多线程编程

code/Java/java-concurrency/src/main/java/com/heibaiying/threadLocal/J1_ThreadUnsafe.java

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+package com.heibaiying.threadLocal;
+
+import java.text.ParseException;
+import java.text.SimpleDateFormat;
+import java.util.Date;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.atomic.AtomicInteger;
+
+/**
+ * 线程不安全的SimpleDateFormat
+ */
+public class J1_ThreadUnsafe {
+
+	private static final SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
+	private static int sum = 1000;
+	private static CountDownLatch countDownLatch = new CountDownLatch(sum);
+	private static AtomicInteger atomicInteger = new AtomicInteger(0);
+
+	static class Task implements Runnable {
+
+		@Override
+		public void run() {
+			try {
+				Date parse = sdf.parse("2018-08-08 08:08:08");
+				System.out.println(parse);
+				atomicInteger.incrementAndGet();
+			} catch (ParseException e) {
+				e.printStackTrace();
+			} finally {
+				countDownLatch.countDown();
+			}
+		}
+	}
+
+	public static void main(String[] args) throws InterruptedException {
+		ExecutorService executorService = Executors.newFixedThreadPool(10);
+		for (int i = 0; i < sum; i++) {
+			executorService.execute(new Task());
+		}
+		countDownLatch.await();
+		System.out.println("格式化成功次数为：" + atomicInteger.get());
+	}
+}

code/Java/java-concurrency/src/main/java/com/heibaiying/threadLocal/J2_ThreadSafe.java

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+package com.heibaiying.threadLocal;
+
+import java.text.ParseException;
+import java.text.SimpleDateFormat;
+import java.util.Date;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.atomic.AtomicInteger;
+
+/**
+ * 使用ThreadLocal来保证线程安全
+ */
+public class J2_ThreadSafe {
+
+	private static ThreadLocal<SimpleDateFormat> threadLocal = new ThreadLocal<>();
+	private static int sum = 1000;
+	private static CountDownLatch countDownLatch = new CountDownLatch(sum);
+	private static AtomicInteger atomicInteger = new AtomicInteger(0);
+
+	static class Task implements Runnable {
+
+		@Override
+		public void run() {
+			try {
+				if (threadLocal.get() == null) {
+					threadLocal.set(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));
+				}
+				Date parse = threadLocal.get().parse("2018-08-08 08:08:08");
+				System.out.println(parse);
+				atomicInteger.incrementAndGet();
+			} catch (ParseException e) {
+				e.printStackTrace();
+			} finally {
+				countDownLatch.countDown();
+			}
+		}
+	}
+
+	public static void main(String[] args) throws InterruptedException {
+		ExecutorService executorService = Executors.newFixedThreadPool(10);
+		for (int i = 0; i < sum; i++) {
+			executorService.execute(new Task());
+		}
+		countDownLatch.await();
+		System.out.println("格式化成功次数为：" + atomicInteger.get());
+		executorService.shutdown();
+	}
+}