Java tutorial
/* * Copyright 2002-2019 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * https://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.springframework.cache.concurrent; import java.io.ByteArrayInputStream; import java.io.ByteArrayOutputStream; import java.io.IOException; import java.util.concurrent.Callable; import java.util.concurrent.ConcurrentHashMap; import java.util.concurrent.ConcurrentMap; import org.springframework.cache.support.AbstractValueAdaptingCache; import org.springframework.core.serializer.support.SerializationDelegate; import org.springframework.lang.Nullable; import org.springframework.util.Assert; /** * Simple {@link org.springframework.cache.Cache} implementation based on the * core JDK {@code java.util.concurrent} package. * * <p>Useful for testing or simple caching scenarios, typically in combination * with {@link org.springframework.cache.support.SimpleCacheManager} or * dynamically through {@link ConcurrentMapCacheManager}. * * <p><b>Note:</b> As {@link ConcurrentHashMap} (the default implementation used) * does not allow for {@code null} values to be stored, this class will replace * them with a predefined internal object. This behavior can be changed through the * {@link #ConcurrentMapCache(String, ConcurrentMap, boolean)} constructor. * * @author Costin Leau * @author Juergen Hoeller * @author Stephane Nicoll * @since 3.1 */ public class ConcurrentMapCache extends AbstractValueAdaptingCache { private final String name; private final ConcurrentMap<Object, Object> store; @Nullable private final SerializationDelegate serialization; /** * Create a new ConcurrentMapCache with the specified name. * @param name the name of the cache */ public ConcurrentMapCache(String name) { this(name, new ConcurrentHashMap<>(256), true); } /** * Create a new ConcurrentMapCache with the specified name. * @param name the name of the cache * @param allowNullValues whether to accept and convert {@code null} * values for this cache */ public ConcurrentMapCache(String name, boolean allowNullValues) { this(name, new ConcurrentHashMap<>(256), allowNullValues); } /** * Create a new ConcurrentMapCache with the specified name and the * given internal {@link ConcurrentMap} to use. * @param name the name of the cache * @param store the ConcurrentMap to use as an internal store * @param allowNullValues whether to allow {@code null} values * (adapting them to an internal null holder value) */ public ConcurrentMapCache(String name, ConcurrentMap<Object, Object> store, boolean allowNullValues) { this(name, store, allowNullValues, null); } /** * Create a new ConcurrentMapCache with the specified name and the * given internal {@link ConcurrentMap} to use. If the * {@link SerializationDelegate} is specified, * {@link #isStoreByValue() store-by-value} is enabled * @param name the name of the cache * @param store the ConcurrentMap to use as an internal store * @param allowNullValues whether to allow {@code null} values * (adapting them to an internal null holder value) * @param serialization the {@link SerializationDelegate} to use * to serialize cache entry or {@code null} to store the reference * @since 4.3 */ protected ConcurrentMapCache(String name, ConcurrentMap<Object, Object> store, boolean allowNullValues, @Nullable SerializationDelegate serialization) { super(allowNullValues); Assert.notNull(name, "Name must not be null"); Assert.notNull(store, "Store must not be null"); this.name = name; this.store = store; this.serialization = serialization; } /** * Return whether this cache stores a copy of each entry ({@code true}) or * a reference ({@code false}, default). If store by value is enabled, each * entry in the cache must be serializable. * @since 4.3 */ public final boolean isStoreByValue() { return (this.serialization != null); } @Override public final String getName() { return this.name; } @Override public final ConcurrentMap<Object, Object> getNativeCache() { return this.store; } @Override @Nullable protected Object lookup(Object key) { return this.store.get(key); } @SuppressWarnings("unchecked") @Override @Nullable public <T> T get(Object key, Callable<T> valueLoader) { return (T) fromStoreValue(this.store.computeIfAbsent(key, k -> { try { return toStoreValue(valueLoader.call()); } catch (Throwable ex) { throw new ValueRetrievalException(key, valueLoader, ex); } })); } @Override public void put(Object key, @Nullable Object value) { this.store.put(key, toStoreValue(value)); } @Override @Nullable public ValueWrapper putIfAbsent(Object key, @Nullable Object value) { Object existing = this.store.putIfAbsent(key, toStoreValue(value)); return toValueWrapper(existing); } @Override public void evict(Object key) { this.store.remove(key); } @Override public boolean evictIfPresent(Object key) { return (this.store.remove(key) != null); } @Override public void clear() { this.store.clear(); } @Override public boolean invalidate() { boolean notEmpty = !this.store.isEmpty(); this.store.clear(); return notEmpty; } @Override protected Object toStoreValue(@Nullable Object userValue) { Object storeValue = super.toStoreValue(userValue); if (this.serialization != null) { try { return serializeValue(this.serialization, storeValue); } catch (Throwable ex) { throw new IllegalArgumentException( "Failed to serialize cache value '" + userValue + "'. Does it implement Serializable?", ex); } } else { return storeValue; } } private Object serializeValue(SerializationDelegate serialization, Object storeValue) throws IOException { ByteArrayOutputStream out = new ByteArrayOutputStream(); try { serialization.serialize(storeValue, out); return out.toByteArray(); } finally { out.close(); } } @Override protected Object fromStoreValue(@Nullable Object storeValue) { if (storeValue != null && this.serialization != null) { try { return super.fromStoreValue(deserializeValue(this.serialization, storeValue)); } catch (Throwable ex) { throw new IllegalArgumentException("Failed to deserialize cache value '" + storeValue + "'", ex); } } else { return super.fromStoreValue(storeValue); } } private Object deserializeValue(SerializationDelegate serialization, Object storeValue) throws IOException { ByteArrayInputStream in = new ByteArrayInputStream((byte[]) storeValue); try { return serialization.deserialize(in); } finally { in.close(); } } }