Date parse() { calendar.clear(); // 清理calendar ... // 执行一些操作, 设置 calendar 的日期什么的 calendar.getTime(); // 获取calendar的时间 }
import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.Date; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.TimeUnit; public class DateFormatTest extends Thread { private static SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd"); private String name; private String dateStr; private boolean sleep; public DateFormatTest(String name, String dateStr, boolean sleep) { this.name = name; this.dateStr = dateStr; this.sleep = sleep; } @Override public void run() { Date date = null; if (sleep) { try { TimeUnit.MILLISECONDS.sleep(2000); } catch (InterruptedException e) { e.printStackTrace(); } } try { date = sdf.parse(dateStr); } catch (ParseException e) { e.printStackTrace(); } System.out.println(name " : date: " date); } public static void main(String[] args) throws InterruptedException { ExecutorService executor = Executors.newCachedThreadPool(); // A 会sleep 2s 后开始执行sdf.parse() executor.execute(new DateFormatTest("A", "1991-09-13", true)); // B 打了断点,会卡在方法中间 executor.execute(new DateFormatTest("B", "2013-09-13", false)); executor.shutdown(); } }
parse() { calendar.clear() // 这里打一个断点 calendar.getTime() }
import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.Date; import java.util.HashMap; import java.util.Map; public class DateUtil { /** 锁对象 */ private static final Object lockObj = new Object(); /** 存放不同的日期模板格式的sdf的Map */ private static Map<String, ThreadLocal<SimpleDateFormat>> sdfMap = new HashMap<String, ThreadLocal<SimpleDateFormat>>(); /** * 返回一个ThreadLocal的sdf,每个线程只会new一次sdf * * @param pattern * @return */ private static SimpleDateFormat getSdf(final String pattern) { ThreadLocal<SimpleDateFormat> tl = sdfMap.get(pattern); // 此处的双重判断和同步是为了防止sdfMap这个单例被多次put重复的sdf if (tl == null) { synchronized (lockObj) { tl = sdfMap.get(pattern); if (tl == null) { // 只有Map中还没有这个pattern的sdf才会生成新的sdf并放入map System.out.println("put new sdf of pattern " pattern " to map"); // 这里是关键,使用ThreadLocal<SimpleDateFormat>替代原来直接new SimpleDateFormat tl = new ThreadLocal<SimpleDateFormat>() { @Override protected SimpleDateFormat initialValue() { System.out.println("thread: " Thread.currentThread() " init pattern: " pattern); return new SimpleDateFormat(pattern); } }; sdfMap.put(pattern, tl); } } } return tl.get(); } /** * 是用ThreadLocal<SimpleDateFormat>来获取SimpleDateFormat,这样每个线程只会有一个SimpleDateFormat * * @param date * @param pattern * @return */ public static String format(Date date, String pattern) { return getSdf(pattern).format(date); } public static Date parse(String dateStr, String pattern) throws ParseException { return getSdf(pattern).parse(dateStr); } }
import java.text.ParseException; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.TimeUnit; public class Test { public static void main(String[] args) { final String patten1 = "yyyy-MM-dd"; final String patten2 = "yyyy-MM"; Thread t1 = new Thread() { @Override public void run() { try { DateUtil.parse("1992-09-13", patten1); } catch (ParseException e) { e.printStackTrace(); } } }; Thread t2 = new Thread() { @Override public void run() { try { DateUtil.parse("2000-09", patten2); } catch (ParseException e) { e.printStackTrace(); } } }; Thread t3 = new Thread() { @Override public void run() { try { DateUtil.parse("1992-09-13", patten1); } catch (ParseException e) { e.printStackTrace(); } } }; Thread t4 = new Thread() { @Override public void run() { try { DateUtil.parse("2000-09", patten2); } catch (ParseException e) { e.printStackTrace(); } } }; Thread t5 = new Thread() { @Override public void run() { try { DateUtil.parse("2000-09-13", patten1); } catch (ParseException e) { e.printStackTrace(); } } }; Thread t6 = new Thread() { @Override public void run() { try { DateUtil.parse("2000-09", patten2); } catch (ParseException e) { e.printStackTrace(); } } }; System.out.println("单线程执行: "); ExecutorService exec = Executors.newFixedThreadPool(1); exec.execute(t1); exec.execute(t2); exec.execute(t3); exec.execute(t4); exec.execute(t5); exec.execute(t6); exec.shutdown(); sleep(1000); System.out.println("双线程执行: "); ExecutorService exec2 = Executors.newFixedThreadPool(2); exec2.execute(t1); exec2.execute(t2); exec2.execute(t3); exec2.execute(t4); exec2.execute(t5); exec2.execute(t6); exec2.shutdown(); } private static void sleep(long millSec) { try { TimeUnit.MILLISECONDS.sleep(millSec); } catch (InterruptedException e) { e.printStackTrace(); } } }
单线程执行: put new sdf of pattern yyyy-MM-dd to map thread: Thread[pool-1-thread-1,5,main] init pattern: yyyy-MM-dd put new sdf of pattern yyyy-MM to map thread: Thread[pool-1-thread-1,5,main] init pattern: yyyy-MM 双线程执行: thread: Thread[pool-2-thread-1,5,main] init pattern: yyyy-MM-dd thread: Thread[pool-2-thread-2,5,main] init pattern: yyyy-MM thread: Thread[pool-2-thread-1,5,main] init pattern: yyyy-MM thread: Thread[pool-2-thread-2,5,main] init pattern: yyyy-MM-dd