SimpleDateFormat-多线程问题：
SimpleDateFormat类在多线程环境下中处理日期，极易出现日期转换错误的情况
1 import java.text.ParseException;
2 import java.text.SimpleDateFormat;
3 import java.util.Date;
4
5 /**
6 * 线程类
7 */
8 public class MyThread extends Thread {
9
10 private SimpleDateFormat sdf;
11 private String dateString;
12
13 public MyThread(SimpleDateFormat sdf,String dateString) {
14 this.sdf = sdf;
15 this.dateString = dateString;
16 }
17
18 @Override
19 public void run() {
20 try {
21 Date dateRef = sdf.parse(dateString);
22 String newDateString = sdf.format(dateRef).toString();
23 if(!newDateString.equals(dateString)) {
24 System.out.println("ThreadName = " + Thread.currentThread().getName()
25 + "报错了 日期字符串：" + dateString + "转换成日期为：" + newDateString);
26 }
27 } catch (ParseException e) {
28 e.printStackTrace();
29 }
30 }
31 }
1 import java.text.SimpleDateFormat;
2
3 public class Test {
4
5 /**
6 * 测试单例的SimpleDateFormat类在多线程环境下中处理日期，极易出现日期转换错误的情况
7 */
8 public static void main(String[] args) {
9 SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
10 String[] dateStringArray = new String[] {
11 "2000-01-01","2000-01-02","2000-01-03",
12 "2000-01-04","2000-01-05","2000-01-06",
13 "2000-01-07","2000-01-08","2000-01-09",
14 "2000-01-10"
15 };
16
17 MyThread[] threadArray = new MyThread[10];
18 for (int i = 0; i < 10; i++) {
19 threadArray[i] = new MyThread(sdf, dateStringArray[i]);
20 }
21 for (int i = 0; i < 10; i++) {
22 threadArray[i].start();
23 }
24 }
25 }
运行之后会输出很多的错误信息！
解决多线程出现的问题-为每个线程实例一个SimpleDateFormat：
1 import java.text.ParseException;
2 import java.util.Date;
3
4 /**
5 * 线程类
6 */
7 public class MyThread extends Thread {
8
9 private String dateString;
10 public MyThread(String dateString) {
11 this.dateString = dateString;
12 }
13
14 @Override
15 public void run() {
16 try {
17 Date dateRef = DateTools.parse("yyyy-MM-dd", dateString);
18 String newDateString = DateTools.format("yyyy-MM-dd",dateRef).toString();
19 if(!newDateString.equals(dateString)) {
20 System.out.println("ThreadName = " + Thread.currentThread().getName()
21 + "报错了 日期字符串：" + dateString + "转换成日期为：" + newDateString);
22 }
23 } catch (ParseException e) {
24 e.printStackTrace();
25 }
26 }
27 }
1 import java.text.ParseException;
2 import java.text.SimpleDateFormat;
3 import java.util.Date;
4
5 /**
6 * 日期格式化工具类
7 */
8 public class DateTools {
9
10 public static Date parse(String formatPattern,String dateString) throws ParseException {
11 return new SimpleDateFormat(formatPattern).parse(dateString);
12 }
13
14 public static String format(String formatPattern,Date date) throws ParseException {
15 return new SimpleDateFormat(formatPattern).format(date).toString();
16 }
17 }
1 public class Test {
2
3 /**
4 * 测试,运行程序后，控制台没有任何输出，也就是转换没有任何异常，
5 * 原理：创建了多个SimpleDateFormat实例
6 */
7 public static void main(String[] args) {
8 String[] dateStringArray = new String[] {
9 "2000-01-01","2000-01-02","2000-01-03",
10 "2000-01-04","2000-01-05","2000-01-06",
11 "2000-01-07","2000-01-08","2000-01-09",
12 "2000-01-10"
13 };
14
15 MyThread[] threadArray = new MyThread[10];
16 for (int i = 0; i < 10; i++) {
17 threadArray[i] = new MyThread(dateStringArray[i]);
18 }
19 for (int i = 0; i < 10; i++) {
20 threadArray[i].start();
21 }
22 }
23 }
解决多线程出现的问题-使用ThreadLocal：
1 import java.text.ParseException;
2 import java.util.Date;
3
4 /**
5 * 线程类
6 */
7 public class MyThread extends Thread {
8
9 private String dateString;
10 public MyThread(String dateString) {
11 this.dateString = dateString;
12 }
13
14 @Override
15 public void run() {
16 try {
17 Date dateRef = DateTools.getSimpleDateFormat("yyyy-MM-dd").parse(dateString);
18 String newDateString = DateTools.getSimpleDateFormat("yyyy-MM-dd").format(dateRef).toString();
19 if(!newDateString.equals(dateString)) {
20 System.out.println("ThreadName = " + Thread.currentThread().getName()
21 + "报错了 日期字符串：" + dateString + "转换成日期为：" + newDateString);
22 }
23 } catch (ParseException e) {
24 e.printStackTrace();
25 }
26 }
27 }
1 import java.text.SimpleDateFormat;
2
3 /**
4 * 日期格式化工具类,使用ThreadLocal解决SimpleDateFormat非线程安全问题
5 */
6 public class DateTools {
7
8 private static ThreadLocal t1 = new ThreadLocal<>();
9
10 public static SimpleDateFormat getSimpleDateFormat(String datePattern) {
11 SimpleDateFormat sdf = null;
12 sdf = t1.get();
13 if(sdf == null) {
14 sdf = new SimpleDateFormat(datePattern);
15 t1.set(sdf);
16 }
17 return sdf;
18 }
19 }
1 public class Test {
2
3 /**
4 * 测试,运行程序后，控制台没有任何输出，也就是转换没有任何异常
5 * 原理：每个线程都会有自己的ThreadLocal存储全局变量，也就是每个线程都有自己的SimpleDateFormat实例
6 */
7 public static void main(String[] args) {
8 String[] dateStringArray = new String[] {
9 "2000-01-01","2000-01-02","2000-01-03",
10 "2000-01-04","2000-01-05","2000-01-06",
11 "2000-01-07","2000-01-08","2000-01-09",
12 "2000-01-10"
13 };
14
15 MyThread[] threadArray = new MyThread[10];
16 for (int i = 0; i < 10; i++) {
17 threadArray[i] = new MyThread(dateStringArray[i]);
18 }
19 for (int i = 0; i < 10; i++) {
20 threadArray[i].start();
21 }
22 }
23 }