如何禁用Guava缓存？

Question

JavaCachingWithGuava suggests the canonical way to turn off caching is to set maximumSize=0 . However, I'd expect the test below to pass:

public class LoadingCacheTest {
    private static final Logger LOG = LoggerFactory.getLogger(LoadingCacheTest.class);

    LoadingCache<String, Long> underTest;

    @Before
    public void setup() throws Exception {
        underTest = CacheBuilder.from("maximumSize=0").newBuilder()
                .recordStats()
                .removalListener(new RemovalListener<String, Long>() {
                    @Override
                    public void onRemoval(RemovalNotification<String, Long> removalNotification) {
                        LOG.info(String.format("%s cached value %s for key %s is evicted.", removalNotification.getCause().name(), removalNotification.getValue(), removalNotification.getKey()));
                    }
                })
                .build(new CacheLoader<String, Long>() {
                    private final AtomicLong al = new AtomicLong(0);
                    @Override
                    public Long load(@NotNull final String key) throws Exception {
                        LOG.info(String.format("Cache miss for key '%s'.", key));
                        return al.incrementAndGet();
                    }
                });
    }

    @Test
    public void testAlwaysCacheMissIfCacheDisabled() throws Exception {
        String key1 = "Key1";
        String key2 = "Key2";
        underTest.get(key1);
        underTest.get(key1);
        underTest.get(key2);
        underTest.get(key2);
        LOG.info(underTest.stats().toString());
        Assert.assertThat(underTest.stats().missCount(), is(equalTo(4L)));
    }
}

That is, turning off the cache always results in a cache miss.

The test fails, though. Is my interpretation incorrect?

Answer 1

The method newBuilder constructs a new CacheBuilder instance with default settings, ignoring the call to from . However, you want to construct a CacheBuilder with a specific maximum size. So, remove the call to newBuider . You should use your call to build to get a CacheBuilder matching your spec rather than getting one with default settings:

underTest = CacheBuilder.from("maximumSize=0")
                .recordStats()
                .removalListener(new RemovalListener<String, Long>() {
                    @Override
                    public void onRemoval(RemovalNotification<String, Long> removalNotification) {
                        LOG.info(String.format("%s cached value %s for key %s is evicted.", removalNotification.getCause().name(), removalNotification.getValue(), removalNotification.getKey()));
                    }
                })
                .build(new CacheLoader<String, Long>() {
                    private final AtomicLong al = new AtomicLong(0);
                    @Override
                    public Long load(@NotNull final String key) throws Exception {
                        LOG.info(String.format("Cache miss for key '%s'.", key));
                        return al.incrementAndGet();
                    }
                });