这是我从 Xaerxess 的答案中得出的用法:
private final Map<String, List<Condition>> waitersByKey=MapUtil.create(5, 1000);
MapUtil.java:
import java.util.Map;
import java.util.concurrent.TimeUnit;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.RemovalListener;
public class MapUtil {
/**
* Value for items which are unrestricted (-1)
*/
public static final int UNRESTRICTED=-1;
/**
* Create a generic map that will not exceed max size
* @param maxSize
* @return created map
*/
public static <K,V> Map<K,V> createWithMaxSize(int maxSize) {
return create(UNRESTRICTED,maxSize);
}
/**
* Create a generic map that will expire objects if not accessed within a given number of minutes
* @param expireInMins
* @return created map
*/
public static <K,V> Map<K,V> createWithExpiration(int expireInMins) {
return create(expireInMins,UNRESTRICTED,UNRESTRICTED);
}
/**
* Creates a map with an initial size. Reduces growth performance hit.
* @param initialSize
* @return created map
*/
public static <K,V> Map<K,V> createWithInitialSize(int initialSize) {
return create(UNRESTRICTED,UNRESTRICTED,initialSize);
}
/**
* Create generic map that expires values with max size
* @param expireInMins max age of unaccessed items in minutes, or UNRESTRICTED
* @param maxSize max number of items before oldest is removed, or UNRESTRICTED
* @return created map
*/
public static <K,V> Map<K,V> create(int expireInMins, int maxSize) {
return create(expireInMins,maxSize,UNRESTRICTED);
}
/**
* Create generic map that expires values with max size
* @param expireInMins max age of unaccessed items in minutes, or UNRESTRICTED
* @param maxSize max number of items before oldest is removed, or UNRESTRICTED
* @param removalListener listener called on item removal, if not null
* @return created map
*/
public static <K,V> Map<K,V> create(int expireInMins, int maxSize, RemovalListener<K, V> removalListener) {
return create(expireInMins,maxSize,UNRESTRICTED, removalListener);
}
/**
* Convenience method to build a Guava cache as generic map.
* http://stackoverflow.com/a/14730359/303442
* @param expireInMins max age of unaccessed items in minutes, or UNRESTRICTED
* @param maxSize max number of items before oldest is removed, or UNRESTRICTED
* @param initialCapacity initial size in elements, reduces growth performance hit. UNRESTRICTED for default
* @return created map
*/
public static <K,V> Map<K,V> create(int expireInMins, int maxSize, int initialCapacity) {
return create(expireInMins,maxSize,initialCapacity,null);
}
/**
* Convenience method to build a Guava cache as generic map.
* http://stackoverflow.com/a/14730359/303442
* @param expireInMins max age of unaccessed items in minutes, or UNRESTRICTED
* @param maxSize max number of items before oldest is removed, or UNRESTRICTED
* @param initialCapacity initial size in elements, reduces growth performance hit. UNRESTRICTED for default
* @param removalListener listener called on item removal, if not null
* @return created map
*/
public static <K,V> Map<K,V> create(int expireInMins, int maxSize, int initialCapacity,RemovalListener<K, V> removalListener) {
CacheBuilder<Object, Object> builder = CacheBuilder.newBuilder();
if (expireInMins>-1)
builder.expireAfterWrite(expireInMins, TimeUnit.MINUTES);
if (maxSize>-1)
builder.maximumSize(1000);
if (initialCapacity>-1)
builder.initialCapacity(initialCapacity);
if (removalListener!=null)
builder.removalListener(removalListener);
return builder.<K,V>build().asMap();
}
}