ThreadLocal原理与应用

ThreadLocal原理与应用

需求：项目中用户需要在敏感的操作上加比较详细的日志，日志的功能在dao根据需求手动写入，主要的问题是原有的接口没有传入request的相关信息，比如用户信息，我想到了 ThreadLocal，因为每个servlet是基于多线程，但是每个request的执行是再一个独立的线程中完成，ThreadLocal正适合了我这种需求，可以用来完成我对这个系统的业务扩展。

在比如struts2的ServletActionContext中对request的获取，还有hibernate中对sessin的管理就是基于ThreadLocal来实现。

看了下ThreadLocal的源码，相对简单，主要的思路是在每个Thread中维护一个ThreadLocalMap,调用ThreadLocal的 set(T value)的时候，以当前的ThreadLocal实例为key保存到当前线程的ThreadLocalMap中。

关键源码如下：

public void set(T value) {

Thread t = Thread.currentThread();

ThreadLocalMap map = getMap(t);

if (map != null)

map.set(this, value);

else

createMap(t, value);

}

public T get() {

Thread t = Thread.currentThread();

ThreadLocalMap map = getMap(t);

if (map != null) {

ThreadLocalMap.Entry e = map.getEntry(this);

if (e != null)

return (T)e.value;

}

return setInitialValue();

}

理解了上面的以后，使用起来就方便了。我的地体实现如在

1.在web.xml中配置系统每个请求都经过的过滤器

<filter>

<filter-name>AppRequestFilter</filter-name>

<filter-class>com.clifford.restaurant.AppRequestFilter</filter-class>

</filter>

<filter-mapping>

<filter-name>AppRequestFilter</filter-name>

<url-pattern>*.jsp</url-pattern>

</filter-mapping>

<filter-mapping>

<filter-name>AppRequestFilter</filter-name>

<url-pattern>*.do</url-pattern>

</filter-mapping>

2.过滤器实现

public class AppRequestFilter implements Filter{

public void destroy() {

}

public void doFilter(ServletRequest arg0, ServletResponse response,

FilterChain filterChain) throws IOException, ServletException {

HttpServletRequest request = ((HttpServletRequest)arg0);

RequestThreadLocal.setRequestThreadLocal(request);

filterChain.doFilter(request, response);

}

}

3.ThreadLocal相关实现

public class RequestThreadLocal {

private static ThreadLocal<HttpServletRequest> requestThreadLocal = new ThreadLocal<HttpServletRequest>();

public static void setRequestThreadLocal(HttpServletRequest request) {

requestThreadLocal.set(request);

}

public static User getLoginUser() {

HttpServletRequest request = requestThreadLocal.get();

Session session = request==null?null:request.getSession(false);

return session==null?null:(User)session.getAttribute(IConstants.USER_KEY);

}

public static String getRequestIp() {

HttpServletRequest request = requestThreadLocal.get();

return request==null?"":request.getRemoteHost();

}

}