ThreadLocal实现伪单例并测试线程安全性

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

@@ -0,0 +1,28 @@
+package top.fjy8018.designpattern.pattern.creational.singleton;
+
+/**
+ * 基于{@link ThreadLocalInstance} 的（伪）单例模式，只能保证线程内单例唯一（空间换时间思想）
+ *
+ * @author F嘉阳
+ * @date 2018-09-25 16:24
+ */
+public class ThreadLocalInstance {
+    private static ThreadLocal<ThreadLocalInstance> instanceThreadLocal = new ThreadLocal<ThreadLocalInstance>() {
+        @Override
+        protected ThreadLocalInstance initialValue() {
+            return new ThreadLocalInstance();
+        }
+    };
+
+    private ThreadLocalInstance() {
+    }
+
+    /**
+     * 其基于{@link java.lang.ThreadLocal.ThreadLocalMap}实现，维护线程隔离，故不用指定key
+     *
+     * @return
+     */
+    public static ThreadLocalInstance getInstance() {
+        return instanceThreadLocal.get();
+    }
+}

src/test/java/top/fjy8018/designpattern/pattern/creational/singleton/ThreadLocalInstanceTest.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 ThreadLocalInstanceTest {
+
+    /**
+     * {@link ThreadLocal} 只能保证在同一个线程中单例安全
+     *
+     * @throws InterruptedException
+     */
+    @Test
+    void getInstance() throws InterruptedException {
+        // 在主线程中取
+        for (int i = 0; i < 5; i++) {
+            ThreadLocalInstance instance = ThreadLocalInstance.getInstance();
+            log.info(Thread.currentThread().getName() + " " + instance);
+        }
+
+        Thread thread1 = new Thread(new ThreadLocalInstanceTest.MyRunnable());
+        Thread thread2 = new Thread(new ThreadLocalInstanceTest.MyRunnable());
+
+        thread1.start();
+        thread2.start();
+
+        Thread.sleep(2000);
+        log.debug("finish");
+    }
+
+    private class MyRunnable implements Runnable {
+        @Override
+        public void run() {
+            ThreadLocalInstance instance = null;
+            try {
+                instance = ThreadLocalInstance.getInstance();
+            } catch (Exception e) {
+                e.printStackTrace();
+            }
+            log.info(Thread.currentThread().getName() + " " + instance);
+        }
+    }
+}