feat: 👍 单例模式

src/main/java/cc/niushuai/demo/designpattern/creatormodel/singleton/CASSingleton.java

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+/*
+ * Copyright (C) 2023 niushuai233 niushuai.cc
+ *
+ * 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
+ *
+ *         http://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 cc.niushuai.demo.designpattern.creatormodel.singleton;
+
+import cn.hutool.core.thread.ThreadUtil;
+
+import java.util.concurrent.atomic.AtomicReference;
+
+/**
+ * TODO
+ *
+ * @author niushuai233
+ * @date 2024/1/5 11:49
+ * @since 0.0.1
+ */
+public class CASSingleton {
+
+    private static final AtomicReference<CASSingleton> INSTANCE = new AtomicReference<>();
+
+    private CASSingleton() {
+        ThreadUtil.sleep(3000);
+        System.out.println(Thread.currentThread().getName() + " -> " + getClass().getName() + " has been initialized");
+    }
+
+    public static CASSingleton getInstance() {
+
+        CASSingleton casSingleton = INSTANCE.get();
+        if (casSingleton != null) {
+            return casSingleton;
+        }
+        INSTANCE.compareAndSet(null, new CASSingleton());
+
+        return INSTANCE.get();
+    }
+
+    public static CASSingleton getInstance_forEach() {
+
+        while (true) {
+            CASSingleton casSingleton = INSTANCE.get();
+            if (casSingleton != null) {
+                return casSingleton;
+            }
+            if (INSTANCE.compareAndSet(null, new CASSingleton())) {
+                return INSTANCE.get();
+            }
+        }
+    }
+
+    public void hello(String world) {
+        System.out.println("hello " + world);
+    }
+}

src/main/java/cc/niushuai/demo/designpattern/creatormodel/singleton/EnumSingleton.java

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+/*
+ * Copyright (C) 2023 niushuai233 niushuai.cc
+ *
+ * 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
+ *
+ *         http://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 cc.niushuai.demo.designpattern.creatormodel.singleton;
+
+/**
+ * 枚举单例模式
+ *
+ * @author niushuai233
+ * @date 2024/1/5 14:00
+ * @since 0.0.1
+ */
+public enum EnumSingleton {
+
+    INSTANCE;
+
+    public void hello(String item) {
+        System.out.println("Hello " + item);
+    }
+}

src/main/java/cc/niushuai/demo/designpattern/creatormodel/singleton/Singleton.java

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+/*
+ * Copyright (C) 2023 niushuai233 niushuai.cc
+ *
+ * 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
+ *
+ *         http://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 cc.niushuai.demo.designpattern.creatormodel.singleton;
+
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+/**
+ * 简单单例模式
+ *
+ * @author niushuai233
+ * @date 2024/1/5 11:17
+ * @since 0.0.1
+ */
+public class Singleton {
+
+    public static final Map<String, Object> map = new ConcurrentHashMap<>();
+
+    private Singleton() {
+        System.out.println(Thread.currentThread().getName() + " -> " + getClass().getName() + " has been initialized");
+    }
+
+    /**
+     * 简单单例模式
+     *
+     * @return
+     * @author niushuai233
+     * @date 2024/1/5 11:18
+     * @since 0.0.1
+     */
+    public static Map<String, Object> getMap() {
+        return map;
+    }
+}

src/main/java/cc/niushuai/demo/designpattern/creatormodel/singleton/lazy/LazySingleton.java

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+/*
+ * Copyright (C) 2023 niushuai233 niushuai.cc
+ *
+ * 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
+ *
+ *         http://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 cc.niushuai.demo.designpattern.creatormodel.singleton.lazy;
+
+import cn.hutool.core.date.DateUtil;
+
+/**
+ * 懒汉模式
+ *
+ * @author niushuai233
+ * @date 2024/1/5 11:14
+ * @since 0.0.1
+ */
+public class LazySingleton {
+
+    private static LazySingleton INSTANCE;
+
+    private LazySingleton() {
+        System.out.println(Thread.currentThread().getName() + " -> " + getClass().getName() + " has been initialized");
+    }
+
+    /**
+     * 获取LazySingleton 线程不安全 存在同时获取多个实例时new了多个instance到内存中
+     *
+     * @return
+     * @author niushuai233
+     * @date 2024/1/5 11:15
+     * @since 0.0.1
+     */
+    public static LazySingleton getInstance_threadUnsafe() {
+        if (null == INSTANCE) {
+            INSTANCE = new LazySingleton();
+        }
+        return INSTANCE;
+    }
+
+
+    /**
+     * 获取LazySingleton 线程安全
+     *
+     * @return
+     * @author niushuai233
+     * @date 2024/1/5 11:16
+     * @since 0.0.1
+     */
+    public static synchronized LazySingleton getInstance_threadSafe() {
+        if (null == INSTANCE) {
+            INSTANCE = new LazySingleton();
+        }
+        return INSTANCE;
+    }
+
+    public void hello(String str) {
+        System.out.println(Thread.currentThread().getName() + ": hello " + str + " ==>" + DateUtil.now());
+    }
+}

src/main/java/cc/niushuai/demo/designpattern/creatormodel/singleton/lazy/LazySingletonInnerClass.java

