Java之——SimpleDateFormat 线程不安全问题及解决方法

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今天，给大家带来一篇Java SimpleDateFormat在多线程环境下不安全的文章，Java SimpleDateFormat 是线程不安全的，当在多线程环境下使用一个DateFormat的时候是有问题的，如下面的例子

package com.lya.date;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

/**
* SimpleDateFormat在多线程下会变得不安全
* @author liuyazhuang
*
*/
public class DateFormatTest {
private static final SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
public static void main(String[] args) throws Exception {
Callable<Date> task = new Callable<Date>() {
public Date call() throws Exception {
return format.parse("2016-12-18 15:00:00");
}
};
// 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) {
System.out.println(result.get());
}
}
}

一、问题

异常1：

Exception in thread "main" java.util.concurrent.ExecutionException: java.lang.NumberFormatException: multiple points
at java.util.concurrent.FutureTask.report(FutureTask.java:122)
at java.util.concurrent.FutureTask.get(FutureTask.java:192)
at com.lya.date.DateFormatThreadSafe.main(DateFormatThreadSafe.java:35)
Caused by: java.lang.NumberFormatException: multiple points
at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1890)
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:1869)
at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1514)
at java.text.DateFormat.parse(DateFormat.java:364)
at com.lya.date.DateFormatThreadSafe$1.call(DateFormatThreadSafe.java:23)
at com.lya.date.DateFormatThreadSafe$1.call(DateFormatThreadSafe.java:1)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)

异常2

Sun Dec 18 15:00:00 CST 2016
Exception in thread "main" java.util.concurrent.ExecutionException: java.lang.NumberFormatException: For input string: "E.2122"
at java.util.concurrent.FutureTask.report(FutureTask.java:122)
at java.util.concurrent.FutureTask.get(FutureTask.java:192)
at com.lya.date.DateFormatThreadSafe.main(DateFormatThreadSafe.java:35)
Caused by: java.lang.NumberFormatException: For input string: "E.2122"
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:1869)
at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1514)
at java.text.DateFormat.parse(DateFormat.java:364)
at com.lya.date.DateFormatThreadSafe$1.call(DateFormatThreadSafe.java:23)
at com.lya.date.DateFormatThreadSafe$1.call(DateFormatThreadSafe.java:1)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)

异常3

Sun Dec 18 15:00:00 CST 2016
Sun Jan 14 00:00:00 CST 4317
Exception in thread "main" 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 com.lya.date.DateFormatThreadSafe.main(DateFormatThreadSafe.java:35)
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:1869)
at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1514)
at java.text.DateFormat.parse(DateFormat.java:364)
at com.lya.date.DateFormatThreadSafe$1.call(DateFormatThreadSafe.java:23)
at com.lya.date.DateFormatThreadSafe$1.call(DateFormatThreadSafe.java:1)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)

二、解决方案

我们可以将把DateFormat 放到ThreadLocal中解决线程安全问题，如下所示

package com.lya.date;

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

/**
* 解决SimpleDateFormat线程安全问题
* @author liuyazhuang
*
*/
public class DateFormatThreadSafe {
private static final ThreadLocal<DateFormat> DF = new ThreadLocal<DateFormat>() {
@Override
protected DateFormat initialValue() {
return new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
}
};

public static Date convert(String source) throws ParseException {
Date d = DF.get().parse(source);
return d;
}

}

测试代码如下：

package com.lya.date;

import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

/**
* 测试线程安全的DateFormat
* @author liuyazhuang
*
*/
public class DateTest {
public static void main(String[] args) throws Exception {
Callable<Date> task = new Callable<Date>() {
public Date call() throws Exception {
return DateFormatThreadSafe.convert("2016-12-18 15:00:00");
}
};
// 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) {
System.out.println(result.get());
}
}
}

输出结果如下：

Sun Dec 18 15:00:00 CST 2016
Sun Dec 18 15:00:00 CST 2016
Sun Dec 18 15:00:00 CST 2016
Sun Dec 18 15:00:00 CST 2016
Sun Dec 18 15:00:00 CST 2016
Sun Dec 18 15:00:00 CST 2016
Sun Dec 18 15:00:00 CST 2016
Sun Dec 18 15:00:00 CST 2016
Sun Dec 18 15:00:00 CST 2016
Sun Dec 18 15:00:00 CST 2016

至此，Java中的SimpleDateFormat就是线程安全的了。