spring_boot_starter_cache 0.4.1

Cache starter for spring_boot_dart: @Cacheable, @CachePut, @CacheEvict and @Caching on bean methods, SpEL keys, a CacheManager with TTL and size limits.

spring_boot_starter_cache

No backward compatibility before 1.0. Any release may rename or change APIs, properties and behaviour; the breaking changes are listed in each package's CHANGELOG.

Caching for spring_boot_dart applications, like spring-boot-starter-cache: put @Cacheable on a bean method and repeated calls with the same arguments return the stored result instead of running the method again.

@Service()
class Books {
  Books(this.api);
  final CatalogApi api;

  @Cacheable('books')
  Future<Book> find(String isbn) => api.load(isbn); // slow: called once per isbn

  @CacheEvict('books', key: '#isbn')
  Future<void> delete(String isbn) => api.delete(isbn);
}

In the guides: server, 8. Cache and scheduling, app, 8. Cache & scheduling.

Setup

Add the dependency and run the generator again. The starter is found and switched on automatically — no @EnableCaching.

dependencies:
  spring_boot_starter_cache: ^0.4.1

dev_dependencies:
  build_runner: ^2.17.0
  spring_core_dart_generator: ^0.4.1   # required: generates the proxies caching runs on

dart run build_runner build

One import is enough: package:spring_boot_starter_cache/spring_boot_starter_cache.dart re-exports spring_boot_dart and spring_boot_starter_logging. The starter is the only dependency an application needs: it brings the others, logging included, like every Spring Boot starter.

How it works: the generator writes an AOP proxy for each bean (option aop_proxies, all by default), and the starter registers an advisor that wraps every method with a cache annotation. So, exactly as in Spring:

• the cache applies to calls from other beans (through the proxy);
• a call through this inside the same class skips the cache. To call a cached method of your own class, inject the bean into itself with @Lazy():

@Service()
class Books implements BookService {
  Books(@Lazy() this._self);
  final BookService _self;

  @Cacheable('books')
  @override
  Book find(String isbn) => ...;

  List<Book> findAll(List<String> isbns) =>
      [for (final isbn in isbns) _self.find(isbn)]; // cached; find(isbn) is not
}

Annotations

Annotation	What it does
@Cacheable('books')	Returns the cached result when there is one; otherwise runs the method and stores the result.
@CachePut('books', key: '#isbn')	Always runs the method and stores the result (refreshes the entry); next to a @Cacheable hit only when its condition passes (one reading #result counts as passing), like Spring.
@CacheEvict('books', key: '#isbn')	Removes the entry after the method returned. allEntries: true clears the cache, beforeInvocation: true evicts before the call (also when it throws).
@Caching(cacheable: [...], put: [...], evict: [...])	Several operations on one method. Repeating an annotation works too.
@CacheConfig(cacheNames: ['books'])	On the class: default cache names, keyGenerator, cacheManager, cacheResolver for its methods.

@Cacheable, @CachePut, @CacheEvict and @Caching on the class apply to every public method that has no cache annotation of its own, like Spring (not to getters, setters or toString).

As in Spring, both are read from the class that declares the method's body and, when it has none, from its superclasses (the nearest wins): a base class with @CacheConfig or @Cacheable serves the beans that extend it; a subclass's class-level annotations don't apply to the methods it inherits.

@Cacheable('books') names one cache. For several caches, or to take them from @CacheConfig, use .of: @Cacheable.of(cacheNames: ['books', 'isbn']), @Cacheable.of(key: '#isbn') (same for CachePut.of and CacheEvict.of).

Options of @Cacheable (and, where they make sense, of the others):

Option	Meaning
key	SpEL computing the key. Default: the arguments (see below).
condition	SpEL; the cache is used only when it is true.
unless	SpEL with #result; the result is not stored when it is true.
sync	For Future methods: concurrent calls with the same key share one call.
keyGenerator	Name of a KeyGenerator bean computing the key (not with key).
cacheManager	Name of the CacheManager bean to use.
cacheResolver	Name of a CacheResolver bean that picks the caches (not with cacheManager).

