一、java.text.SimpleDateFormat
java.text.SimpleDateFormat 的实例对象在多线程共享使用的时候会抛出转换异常，正确的使用方法应该是采用堆栈封闭，将其作为方法内的局部变量而不是全局变量，在每次调用方法的时候才去创建一个SimpleDateFormat实例对象，这样利用堆栈封闭就不会出现并发问题。
线程不安全，抛出异常写法：
package com.nobody.part02;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;
/**
* @author Mr.nobody
* @Description
* @date 2020/9/17
*/
public class SimpleDateFormatDemo { // 请求总数 private static int CLIENT_COUNT = 10000; // 并发线程数 private static int THREAD_COUNT = 500; // 全局变量，多线程访问会线程不安全，抛异常 private static SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyMMdd"); public static void main(String[] args) throws InterruptedException { // 固定线程池 ExecutorService executorService = Executors.newFixedThreadPool(CLIENT_COUNT); // 控制同一个时刻，只能有多少个线程同时运行指定代码，即acquire和release之间的代码 Semaphore semaphore = new Semaphore(THREAD_COUNT); CountDownLatch countDownLatch = new CountDownLatch(CLIENT_COUNT); for (int i = 0; i < CLIENT_COUNT; i++) { executorService.execute(() -> { try { semaphore.acquire(); simpleDateFormat.parse("20200917"); semaphore.release(); } catch (InterruptedException e) { e.printStackTrace(); } catch (ParseException e) { e.printStackTrace(); } finally { countDownLatch.countDown(); } }); } // 等待所有请求执行完 countDownLatch.await(); // 关闭线程池 executorService.shutdown(); }
}
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线程安全写法：
package com.nobody.part02;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;
/**
* @author Mr.nobody
* @Description
* @date 2020/9/17
*/
public class SimpleDateFormatDemo { // 请求总数 private static int CLIENT_COUNT = 10000; // 并发线程数 private static int THREAD_COUNT = 500; // 全局变量，多线程访问会线程不安全，抛异常 //private static SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyMMdd"); public static void main(String[] args) throws InterruptedException { // 固定线程池 ExecutorService executorService = Executors.newFixedThreadPool(CLIENT_COUNT); // 控制同一个时刻，只能有多少个线程同时运行指定代码，即acquire和release之间的代码 Semaphore semaphore = new Semaphore(THREAD_COUNT); CountDownLatch countDownLatch = new CountDownLatch(CLIENT_COUNT); for (int i = 0; i < CLIENT_COUNT; i++) { executorService.execute(() -> { try { semaphore.acquire(); // 局部变量，线程安全 SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyMMdd"); simpleDateFormat.parse("20200917"); semaphore.release(); } catch (InterruptedException e) { e.printStackTrace(); } catch (ParseException e) { e.printStackTrace(); } finally { countDownLatch.countDown(); } }); } // 等待所有请求执行完 countDownLatch.await(); // 关闭线程池 executorService.shutdown(); }
}
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二、joda-time
第三方库 joda-time 的 DateTimeFormatter 类是线程安全的。
package com.nobody.part02;
import org.joda.time.DateTime;
import org.joda.time.format.DateTimeFormat;
import org.joda.time.format.DateTimeFormatter;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;
/**
* @author Mr.nobody
* @Description
* @date 2020/9/17
*/
public class JodaTimeDemo { // 请求总数 private static int CLIENT_COUNT = 10000; // 并发线程数 private static int THREAD_COUNT = 500; // 全局变量，线程安全 private static DateTimeFormatter dateTimeFormatter = DateTimeFormat.forPattern("yyyyMMdd"); public static void main(String[] args) throws InterruptedException { // 固定线程池 ExecutorService executorService = Executors.newFixedThreadPool(CLIENT_COUNT); // 控制同一个时刻，只能有多少个线程同时运行指定代码，即acquire和release之间的代码 Semaphore semaphore = new Semaphore(THREAD_COUNT); CountDownLatch countDownLatch = new CountDownLatch(CLIENT_COUNT); for (int i = 0; i < CLIENT_COUNT; i++) { executorService.execute(() -> { try { semaphore.acquire(); DateTime.parse("20200917", dateTimeFormatter).toDate(); semaphore.release(); } catch (InterruptedException e) { e.printStackTrace(); } finally { countDownLatch.countDown(); } }); } // 等待所有请求执行完 countDownLatch.await(); // 关闭线程池 executorService.shutdown(); }
}
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三、java.time.format.DateTimeFormatter
JDK8提供了许多不可变且线程安全的类，例如 java.time.LocalDate 、java.time.LocalTime，java.time.LocalDateTime 以及java.time.format.DateTimeFormatter等等。
package com.nobody.part02;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;
/**
* @author Mr.nobody
* @Description
* @date 2020/9/17
*/
public class JDK8TimeDemo { // 请求总数 private static int CLIENT_COUNT = 10000; // 并发线程数 private static int THREAD_COUNT = 500; // 全局变量，JDK8时间类，线程安全 private static DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyyMMdd"); public static void main(String[] args) throws InterruptedException { // 固定线程池 ExecutorService executorService = Executors.newFixedThreadPool(CLIENT_COUNT); // 控制同一个时刻，只能有多少个线程同时运行指定代码，即acquire和release之间的代码 Semaphore semaphore = new Semaphore(THREAD_COUNT); CountDownLatch countDownLatch = new CountDownLatch(CLIENT_COUNT); for (int i = 0; i < CLIENT_COUNT; i++) { executorService.execute(() -> { try { semaphore.acquire(); System.out.println(LocalDate.parse("20200917", dateTimeFormatter)); semaphore.release(); } catch (InterruptedException e) { e.printStackTrace(); } finally { countDownLatch.countDown(); } }); } // 等待所有请求执行完 countDownLatch.await(); // 关闭线程池 executorService.shutdown(); }
}
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线程安全，正常输出
文章来源: javalib.blog.csdn.net，作者：陈皮的JavaLib，版权归原作者所有，如需转载，请联系作者。
原文链接：javalib.blog.csdn.net/article/details/108655440