线程不安全的类与写法 线程不安全的类与写法线程不安全的类：类的对象可以同时被多个线程访问，比如抛出异常，逻辑错误。下面介绍一些常见的类。StringBuilderStringBuilder线程不安全的类代码示例package com.yanxizhu.demo.concurrency.threadUnSafetyClass; import com.yanxizhu.demo.concurrency.annotation.UnThreadSafety; import lombok.extern.slf4j.Slf4j; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; /** * @description: 线程不安全的类：StringBuilder * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/24 9:01 * @version: 1.0 */ @Slf4j @UnThreadSafety public class DemoStringBuilder { //用户数量 private static final int clientsTotal = 5000; //并发数量 private static final int concurrencyTotal = 200; //累加总和 private static StringBuilder stringBuilder = new StringBuilder(); public static void main(String[] args) throws InterruptedException { ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 final Semaphore semaphore = new Semaphore(concurrencyTotal); //闭锁 final CountDownLatch countDownLatch = new CountDownLatch(clientsTotal); for (int i = 0; i < clientsTotal; i++) { executorService.execute(()->{ try { semaphore.acquire(); update(); semaphore.release(); } catch (InterruptedException e) { log.error("出现错误:【{}】", e.getMessage()); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); log.info("字符长度Length=【{}】",stringBuilder.length()); } /** * 累加 */ private static void update(){ stringBuilder.append(1); } }每次输出字符长度不一样，也不等于5000StringBuffer线程安全的类代码示例package com.yanxizhu.demo.concurrency.threadUnSafetyClass; import com.yanxizhu.demo.concurrency.annotation.ThreadSafety; import lombok.extern.slf4j.Slf4j; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; /** * @description: 线程安全的类：StringBuffer * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/24 9:06 * @version: 1.0 */ @Slf4j @ThreadSafety public class DemoStringBuffer { //用户数量 private static final int clientsTotal = 5000; //并发数量 private static final int concurrencyTotal = 200; //累加总和 private static StringBuffer stringBuffer = new StringBuffer(); public static void main(String[] args) throws InterruptedException { ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 final Semaphore semaphore = new Semaphore(concurrencyTotal); //闭锁 final CountDownLatch countDownLatch = new CountDownLatch(clientsTotal); for (int i = 0; i < clientsTotal; i++) { executorService.execute(()->{ try { semaphore.acquire(); update(); semaphore.release(); } catch (InterruptedException e) { log.error("出现错误:【{}】", e.getMessage()); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); log.info("字符长度Length=【{}】", stringBuffer.length()); } /** * 累加 */ private static void update(){ stringBuffer.append(1); } }输出结果：每次都是长度为5000.StringBuffer为什么线程安全，看源码 @Override @HotSpotIntrinsicCandidate public synchronized StringBuffer append(int i) { toStringCache = null; super.append(i); return this; }因为StringBuffer所有的方法操作都加了synchronized。区别StringBuffer由于加了synchronized，性能上有损耗，没有StringBuilder性能高，在线程封闭中，堆栈封闭时，一般处理字符串局部变量时用StringBuilfer就行了。SimpleDateFormat线程不安全的类代码示例package com.yanxizhu.demo.concurrency.threadUnSafetyClass; import com.yanxizhu.demo.concurrency.annotation.UnThreadSafety; import lombok.extern.slf4j.Slf4j; 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; /** * @description: 线程不安全类： SimpleDateFormat * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/24 9:18 * @version: 1.0 */ @Slf4j @UnThreadSafety public class DemoSimpleDateFormat { private static SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyyMMMdd"); //用户数量 private static final int clientsTotal = 5000; //并发数量 private static final int concurrencyTotal = 200; public static void main(String[] args) throws InterruptedException { ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 final Semaphore semaphore = new Semaphore(concurrencyTotal); //闭锁 final CountDownLatch countDownLatch = new CountDownLatch(clientsTotal); for (int i = 0; i < clientsTotal; i++) { executorService.execute(()->{ try { semaphore.acquire(); update(); semaphore.release(); } catch (InterruptedException e) { log.error("出现错误:【{}】", e.getMessage()); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); } /** * 累加 */ private static void update(){ try { simpleDateFormat.parse("20220424"); } catch (ParseException e) { log.error(e.getMessage()); } } }输出结果： at java.base/java.lang.Double.parseDouble(Double.java:543) at java.base/java.text.DigitList.getDouble(DigitList.java:169) at java.base/java.text.DecimalFormat.parse(DecimalFormat.java:2126) at java.base/java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1933) at java.base/java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1541) at java.base/java.text.DateFormat.parse(DateFormat.java:393) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.update(DemoSimpleDateFormat.java:57) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.lambda$main$0(DemoSimpleDateFormat.java:40) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) at java.base/java.lang.Thread.run(Thread.java:834) Exception in thread "pool-1-thread-824" java.lang.NumberFormatException: For input string: "E.0220E0" at java.base/jdk.internal.math.