As in Spring, @CacheConfig fills in only what an operation leaves open: its cache names when the operation names none, its keyGenerator when the operation sets neither key nor keyGenerator, its cacheResolver (else its cacheManager) when the operation sets neither of those.

The annotations of every proxied bean are checked when the bean is created, so a wrong combination fails the startup with the member's name (not the first call): key with keyGenerator, cacheManager with cacheResolver, sync with other operations, several caches or unless, an operation without cache names (unless a cache resolver picks them), @Cacheable / @CachePut on a method returning a Stream.

Keys

Without key, the key is made of the arguments, like Spring's SimpleKeyGenerator: no arguments → SimpleKey.empty, one argument → the argument itself, several → SimpleKey([...]), which compares by content (lists, sets and maps inside too).

key, condition and unless are SpEL expressions — plain, without #{}:

Expression	Value
#isbn	the argument named isbn
#p0, #a0	the first argument
#result	the result (unless; key and condition of @CachePut; @CacheEvict after the call)
#root.methodName	find
#root.method.name	find (also returnType, parameterTypes, parameterNames, parameterCount)
#root.args	all arguments, #root.args[1]
#root.target	the bean
#root.targetClass	the bean class name, Books
#root.caches	the cache names of the operation
@region	the bean named region

A key that comes out null (from key or a key generator) fails the call with an ArgumentError, like Spring.

Examples:

@Cacheable('books', key: '#isbn')                         // ignore the other arguments
Book find(String isbn, bool includeReviews) => ...;

@Cacheable('books', key: "#isbn + '-' + #lang")            // a combined key
Book translated(String isbn, String lang) => ...;

@Cacheable('books', condition: '#isbn.length() == 13')     // cache 13-digit ISBNs only
Book findIsbn(String isbn) => ...;

@Cacheable('books', unless: '#result == null')            // do not remember misses
Book? maybe(String isbn) => ...;

@CachePut('books', key: '#result.isbn')                   // Book is @Introspected
Book save(Book book) => ...;

Reading properties or calling methods of your own objects (#book.isbn, #result.isbn, @clock.zone()) needs @Introspected() on their class, because Dart has no reflection: the generator then writes the accessors SpEL uses. Strings, numbers, lists and maps work as they are (#isbn.length(), #tags.size()).

Async methods

Methods returning a Future cache the value, not the future: the value is stored when the future completes, a hit returns an already completed Future, and errors are never cached (the next call tries again).

@Cacheable('prices', sync: true)
Future<double> price(String isbn) => api.price(isbn);

With sync: true, calls that arrive while the first one is still running wait for it instead of calling api.price again. Like in Spring, a sync operation must be the only cache annotation of the method, use one cache and no unless.

A Stream cannot be cached — it can be listened to once, so the cached stream would fail every later caller. @Cacheable and @CachePut on a method returning a Stream fail the build (and the startup, for hand-written proxies); collect the values instead:

@Cacheable('events')
Future<List<Event>> recent() => api.events().toList();

The default: caches in memory

Without any setup the starter creates the cacheManager bean, an InMemoryCacheManager (Spring's ConcurrentMapCacheManager):

• each cache is an InMemoryCache, a map in the memory of the running app, created the first time an annotation names it ('books', ...);
• entries are lost when the app stops, and after a restart of the context (also a hot reload that changes beans): the cache starts empty;
• nothing expires and there is no size limit unless you set them (below); expired entries are dropped when they are read;
• null results are stored too (a stored null is a hit, like in Spring);
• one app, one isolate: the cache is not shared between processes, isolates or devices.

That is right for most caches: results of slow calls that are cheap to recompute after a restart.

