Clear MDC so that no “leaked” MDC values stick around for the next request.

Author: samirgarg

src/main/java/uk/gov/hmcts/cp/filters/tracing/TracingFilter.java

@@ -28,6 +28,14 @@ public TracingFilter(@Value("${spring.application.name}") final String applicati
 
     @Override
     protected void doFilterInternal(final HttpServletRequest request, final HttpServletResponse response, final FilterChain filterChain) throws ServletException, IOException {
+        try {
+            populateMDC(request, response, filterChain);
+        } finally {
+            MDC.clear();
+        }
+    }
+
+    void populateMDC(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throws IOException, ServletException {
         MDC.put(APPLICATION_NAME, applicationName);
         if (request.getHeader(TRACE_ID) != null) {
             MDC.put(TRACE_ID, request.getHeader(TRACE_ID));

src/test/java/uk/gov/hmcts/cp/filters/tracing/TracingFilterTest.java

@@ -35,7 +35,7 @@ void filter_should_use_incoming_traceId() throws ServletException, IOException {
         when(request.getHeader(TRACE_ID)).thenReturn("incoming-traceId");
         when(request.getHeader(SPAN_ID)).thenReturn("incoming-spanId");
 
-        tracingFilter.doFilterInternal(request, response, filterChain);
+        tracingFilter.populateMDC(request, response, filterChain);
 
         assertThat(MDC.get(APPLICATION_NAME)).isEqualTo("myAppName");
         verify(response).setHeader(TRACE_ID, "incoming-traceId");