淺談 SimpleDateFormat，第三方庫joda-time，JDK8提供時間類 之性能和線程安全

文章目錄

一、java.text.SimpledateFormat

線程不安全，拋出異常寫法：

線程安全寫法：

二、joda-time

三、java.time.format.DateTimeFormatter

一、java.text.SimpleDateFormat

java.text.SimpleDateFormat 的實例對象在多線程共享使用的時候會拋出轉換異常，正確的使用方法應該是采用堆棧封閉，將其作為方法內的局部變量而不是全局變量，在每次調用方法的時候才去創建一個SimpleDateFormat實例對象，這樣利用堆棧封閉就不會出現并發問題。

線程不安全，拋出異常寫法：

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 { // 請求總數 private static int CLIENT_COUNT = 10000; // 并發線程數 private static int THREAD_COUNT = 500; // 全局變量，多線程訪問會線程不安全，拋異常 private static SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyMMdd"); public static void main(String[] args) throws InterruptedException { // 固定線程池 ExecutorService executorService = Executors.newFixedThreadPool(CLIENT_COUNT); // 控制同一個時刻，只能有多少個線程同時運行指定代碼，即acquire和release之間的代碼 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(); } }); } // 等待所有請求執行完 countDownLatch.await(); // 關閉線程池 executorService.shutdown(); } }

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線程安全寫法：

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 { // 請求總數 private static int CLIENT_COUNT = 10000; // 并發線程數 private static int THREAD_COUNT = 500; // 全局變量，多線程訪問會線程不安全，拋異常 //private static SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyMMdd"); public static void main(String[] args) throws InterruptedException { // 固定線程池 ExecutorService executorService = Executors.newFixedThreadPool(CLIENT_COUNT); // 控制同一個時刻，只能有多少個線程同時運行指定代碼，即acquire和release之間的代碼 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(); // 局部變量，線程安全 SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyMMdd"); simpleDateFormat.parse("20200917"); semaphore.release(); } catch (InterruptedException e) { e.printStackTrace(); } catch (ParseException e) { e.printStackTrace(); } finally { countDownLatch.countDown(); } }); } // 等待所有請求執行完 countDownLatch.await(); // 關閉線程池 executorService.shutdown(); } }

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二、joda-time

第三方庫 joda-time 的 DateTimeFormatter 類是線程安全的。

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 { // 請求總數 private static int CLIENT_COUNT = 10000; // 并發線程數 private static int THREAD_COUNT = 500; // 全局變量，線程安全 private static DateTimeFormatter dateTimeFormatter = DateTimeFormat.forPattern("yyyyMMdd"); public static void main(String[] args) throws InterruptedException { // 固定線程池 ExecutorService executorService = Executors.newFixedThreadPool(CLIENT_COUNT); // 控制同一個時刻，只能有多少個線程同時運行指定代碼，即acquire和release之間的代碼 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(); } }); } // 等待所有請求執行完 countDownLatch.await(); // 關閉線程池 executorService.shutdown(); } }

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三、java.time.format.DateTimeFormatter

JDK8提供了許多不可變且線程安全的類，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 { // 請求總數 private static int CLIENT_COUNT = 10000; // 并發線程數 private static int THREAD_COUNT = 500; // 全局變量，JDK8時間類，線程安全 private static DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyyMMdd"); public static void main(String[] args) throws InterruptedException { // 固定線程池 ExecutorService executorService = Executors.newFixedThreadPool(CLIENT_COUNT); // 控制同一個時刻，只能有多少個線程同時運行指定代碼，即acquire和release之間的代碼 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(); } }); } // 等待所有請求執行完 countDownLatch.await(); // 關閉線程池 executorService.shutdown(); } }

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線程安全，正常輸出

JDK 任務調度

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