Properties

The default manager is built from spring.cache.* (only when the application declares no CacheManager of its own):

Property	Default	Meaning
spring.cache.type	generic with Cache beans, else simple	generic: a SimpleCacheManager of the Cache beans; simple: caches in memory; none: cache nothing (annotations stay, methods always run)
spring.cache.cache-names	—	A fixed set of caches, e.g. books,authors or a YAML list; an unknown name is then an error. Without it (or empty) caches are created on first use.
spring.cache.simple.time-to-live	none	How long entries live: 10m, 30s, PT1H, or milliseconds.
spring.cache.simple.max-size	none	Maximum entries per cache; the least recently used go first.
spring.cache.simple.caches.<name>.time-to-live	—	The same for one cache.
spring.cache.simple.caches.<name>.max-size	—	The same for one cache.

# lib/resources/application.properties
spring.cache.simple.time-to-live=10m
spring.cache.simple.max-size=1000
spring.cache.simple.caches.prices.time-to-live=30s

Inject the manager to look at or clear caches by hand:

@Component()
class CacheAdmin {
  CacheAdmin(this.caches);
  final CacheManager caches;

  void clearBooks() => caches.getCache('books')?.clear();
}

Your own cache or manager

The annotations only talk to two interfaces, so anything can stand behind them:

Type	What it does	Built in
CacheManager	finds a cache by name (getCache('books'))	InMemoryCacheManager, SimpleCacheManager, NoOpCacheManager
Cache	one cache: get, put, evict, clear, ...	InMemoryCache, NoOpCache

Declare a CacheManager bean and the starter's one steps aside (it is created only when there is none). The spring.cache.* properties then no longer apply: your bean decides.

1. The default, configured in code

@Configuration()
class CacheSetup {
  @Bean()
  CacheManager cacheManager() => InMemoryCacheManager(
    cacheNames: ['books', 'prices'],                     // only these two
    defaultSpec: const CacheSpec(timeToLive: Duration(minutes: 10)),
    specs: {'prices': const CacheSpec(timeToLive: Duration(seconds: 30))},
  );
}

2. Your own storage

Implement Cache. With the CacheDefaults mixin four methods are enough (putIfAbsent, evictIfPresent and invalidate are derived from them). Then hand your caches to a SimpleCacheManager (Spring's SimpleCacheManager), alone or mixed with in-memory ones:

import 'dart:convert';

/// Any synchronous key-value storage: a file, a key-value database, ...
abstract interface class KeyValueStore {
  String? read(String key);
  void write(String key, String value);
  void delete(String key);
  void deleteAll({required String prefix});
}

/// Entries kept in the store as JSON, so they survive a restart.
final class StoreCache with CacheDefaults implements Cache {
  StoreCache(this.name, this.store);

  @override
  final String name;
  final KeyValueStore store;

  String _key(Object? key) => '$name:$key';

  @override
  ValueWrapper? get(Object? key) => switch (store.read(_key(key))) {
    null => null,                               // a miss: the method runs
    final json => ValueWrapper(jsonDecode(json)), // a hit (also a stored null)
  };

  @override
  void put(Object? key, Object? value) =>
      store.write(_key(key), jsonEncode(value));

  @override
  void evict(Object? key) => store.delete(_key(key));

  @override
  void clear() => store.deleteAll(prefix: '$name:');
}

@Configuration()
class CacheSetup {
  @Bean()
  CacheManager cacheManager(KeyValueStore store) => SimpleCacheManager([
    StoreCache('books', store),   // kept in the store
    InMemoryCache('prices'),      // in memory
  ]);
}

What to keep in mind:

• Return ValueWrapper for a hit and null for a miss. ValueWrapper(null) is a cached null; returning plain null makes the method run again.

• Keys are the method arguments (one argument: the argument itself; several: a SimpleKey), or what key: computes. A store that needs strings must turn them into strings: '$key' works for strings, numbers and SimpleKey; for your own classes override toString, or set key: '#isbn' so the key is a string anyway.

• Values are whatever the methods return. A store outside memory must serialize them: JSON for maps, lists, strings and numbers; your classes need toJson / fromJson (decode in get into the right type).

