#118 - Always default to fallback ConversionService in WebMvcLinkBuilder.

Author: odrotbohm

src/main/java/org/springframework/hateoas/server/mvc/WebMvcLinkBuilderFactory.java

@@ -148,15 +148,14 @@ public WebMvcLinkBuilder linkTo(Method method, Object... parameters) {
 		return WebMvcLinkBuilder.linkTo(method, parameters);
 	}
 
-	@SuppressWarnings("null")
-	private Supplier<ConversionService> getConversionService() {
+	private static Supplier<ConversionService> getConversionService() {
 
 		return () -> {
 
 			RequestAttributes attributes = RequestContextHolder.getRequestAttributes();
 
-			if (!ServletRequestAttributes.class.isInstance(attributes)) {
-				return null;
+			if (attributes == null || !ServletRequestAttributes.class.isInstance(attributes)) {
+				return FALLBACK_CONVERSION_SERVICE;
 			}
 
 			ServletContext servletContext = ((ServletRequestAttributes) attributes).getRequest().getServletContext();

src/test/java/org/springframework/hateoas/server/mvc/WebMvcLinkBuilderUnitTest.java

@@ -38,6 +38,7 @@
 import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.annotation.RequestParam;
 import org.springframework.web.bind.annotation.RestController;
+import org.springframework.web.context.request.RequestContextHolder;
 import org.springframework.web.util.UriComponents;
 import org.springframework.web.util.UriComponentsBuilder;
 
@@ -625,6 +626,14 @@ void parentInterfaceCanHoldSpringWebAnnotations() {
 		assertThat(link.getHref()).endsWith("/api?view=short");
 	}
 
+	@Test // #118
+	void usesFallbackConversionServiceIfNoContextIsCurrentlyPresent() {
+
+		RequestContextHolder.setRequestAttributes(null);
+
+		linkTo(methodOn(ControllerWithHandlerMethodParameterThatNeedsConversion.class).method(41L)).withSelfRel();
+	}
+
 	private static UriComponents toComponents(Link link) {
 		return UriComponentsBuilder.fromUriString(link.expand().getHref()).build();
 	}
@@ -752,4 +761,11 @@ public HttpEntity<?> root(String view) {
 			return ResponseEntity.noContent().build();
 		}
 	}
+
+	// #???
+	interface ControllerWithHandlerMethodParameterThatNeedsConversion {
+
+		@GetMapping("/{id}")
+		HttpEntity<?> method(@PathVariable Long id);
+	}
 }