guava cache

最新推荐文章于 2025-03-26 17:19:18 发布

原创最新推荐文章于 2025-03-26 17:19:18 发布 · 403 阅读

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本文介绍了如何使用Guava Cache，包括通过 `.newBuilder()` 创建缓存对象，设置 `.maximumSize()` 缓存大小，`.expireAfterWrite()` 缓存失效时间，以及添加 `.removalListener()` 移除监听器。自定义`RemovalListener`可以在键被移除时进行操作，`.recordStats()` 用于记录缓存状态。Guava Cache内部基于类似`ConcurrentHashMap`的数据结构，并管理失效时间和状态信息，注意键值均不能为null。

Cache<String, Map<String, String>> cache = CacheBuilder.newBuilder().maximumSize(CACHR_MAX_SIZE)
            .expireAfterWrite(CACHE_EXPIRE_TIME, TimeUnit.HOURS)
             .removalListener() 
            .recordStats().build();

.newBuilder() //创建缓存对象

public static CacheBuilder<Object, Object> newBuilder() {
    return new CacheBuilder<Object, Object>();
  }

.maximumSize(CACHR_MAX_SIZE)//设置缓存大小
这里会有几个参数的校验，初始化时都是通过的，设置完之后如果再次设置则会抛异常

public CacheBuilder<K, V> maximumSize(long size) {
    checkState(this.maximumSize == UNSET_INT, "maximum size was already set to %s",
        this.maximumSize);
    checkState(this.maximumWeight == UNSET_INT, "maximum weight was already set to %s",
        this.maximumWeight);
    checkState(this.weigher == null, "maximum size can not be combined with weigher");
    checkArgument(size >= 0, "maximum size must not be negative");
    this.maximumSize = size;
    return this;
  }

.expireAfterWrite(CACHE_EXPIRE_TIME, TimeUnit.HOURS)//设置缓存失效时间
这里也会有校验，底层通过纳秒存储

public CacheBuilder<K, V> expireAfterWrite(long duration, TimeUnit unit) {
    checkState(expireAfterWriteNanos == UNSET_INT, "expireAfterWrite was already set to %s ns",
        expireAfterWriteNanos);
    checkArgument(duration >= 0, "duration cannot be negative: %s %s", duration, unit);
    this.expireAfterWriteNanos = unit.toNanos(duration);//时间转成纳秒
    return this;
  }

.removalListener() //移除监听，在key从缓存中remove时会调用
自定义实现RemovalListener中的onRemoval方法在key移除时会调用

public <K1 extends K, V1 extends V> CacheBuilder<K1, V1> removalListener(
      RemovalListener<? super K1, ? super V1> listener) {
    checkState(this.removalListener == null);

    // safely limiting the kinds of caches this can produce
    @SuppressWarnings("unchecked")
    CacheBuilder<K1, V1> me = (CacheBuilder<K1, V1>) this;
    me.removalListener = checkNotNull(listener);
    return me;
  }

.recordStats()//主要记录cache的状态，包括hit命中数量，miss数量，加载成功数量，加载异常数量，总加载时间，驱逐数量

public CacheBuilder<K, V> recordStats() {
    statsCounterSupplier = CACHE_STATS_COUNTER;
    return this;
  }
  static final Supplier<StatsCounter> CACHE_STATS_COUNTER =
      new Supplier<StatsCounter>() {
    @Override
    public StatsCounter get() {
      return new SimpleStatsCounter();
    }
public static final class SimpleStatsCounter implements StatsCounter {
    private final LongAddable hitCount = LongAddables.create();
    private final LongAddable missCount = LongAddables.create();
    private final LongAddable loadSuccessCount = LongAddables.create();
    private final LongAddable loadExceptionCount = LongAddables.create();
    private final LongAddable totalLoadTime = LongAddables.create();
    private final LongAddable evictionCount = LongAddables.create();
  };
  }

guava cache底层使用类似ConcurrentHashMap的实现，加上了失效时间、状态信息的管理。结构图如下
在这里插入图片描述