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:2054) at java.base/jdk.internal.math.FloatingDecimal.parseDouble(FloatingDecimal.java:110) at java.base/java.lang.Double.parseDouble(Double.java:543) at java.base/java.text.DigitList.getDouble(DigitList.java:169) at java.base/java.text.DecimalFormat.parse(DecimalFormat.java:2126) at java.base/java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1933) at java.base/java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1541) at java.base/java.text.DateFormat.parse(DateFormat.java:393) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.update(DemoSimpleDateFormat.java:57) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.lambda$main$0(DemoSimpleDateFormat.java:40) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) at java.base/java.lang.Thread.run(Thread.java:834) Exception in thread "pool-1-thread-717" java.lang.NumberFormatException: multiple points at java.base/jdk.internal.math.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1890) at java.base/jdk.internal.math.FloatingDecimal.parseDouble(FloatingDecimal.java:110) at java.base/java.lang.Double.parseDouble(Double.java:543) at java.base/java.text.DigitList.getDouble(DigitList.java:169) at java.base/java.text.DecimalFormat.parse(DecimalFormat.java:2126) at java.base/java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1933) at java.base/java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1541) at java.base/java.text.DateFormat.parse(DateFormat.java:393) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.update(DemoSimpleDateFormat.java:57) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.lambda$main$0(DemoSimpleDateFormat.java:40) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) at java.base/java.lang.Thread.run(Thread.java:834) Exception in thread "pool-1-thread-671" java.lang.NumberFormatException: For input string: "" at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:65) at java.base/java.lang.Long.parseLong(Long.java:702) at java.base/java.lang.Long.parseLong(Long.java:817) at java.base/java.text.DigitList.getLong(DigitList.java:195) at java.base/java.text.DecimalFormat.parse(DecimalFormat.java:2121) at java.base/java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1933) at java.base/java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1541) at java.base/java.text.DateFormat.parse(DateFormat.java:393) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.update(DemoSimpleDateFormat.java:57) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.lambda$main$0(DemoSimpleDateFormat.java:40) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) at java.base/java.lang.Thread.run(Thread.java:834) Exception in thread "pool-1-thread-805" java.lang.NumberFormatException: multiple points at java.base/jdk.internal.math.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1914) at java.base/jdk.internal.math.FloatingDecimal.parseDouble(FloatingDecimal.java:110) at java.base/java.lang.Double.parseDouble(Double.java:543) at java.base/java.text.DigitList.getDouble(DigitList.java:169) at java.base/java.text.DecimalFormat.parse(DecimalFormat.java:2126) at java.base/java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1933) at java.base/java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1541) at java.base/java.text.DateFormat.parse(DateFormat.java:393) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.update(DemoSimpleDateFormat.java:57) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.lambda$main$0(DemoSimpleDateFormat.java:40) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) at java.base/java.lang.Thread.run(Thread.java:834) Exception in thread "pool-1-thread-736" java.lang.NumberFormatException: