public class DateFormatTest {
 
 private final DateFormat format =
      new SimpleDateFormat("yyyyMMdd");
 
 public Date convert(String source)
           throws ParseException{
  Date d = format.parse(source);
  return d;
 }
}

final DateFormatTest t =new DateFormatTest();
Callable<Date> task =new Callable<Date>(){
  public Date call()throws Exception {
    return t.convert("20100811");
  }
};
 
//让我们尝试2个线程的情况
ExecutorService exec = Executors.newFixedThreadPool(2);
List<Future<Date>> results =
       new ArrayList<Future<Date>>();
 
//实现5次日期转换
for(int i =0; i <5; i++){
  results.add(exec.submit(task));
}
exec.shutdown();
 
//查看结果
for(Future<Date> result : results){
  System.out.println(result.get());
}

public Date convert(String source)
          throws ParseException{
 synchronized(format) {
  Date d = format.parse(source);
  return d;
 }
}

public class DateFormatTest {
 
 private static final ThreadLocal<DateFormat> df
         = new ThreadLocal<DateFormat>(){
  @Override
  protected DateFormat initialValue() {
    return new SimpleDateFormat("yyyyMMdd");
  }
 };
 
 public Date convert(String source)
           throws ParseException{
  Date d = df.get().parse(source);
  return d;
 }
}

import org.joda.time.DateTime;
import org.joda.time.format.DateTimeFormat;
import org.joda.time.format.DateTimeFormatter;
import java.util.Date;
 
public class DateFormatTest {
 
 private final DateTimeFormatter fmt =
    DateTimeFormat.forPattern("yyyyMMdd");
 
 public Date convert(String source){
  DateTime d = fmt.parseDateTime(source);
  returnd.toDate();
 }
}