util: LinkedHashMapRemoveEldest implemented with test

common/util/pom.xml

@@ -74,6 +74,11 @@
             <artifactId>junit</artifactId>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.hamcrest</groupId>
+            <artifactId>hamcrest</artifactId>
+            <scope>test</scope>
+        </dependency>
         <dependency>
             <groupId>org.mockito</groupId>
             <artifactId>mockito-core</artifactId>

common/util/src/main/java/org/thingsboard/common/util/LinkedHashMapRemoveEldest.java

@@ -0,0 +1,83 @@
+/**
+ * ThingsBoard, Inc. ("COMPANY") CONFIDENTIAL
+ *
+ * Copyright © 2016-2021 ThingsBoard, Inc. All Rights Reserved.
+ *
+ * NOTICE: All information contained herein is, and remains
+ * the property of ThingsBoard, Inc. and its suppliers,
+ * if any.  The intellectual and technical concepts contained
+ * herein are proprietary to ThingsBoard, Inc.
+ * and its suppliers and may be covered by U.S. and Foreign Patents,
+ * patents in process, and are protected by trade secret or copyright law.
+ *
+ * Dissemination of this information or reproduction of this material is strictly forbidden
+ * unless prior written permission is obtained from COMPANY.
+ *
+ * Access to the source code contained herein is hereby forbidden to anyone except current COMPANY employees,
+ * managers or contractors who have executed Confidentiality and Non-disclosure agreements
+ * explicitly covering such access.
+ *
+ * The copyright notice above does not evidence any actual or intended publication
+ * or disclosure  of  this source code, which includes
+ * information that is confidential and/or proprietary, and is a trade secret, of  COMPANY.
+ * ANY REPRODUCTION, MODIFICATION, DISTRIBUTION, PUBLIC  PERFORMANCE,
+ * OR PUBLIC DISPLAY OF OR THROUGH USE  OF THIS  SOURCE CODE  WITHOUT
+ * THE EXPRESS WRITTEN CONSENT OF COMPANY IS STRICTLY PROHIBITED,
+ * AND IN VIOLATION OF APPLICABLE LAWS AND INTERNATIONAL TREATIES.
+ * THE RECEIPT OR POSSESSION OF THIS SOURCE CODE AND/OR RELATED INFORMATION
+ * DOES NOT CONVEY OR IMPLY ANY RIGHTS TO REPRODUCE, DISCLOSE OR DISTRIBUTE ITS CONTENTS,
+ * OR TO MANUFACTURE, USE, OR SELL ANYTHING THAT IT  MAY DESCRIBE, IN WHOLE OR IN PART.
+ */
+package org.thingsboard.common.util;
+
+import lombok.EqualsAndHashCode;
+import lombok.Getter;
+import lombok.ToString;
+
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+/**
+ * HashMap that removed eldest (by put order) entries
+ * It guaranteed that size is not greater then maxEntries parameter. And remove time is constant O(1).
+ * Use withMaxEntries to setup maxEntries.
+ * Because overloaded constructor will look similar to LinkedHashMap(initCapacity)
+ * Example:
+ *   new LinkedHashMapRemoveEldest<Long, String>().withMaxEntries(100L)
+ * */
+@Getter
+@ToString(callSuper = true)
+@EqualsAndHashCode(callSuper = true)
+public class LinkedHashMapRemoveEldest<K,V> extends LinkedHashMap<K,V> {
+    long maxEntries = Long.MAX_VALUE;
+
+    public LinkedHashMapRemoveEldest() {
+        super();
+    }
+
+    public LinkedHashMapRemoveEldest(int initialCapacity) {
+        super(initialCapacity);
+    }
+
+    public LinkedHashMapRemoveEldest(int initialCapacity, float loadFactor) {
+        super(initialCapacity, loadFactor);
+    }
+
+    public LinkedHashMapRemoveEldest(Map<? extends K, ? extends V> m) {
+        super(m);
+    }
+
+    public LinkedHashMapRemoveEldest(int initialCapacity, float loadFactor, boolean accessOrder) {
+        super(initialCapacity, loadFactor, accessOrder);
+    }
+
+    public LinkedHashMapRemoveEldest<K,V> withMaxEntries(long maxEntries) {
+        this.maxEntries = maxEntries;
+        return this;
+    }
+
+    @Override
+    protected boolean removeEldestEntry(Map.Entry eldest) {
+        return size() > maxEntries;
+    }
+}

common/util/src/test/java/org/thingsboard/common/util/LinkedHashMapRemoveEldestTest.java

