DATAREST-1193 - DelegatingHandlerMapping is now a MatchableHandlerMapping.

DelegatingHandlerMapping now implements MatchableHandlerMapping by selecting the a delegate based on the already implemented algorithm and then invoking the ….match(…) method in case the selected one is a MatchableHandlerMapping in turn.

Refactored the internals a bit to be able to reuse the selection algorithm from both ….getHandler(…) and ….match(…).

spring-data-rest-webmvc/src/main/java/org/springframework/data/rest/webmvc/support/DelegatingHandlerMapping.java

@@ -16,6 +16,8 @@
 package org.springframework.data.rest.webmvc.support;
 
 import lombok.Getter;
+import lombok.NonNull;
+import lombok.Value;
 
 import java.util.List;
 
@@ -28,6 +30,8 @@ import org.springframework.web.HttpRequestMethodNotSupportedException;
 import org.springframework.web.bind.UnsatisfiedServletRequestParameterException;
 import org.springframework.web.servlet.HandlerExecutionChain;
 import org.springframework.web.servlet.HandlerMapping;
+import org.springframework.web.servlet.handler.MatchableHandlerMapping;
+import org.springframework.web.servlet.handler.RequestMatchResult;
 
 /**
  * A {@link HandlerMapping} that considers a {@link List} of delegates. It will keep on traversing the delegates in case
@@ -36,7 +40,7 @@ import org.springframework.web.servlet.HandlerMapping;
  * @author Oliver Gierke
  * @soundtrack Benny Greb - Stabila (Moving Parts)
  */
-public class DelegatingHandlerMapping implements HandlerMapping, Ordered {
+public class DelegatingHandlerMapping implements HandlerMapping, Ordered, MatchableHandlerMapping {
 
 	private final @Getter List<HandlerMapping> delegates;
 
@@ -67,32 +71,81 @@ public class DelegatingHandlerMapping implements HandlerMapping, Ordered {
 	 */
 	@Override
 	public HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
+		return HandlerSelectionResult.from(request, delegates).resultOrException();
+	}
 
-		Exception exception = null;
+	/* 
+	 * (non-Javadoc)
+	 * @see org.springframework.web.servlet.handler.MatchableHandlerMapping#match(javax.servlet.http.HttpServletRequest, java.lang.String)
+	 */
+	@Override
+	public RequestMatchResult match(HttpServletRequest request, String pattern) {
 
-		for (HandlerMapping delegate : delegates) {
+		try {
+			return HandlerSelectionResult.from(request, delegates).match(pattern);
+		} catch (Exception o_O) {
+			return null;
+		}
+	}
 
-			try {
+	@Value
+	private static class HandlerSelectionResult {
 
-				HandlerExecutionChain result = delegate.getHandler(request);
+		@NonNull HttpServletRequest request;
+		HandlerMapping mapping;
+		HandlerExecutionChain result;
+		Exception ignoredException;
 
-				if (result != null) {
-					return result;
+		public static HandlerSelectionResult from(HttpServletRequest request, Iterable<HandlerMapping> delegates)
+				throws Exception {
+
+			Exception ignoredException = null;
+
+			for (HandlerMapping delegate : delegates) {
+
+				try {
+
+					HandlerExecutionChain result = delegate.getHandler(request);
+
+					if (result != null) {
+						return HandlerSelectionResult.forResult(request, delegate, result);
+					}
+
+				} catch (HttpMediaTypeNotAcceptableException o_O) {
+					ignoredException = o_O;
+				} catch (HttpRequestMethodNotSupportedException o_O) {
+					ignoredException = o_O;
+				} catch (UnsatisfiedServletRequestParameterException o_O) {
+					ignoredException = o_O;
 				}
-
-			} catch (HttpMediaTypeNotAcceptableException o_O) {
-				exception = o_O;
-			} catch (HttpRequestMethodNotSupportedException o_O) {
-				exception = o_O;
-			} catch (UnsatisfiedServletRequestParameterException o_O) {
-				exception = o_O;
 			}
+
+			return HandlerSelectionResult.withoutResult(request, ignoredException);
 		}
 
