前言:
项目需要缓存实时数据,需要根据时间维度去定期清理缓存中的数据,Guava Cache 就比较适合,是一个轻量的,向本地缓存的适合存储少量数据的cache;
pom 依赖:
<dependency>
<groupId>com.google.guava</groupId>
<artifactId>guava</artifactId>
<version>${guava.version}</version>
</dependency>
构建实例:
Cache<Integer, String> cache = CacheBuilder.newBuilder()
//设置cache的初始大小
.initialCapacity(10)
// 缓存的最大大小
.maximumSize(2000)
// 缓存的最大重量 注:此功能不能与@link maximumsize结合使用。
.maximumWeight(2000)
//设置并发数为5，即同一时间最多只能有5个线程往cache执行写入操作
.concurrencyLevel(16)
//设置cache中的数据在写入之后的存活时间为7天
.expireAfterWrite(7, TimeUnit.DAYS)
//设置缓存多久没阅读就自动清除
.expireAfterAccess(1,TimeUnit.DAYS)
//构建cache实例
.build();
大致选了几种常用的,可以根据自己的需要构建实例;
然后让我们看下Guava Cache提供的方法:(比较懒,源码搬运工)
public interface Cache<K, V> {
/**
* Returns the value associated with {@code key} in this cache, or {@code null} if there is no
* cached value for {@code key}.
*
* @since 11.0
*/
@Nullable
V getIfPresent(Object key);
/**
* Returns the value associated with {@code key} in this cache, obtaining that value from {@code
* loader} if necessary. The method improves upon the conventional "if cached, return; otherwise
* create, cache and return" pattern. For further improvements, use {@link LoadingCache} and its
* {@link LoadingCache#get(Object) get(K)} method instead of this one.
*
* <p>Among the improvements that this method and {@code LoadingCache.get(K)} both provide are:
*
* <ul>
* <li>{@linkplain LoadingCache#get(Object) awaiting the result of a pending load} rather than
* starting a redundant one
* <li>eliminating the error-prone caching boilerplate
* <li>tracking load {@linkplain #stats statistics}
* </ul>
*
* <p>Among the further improvements that {@code LoadingCache} can provide but this method cannot:
*
* <ul>
* <li>consolidation of the loader logic to {@linkplain CacheBuilder#build(CacheLoader) a single
* authoritative location}
* <li>{@linkplain LoadingCache#refresh refreshing of entries}, including {@linkplain
* CacheBuilder#refreshAfterWrite automated refreshing}
* <li>{@linkplain LoadingCache#getAll bulk loading requests}, including {@linkplain
* CacheLoader#loadAll bulk loading implementations}
* </ul>
*
* <p><b>Warning:</b> For any given key, every {@code loader} used with it should compute the same
* value. Otherwise, a call that passes one {@code loader} may return the result of another call
* with a differently behaving {@code loader}. For example, a call that requests a short timeout
* for an RPC may wait for a similar call that requests a long timeout, or a call by an
* unprivileged user may return a resource accessible only to a privileged user making a similar
* call. To prevent this problem, create a key object that includes all values that affect the
* result of the query. Or use {@code LoadingCache.get(K)}, which lacks the ability to refer to
* state other than that in the key.
*
* <p><b>Warning:</b> as with {@link CacheLoader#load}, {@code loader} <b>must not</b> return
* {@code null}; it may either return a non-null value or throw an exception.
*
* <p>No observable state associated with this cache is modified until loading completes.
*
* @throws ExecutionException if a checked exception was thrown while loading the value
* @throws UncheckedExecutionException if an unchecked exception was thrown while loading the
* value
* @throws ExecutionError if an error was thrown while loading the value
*
* @since 11.0
*/
V get(K key, Callable<? extends V> loader) throws ExecutionException;
/**
* Returns a map of the values associated with {@code keys} in this cache. The returned map will
* only contain entries which are already present in the cache.
*
* @since 11.0
*/
ImmutableMap<K, V> getAllPresent(Iterable<?> keys);
/**
* Associates {@code value} with {@code key} in this cache. If the cache previously contained a
* value associated with {@code key}, the old value is replaced by {@code value}.
*
* <p>Prefer {@link #get(Object, Callable)} when using the conventional "if cached, return;
* otherwise create, cache and return" pattern.
*
* @since 11.0
*/
void put(K key, V value);
/**
* Copies all of the mappings from the specified map to the cache. The effect of this call is
* equivalent to that of calling {@code put(k, v)} on this map once for each mapping from key
* {@code k} to value {@code v} in the specified map. The behavior of this operation is undefined
* if the specified map is modified while the operation is in progress.
*
* @since 12.0
*/
void putAll(Map<? extends K, ? extends V> m);
/**
* Discards any cached value for key {@code key}.
*/
void invalidate(Object key);
/**
* Discards any cached values for keys {@code keys}.
*
* @since 11.0
*/
void invalidateAll(Iterable<?> keys);
/**
* Discards all entries in the cache.
*/
void invalidateAll();
/**
* Returns the approximate number of entries in this cache.
*/
long size();
/**
* Returns a current snapshot of this cache's cumulative statistics, or a set of default values if
* the cache is not recording statistics. All statistics begin at zero and never decrease over the
* lifetime of the cache.
*
* <p><b>Warning:</b> this cache may not be recording statistical data. For example, a cache
* created using {@link CacheBuilder} only does so if the {@link CacheBuilder#recordStats} method
* was called. If statistics are not being recorded, a {@code CacheStats} instance with zero for
* all values is returned.
*
*/
CacheStats stats();
/**
* Returns a view of the entries stored in this cache as a thread-safe map. Modifications made to
* the map directly affect the cache.
*
* <p>Iterators from the returned map are at least <i>weakly consistent</i>: they are safe for
* concurrent use, but if the cache is modified (including by eviction) after the iterator is
* created, it is undefined which of the changes (if any) will be reflected in that iterator.
*/
ConcurrentMap<K, V> asMap();
/**
* Performs any pending maintenance operations needed by the cache. Exactly which activities are
* performed -- if any -- is implementation-dependent.
*/
void cleanUp();
因为本项目中只用到了写入,读取两种(写入的时候若key存在,则覆盖,就没有用到删除),以下只展示put,get两种方法:
存:
cache.put(MARKET_REAL_KEY.getCacheKey(vo.getSymbol()), vo);
取:
cache.getIfPresent(MARKET_REAL_KEY.getCacheKey(symbol));
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