懒汉单例、线程不安全测试实例

src/main/java/top/fjy8018/designpattern/pattern/creational/singleton/LazySingleton.java

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+package top.fjy8018.designpattern.pattern.creational.singleton;
+
+import lombok.extern.slf4j.Slf4j;
+
+/**
+ * 懒汉式单例：延迟加载（线程不安全）
+ *
+ * @author F嘉阳
+ * @date 2018-09-24 10:29
+ */
+@Slf4j
+public class LazySingleton {
+    private static LazySingleton lazySingleton = null;
+
+    /**
+     * 单例模式构造器必须是屏蔽的
+     */
+    private LazySingleton() {
+    }
+
+    /**
+     * 线程不安全
+     *
+     * @return
+     */
+    public static LazySingleton getInstance() {
+        if (lazySingleton == null) {
+            log.debug("LazySingleton实例化");
+            lazySingleton = new LazySingleton();
+        }
+        return lazySingleton;
+    }
+
+    /**
+     * 线程不安全验证
+     *
+     * @return
+     */
+    public static LazySingleton getInstance2() throws InterruptedException {
+        if (lazySingleton == null) {
+            // 使用线程等待模拟复杂实例化过程，让多线程同时进入该方法
+            Thread.sleep(1000);
+            log.debug("LazySingleton实例化");
+            lazySingleton = new LazySingleton();
+        }
+        return lazySingleton;
+    }
+}

src/main/java/top/fjy8018/designpattern/pattern/creational/singleton/MyRunnable.java

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+package top.fjy8018.designpattern.pattern.creational.singleton;
+
+import lombok.extern.slf4j.Slf4j;
+
+/**
+ * @author F嘉阳
+ * @date 2018-09-24 10:53
+ */
+@Slf4j
+public class MyRunnable implements Runnable {
+    @Override
+    public void run() {
+        LazySingleton lazySingleton = null;
+        try {
+            lazySingleton = LazySingleton.getInstance2();
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+        log.info(Thread.currentThread().getName() + " " + lazySingleton);
+    }
+}

src/test/java/top/fjy8018/designpattern/pattern/creational/singleton/LazySingletonTest.java

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+package top.fjy8018.designpattern.pattern.creational.singleton;
+
+import lombok.extern.slf4j.Slf4j;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+@Slf4j
+class LazySingletonTest {
+
+    /**
+     * 懒汉式注重延迟加载，当使用时才实例化
+     * 可以使用多线程测试方法或者通过多线程Debug方式测试
+     */
+    @Test
+    void getInstanceOneThread() {
+        LazySingleton lazySingleton = LazySingleton.getInstance();
+
+    }
+
+    @Test
+    void getInstanceMutilThread() throws InterruptedException {
+
+        Thread thread1 = new Thread(new MyRunnable());
+        Thread thread2 = new Thread(new MyRunnable());
+
+        thread1.start();
+        thread2.start();
+
+        Thread.sleep(3000);
+        log.debug("finish");
+
+    }
+}