• The Cache interface is synchronous, as in Spring. For an asynchronous store (SQLite, shared_preferences in Flutter, a server), keep the entries in memory, load the stored ones in the background (until then calls are misses: the methods simply run) and write changes back in the background:

  import 'dart:async'; // unawaited
  
  final class WriteBehindCache with CacheDefaults implements Cache {
    WriteBehindCache(this.name, this.store) {
      unawaited(
        store.readAll(prefix: '$name:').then((entries) {
          entries.forEach((key, json) => _memory.putIfAbsent(
            key.substring(name.length + 1),
            () => jsonDecode(json),
          ));
        }),
      );
    }
  
    @override
    final String name;
    final AsyncStore store;               // Future-based API
    final _memory = <String, Object?>{};
  
    @override
    ValueWrapper? get(Object? key) =>
        _memory.containsKey('$key') ? ValueWrapper(_memory['$key']) : null;
  
    @override
    void put(Object? key, Object? value) {
      _memory['$key'] = value;
      unawaited(store.write('$name:$key', jsonEncode(value)));
    }
  
    @override
    void evict(Object? key) {
      _memory.remove('$key');
      unawaited(store.delete('$name:$key'));
    }
  
    @override
    void clear() {
      _memory.clear();
      unawaited(store.deleteAll(prefix: '$name:'));
    }
  }
  

• Errors thrown by your cache reach the caller of the cached method (Spring's default too); catch them inside the cache if a broken store should only mean "no cache".

3. Caches created on demand

SimpleCacheManager knows only the caches it was given (@Cacheable('other') then fails with "Cannot find cache named 'other'"). To create caches when they are first named, implement CacheManager:

final class StoreCacheManager implements CacheManager {
  StoreCacheManager(this.store);
  final KeyValueStore store;
  final _caches = <String, Cache>{};

  @override
  Cache? getCache(String name) =>
      _caches.putIfAbsent(name, () => StoreCache(name, store));

  @override
  Iterable<String> get cacheNames => _caches.keys;
}

4. Several managers

Keep the starter's manager (or your main one) for most methods and use another one for some: give it a name, hide it from injection by type (autowireCandidate: false), and name it in the annotation:

@Configuration()
class CacheSetup {
  @Bean(autowireCandidate: false)
  CacheManager sessionCaches(KeyValueStore store) =>
      SimpleCacheManager([StoreCache('sessions', store)]);
}

@Cacheable('sessions', cacheManager: 'sessionCaches')
Session load(String token) => ...;

5. Your own keys

Implement KeyGenerator, declare it as a bean and name it in the annotation:

final class IsbnKeys implements KeyGenerator {
  const IsbnKeys();

  @override
  Object? generate(Object target, MethodSignature method, List<Object?> args) =>
      (args.first! as String).replaceAll('-', '');
}

@Configuration()
class Keys {
  @Bean()
  KeyGenerator isbnKeys() => const IsbnKeys();
}

@Cacheable('books', keyGenerator: 'isbnKeys')
Book find(String isbn) => ...;

6. Choosing caches per call: CacheResolver

A CacheResolver decides at each call which caches an operation uses — for example one cache per tenant. It sees the operation (its cache names, key, ...), the bean, the method and the arguments. Declare it as a bean and name it with cacheResolver: (in the annotation or in @CacheConfig):

final class TenantCacheResolver implements CacheResolver {
  TenantCacheResolver(this.manager, this.tenants);
  final CacheManager manager;
  final TenantContext tenants;

  @override
  Iterable<Cache> resolveCaches(CacheOperationInvocationContext context) => [
    for (final name in context.operation.cacheNames)
      manager.getCache('${tenants.current}.$name')!,
  ];
}

@Configuration()
class CacheSetup {
  @Bean()
  CacheResolver tenantCacheResolver(CacheManager manager, TenantContext tenants) =>
      TenantCacheResolver(manager, tenants);
}

@Cacheable('books', cacheResolver: 'tenantCacheResolver')
Book find(String isbn) => ...;

Spring (Java):

@Cacheable(cacheNames = "books", cacheResolver = "tenantCacheResolver")
Book find(String isbn) { ... }

Built in: SimpleCacheResolver(manager) (the default: the operation's names in the cache manager) and NamedCacheResolver(manager, ['audit']) (always the same caches; the operations need no names then). Like Spring Boot, the starter's cacheManager backs off when a bean named cacheResolver exists.

