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feat: Added a generic LRUCache interface and a default implementation (#482)
## Summary Added an interface for a generic LRUCache and a default Implementation. ## Test plan - All existing tests pass. - Added unit tests for the default cache implementation. ## Issues [OASIS-8385](https://optimizely.atlassian.net/browse/OASIS-8385)
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‎core-api/src/main/java/com/optimizely/ab/internal/Cache.java

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/**
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*
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* Copyright 2022, Optimizely
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.optimizely.ab.internal;
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public interface Cache<T> {
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int DEFAULT_MAX_SIZE = 10000;
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int DEFAULT_TIMEOUT_SECONDS = 600;
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void save(String key, T value);
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T lookup(String key);
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void reset();
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}

‎core-api/src/main/java/com/optimizely/ab/internal/DefaultLRUCache.java

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/**
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*
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* Copyright 2022, Optimizely
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.optimizely.ab.internal;
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import com.optimizely.ab.annotations.VisibleForTesting;
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import java.util.*;
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public class DefaultLRUCache<T> implements Cache<T> {
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private final Object lock = new Object();
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private final Integer maxSize;
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private final Long timeoutMillis;
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@VisibleForTesting
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final LinkedHashMap<String, CacheEntity> linkedHashMap = new LinkedHashMap<String, CacheEntity>(16, 0.75f, true) {
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@Override
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protected boolean removeEldestEntry(Map.Entry<String, CacheEntity> eldest) {
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return this.size() > maxSize;
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}
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};
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public DefaultLRUCache() {
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this(DEFAULT_MAX_SIZE, DEFAULT_TIMEOUT_SECONDS);
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}
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public DefaultLRUCache(Integer maxSize, Integer timeoutSeconds) {
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this.maxSize = maxSize < 0 ? Integer.valueOf(0) : maxSize;
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this.timeoutMillis = (timeoutSeconds < 0) ? 0 : (timeoutSeconds * 1000L);
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}
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public void save(String key, T value) {
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if (maxSize == 0) {
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// Cache is disabled when maxSize = 0
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return;
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}
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synchronized (lock) {
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linkedHashMap.put(key, new CacheEntity(value));
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}
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}
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public T lookup(String key) {
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if (maxSize == 0) {
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// Cache is disabled when maxSize = 0
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return null;
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}
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synchronized (lock) {
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if (linkedHashMap.containsKey(key)) {
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CacheEntity entity = linkedHashMap.get(key);
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Long nowMs = new Date().getTime();
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// ttl = 0 means entities never expire.
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if (timeoutMillis == 0 || (nowMs - entity.timestamp < timeoutMillis)) {
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return entity.value;
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}
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linkedHashMap.remove(key);
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}
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return null;
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}
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}
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public void reset() {
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synchronized (lock) {
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linkedHashMap.clear();
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}
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}
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private class CacheEntity {
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public T value;
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public Long timestamp;
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public CacheEntity(T value) {
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this.value = value;
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this.timestamp = new Date().getTime();
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}
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}
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}

