @EnableScheduling on a @Configuration class
Calls must go through the proxy: this.method() skips it
Method is public on a Spring bean

2. Cache annotations and providers

Annotation	Does
`@Cacheable`	reads, or runs and fills
`@CachePut`	always runs, refreshes
`@CacheEvict(allEntries=true)`	clears the cache

Spring BootPage 7

Check yourself

twice(1) calls get(1) two times inside the same bean, and get has @Cacheable. How many times does the body of get run?

Twice: this.get() bypasses the proxy
No cache lookup happens, so nothing is ever stored
Fix: call from another bean, or move get out

@Cacheable("x") public int get(int id) { ... }
public int twice(int id) { return get(id) + get(id); }

An executor has core 2, max 10 and the default queue. You submit 20 slow tasks. How many threads run?

Only 2: the default queue is unbounded and never fills
So the pool never grows past core, and max is ignored
Set queueCapacity to let it grow

A fixedRate=5000 job takes 8s on the default single-threaded scheduler. When does each run start?

Every ~8s, right when the previous run ends

Mode	Timing
`fixedRate`	start to start
`fixedDelay`	end to start
`cron`	6 fields plus `zone`