Caches
設定：
1. maximumSize(long) weigher(Weigher) maxumumWeigher(long)
2. expireAfterAccess(long, TimeUnit) expireAfterWrite(long, TimeUnit)
3. weakKeys() weakValues() softValues()
4. invalidate(key) invalidateAll(keys) invalidateAll()
5. removalListener(RemovalListener)
Refresh：
1. LoadingCache.refresh(K)
2. CacheLoader.reload(K, V)
3. CacheBuilder.refreshAfterWrite(long, TimeUnit)
使い方１：Callable callback (Cache)
import java.util.concurrent.TimeUnit;
import com.google.common.cache.Cache;
import com.google.common.cache.CacheBuilder;
Cache<String, String> cache =
CacheBuilder.newBuilder()
.maximumSize(100)
.expireAfterAccess(3, TimeUnit.SECONDS)
.expireAfterWrite(6, TimeUnit.SECONDS)
.build();
あるいは
String spec = "maximumSize=100,expireAfterAccess=3s,expireAfterWrite=6s";
Cache<String, String> cache = CacheBuilder.from(spec).build();
cache.put("key", "value");
String value = cache.getIfPresent("key");
cache.invalidate("key"); // 削除
cache.invalidateAll(); // 全削除
String result = cache.get("key", new Callable<String>() {
public String call() {
return ...;
}
});
使い方２：CacheLoader (LoadingCache)
import java.util.concurrent.ExecutionException;
import com.google.common.cache.LoadingCache;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
private static String getValue(String key) {
try {
TimeUnit.SECONDS.sleep(3); // 重い処理
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
return "value";
}
LoadingCache<String, String> cache =
CacheBuilder.newBuilder()
.maximumSize(100)
.softValues() //メモリ不足の場合、値がGCの対象になる
.expireAfterAccess(3, TimeUnit.SECONDS)
.expireAfterWrite(6, TimeUnit.SECONDS)
.build(new CacheLoader<String, String>() {
public String load(String key) throws Exception {
return getValue(key);
}
});
try {
String value = cache.get("key"); //ロードと取得が同時に行う
//String value = cache.apply("key");
value = cache.get("key"); //2回目から速くなる
cache.put("xxx", "yyy");
} catch (ExecutionException e) {
...
}
サンプル
@Singleton
public class UserCache {
@Inject
private UserCacheLoader loader;
@Inject
private UserRemovalListener listener;
private final LoadingCache<String, Optional<User>> cache;
public UserCache() {
cache = CacheBuilder.newBuilder()
.maximumSize(100)
.expireAfterWrite(1, TimeUnit.DAYS)
.refreshAfterWrite(5, TimeUnit.SECONDS)
.removalListener(listener)
.build(loader);
}
public Optional<User> getUser(String userId) {
return cache.getUnchecked(userId);
}
}
public class UserCacheLoader
extends CacheLoader<String, Optional<User>>{
@Inject
private UserDAO userDAO;
@Override
public Optional<User> load(String userId) throws Exception {
return loadCache(userId);
}
private Optional<User> loadCache(String userId) {
User user = userDAO.getUserById(userId);
return Optional.fromNullable(user);
}
}
public class UserRemovalListener
implements RemovalListener<String, Optional<User>>{
Logger logger =
LoggerFactory.getLogger(UserRemovalListener.class);
@Override
public void onRemoval(
RemovalNotification<String, Optional<User>> notification) {
logger.info("User (" + notification.getKey()+ ") is removed.");
}
}