-		if (exception != null) {
-			throw exception;
+		private static HandlerSelectionResult forResult(HttpServletRequest request, HandlerMapping delegate,
+				HandlerExecutionChain result) {
+			return new HandlerSelectionResult(request, delegate, result, null);
 		}
 
-		return null;
+		private static HandlerSelectionResult withoutResult(HttpServletRequest request, Exception exception) {
+			return new HandlerSelectionResult(request, null, null, exception);
+		}
+
+		public HandlerExecutionChain resultOrException() throws Exception {
+
+			if (ignoredException != null) {
+				throw ignoredException;
+			}
+
+			return result;
+		}
+
+		public RequestMatchResult match(String pattern) {
+
+			return MatchableHandlerMapping.class.isInstance(mapping) //
+					? ((MatchableHandlerMapping) mapping).match(request, pattern) //
+					: null;
+		}
 	}
 }

spring-data-rest-webmvc/src/test/java/org/springframework/data/rest/webmvc/support/DelegatingHandlerMappingUnitTests.java

@@ -17,6 +17,7 @@ package org.springframework.data.rest.webmvc.support;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.Assert.fail;
+import static org.mockito.ArgumentMatchers.*;
 import static org.mockito.Mockito.*;
 
 import java.util.Arrays;
@@ -25,12 +26,15 @@ import javax.servlet.http.HttpServletRequest;
 
 import org.junit.Test;
 import org.junit.runner.RunWith;
+import org.mockito.Answers;
 import org.mockito.Mock;
 import org.mockito.junit.MockitoJUnitRunner;
 import org.springframework.web.HttpMediaTypeNotAcceptableException;
 import org.springframework.web.HttpRequestMethodNotSupportedException;
 import org.springframework.web.bind.UnsatisfiedServletRequestParameterException;
 import org.springframework.web.servlet.HandlerMapping;
+import org.springframework.web.servlet.handler.MatchableHandlerMapping;
+import org.springframework.web.servlet.handler.RequestMatchResult;
 
 /**
  * Unit tests for {@link DelegatingHandlerMapping}.
@@ -38,7 +42,7 @@ import org.springframework.web.servlet.HandlerMapping;
  * @author Oliver Gierke
  * @soundtrack Benny Greb - Stabila (Moving Parts)
  */
-@RunWith(MockitoJUnitRunner.class)
+@RunWith(MockitoJUnitRunner.Silent.class)
 public class DelegatingHandlerMappingUnitTests {
 
 	@Mock HandlerMapping first, second;
@@ -54,6 +58,24 @@ public class DelegatingHandlerMappingUnitTests {
 		assertHandlerTriedButExceptionThrown(mapping, UnsatisfiedServletRequestParameterException.class);
 	}
 
+	@Test // DATAREST-1193
+	public void exposesMatchabilityOfSelectedMapping() {
+
+		// Given:
+		// A matching mapping that doesn't get selected
+		MatchableHandlerMapping third = mock(MatchableHandlerMapping.class);
+		doReturn(mock(RequestMatchResult.class)).when(third).match(any(), any());
+
+		// A matching mapping that gets selected
+		RequestMatchResult result = mock(RequestMatchResult.class);
+		MatchableHandlerMapping fourth = mock(MatchableHandlerMapping.class, Answers.RETURNS_MOCKS);
+		doReturn(result).when(fourth).match(any(), any());
+
+		DelegatingHandlerMapping mapping = new DelegatingHandlerMapping(Arrays.asList(first, second, third, fourth));
+
+		assertThat(mapping.match(request, "somePattern")).isEqualTo(result);
+	}
+
 	private final void assertHandlerTriedButExceptionThrown(HandlerMapping mapping, Class<? extends Exception> type)
 			throws Exception {