For input string: ".20220424" at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:65) at java.base/java.lang.Long.parseLong(Long.java:678) at java.base/java.lang.Long.parseLong(Long.java:817) at java.base/java.text.DigitList.getLong(DigitList.java:195) at java.base/java.text.DecimalFormat.parse(DecimalFormat.java:2121) at java.base/java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1933) at java.base/java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1541) at java.base/java.text.DateFormat.parse(DateFormat.java:393) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.update(DemoSimpleDateFormat.java:57) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.lambda$main$0(DemoSimpleDateFormat.java:40) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) at java.base/java.lang.Thread.run(Thread.java:834) Exception in thread "pool-1-thread-740" java.lang.NumberFormatException: multiple points at java.base/jdk.internal.math.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1914) at java.base/jdk.internal.math.FloatingDecimal.parseDouble(FloatingDecimal.java:110) at java.base/java.lang.Double.parseDouble(Double.java:543) at java.base/java.text.DigitList.getDouble(DigitList.java:169) at java.base/java.text.DecimalFormat.parse(DecimalFormat.java:2126) at java.base/java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1933) at java.base/java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1541) at java.base/java.text.DateFormat.parse(DateFormat.java:393) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.update(DemoSimpleDateFormat.java:57) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.lambda$main$0(DemoSimpleDateFormat.java:40) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) at java.base/java.lang.Thread.run(Thread.java:834) Exception in thread "pool-1-thread-695" java.lang.NumberFormatException: For input string: "E.0220" at java.base/jdk.internal.math.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:2054) at java.base/jdk.internal.math.FloatingDecimal.parseDouble(FloatingDecimal.java:110) at java.base/java.lang.Double.parseDouble(Double.java:543) at java.base/java.text.DigitList.getDouble(DigitList.java:169) at java.base/java.text.DecimalFormat.parse(DecimalFormat.java:2126) at java.base/java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1933) at java.base/java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1541) at java.base/java.text.DateFormat.parse(DateFormat.java:393) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.update(DemoSimpleDateFormat.java:57) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.lambda$main$0(DemoSimpleDateFormat.java:40) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) at java.base/java.lang.Thread.run(Thread.java:834) Exception in thread "pool-1-thread-888" java.lang.NumberFormatException: For input string: "202204242022042420220424" at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:65) at java.base/java.lang.Long.parseLong(Long.java:692) at java.base/java.lang.Long.parseLong(Long.java:817) at java.base/java.text.DigitList.getLong(DigitList.java:195) at java.base/java.text.DecimalFormat.parse(DecimalFormat.java:2121) at java.base/java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1933) at java.base/java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1541) at java.base/java.text.DateFormat.parse(DateFormat.java:393) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.update(DemoSimpleDateFormat.java:57) at com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormat.lambda$main$0(DemoSimpleDateFormat.java:40) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) at java.base/java.lang.Thread.run(Thread.java:834)虽然SimpleDateFormat是线程不安全的类，但是可以通过线程封闭中，堆栈封闭(栈封闭)方法，将SimpleDateFormat定义到局部变量中，每次是一个新对象，这样来保证线程安全。package com.yanxizhu.demo.concurrency.threadUnSafetyClass; import com.yanxizhu.demo.concurrency.annotation.ThreadSafety; import com.yanxizhu.demo.concurrency.annotation.UnThreadSafety; import lombok.extern.slf4j.Slf4j; 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.Semaphore; /** * @description: 线程不安全类： SimpleDateFormat,通过堆栈封闭，实现线程安全。 * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/24 9:18 * @version: 1.0 */ @Slf4j @ThreadSafety public class DemoSimpleDateFormatOk { //用户数量 private static final int clientsTotal = 5000; //并发数量 private static final int concurrencyTotal = 200; public static void main(String[] args) throws InterruptedException { ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 final Semaphore semaphore = new Semaphore(concurrencyTotal); //闭锁 final CountDownLatch countDownLatch = new CountDownLatch(clientsTotal); for (int i = 0; i < clientsTotal; i++) { executorService.execute(()->{ try { semaphore.acquire(); update(); semaphore.release(); } catch (InterruptedException e) { log.error("出现错误:【{}】", e.getMessage()); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); } /** * 通过线程封闭，将SimpleDateFormat定义在方法内，每次都是一个新的对象，来保证线程安全 */ private static void update(){ try { SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyyMMMdd"); simpleDateFormat.parse("20220424"); } catch (ParseException e) { log.error(e.getMessage()); } } }输出结果：输出5000条，一样的。09:27:17.633 [pool-1-thread-461] ERROR com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormatOk - Unparseable date: "20220424" 09:27:17.633 [pool-1-thread-460] ERROR com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormatOk - Unparseable date: "20220424" 09:27:17.634 [pool-1-thread-452] ERROR com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormatOk - Unparseable date: "20220424" 09:27:17.634 [pool-1-thread-445] ERROR com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormatOk - Unparseable date: "20220424" 09:27:17.634 [pool-1-thread-453] ERROR com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoSimpleDateFormatOk - Unparseable date: "20220424" 。。。。。joda.time第三方包中DateTimeFormatter代码示例package com.yanxizhu.demo.concurrency.threadUnSafetyClass; import com.yanxizhu.demo.concurrency.annotation.ThreadSafety; import lombok.extern.slf4j.Slf4j; import org.joda.time.DateTime; import org.joda.time.format.DateTimeFormat; import org.joda.time.format.DateTimeFormatter; import java.util.Date; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; /** * @description: 线程安全的类：Joda-time包里面的DateTimeFormatter需要单独导入 * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/24 9:31 * @version: 1.0 */ @Slf4j @ThreadSafety public class DemoJodaTime { private static DateTimeFormatter dateTimeFormatter = DateTimeFormat.forPattern("yyyyMMdd"); //用户数量 private static final int clientsTotal = 5000; //并发数量 private static final int concurrencyTotal = 200; public static void main(String[] args) throws InterruptedException { ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 final Semaphore semaphore = new Semaphore(clientsTotal); //闭锁 final CountDownLatch countDownLatch = new CountDownLatch(concurrencyTotal); for (int i = 0; i < clientsTotal; i++) { final int count = i; executorService.execute(()->{ try { semaphore.acquire(); update(count); semaphore.release(); } catch (InterruptedException e) { log.error("出现错误:【{}】", e.getMessage()); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); } /** * 通过线程安全对象dateTimeFormatter处理 */ private static void update(int count){ Date date = DateTime.parse("20220424", dateTimeFormatter).toDate(); log.info("{},{}", count, date); } }输出结果：有5000条，线程安全的09:45:06.164 [pool-1-thread-1947] INFO com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoJodaTime - 1946,Sun Apr 24 00:00:00 CST 2022 09:45:06.154 [pool-1-thread-491] INFO com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoJodaTime - 490,Sun Apr 24 00:00:00 CST 2022 09:45:06.184 [pool-1-thread-2943] INFO com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoJodaTime - 2942,Sun Apr 24 00:00:00 CST 2022 09:45:06.169 [pool-1-thread-1911] INFO com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoJodaTime - 1910,Sun Apr 24 00:00:00 CST 2022 09:45:06.169 [pool-1-thread-616] INFO com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoJodaTime - 615,Sun Apr 24 00:00:00 CST 2022 09:45:06.168 [pool-1-thread-2551] INFO com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoJodaTime - 2550,Sun Apr 24 00:00:00 CST 2022 09:45:06.144 [pool-1-thread-1415] INFO com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoJodaTime - 1414,Sun Apr 24 00:00:00 CST 2022 09:45:06.154 [pool-1-thread-4611] INFO com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoJodaTime - 4610,Sun Apr 24 00:00:00 CST 2022 09:45:06.169 [pool-1-thread-4760] INFO com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoJodaTime - 4759,Sun Apr 24 00:00:00 CST 2022 09:45:06.167 [pool-1-thread-2388] INFO com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoJodaTime - 2387,Sun Apr 24 00:00:00 CST 2022 09:45:06.184 [pool-1-thread-3990] INFO com.yanxizhu.demo.concurrency.threadUnSafetyClass.DemoJodaTime - 3989,Sun Apr 24 00:00:00 CST 2022 。。。。。