浅谈 OKR 与 KPI:okr和kpi的定义和应用场景(浅谈辄止)
507
2022-05-30
文章目录
一、java.text.SimpledateFormat
线程不安全,抛出异常写法:
线程安全写法:
二、joda-time
三、java.time.format.DateTimeFormatter
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
JDK 任务调度
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