7. Defaults for everything: CachingConfigurer

One bean implementing CachingConfigurer sets the defaults of all cache operations; a method returning null (the default) keeps the starter's:

Method	Default
cacheManager()	the CacheManager bean
cacheResolver()	SimpleCacheResolver of the cache manager
keyGenerator()	SimpleKeyGenerator
errorHandler()	SimpleCacheErrorHandler: cache errors reach the caller

@Configuration()
class CacheSetup with CachingConfigurer {
  @override
  KeyGenerator keyGenerator() => const IsbnKeys();

  // A cache that is down: log, run the method, carry on.
  @override
  CacheErrorHandler errorHandler() => const LoggingCacheErrorHandler();
}

Spring (Java):

@Configuration
@EnableCaching
class CacheSetup implements CachingConfigurer {
  @Override
  public KeyGenerator keyGenerator() { return new IsbnKeys(); }

  @Override
  public CacheErrorHandler errorHandler() { return new LoggingCacheErrorHandler(); }
}

The methods are called once, when caching is first used. Return objects (or beans injected into the configuration) rather than marking the methods @Bean: Dart does not proxy @Configuration classes, so calling a @Bean method creates a second instance.

With a CacheErrorHandler that does not rethrow, a failed get counts as a miss (the method runs) and a failed put, evict or clear is skipped. LoggingCacheErrorHandler logs them at warning level to spring.cache (logStackTraces: true adds the stack trace).

Testing

Cached results carry over between calls, which can hide behavior in tests. Switch caching off with a property:

final app = springBootTest(
  springApplication,
  properties: {'spring.cache.type': 'none'},
);

Or keep it on and check the cache through the CacheManager bean (app.getBean<CacheManager>().getCache('books')!.get('978-0')).

Differences from Spring

• No @EnableCaching: adding the starter turns caching on; spring.cache.type=none turns it off.
• @Cacheable('books') takes one name; several names go to @Cacheable.of(cacheNames: [...]) (Dart cannot mix an optional positional parameter with named ones).
• #root.caches holds cache names, #root.targetClass the class name, #root.method the MethodSignature (name, returnType, ... as text).
• CacheManagerCustomizer is not generic: every customizer gets the manager and checks its type (the container finds beans by their exact type, so CacheManagerCustomizer<InMemoryCacheManager> could not be matched against a manager).
• Future results are cached by value (Spring 6.1 does the same for CompletableFuture).
• Built-in store: memory, with time to live and size limit (Spring's ConcurrentMapCacheManager has neither; it needs Caffeine for that).
• spring.cache.simple.time-to-live, spring.cache.simple.max-size and spring.cache.simple.caches.<name>.* are this starter's: Spring Boot's simple type has no settings (time to live and size come from Caffeine or Redis there, under spring.cache.caffeine.* / spring.cache.redis.*). spring.cache.type knows generic, simple and none only.
• SimpleKeyGenerator wraps a single collection argument in a SimpleKey (Dart lists, sets and maps compare by identity; the key compares by content); Spring wraps only arrays.
• Stream results cannot be cached: @Cacheable / @CachePut on a method returning a Stream fail the build (Spring 6.1 collects a Flux into a list and replays it; a generic interceptor cannot create a Stream<T> of the right type without reflection). Return a Future<List<T>>.
• The Cache API is a subset of Spring's: name, get, put, putIfAbsent, evict, evictIfPresent, clear, invalidate; there is no get(key, Class), get(key, Callable) (value loader), retrieve (asynchronous) or getNativeCache.
• CachingConfigurer methods are called once; they must not be @Bean methods (no @Configuration proxies in Dart). CacheErrorHandler methods receive the stack trace next to the error.
• Annotations are checked when the bean is created, for every member; the sync rules too (Spring checks those at the first call).