Merge pull request #330 from AxonFramework/bug/327-instance-without-command-handlers

[#327] Default local `ServiceInstance` to a fixed `URI` i.o. `null`

Author: smcvb

springcloud/src/main/java/org/axonframework/extensions/springcloud/commandhandling/mode/AbstractCapabilityDiscoveryMode.java

@@ -18,8 +18,10 @@
 
 import org.axonframework.commandhandling.distributed.CommandMessageFilter;
 import org.axonframework.common.AxonConfigurationException;
+import org.springframework.cloud.client.DefaultServiceInstance;
 import org.springframework.cloud.client.ServiceInstance;
 
+import java.net.URI;
 import java.util.concurrent.atomic.AtomicReference;
 
 /**
@@ -42,7 +44,7 @@ public abstract class AbstractCapabilityDiscoveryMode<B extends CapabilityDiscov
      */
     protected AbstractCapabilityDiscoveryMode(Builder<B> builder) {
         builder.validate();
-        localInstance = new AtomicReference<>();
+        localInstance = new AtomicReference<>(FixedURIServiceInstance.INSTANCE);
         localCapabilities = new AtomicReference<>(DefaultMemberCapabilities.INCAPABLE_MEMBER);
     }
 
@@ -76,4 +78,23 @@ protected abstract static class Builder<B extends CapabilityDiscoveryMode> {
          */
         protected abstract void validate();
     }
+
+    /**
+     * This no-op version of the {@link DefaultServiceInstance} enforces the {@link ServiceInstance#getUri()} to a fixed
+     * empty {@link URI}. Through this, there's always a {@code ServiceInstance} present that will never match others.
+     * <p>
+     * This no-op version is the default local {@code ServiceInstance}, ensuring that when
+     * {@link #updateLocalCapabilities(ServiceInstance, int, CommandMessageFilter)} is never invoked (when an instance
+     * has zero command handlers) it will still play nicely in the discovery mechanism.
+     */
+    private static class FixedURIServiceInstance extends DefaultServiceInstance {
+
+        private static final ServiceInstance INSTANCE = new FixedURIServiceInstance();
+        private static final URI FIXED_URI = URI.create("");
+
+        @Override
+        public URI getUri() {
+            return FIXED_URI;
+        }
+    }
 }

springcloud/src/test/java/org/axonframework/extensions/springcloud/commandhandling/mode/RestCapabilityDiscoveryModeTest.java

@@ -66,7 +66,7 @@ void setUp() {
     }
 
     @Test
-    void testGetLocalMemberCapabilitiesReturnsIncapableMemberIfLocalCapabilitiesIsNeverUpdated() {
+    void getLocalMemberCapabilitiesReturnsIncapableMemberIfLocalCapabilitiesIsNeverUpdated() {
         SerializedMemberCapabilities result = ((RestCapabilityDiscoveryMode) testSubject).getLocalMemberCapabilities();
 
         DefaultMemberCapabilities deserializableResult =
@@ -76,7 +76,7 @@ void testGetLocalMemberCapabilitiesReturnsIncapableMemberIfLocalCapabilitiesIsNe
     }
 
     @Test
-    void testGetLocalMemberCapabilitiesReturnsUpdatedLocalCapabilities() {
+    void getLocalMemberCapabilitiesReturnsUpdatedLocalCapabilities() {
         testSubject.updateLocalCapabilities(localInstance, LOAD_FACTOR, COMMAND_MESSAGE_FILTER);
 
         SerializedMemberCapabilities result = ((RestCapabilityDiscoveryMode) testSubject).getLocalMemberCapabilities();
@@ -88,7 +88,7 @@ void testGetLocalMemberCapabilitiesReturnsUpdatedLocalCapabilities() {
     }
 
     @Test
-    void testCapabilitiesReturnsLocalCapabilitiesIfLocalServiceInstanceIsUsed() {
+    void capabilitiesReturnsLocalCapabilitiesIfLocalServiceInstanceIsUsed() {
         testSubject.updateLocalCapabilities(localInstance, LOAD_FACTOR, COMMAND_MESSAGE_FILTER);
 
         Optional<MemberCapabilities> resultCapabilities = testSubject.capabilities(localInstance);
@@ -101,7 +101,7 @@ void testCapabilitiesReturnsLocalCapabilitiesIfLocalServiceInstanceIsUsed() {
     }
 
     @Test
-    void testCapabilitiesReturnsLocalCapabilitiesIfServiceInstanceUriMatches() {
+    void capabilitiesReturnsLocalCapabilitiesIfServiceInstanceUriMatches() {
         URI testURI = URI.create("http://remote");
         when(localInstance.getUri()).thenReturn(testURI);
 
@@ -120,9 +120,8 @@ void testCapabilitiesReturnsLocalCapabilitiesIfServiceInstanceUriMatches() {
     }
 
     @Test
-    void testCapabilitiesGetsCapabilitiesThroughRestTemplate() {
+    void capabilitiesGetsCapabilitiesThroughRestTemplate() {
         MemberCapabilities expectedCapabilities = new DefaultMemberCapabilities(LOAD_FACTOR, COMMAND_MESSAGE_FILTER);
-        testSubject.updateLocalCapabilities(localInstance, LOAD_FACTOR, COMMAND_MESSAGE_FILTER);
 
         URI testURI = URI.create("http://remote");
         ServiceInstance testServiceInstance = mock(ServiceInstance.class);
@@ -158,7 +157,7 @@ void testCapabilitiesGetsCapabilitiesThroughRestTemplate() {
     }
 
     @Test
-    void testCapabilitiesRethrowsHttpClientErrorExceptionAsServiceInstanceClientException() {
+    void capabilitiesRethrowsHttpClientErrorExceptionAsServiceInstanceClientException() {
         testSubject.updateLocalCapabilities(localInstance, LOAD_FACTOR, COMMAND_MESSAGE_FILTER);
 
         when(restTemplate.exchange(
@@ -182,7 +181,7 @@ void testCapabilitiesRethrowsHttpClientErrorExceptionAsServiceInstanceClientExce
     }
 
     @Test
-    void testCapabilitiesReturnsIncapableMemberWhenNonHttpClientErrorExceptionIsThrown() {
+    void capabilitiesReturnsIncapableMemberWhenNonHttpClientErrorExceptionIsThrown() {
         testSubject.updateLocalCapabilities(localInstance, LOAD_FACTOR, COMMAND_MESSAGE_FILTER);
 
         when(restTemplate.exchange(