Guava入门~Guava caches

Cache 接口

put(key,value)：往缓存中添加值；

V value = cache.get(key, Callable value)：从缓存中获取值；

// 等价
value = cache.get(key);
if(value == null){
	value = someService.retrieveValue();
	cache.put(key,value);
}

如果不想执行异步任务，可以使用Callables

Callable<String> value = Callables.returning("Foo");
 
cache.get(key,Callables.returning(someService.retrieveValue());

getIfPresent(key)：如果存在返回value，否则null；

丢弃缓存

invalidate(key)

invalidateAll()

invalidateAll(Iterable keys)

LoadingCache

Book book = loadingCache.get(id);

Loading values

ImmutableMap<key,value> map = cache.getAll(Iterable<? Extends key>);

Refreshing values in the cache

refresh(key);

示例

package bbejeck.guava.chapter6.cache;
 
import bbejeck.guava.common.model.TradeAccount;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import org.junit.Test;
 
import java.util.concurrent.TimeUnit;
 
import static org.hamcrest.CoreMatchers.is;
import static org.junit.Assert.assertThat;
import static org.mockito.Mockito.*;
 
/**
 * User: Bill Bejeck
 * Date: 7/22/13
 * Time: 10:53 PM
 */
public class LoadingCacheTest {
    private CacheLoader<String, TradeAccount> cacheLoader = mock(CacheLoader.class);
 
    @Test
    public void testCacheLoaderOnlyCalledOnce() throws Exception {
        TradeAccount expectedTradeAccount = new TradeAccount.Builder().balance(250000.12).build();
        when(cacheLoader.load("223")).thenReturn(expectedTradeAccount);
        LoadingCache<String, TradeAccount> tradeAccountCache = CacheBuilder.newBuilder()
                .maximumSize(5000L)
                .build(cacheLoader);
 
        TradeAccount tradeAccount = tradeAccountCache.get("223");
        assertThat(tradeAccount, is(expectedTradeAccount));
 
        for (int i = 0; i < 10; i++) {
            TradeAccount tradeAccount1 = tradeAccountCache.get("223");
            assertThat(tradeAccount1, is(expectedTradeAccount));
        }
        verify(cacheLoader, times(1)).load("223");
    }
 
    @Test
    public void testCacheLoaderCalledInitiallyAndAfterExpiration() throws Exception {
        TradeAccount expectedTradeAccount = new TradeAccount.Builder().balance(250000.12).build();
        when(cacheLoader.load("223")).thenReturn(expectedTradeAccount);
        LoadingCache<String, TradeAccount> tradeAccountCache = CacheBuilder.newBuilder()
                .maximumSize(5000L)
                .expireAfterAccess(500l, TimeUnit.MILLISECONDS)
                .build(cacheLoader);
 
        TradeAccount tradeAccount = tradeAccountCache.get("223");
        assertThat(tradeAccount, is(expectedTradeAccount));
 
        Thread.sleep(1000);
 
        TradeAccount tradeAccount1 = tradeAccountCache.get("223");
        assertThat(tradeAccount1, is(expectedTradeAccount));
        verify(cacheLoader, times(2)).load("223");
    }
 
}