‎core-api/src/test/java/com/optimizely/ab/internal/DefaultLRUCacheTest.java

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/**
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*
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* Copyright 2022, Optimizely
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.optimizely.ab.internal;
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import org.junit.Test;
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import java.util.Arrays;
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import java.util.List;
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import static org.junit.Assert.*;
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public class DefaultLRUCacheTest {
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@Test
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public void createSaveAndLookupOneItem() {
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Cache<String> cache = new DefaultLRUCache<>();
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assertNull(cache.lookup("key1"));
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cache.save("key1", "value1");
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assertEquals("value1", cache.lookup("key1"));
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}
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@Test
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public void saveAndLookupMultipleItems() {
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DefaultLRUCache<List<String>> cache = new DefaultLRUCache<>();
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cache.save("user1", Arrays.asList("segment1", "segment2"));
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cache.save("user2", Arrays.asList("segment3", "segment4"));
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cache.save("user3", Arrays.asList("segment5", "segment6"));
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String[] itemKeys = cache.linkedHashMap.keySet().toArray(new String[0]);
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assertEquals("user1", itemKeys[0]);
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assertEquals("user2", itemKeys[1]);
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assertEquals("user3", itemKeys[2]);
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assertEquals(Arrays.asList("segment1", "segment2"), cache.lookup("user1"));
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itemKeys = cache.linkedHashMap.keySet().toArray(new String[0]);
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// Lookup should move user1 to bottom of the list and push up others.
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assertEquals("user2", itemKeys[0]);
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assertEquals("user3", itemKeys[1]);
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assertEquals("user1", itemKeys[2]);
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assertEquals(Arrays.asList("segment3", "segment4"), cache.lookup("user2"));
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itemKeys = cache.linkedHashMap.keySet().toArray(new String[0]);
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// Lookup should move user2 to bottom of the list and push up others.
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assertEquals("user3", itemKeys[0]);
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assertEquals("user1", itemKeys[1]);
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assertEquals("user2", itemKeys[2]);
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assertEquals(Arrays.asList("segment5", "segment6"), cache.lookup("user3"));
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itemKeys = cache.linkedHashMap.keySet().toArray(new String[0]);
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// Lookup should move user3 to bottom of the list and push up others.
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assertEquals("user1", itemKeys[0]);
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assertEquals("user2", itemKeys[1]);
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assertEquals("user3", itemKeys[2]);
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}
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@Test
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public void saveShouldReorderList() {
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DefaultLRUCache<List<String>> cache = new DefaultLRUCache<>();
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cache.save("user1", Arrays.asList("segment1", "segment2"));
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cache.save("user2", Arrays.asList("segment3", "segment4"));
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cache.save("user3", Arrays.asList("segment5", "segment6"));
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String[] itemKeys = cache.linkedHashMap.keySet().toArray(new String[0]);
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assertEquals("user1", itemKeys[0]);
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assertEquals("user2", itemKeys[1]);
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assertEquals("user3", itemKeys[2]);
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cache.save("user1", Arrays.asList("segment1", "segment2"));
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itemKeys = cache.linkedHashMap.keySet().toArray(new String[0]);
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// save should move user1 to bottom of the list and push up others.
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assertEquals("user2", itemKeys[0]);
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assertEquals("user3", itemKeys[1]);
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assertEquals("user1", itemKeys[2]);
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cache.save("user2", Arrays.asList("segment3", "segment4"));
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itemKeys = cache.linkedHashMap.keySet().toArray(new String[0]);
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// save should move user2 to bottom of the list and push up others.
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assertEquals("user3", itemKeys[0]);
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assertEquals("user1", itemKeys[1]);
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assertEquals("user2", itemKeys[2]);
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cache.save("user3", Arrays.asList("segment5", "segment6"));
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itemKeys = cache.linkedHashMap.keySet().toArray(new String[0]);
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// save should move user3 to bottom of the list and push up others.
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assertEquals("user1", itemKeys[0]);
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assertEquals("user2", itemKeys[1]);
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assertEquals("user3", itemKeys[2]);
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}
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@Test
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public void whenCacheIsDisabled() {
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DefaultLRUCache<List<String>> cache = new DefaultLRUCache<>(0,Cache.DEFAULT_TIMEOUT_SECONDS);
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cache.save("user1", Arrays.asList("segment1", "segment2"));
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cache.save("user2", Arrays.asList("segment3", "segment4"));
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cache.save("user3", Arrays.asList("segment5", "segment6"));
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assertNull(cache.lookup("user1"));
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assertNull(cache.lookup("user2"));
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assertNull(cache.lookup("user3"));
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}
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@Test
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public void whenItemsExpire() throws InterruptedException {
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DefaultLRUCache<List<String>> cache = new DefaultLRUCache<>(Cache.DEFAULT_MAX_SIZE, 1);
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cache.save("user1", Arrays.asList("segment1", "segment2"));
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assertEquals(Arrays.asList("segment1", "segment2"), cache.lookup("user1"));
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assertEquals(1, cache.linkedHashMap.size());
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Thread.sleep(1000);
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assertNull(cache.lookup("user1"));
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assertEquals(0, cache.linkedHashMap.size());
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}
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@Test
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public void whenCacheReachesMaxSize() {
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DefaultLRUCache<List<String>> cache = new DefaultLRUCache<>(2, Cache.DEFAULT_TIMEOUT_SECONDS);
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cache.save("user1", Arrays.asList("segment1", "segment2"));
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cache.save("user2", Arrays.asList("segment3", "segment4"));
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cache.save("user3", Arrays.asList("segment5", "segment6"));
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assertEquals(2, cache.linkedHashMap.size());
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assertEquals(Arrays.asList("segment5", "segment6"), cache.lookup("user3"));
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assertEquals(Arrays.asList("segment3", "segment4"), cache.lookup("user2"));
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assertNull(cache.lookup("user1"));
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}
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@Test
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public void whenCacheIsReset() {
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DefaultLRUCache<List<String>> cache = new DefaultLRUCache<>();
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cache.save("user1", Arrays.asList("segment1", "segment2"));
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cache.save("user2", Arrays.asList("segment3", "segment4"));
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cache.save("user3", Arrays.asList("segment5", "segment6"));
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assertEquals(Arrays.asList("segment1", "segment2"), cache.lookup("user1"));
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assertEquals(Arrays.asList("segment3", "segment4"), cache.lookup("user2"));
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assertEquals(Arrays.asList("segment5", "segment6"), cache.lookup("user3"));
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assertEquals(3, cache.linkedHashMap.size());
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cache.reset();
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assertNull(cache.lookup("user1"));
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assertNull(cache.lookup("user2"));
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assertNull(cache.lookup("user3"));
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assertEquals(0, cache.linkedHashMap.size());
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}
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}

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