java中ThreadLocal的应用场景实例分析

 //Spring TransactionSynchronizationManager类 @Override protected void doBegin(Object transaction, TransactionDefinition definition) { DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction; Connection con = null; try { //此处省略N行代码 if (txObject.isNewConnectionHolder()) { //绑定数据库连接到线程中 TransactionSynchronizationManager.bindResource(obtainDataSource(), txObject.getConnectionHolder()); } } catch (Throwable ex) { if (txObject.isNewConnectionHolder()) { //当发生异常时，移除线程中的连接 DataSourceUtils.releaseConnection(con, obtainDataSource()); txObject.setConnectionHolder(null, false); } throw new CannotCreateTransactionException("Could not open JDBC Connection for transaction", ex); } }

 private static final ThreadLocal loginUserLocal = new ThreadLocal(); public static LoginUser getLoginUser() { return loginUserLocal.get(); } public static void setLoginUser(LoginUser loginUser) { loginUserLocal.set(loginUser); } public static void clear() { loginUserLocal.remove(); } //在使用完后一定要清理防止内存泄露 try{ loginUserLocal.set(loginUser); //执行其他业务逻辑 }finally{ loginUserLocal.remove(); }

 /** * 日期工具类(使用了ThreadLocal获取SimpleDateFormat,其他方法可以直接拷贝common-lang) * @author Niu Li * @date 2016/11/19 */ public class DateUtil { private static Map> sdfMap = new HashMap>(); private static Logger logger = LoggerFactory.getLogger(DateUtil.class); public final static String MDHMSS = "MMddHHmmssSSS"; public final static String YMDHMS = "yyyyMMddHHmmss"; public final static String YMDHMS_ = "yyyy-MM-dd HH:mm:ss"; public final static String YMD = "yyyyMMdd"; public final static String YMD_ = "yyyy-MM-dd"; public final static String HMS = "HHmmss"; /** * 根据map中的key得到对应线程的sdf实例 * @param pattern map中的key * @return 该实例 */ private static SimpleDateFormat getSdf(final String pattern){ ThreadLocal sdfThread = sdfMap.get(pattern); if (sdfThread == null){ //双重检验,防止sdfMap被多次put进去值,和双重锁单例原因是一样的 synchronized (DateUtil.class){ sdfThread = sdfMap.get(pattern); if (sdfThread == null){ logger.debug("put new sdf of pattern " + pattern + " to map"); sdfThread = new ThreadLocal(){ @Override protected SimpleDateFormat initialValue() { logger.debug("thread: " + Thread.currentThread() + " init pattern: " + pattern); return new SimpleDateFormat(pattern); } }; sdfMap.put(pattern,sdfThread); } } } return sdfThread.get(); } /** * 按照指定pattern解析日期 * @param date 要解析的date * @param pattern 指定格式 * @return 解析后date实例 */ public static Date parseDate(String date,String pattern){ if(date == null) { throw new IllegalArgumentException("The date must not be null"); } try { return getSdf(pattern).parse(date); } catch (ParseException e) { e.printStackTrace(); logger.error("解析的格式不支持:"+pattern); } return null; } /** * 按照指定pattern格式化日期 * @param date 要格式化的date * @param pattern 指定格式 * @return 解析后格式 */ public static String formatDate(Date date,String pattern){ if (date == null){ throw new IllegalArgumentException("The date must not be null"); }else { return getSdf(pattern).format(date); } } }