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+/*
+ * Copyright (C) 2023 niushuai233 niushuai.cc
+ *
+ * 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
+ *
+ *         http://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 cc.niushuai.demo.designpattern.creatormodel.singleton.lazy;
+
+import cn.hutool.core.date.DateUtil;
+
+/**
+ * 使用内部类的方式进行懒加载 自身线程安全 不需要锁来管控线程安全
+ *
+ * @author niushuai233
+ * @date 2024/1/5 11:21
+ * @since 0.0.1
+ */
+public class LazySingletonInnerClass {
+
+    public static LazySingletonInnerClass INSTANCE = new LazySingletonInnerClass();
+
+    private LazySingletonInnerClass() {
+        System.out.println(Thread.currentThread().getName() + " -> " + getClass().getName() + " has been initialized");
+    }
+
+    public static void say() {
+        INSTANCE.hello("say");
+    }
+
+    /**
+     * 自身线程安全 不需要锁 只有加载内部类时单例才会被实例化
+     *
+     * @return
+     * @author niushuai233
+     * @date 2024/1/5 11:23
+     * @since 0.0.1
+     */
+    public static LazySingletonInnerClass getInstance() {
+        return LazySingletonInnerClassHolder.INSTANCE;
+    }
+
+    public void hello(String str) {
+        System.out.println(Thread.currentThread().getName() + ": hello " + str + " ==>" + DateUtil.now());
+    }
+
+    public static class LazySingletonInnerClassHolder {
+
+        private LazySingletonInnerClassHolder() {
+            System.out.println(Thread.currentThread().getName() + " -> " + getClass().getName() + " has been initialized");
+        }
+
+        public static final LazySingletonInnerClass INSTANCE = new LazySingletonInnerClass();
+    }
+}

src/main/java/cc/niushuai/demo/designpattern/creatormodel/singleton/package-info.java

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+/*
+ * Copyright (C) 2023 niushuai233 niushuai.cc
+ *
+ * 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
+ *
+ *         http://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.
+ */
+
+/**
+ * 单例模式
+ *
+ * @author niushuai233
+ * @date 2024/1/5 11:09
+ * @since 0.0.1
+ */
+package cc.niushuai.demo.designpattern.creatormodel.singleton;

src/test/java/cc/niushuai/demo/designpattern/creatormodel/singleton/SingletonTest.java

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+/*
+ * Copyright (C) 2023 niushuai233 niushuai.cc
+ *
+ * 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
+ *
+ *         http://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 cc.niushuai.demo.designpattern.creatormodel.singleton;
+
+import cc.niushuai.demo.designpattern.creatormodel.singleton.lazy.LazySingleton;
+import cc.niushuai.demo.designpattern.creatormodel.singleton.lazy.LazySingletonInnerClass;
+import cn.hutool.core.date.DateUtil;
+import cn.hutool.core.thread.ThreadUtil;
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+import java.util.concurrent.ForkJoinPool;
+
+/**
+ * 单例模式 test
+ *
+ * @author niushuai233
+ * @date 2024/1/5 14:05
+ * @since 0.0.1
+ */
+public class SingletonTest {
+
+    @Test
+    public void testSingleton() {
+        Singleton.map.put("date", DateUtil.now());
+        System.out.println(Singleton.map.get("date"));
+    }
+
+
+    @Test
+    public void testSingleton_lazy_unsafe() {
+
+        List<String> strings = List.of("1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12");
+
+        new ForkJoinPool().submit(() -> strings.parallelStream().forEach(item -> LazySingleton.getInstance_threadUnsafe().hello(item)));
+        ThreadUtil.sleep(3000);
+        System.out.println("testSingleton_lazy_unsafe end");
+    }
+
+    @Test
+    public void testSingleton_lazy_safe() {
+
+        List<String> strings = List.of("1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12");
+
+        new ForkJoinPool().submit(() -> strings.parallelStream().forEach(item -> LazySingleton.getInstance_threadSafe().hello(item)));
+        ThreadUtil.sleep(3000);
+        System.out.println("testSingleton_lazy_unsafe end");
+    }
+
+    @Test
+    public void testSingletonInnerClass() {
+
+        LazySingletonInnerClass.say();
+        System.out.println("============================================================================================");
+
+        List<String> strings = List.of("1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12");
+        new ForkJoinPool().submit(() -> strings.parallelStream().forEach(item -> LazySingletonInnerClass.getInstance().hello(item)));
+
+        ThreadUtil.sleep(3000);
+        System.out.println("testSingletonInnerClass end");
+    }
+
+    /**
+     * 仍然有可能创建出多个对象，但是INSTANCE一旦被赋予 则不再被改变 其他已创建的对象可认同为无用对象 并且等待被GC回收
+     *
+     * @return
+     * @author niushuai233
+     * @date 2024/1/5 14:54
+     * @since 0.0.1
+     */
+    @Test
+    public void testCASSingleton() {
+
+        List<String> strings = List.of("1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12");
+        new ForkJoinPool().submit(() -> strings.parallelStream().forEach(item -> CASSingleton.getInstance().hello(item)));
+
+        CASSingleton.getInstance().hello("world");
+
+        ThreadUtil.sleep(3000);
+        System.out.println("testSingletonInnerClass end");
+    }
+
+    @Test
+    public void testEnumSingleton() {
+
+        List<String> strings = List.of("1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12");
+        new ForkJoinPool().submit(() -> strings.parallelStream().forEach(item -> EnumSingleton.INSTANCE.hello(item)));
+
+        EnumSingleton.INSTANCE.hello("world");
+
+        ThreadUtil.sleep(3000);
+        System.out.println("testEnumSingleton end");
+    }
+}