log4j MDC NDC应用场景
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NDC(Nested Diagnostic Context)和MDC(Mapped Diagnostic Context)是log4j种非常有用的两个类,它们用于存储应用程序的上下文信息(context infomation),从而便于在log中使用这些上下文信息。
NDC的实现是用hashtable来存储每个线程的stack信息,这个stack是每个线程可以设置当前线程的request的相关信息,然后当前线程在处理过程中只要在log4j配置打印出%x的信息,那么当前线程的整个stack信息就会在log4j打印日志的时候也会都打印出来,这样可以很好的跟踪当前request的用户行为功能。
MDC的实现是使用threadlocal来保存每个线程的Hashtable的类似map的信息,其他功能类似。
NDC的实现代码:
- public class NDC {
-
-
- static Hashtable ht = new Hashtable();
-
-
- private static Stack getCurrentStack() {
- if (ht != null) {
- return (Stack) ht.get(Thread.currentThread());
- }
- return null;
- }
-
- public
- static
- String pop() {
- Stack stack = getCurrentStack();
- if(stack != null && !stack.isEmpty())
- return ((DiagnosticContext) stack.pop()).message;
- else
- return "";
- }
- public
- static
- String peek() {
- Stack stack = getCurrentStack();
- if(stack != null && !stack.isEmpty())
- return ((DiagnosticContext) stack.peek()).message;
- else
- return "";
- }
- public
- static
- void push(String message) {
- Stack stack = getCurrentStack();
-
- if(stack == null) {
- DiagnosticContext dc = new DiagnosticContext(message, null);
- stack = new Stack();
- Thread key = Thread.currentThread();
- ht.put(key, stack);
- stack.push(dc);
- } else if (stack.isEmpty()) {
- DiagnosticContext dc = new DiagnosticContext(message, null);
- stack.push(dc);
- } else {
- DiagnosticContext parent = (DiagnosticContext) stack.peek();
- stack.push(new DiagnosticContext(message, parent));
- }
- }
MDC的实现:
在webx框架中对于log4j的MDC的处理:
先配置一个filter,这个filter是放置web.xml的最前面
- protected void populateMDC(Map<String, String> mdc) {
-
- putMDC(mdc, MDC_METHOD, request.getMethod());
-
-
- StringBuffer requestURL = request.getRequestURL();
- String queryString = trimToNull(request.getQueryString());
-
- putMDC(mdc, MDC_REQUEST_URL, getRequestURL(requestURL, null));
- putMDC(mdc, MDC_REQUEST_URL_WITH_QUERY_STRING, getRequestURL(requestURL, queryString));
-
-
- String requestURI = request.getRequestURI();
- String requestURIWithQueryString = queryString == null ? requestURI : requestURI + "?" + queryString;
-
- putMDC(mdc, MDC_REQUEST_URI, requestURI);
- putMDC(mdc, MDC_REQUEST_URI_WITH_QUERY_STRING, requestURIWithQueryString);
- putMDC(mdc, MDC_QUERY_STRING, queryString);
-
-
- putMDC(mdc, MDC_REMOTE_HOST, request.getRemoteHost());
- putMDC(mdc, MDC_REMOTE_ADDR, request.getRemoteAddr());
-
-
- putMDC(mdc, MDC_USER_AGENT, request.getHeader("User-Agent"));
-
-
- putMDC(mdc, MDC_REFERRER, request.getHeader("Referer"));
-
-
- Cookie[] cookies = request.getCookies();
- List<String> names = emptyList();
-
- if (cookies != null) {
- names = createArrayList(cookies.length);
-
- for (Cookie cookie : cookies) {
- names.add(cookie.getName());
- putMDC(mdc, MDC_COOKIE_PREFIX + cookie.getName(), cookie.getValue());
- }
-
- sort(names);
- }
-
- putMDC(mdc, MDC_COOKIES, names.toString());
- }
在finally中记住cleanMDC,否则可能会造成OOM。- try { helper.setLoggingContext();
-
- chain.doFilter(request, response);
- } finally {
- helper.clearLoggingContext();
- }
在 NDC 简介部分,我们曾经说过,%x 表示会在每个日志行上打印当前 NDC 上下文。
MDC %X{remoteAddr} {remoteAddr} 表示对应map中的remoteAddr的值
配置log4j:
- <param name="ConversionPattern" value="%d{yyyy-MM-dd HH\:mm\:ss} %X{remoteAddr} %X{requestURI} %X{referrer} %X{userAgent} %c %c - %m%n "/>
打印日志如下:2012-05-22 22:16:30 127.0.0.1 /cta/index.htm Mozilla/5.0 (Windows NT 6.1) AppleWebKit/535.19 (KHTML, like Gecko) Chrome/18.0.1025.168 Safari/535.19 com.alibaba.citrus.webx.impl.WebxRootControllerImpl com.alibaba.citrus.webx.impl.WebxRootControllerImpl - Error occurred while process request /cta/index.htm- java.lang.NullPointerException
- at com.alibaba.citrus.webx.impl.WebxControllerImpl.service(WebxControllerImpl.java:42)
- at com.alibaba.citrus.webx.impl.WebxRootControllerImpl.handleRequest(WebxRootControllerImpl.java:53)
- at com.alibaba.citrus.webx.support.AbstractWebxRootController.service(AbstractWebxRootController.java:156)
- at com.alibaba.citrus.webx.servlet.WebxFrameworkFilter.doFilter(WebxFrameworkFilter.java:141)
- at com.alibaba.citrus.webx.servlet.FilterBean.doFilter(FilterBean.java:164)
- at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1322)
- at com.alibaba.citrus.webx.servlet.SetLoggingContextFilter.doFilter(SetLoggingContextFilter.java:62)
- at com.alibaba.citrus.webx.servlet.FilterBean.doFilter(FilterBean.java:164)
- at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1322)
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