SimpleDateFormat线程不安全原因

最新推荐文章于 2025-06-17 16:42:16 发布

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最新推荐文章于 2025-06-17 16:42:16 发布

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分类专栏：技术类文章标签：多线程

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本文探讨了SimpleDateFormat在多线程环境下引发的线程安全问题，并提供了几种解决方案，包括在每个线程中创建独立的SimpleDateFormat实例，使用ThreadLocal，以及对共享实例进行同步。

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SimpleDateFormat线上报了各种各样奇怪的格式转换的错误，通过小的demo来解决这个问题

public static void main(String[] args) {
	final DateFormat YYYY_MM_DD_HH_MM_SS = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
	Callable<Date> task = new Callable<Date>() {
		public Date call() throws Exception {
			return YYYY_MM_DD_HH_MM_SS.parse("2016-12-18 15:00:34");
		}
	};
	
	// 创建5个线程的线程池
	ExecutorService exec = Executors.newFixedThreadPool(5);
	List<Future<Date>> results = new ArrayList<Future<Date>>();
	for (int i = 0; i < 10; i++) {
		results.add(exec.submit(task));
	}
	exec.shutdown();
	// 输出结果
	for (Future<Date> result : results) {
		try {
			System.out.println(result.get());
		} catch (InterruptedException e) {
			e.printStackTrace();
		} catch (ExecutionException e) {
			e.printStackTrace();
		}
	}
}

错误如下：
[^2]java.util.concurrent.ExecutionException: java.lang.NumberFormatException: multiple points
Sun Dec 18 15:00:34 CST 2016
Sun Dec 18 15:00:34 CST 2016
Sun Dec 18 15:00:34 CST 2016
at java.util.concurrent.FutureTask.report(FutureTask.java:122)
Sun Dec 18 15:00:34 CST 2016
at java.util.concurrent.FutureTask.get(FutureTask.java:188)
at com.lucky.waimai.api.controller.callback.meituan.order.OrderControllerTest.main(OrderControllerTest.java:96)
Caused by: java.lang.NumberFormatException: multiple points
at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1110)
at java.lang.Double.parseDouble(Double.java:540)
at java.text.DigitList.getDouble(DigitList.java:168)
at java.text.DecimalFormat.parse(DecimalFormat.java:1321)
at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:2088)
at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1455)
at java.text.DateFormat.parse(DateFormat.java:355)
at com.lucky.waimai.api.controller.callback.meituan.order.OrderControllerTest$1.call(OrderControllerTest.java:82)
at com.lucky.waimai.api.controller.callback.meituan.order.OrderControllerTest $1 . c a l l (O r d e r C o n t r o l l e r T e s t . j a v a : 79) a t j a v a . u t i l . c o n c u r r e n t . F u t u r e T a s k . r u n (F u t u r e T a s k . j a v a : 262) a t j a v a . u t i l . c o n c u r r e n t . T h r e a d P o o l E x e c u t o r . r u n W o r k e r (T h r e a d P o o l E x e c u t o r . j a v a : 1145) a t j a v a . u t i l . c o n c u r r e n t . T h r e a d P o o l E x e c u t o r$ Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)
java.util.concurrent.ExecutionException: java.lang.NumberFormatException: multiple points
at java.util.concurrent.FutureTask.report(FutureTask.java:122)
at java.util.concurrent.FutureTask.get(FutureTask.java:188)
Sun Dec 18 15:00:34 CST 2016
at com.lucky.waimai.api.controller.callback.meituan.order.OrderControllerTest.main(OrderControllerTest.java:96)
Caused by: java.lang.NumberFormatException: multiple points
at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1110)
at java.lang.Double.parseDouble(Double.java:540)
at java.text.DigitList.getDouble(DigitList.java:168)
at java.text.DecimalFormat.parse(DecimalFormat.java:1321)
at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1793)
at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1455)
at java.text.DateFormat.parse(DateFormat.java:355)
at com.lucky.waimai.api.controller.callback.meituan.order.OrderControllerTest$1.call(OrderControllerTest.java:82)
at com.lucky.waimai.api.controller.callback.meituan.order.OrderControllerTest $1 . c a l l (O r d e r C o n t r o l l e r T e s t . j a v a : 79) a t j a v a . u t i l . c o n c u r r e n t . F u t u r e T a s k . r u n (F u t u r e T a s k . j a v a : 262) a t j a v a . u t i l . c o n c u r r e n t . T h r e a d P o o l E x e c u t o r . r u n W o r k e r (T h r e a d P o o l E x e c u t o r . j a v a : 1145) a t j a v a . u t i l . c o n c u r r e n t . T h r e a d P o o l E x e c u t o r$ Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)
java.util.concurrent.ExecutionException: java.lang.NumberFormatException: For input string: “”
at java.util.concurrent.FutureTask.report(FutureTask.java:122)
at java.util.concurrent.FutureTask.get(FutureTask.java:188)
at com.lucky.waimai.api.controller.callback.meituan.order.OrderControllerTest.main(OrderControllerTest.java:96)
Caused by: java.lang.NumberFormatException: For input string: “”
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
at java.lang.Long.parseLong(Long.java:453)
at java.lang.Long.parseLong(Long.java:483)

查询资料，SimpleDateFormat是线程非安全的，顾需要对之前代码作出改造：

public static void main(String[] args) {
	Callable<Date> task = new Callable<Date>() {
		public Date call() throws Exception {
			DateFormat YYYY_MM_DD_HH_MM_SS = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
			return YYYY_MM_DD_HH_MM_SS.parse("2016-12-18 15:00:34");
		}
	};
	
	// 创建5个线程的线程池
	ExecutorService exec = Executors.newFixedThreadPool(5);
	List<Future<Date>> results = new ArrayList<Future<Date>>();
	for (int i = 0; i < 10; i++) {
		results.add(exec.submit(task));
	}
	exec.shutdown();
	// 输出结果
	for (Future<Date> result : results) {
		try {
			System.out.println(result.get());
		} catch (InterruptedException e) {
			e.printStackTrace();
		} catch (ExecutionException e) {
			e.printStackTrace();
		}
	}
}

运行结果如下：
在这里插入图片描述
实质上就是每次在线程开始时都要去初始化SimpleDateFormat，这样每个线程单独分配空间，就可以避免线程非安全问题。