懒汉单例、synchronized确保线程安全测试实例

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

@@ -0,0 +1,52 @@
+package top.fjy8018.designpattern.pattern.creational.singleton;
+
+import lombok.extern.slf4j.Slf4j;
+
+/**
+ * 懒汉式单例：延迟加载（线程安全）
+ *
+ * @author F嘉阳
+ * @date 2018-09-24 10:29
+ */
+@Slf4j
+public class LazySingletonSynchronized {
+    private static LazySingletonSynchronized lazySingleton = null;
+
+    /**
+     * 单例模式构造器必须是屏蔽的
+     */
+    private LazySingletonSynchronized() {
+    }
+
+    /**
+     * synchronized确保线程安全
+     * synchronized用于静态方法是对class文件加锁，用于普通方法则是对堆内存中的实例方法加锁
+     * synchronized(LazySingletonSynchronized.class)与在方法名上加锁效果一致
+     *
+     * @return
+     */
+    public static LazySingletonSynchronized getInstance() {
+        synchronized (LazySingletonSynchronized.class) {
+            if (lazySingleton == null) {
+                log.debug("LazySingletonSynchronized实例化");
+                lazySingleton = new LazySingletonSynchronized();
+            }
+        }
+        return lazySingleton;
+    }
+
+    /**
+     * 线程安全验证
+     *
+     * @return
+     */
+    public synchronized static LazySingletonSynchronized 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("LazySingletonSynchronized实例化");
+            lazySingleton = new LazySingletonSynchronized();
+        }
+        return lazySingleton;
+    }
+}

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

@@ -1,21 +0,0 @@
-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/LazySingletonSynchronizedTest.java

@@ -0,0 +1,40 @@
+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 LazySingletonSynchronizedTest {
+
+    @Test
+    void getInstance() {
+        LazySingletonSynchronized.getInstance();
+    }
+
+    @Test
+    void getInstance2() throws InterruptedException {
+        Thread thread1 = new Thread(new LazySingletonSynchronizedTest.MyRunnable());
+        Thread thread2 = new Thread(new LazySingletonSynchronizedTest.MyRunnable());
+
+        thread1.start();
+        thread2.start();
+
+        Thread.sleep(3000);
+        log.debug("finish");
+    }
+
+    private class MyRunnable implements Runnable {
+        @Override
+        public void run() {
+            LazySingletonSynchronized lazySingleton = null;
+            try {
+                lazySingleton = LazySingletonSynchronized.getInstance2();
+            } catch (InterruptedException e) {
+                e.printStackTrace();
+            }
+            log.info(Thread.currentThread().getName() + " " + lazySingleton);
+        }
+    }
+}

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

@@ -31,4 +31,17 @@ class LazySingletonTest {
         log.debug("finish");
 
     }
+
+    private 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);
+        }
+    }
 }