分布式链路追踪：TraceIdFilter + MDC + Skywalking

import org.apache.skywalking.apm.toolkit.trace.TraceContext;
import org.slf4j.MDC;
 
import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;
 
public class TraceIdFilter implements Filter {
 
    @Override
    public void init(FilterConfig filterConfig) {
        // 过滤器初始化
    }
 
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        try {
            HttpServletRequest httpServletRequest = (HttpServletRequest) request;
            String traceId = TraceContext.traceId();
            if (traceId == null) {
                traceId = httpServletRequest.getHeader("sw64");
                if (traceId == null) {
                    traceId = "no-traceId";
                }
            }
            MDC.put("traceId", traceId);
            chain.doFilter(request, response);
        } finally {
            MDC.clear();
        }
    }
 
    @Override
    public void destroy() {
        // 过滤器销毁
    }
}

这段代码实现了一个Filter，用于在请求处理的过程中设置SkyWalking的traceId到MDC中，以便于日志记录时携带跟踪信息。如果没有获取到SkyWalking的traceId，则使用"no-traceId"作为备用。在请求处理完成后，使用MDC.clear()清除MDC中的信息，避免内存泄漏。