java tips

标签：csdn   源码   end   call   阅读   date   ted   chain   线程   

getWriter() has already been called for this response

reason: getWriter和getOutputStream(chain.doFilter(request, response);) 二者只能选其一，调用了其中一个就不能调用另一个了

3 ways to cut out a string

• split(using RegEx, not KMP string matching arithmetic, splite one time)
• StringTokenizer(not recommended by jdk, just a legacy class, be retained for compatibility reason, split in turn)
• substring

java中获取比毫秒更为精确的时间  

System.currentTimeMillis() 的文档，原来这个方法调用了个native方法，获取的时间精度会依赖于操作系统的实现机制

在Java中可以通过System.currentTimeMillis()或者System.nanoTime() (JDK>=5.0) 方法获得当前的时间的精确值。但是通过阅读Javadoc，我们发现这两个方法并不一定保证得到你所期望的精度。先来看System.currentTimeMillis()：

Returns the current time in milliseconds. Note that while the unit of time of the return value is a millisecond, the granularity of the value depends on the underlying operating system and may be larger. For example, many operating systems measure time in units of tens of milliseconds.

如何在windows上实现精确的毫秒计时呢。答案就是用“System.nanoTime()/1000000L”代替“System.currentTimeInMills()”

http://blog.csdn.net/paul_lh/article/details/6419982

秒的换算：ms(毫秒),μs(微秒),ns(纳秒),ps(皮秒)

SimpleDateFormat && Calendar is not thread safe

java tips

标签：csdn   源码   end   call   阅读   date   ted   chain   线程   

原文地址：https://www.cnblogs.com/xiaowater/p/9552896.html