Add Feign expanders based on Spring conversion service

Automatically registers Spring conversion-based Feign Expanders
when available

Fixes gh-841

spring-cloud-netflix-core/src/main/java/org/springframework/cloud/netflix/feign/support/SpringMvcContract.java

@@ -33,12 +33,15 @@ import org.springframework.cloud.netflix.feign.annotation.RequestParamParameterP
 import org.springframework.core.DefaultParameterNameDiscoverer;
 import org.springframework.core.ParameterNameDiscoverer;
 import org.springframework.core.annotation.AnnotationUtils;
+import org.springframework.core.convert.ConversionService;
+import org.springframework.core.convert.support.DefaultConversionService;
 import org.springframework.util.Assert;
 import org.springframework.web.bind.annotation.RequestMapping;
 
 import feign.Contract;
 import feign.Feign;
 import feign.MethodMetadata;
+import feign.Param;
 
 import static feign.Util.checkState;
 import static feign.Util.emptyToNull;
@@ -58,14 +61,24 @@ public class SpringMvcContract extends Contract.BaseContract {
 	private final Map<Class<? extends Annotation>, AnnotatedParameterProcessor> annotatedArgumentProcessors;
 	private final Map<String, Method> processedMethods = new HashMap<>();
 
+	private final ConversionService conversionService;
+
 	public SpringMvcContract() {
 		this(Collections.<AnnotatedParameterProcessor> emptyList());
 	}
 
 	public SpringMvcContract(
 			List<AnnotatedParameterProcessor> annotatedParameterProcessors) {
+		this(annotatedParameterProcessors, new DefaultConversionService());
+	}
+
+	public SpringMvcContract(
+			List<AnnotatedParameterProcessor> annotatedParameterProcessors,
+			ConversionService conversionService) {
 		Assert.notNull(annotatedParameterProcessors,
 				"Parameter processors can not be null.");
+		Assert.notNull(conversionService,
+				"ConversionService can not be null.");
 
 		List<AnnotatedParameterProcessor> processors;
 		if (!annotatedParameterProcessors.isEmpty()) {
@@ -75,6 +88,8 @@ public class SpringMvcContract extends Contract.BaseContract {
 			processors = getDefaultAnnotatedArgumentsProcessors();
 		}
 		this.annotatedArgumentProcessors = toAnnotatedArgumentProcessorMap(processors);
+		this.conversionService = conversionService;
+		ConvertingExpander.CONVERSION_SERVICE.set(conversionService);
 	}
 
 	@Override
@@ -183,6 +198,11 @@ public class SpringMvcContract extends Contract.BaseContract {
 						processParameterAnnotation);
 			}
 		}
+		if (isHttpAnnotation && data.indexToExpanderClass().get(paramIndex) == null
+				&& this.conversionService.canConvert(
+						method.getParameterTypes()[paramIndex], String.class)) {
+			data.indexToExpanderClass().put(paramIndex, ConvertingExpander.class);
+		}
 		return isHttpAnnotation;
 	}
 
@@ -292,4 +312,23 @@ public class SpringMvcContract extends Contract.BaseContract {
 		}
 	}
 
+	public static class ConvertingExpander implements Param.Expander {
+		static final ThreadLocal<ConversionService> CONVERSION_SERVICE = new ThreadLocal<ConversionService>() {
+			protected ConversionService initialValue() {
+				return new DefaultConversionService();
+			}
+		};
+
+		private final ConversionService conversionService;
+
+		public ConvertingExpander() {
+			this.conversionService = CONVERSION_SERVICE.get();
+		}
+
+		@Override
+		public String expand(Object value) {
+			return conversionService.convert(value, String.class);
+		}
+
+	}
 }

spring-cloud-netflix-core/src/test/java/org/springframework/cloud/netflix/feign/valid/FeignClientTests.java

@@ -29,6 +29,7 @@ import java.lang.reflect.Proxy;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Locale;
 import java.util.concurrent.Future;
 import java.util.concurrent.TimeUnit;
 
@@ -105,6 +106,15 @@ public class FeignClientTests {
 	@Autowired
 	HystrixClient hystrixClient;
 
+	protected enum Arg {
+		A, B;
+
+		@Override
+		public String toString() {
+			return name().toLowerCase(Locale.ENGLISH);
+		}
+	}
+
 	@FeignClient(value = "localapp", configuration = TestClientConfig.class)
 	protected interface TestClient {
 		@RequestMapping(method = RequestMethod.GET, value = "/hello")
@@ -130,6 +140,9 @@ public class FeignClientTests {
 
 		@RequestMapping(method = RequestMethod.HEAD, value = "/head")
 		ResponseEntity head();
+
+		@RequestMapping(method = RequestMethod.GET, value = "/tostring")
+		String getToString(@RequestParam("arg") Arg arg);
 	}
 
 	public static class TestClientConfig {
@@ -271,6 +284,10 @@ public class FeignClientTests {
 			return ResponseEntity.status(HttpStatus.NOT_FOUND).body((String)null);
 		}
 
+		@RequestMapping(method = RequestMethod.GET, value = "/tostring")
+		String getToString(@RequestParam("arg") Arg arg) {
+			return arg.toString();
+		}
 
 		public static void main(String[] args) {
 			new SpringApplicationBuilder(Application.class).properties(
@@ -375,6 +392,12 @@ public class FeignClientTests {
 		assertNull("response body was not null", response.getBody());
 	}
 
+	@Test
+	public void testConvertingExpander() {
+		assertEquals(Arg.A.toString(), testClient.getToString(Arg.A));
+		assertEquals(Arg.B.toString(), testClient.getToString(Arg.B));
+	}
+
 	@Test
 	public void testHystrixFallbackWorks() {
 		Hello hello = hystrixClient.fail();