ArrayList线程不安全的代码示例package com.yanxizhu.demo.concurrency.threadUnSafetyClass; import com.yanxizhu.demo.concurrency.annotation.UnThreadSafety; import lombok.extern.slf4j.Slf4j; import org.checkerframework.checker.units.qual.A; import org.joda.time.DateTime; import java.util.ArrayList; import java.util.Date; import java.util.List; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; /** * @description: 线程不安全类：ArrayList * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/24 9:52 * @version: 1.0 */ @Slf4j @UnThreadSafety public class DemoArrayList { private static List<Integer> list = new ArrayList<>(); //用户数量 private static final int clientsTotal = 5000; //并发数量 private static final int concurrencyTotal = 200; public static void main(String[] args) throws InterruptedException { ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 final Semaphore semaphore = new Semaphore(concurrencyTotal); //闭锁 final CountDownLatch countDownLatch = new CountDownLatch(clientsTotal); for (int i = 0; i < clientsTotal; i++) { final int count = i; executorService.execute(()->{ try { semaphore.acquire(); update(count); semaphore.release(); } catch (InterruptedException e) { log.error("出现错误:【{}】", e.getMessage()); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); log.info("list size:{}", list.size()); } /** * 通过线程安全对象dateTimeFormatter处理 */ private static void update(int count){ list.add(count); } }输出结果：每次输出ist长度不同，线程不安全的。HashSet线程不安全类代码示例package com.yanxizhu.demo.concurrency.threadUnSafetyClass; import com.yanxizhu.demo.concurrency.annotation.UnThreadSafety; import lombok.extern.slf4j.Slf4j; import java.util.HashSet; import java.util.Set; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; /** * @description: 线程不安全类：HashSet * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/24 9:52 * @version: 1.0 */ @Slf4j @UnThreadSafety public class DemoHashSet { private static Set<Integer> set = new HashSet<>(); //用户数量 private static final int clientsTotal = 5000; //并发数量 private static final int concurrencyTotal = 200; public static void main(String[] args) throws InterruptedException { ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 final Semaphore semaphore = new Semaphore(concurrencyTotal); //闭锁 final CountDownLatch countDownLatch = new CountDownLatch(clientsTotal); for (int i = 0; i < clientsTotal; i++) { final int count = i; executorService.execute(()->{ try { semaphore.acquire(); update(count); semaphore.release(); } catch (InterruptedException e) { log.error("出现错误:【{}】", e.getMessage()); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); log.info("set size:{}", set.size()); } /** * 通过线程安全对象dateTimeFormatter处理 */ private static void update(int count){ set.add(count); } }输出结果：每次长度不同，不是5000，线程不安全。HashMap线程不安全的代码示例package com.yanxizhu.demo.concurrency.threadUnSafetyClass; import com.yanxizhu.demo.concurrency.annotation.UnThreadSafety; import lombok.extern.slf4j.Slf4j; import java.util.*; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; /** * @description: 线程不安全类：HashMap * @author: <a href="mailto:batis@foxmail.com">清风</a> * @date: 2022/4/24 9:52 * @version: 1.0 */ @Slf4j @UnThreadSafety public class DemoHashMap { private static Map<Integer, Integer> map = new HashMap(); //用户数量 private static final int clientsTotal = 5000; //并发数量 private static final int concurrencyTotal = 200; public static void main(String[] args) throws InterruptedException { ExecutorService executorService = Executors.newCachedThreadPool(); //信号量 final Semaphore semaphore = new Semaphore(concurrencyTotal); //闭锁 final CountDownLatch countDownLatch = new CountDownLatch(clientsTotal); for (int i = 0; i < clientsTotal; i++) { final int count = i; executorService.execute(()->{ try { semaphore.acquire(); update(count); semaphore.release(); } catch (InterruptedException e) { log.error("出现错误:【{}】", e.getMessage()); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); log.info("map size:{}", map.size()); } /** * 通过线程安全对象dateTimeFormatter处理 */ private static void update(int count){ map.put(count, count); } }输出结果： 长度不是5000，每次长度不一样，线程不安全。总结：线程安全类对应的不只一个。后面专门说明。注意：先检查再执行这种类是线程不安全的，因为被分成2步了，if (condition(a)) { handle(1);}