MDC简介
MDC[http://logback.qos.ch/manual/mdc.html]是为每个线程建立一个独立的存储空间,开发人员可以根据需要把信息存入其中。MDC使用Map机制来存储信息,信息以key/value对的形式存储在Map中。
使用Servlet Filter在接收到请求时,生成UUID填充MDC。在log4j的配置中就可以使用%X{key}打印MDC中的内容,从而识别出同一次请求中的log。
以下是一个简单的MDCFilter实现示例,在MDC中填充了UUID、主机IP和主机名。UUID用于标记同一次请求中的log,主机IP和主机名方便异常发生时到相应机器上检查log。
log4j 1.x中MDCFilter实现
//MDC填充的KEY
public static final String REQUEST_UUID = "REQUEST_UUID";
public static final String HOST_IP = "HOST_IP";
public static final String HOST_NAME = "HOST_NAME";
public static final String APPKEY = "APPKEY";
private String appkey = null;
@Override
public void init(FilterConfig filterConfig) throws ServletException {
appkey = filterConfig.getInitParameter("appkey");//appkey可以在filter init-param中配置
if(appkey == null) {
appkey = "";
}
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
try {
insertIntoMDC(request);//填充MDC
chain.doFilter(request, response);
} finally {
clearMDC();//请求结束,注意清除MDC中的内容,否则会造成内存泄露问题
}
}
// 默认实现中填充了UUID,主机IP和主机地址
protected void insertIntoMDC(ServletRequest request) {
MDC.put(MDCFilter.REQUEST_UUID, UUID.randomUUID().toString());
MDC.put(MDCFilter.HOST_IP, getHostIP());
MDC.put(MDCFilter.HOST_NAME, getHostName());
MDC.put(MDCFilter.APPKEY, appkey);
}
protected void clearMDC() {
MDC.remove(MDCFilter.REQUEST_UUID);
MDC.remove(MDCFilter.HOST_IP);
MDC.remove(MDCFilter.HOST_NAME);
MDC.remove(MDCFilter.APPKEY);
}
log4j2.0中MDCFilter实现
在log4j 2.0 中,使用ThreadContext代替了MDC和
NDC[http://logging.apache.org/log4j/2.x/manual/thread-context.html]。
log4j 2.x 中,类似MDCFilter的实现:
ThreadContextFilter
public static final String REQUEST_UUID = "REQUEST_UUID";
public static final String HOST_IP = "HOST_IP";
public static final String HOST_NAME = "HOST_NAME";
public static final String APPKEY = "APPKEY";
private String appkey = null;
@Override
public void init(FilterConfig filterConfig) throws ServletException {
appkey = filterConfig.getInitParameter("appkey");//appkey可以在filter init-param中配置
if(appkey == null) {
appkey = "";
}
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
try {
insertIntoMDC(request);
chain.doFilter(request, response);
} finally {
clearMDC();
}
}
protected void insertIntoMDC(ServletRequest request) {
ThreadContext.put(ThreadContextFilter.REQUEST_UUID, UUID.randomUUID().toString());
ThreadContext.put(ThreadContextFilter.HOST_IP, getHostIP());
ThreadContext.put(ThreadContextFilter.HOST_NAME, getHostName());
ThreadContext.put(ThreadContextFilter.APPKEY, appkey);
}
protected void clearMDC() {
ThreadContext.remove(ThreadContextFilter.REQUEST_UUID);
ThreadContext.remove(ThreadContextFilter.HOST_IP);
ThreadContext.remove(ThreadContextFilter.HOST_NAME);
ThreadContext.remove(ThreadContextFilter.APPKEY);
}
log4j配置中,使用MDC
在log4j配置中,使用mdc:(log4j 1.x 与 2.x中都可以使用此配置)
log4j配置
%X{REQUEST_UUID} %X{HOST_IP} %X{HOST_NAME} %X{APPKEY}