Add additional code comments about the thread specific implementations

Author: halprin

app/src/main/java/gov/hhs/cdc/trustedintermediary/external/javalin/DomainsRegistration.java

@@ -122,7 +122,9 @@ static DomainConnector constructNewDomainConnector(Class<? extends DomainConnect
     static Handler createHandler(
             Function<DomainRequest, DomainResponse> handler, boolean isProtected) {
         return (Context ctx) -> {
-            ApplicationContext.clearThreadRegistrations();
+            ApplicationContext
+                    .clearThreadRegistrations(); // clear this thread's specific registrations from
+            // its previous use
 
             LOGGER.logInfo(ctx.method().name() + " " + ctx.url());
 

etor/src/main/java/gov/hhs/cdc/trustedintermediary/etor/EtorDomainRegistration.java

@@ -134,7 +134,6 @@ public Map<HttpEndpoint, Function<DomainRequest, DomainResponse>> domainRegistra
                     MessageLinkStorage.class, FileMessageLinkStorage.getInstance());
         }
 
-        // these are default implementations
         if (ApplicationContext.isPropertyPresent("REPORT_STREAM_URL_PREFIX")) {
             ApplicationContext.register(
                     RSEndpointClient.class, ReportStreamEndpointClient.getInstance());
@@ -176,6 +175,8 @@ DomainResponse handleResults(DomainRequest request) {
     DomainResponse handleMetadata(DomainRequest request) {
         if (Boolean.parseBoolean(request.getHeaders().get("load-test"))
                 && ApplicationContext.isPropertyPresent("REPORT_STREAM_URL_PREFIX")) {
+            // register the mock RS endpoint for this HTTP request because we don't want to call RS
+            // for real when doing a load test.
             ApplicationContext.registerForThread(
                     RSEndpointClient.class, MockRSEndpointClient.getInstance());
         }
@@ -235,6 +236,8 @@ protected DomainResponse handleMessageRequest(
 
         if (Boolean.parseBoolean(request.getHeaders().get("load-test"))
                 && ApplicationContext.isPropertyPresent("REPORT_STREAM_URL_PREFIX")) {
+            // register the mock RS endpoint for this HTTP request because we don't want to call RS
+            // for real when doing a load test.
             ApplicationContext.registerForThread(
                     RSEndpointClient.class, MockRSEndpointClient.getInstance());
         }

etor/src/main/java/gov/hhs/cdc/trustedintermediary/etor/metadata/partner/PartnerMetadataOrchestrator.java

@@ -44,6 +44,7 @@ private PartnerMetadataOrchestrator() {}
     public void updateMetadataForInboundMessage(PartnerMetadata partnerMetadata)
             throws PartnerMetadataException {
 
+        // can't @Inject because the implementation can be different for this specific thread
         RSEndpointClient rsclient = ApplicationContext.getImplementation(RSEndpointClient.class);
 
         logger.logInfo(
@@ -133,6 +134,7 @@ public Optional<PartnerMetadata> getMetadata(String inboundReportId)
         var outboundReportId = partnerMetadata.outboundReportId();
         if (metadataIsStale(partnerMetadata) && outboundReportId != null) {
 
+            // can't @Inject because the implementation can be different for this specific thread
             RSEndpointClient rsclient =
                     ApplicationContext.getImplementation(RSEndpointClient.class);
 

etor/src/main/java/gov/hhs/cdc/trustedintermediary/external/reportstream/ReportStreamSenderHelper.java

@@ -42,6 +42,7 @@ protected Optional<String> sendToReportStream(
             String body, String fhirResourceId, PartnerMetadataMessageType messageType)
             throws UnableToSendMessageException {
 
+        // can't @Inject because the implementation can be different for this specific thread
         RSEndpointClient rsclient = ApplicationContext.getImplementation(RSEndpointClient.class);
 
         String bearerToken;

shared/src/main/java/gov/hhs/cdc/trustedintermediary/context/ApplicationContext.java

@@ -43,6 +43,10 @@ public static void register(Class<?> clazz, Object implementation) {
         IMPLEMENTATIONS.add(implementation.getClass());
     }
 
+    /**
+     * Registers an implementation for a class _only_ for the current executing thread (which
+     * currently is one-to-one with an HTTP request).
+     */
     public static void registerForThread(Class<?> clazz, Object implementation) {
         Map<Class<?>, Object> threadObjectMap = THREAD_OBJECT_MAP.get();
         if (threadObjectMap == null) {
@@ -60,6 +64,7 @@ public static void registerForThread(Class<?> clazz, Object implementation) {
         injectIntoNonSingleton(implementation);
     }
 
+    /** Removes the stored implementations for the current thread that calls this method. */
     public static void clearThreadRegistrations() {
         THREAD_OBJECT_MAP.remove();
     }