SimpleDateFormat 格式化时间之线程安全问题

错误的示例：

package extthread;

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

public class MyThread extends Thread {

	private SimpleDateFormat sdf;
	private String dateString;

	public MyThread(SimpleDateFormat sdf, String dateString) {
		super();
		this.sdf = sdf;
		this.dateString = dateString;
	}

	@Override
	public void run() {
		try {
			Date dateRef = sdf.parse(dateString);
			String newDateString = sdf.format(dateRef).toString();
			if (!newDateString.equals(dateString)) {
				System.out.println("ThreadName=" + this.getName()
						+ "报错了 日期字符串：" + dateString + " 转换成的日期为："
						+ newDateString);
			}
		} catch (ParseException e) {
			e.printStackTrace();
		}

	}

}

package test.run;

import java.text.SimpleDateFormat;

import extthread.MyThread;

public class Test {

	public static void main(String[] args) {

		SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");

		String[] dateStringArray = new String[] { "2000-01-01", "2000-01-02",
				"2000-01-03", "2000-01-04", "2000-01-05", "2000-01-06",
				"2000-01-07", "2000-01-08", "2000-01-09", "2000-01-10" };

		MyThread[] threadArray = new MyThread[10];
		for (int i = 0; i < 10; i++) {
			threadArray[i] = new MyThread(sdf, dateStringArray[i]);
		}
		for (int i = 0; i < 10; i++) {
			threadArray[i].start();
		}

	}
}

正确的示例

package extthread;

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

import tools.DateTools;

public class MyThread extends Thread {

	private SimpleDateFormat sdf;
	private String dateString;

	public MyThread(SimpleDateFormat sdf, String dateString) {
		super();
		this.sdf = sdf;
		this.dateString = dateString;
	}

	@Override
	public void run() {
		try {
			Date dateRef = DateTools.parse("yyyy-MM-dd", dateString);
			String newDateString = DateTools.format("yyyy-MM-dd", dateRef)
					.toString();
			if (!newDateString.equals(dateString)) {
				System.out.println("ThreadName=" + this.getName()
						+ "报错了 日期字符串：" + dateString + " 转换成的日期为："
						+ newDateString);
			}
		} catch (ParseException e) {
			e.printStackTrace();
		}

	}

}

package tools;

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

public class DateTools {

	public static Date parse(String formatPattern, String dateString)
			throws ParseException {
		return new SimpleDateFormat(formatPattern).parse(dateString);
	}

	public static String format(String formatPattern, Date date) {
		return new SimpleDateFormat(formatPattern).format(date).toString();
	}

}

正确示例2

package tools;

import java.text.SimpleDateFormat;

public class DateTools {

	private static ThreadLocal<SimpleDateFormat> tl = new ThreadLocal<SimpleDateFormat>();

	public static SimpleDateFormat getSimpleDateFormat(String datePattern) {
		SimpleDateFormat sdf = null;
		sdf = tl.get();
		if (sdf == null) {
			sdf = new SimpleDateFormat(datePattern);
			tl.set(sdf);
		}
		return sdf;
	}

}