Add new feature to show input mapping

src/main/java/org/springframework/samples/petclinic/system/AddSpanTagsToServlet.java

@@ -0,0 +1,47 @@
+package org.springframework.samples.petclinic.system;
+
+import brave.Span;
+import brave.Tracer;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.stereotype.Component;
+import org.springframework.web.filter.GenericFilterBean;
+
+import javax.servlet.FilterChain;
+import javax.servlet.ServletException;
+import javax.servlet.ServletRequest;
+import javax.servlet.ServletResponse;
+import java.io.IOException;
+
+@Component
+public class AddSpanTagsToServlet extends GenericFilterBean {
+
+	@Value("${petclinic.inboudExternalService.serviceType:LB}")
+	String serviceType;
+
+	@Value("${petclinic.inboudExternalService.ApplicationName:Proxy}")
+	String applicationName;
+
+	@Value("${petclinic.inboudExternalService.ComponentName:locallb}")
+	String componentName;
+
+	private final Tracer tracer;
+
+	AddSpanTagsToServlet(Tracer tracer) {
+		this.tracer = tracer;
+	}
+
+	@Override
+	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
+			throws IOException, ServletException {
+		Span currentSpan = this.tracer.currentSpan();
+		if (currentSpan == null) {
+			chain.doFilter(request, response);
+			return;
+		}
+		currentSpan.tag("_inboundExternalService", serviceType);
+		currentSpan.tag("_externalApplication", applicationName);
+		currentSpan.tag("_externalComponent", componentName);
+		chain.doFilter(request, response);
+	}
+
+}