SimpleDateFormat--线程安全的操作方法(有实例)

原文网址：SimpleDateFormat--线程安全的操作方法(有实例)_IT利刃出鞘的博客-CSDN博客

简介

本文用示例介绍Java中的SimpleDateFormat的线程安全的操作方法，也介绍SimpleDateFormat为什么不是线程安全的。这两个问题也是面试中常见的问题。

线程不安全实例

package org.example.a;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.concurrent.*;

public class Demo{
    public static void main(String[] args) {
        final DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Callable<Date> task = new Callable<Date>() {
            public Date call() throws Exception {
                return dateFormat.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();
            }
        }
    }
}

执行结果（出现异常）

Sun Dec 18 15:00:34 CST 2016
Sun Dec 18 15:00:34 CST 2016
Sun Dec 18 15:00:34 CST 2016
java.util.concurrent.ExecutionException: java.lang.NumberFormatException: For input string: "E34"
    at java.util.concurrent.FutureTask.report(FutureTask.java:122)
    at java.util.concurrent.FutureTask.get(FutureTask.java:192)
    at org.example.a.Demo.main(Demo.java:29)
Caused by: java.lang.NumberFormatException: For input string: "E34"
    at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
    at java.lang.Long.parseLong(Long.java:589)
    at java.lang.Long.parseLong(Long.java:631)
    at java.text.DigitList.getLong(DigitList.java:195)
    at java.text.DecimalFormat.parse(DecimalFormat.java:2051)
    at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:2162)
    at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1514)
    at java.text.DateFormat.parse(DateFormat.java:364)
    at org.example.a.Demo$1.call(Demo.java:15)
    at org.example.a.Demo$1.call(Demo.java:13)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)
java.util.concurrent.ExecutionException: java.lang.NumberFormatException: For input string: "E342"
    at java.util.concurrent.FutureTask.report(FutureTask.java:122)
    at java.util.concurrent.FutureTask.get(FutureTask.java:192)
Sun Dec 18 15:00:34 CST 2016    at org.example.a.Demo.main(Demo.java:29)
Caused by: java.lang.NumberFormatException: For input string: "E342"
    at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:2043)
    at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:110)
    at java.lang.Double.parseDouble(Double.java:538)
    at java.text.DigitList.getDouble(DigitList.java:169)
    at java.text.DecimalFormat.parse(DecimalFormat.java:2056)
    at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:2162)
    at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1514)
    at java.text.DateFormat.parse(DateFormat.java:364)
    at org.example.a.Demo$1.call(Demo.java:15)
    at org.example.a.Demo$1.call(Demo.java:13)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    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:192)
    at org.example.a.Demo.main(Demo.java:29)
Caused by: java.lang.NumberFormatException: For input string: ""
    at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
    at java.lang.Long.parseLong(Long.java:601)
    at java.lang.Long.parseLong(Long.java:631)
    at java.text.DigitList.getLong(DigitList.java:195)
    at java.text.DecimalFormat.parse(DecimalFormat.java:2051)
    at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:2162)
    at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1514)
    at java.text.DateFormat.parse(DateFormat.java:364)
    at org.example.a.Demo$1.call(Demo.java:15)
    at org.example.a.Demo$1.call(Demo.java:13)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)
Sun Dec 18 15:00:34 CST 2016
Sun Dec 18 15:00:34 CST 2016
Sun Dec 18 15:00:34 CST 2016 

线程不安全原因

上边是文章的部分内容，为便于维护，全文已迁移到此网址：SimpleDateFormat-线程安全的操作方法(有实例) - 自学精灵