@@ -0,0 +1,70 @@
+/**
+ * ThingsBoard, Inc. ("COMPANY") CONFIDENTIAL
+ *
+ * Copyright © 2016-2021 ThingsBoard, Inc. All Rights Reserved.
+ *
+ * NOTICE: All information contained herein is, and remains
+ * the property of ThingsBoard, Inc. and its suppliers,
+ * if any.  The intellectual and technical concepts contained
+ * herein are proprietary to ThingsBoard, Inc.
+ * and its suppliers and may be covered by U.S. and Foreign Patents,
+ * patents in process, and are protected by trade secret or copyright law.
+ *
+ * Dissemination of this information or reproduction of this material is strictly forbidden
+ * unless prior written permission is obtained from COMPANY.
+ *
+ * Access to the source code contained herein is hereby forbidden to anyone except current COMPANY employees,
+ * managers or contractors who have executed Confidentiality and Non-disclosure agreements
+ * explicitly covering such access.
+ *
+ * The copyright notice above does not evidence any actual or intended publication
+ * or disclosure  of  this source code, which includes
+ * information that is confidential and/or proprietary, and is a trade secret, of  COMPANY.
+ * ANY REPRODUCTION, MODIFICATION, DISTRIBUTION, PUBLIC  PERFORMANCE,
+ * OR PUBLIC DISPLAY OF OR THROUGH USE  OF THIS  SOURCE CODE  WITHOUT
+ * THE EXPRESS WRITTEN CONSENT OF COMPANY IS STRICTLY PROHIBITED,
+ * AND IN VIOLATION OF APPLICABLE LAWS AND INTERNATIONAL TREATIES.
+ * THE RECEIPT OR POSSESSION OF THIS SOURCE CODE AND/OR RELATED INFORMATION
+ * DOES NOT CONVEY OR IMPLY ANY RIGHTS TO REPRODUCE, DISCLOSE OR DISTRIBUTE ITS CONTENTS,
+ * OR TO MANUFACTURE, USE, OR SELL ANYTHING THAT IT  MAY DESCRIBE, IN WHOLE OR IN PART.
+ */
+package org.thingsboard.common.util;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.LinkedHashMap;
+
+import static org.hamcrest.CoreMatchers.instanceOf;
+import static org.hamcrest.CoreMatchers.is;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+public class LinkedHashMapRemoveEldestTest {
+
+    public static final long MAX_ENTRIES = 10L;
+    LinkedHashMapRemoveEldest<Long, String> map;
+
+    @Before
+    public void setUp() throws Exception {
+        map = new LinkedHashMapRemoveEldest<Long, String>().withMaxEntries(MAX_ENTRIES);
+    }
+
+    @Test
+    public void givenMap_whenOverSized_thenVerifyRemovedEldest() {
+        assertThat(map.getMaxEntries(), is(MAX_ENTRIES));
+        assertThat(map, instanceOf(LinkedHashMap.class));
+        assertThat(map, instanceOf(LinkedHashMapRemoveEldest.class));
+        assertThat(map.size(), is(0));
+
+        for (long i = 0; i < MAX_ENTRIES * 2; i++) {
+            map.put(i, String.valueOf(i));
+        }
+
+        assertThat(map.size(), is((int) MAX_ENTRIES));
+
+        for (long i = MAX_ENTRIES; i < MAX_ENTRIES * 2; i++) {
+            assertThat(map.get(i), is(String.valueOf(i)));
+        }
+    }
+
+}