Fix Class isAssignableFrom checks for Resource conversion

Issue: SPR-16606

spring-core/src/main/java/org/springframework/core/codec/ResourceDecoder.java

@@ -51,9 +51,7 @@ public class ResourceDecoder extends AbstractDataBufferDecoder<Resource> {
 	@Override
 	public boolean canDecode(ResolvableType elementType, @Nullable MimeType mimeType) {
 		Class<?> clazz = elementType.getRawClass();
-		return (clazz != null &&
-				(InputStreamResource.class == clazz || clazz.isAssignableFrom(ByteArrayResource.class)) &&
-				super.canDecode(elementType, mimeType));
+		return clazz != null && Resource.class.isAssignableFrom(clazz) && super.canDecode(elementType, mimeType);
 	}
 
 	@Override
@@ -77,7 +75,7 @@ public class ResourceDecoder extends AbstractDataBufferDecoder<Resource> {
 		if (InputStreamResource.class == clazz) {
 			return new InputStreamResource(new ByteArrayInputStream(bytes));
 		}
-		else if (clazz.isAssignableFrom(ByteArrayResource.class)) {
+		else if (Resource.class.isAssignableFrom(clazz)) {
 			return new ByteArrayResource(bytes);
 		}
 		else {

spring-core/src/test/java/org/springframework/core/codec/ResourceDecoderTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -23,7 +23,6 @@ import org.junit.Test;
 import reactor.core.publisher.Flux;
 import reactor.test.StepVerifier;
 
-import org.springframework.core.ResolvableType;
 import org.springframework.core.io.ByteArrayResource;
 import org.springframework.core.io.InputStreamResource;
 import org.springframework.core.io.Resource;
@@ -32,9 +31,8 @@ import org.springframework.core.io.buffer.DataBuffer;
 import org.springframework.util.MimeTypeUtils;
 import org.springframework.util.StreamUtils;
 
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertTrue;
-import static org.junit.Assert.fail;
+import static org.junit.Assert.*;
+import static org.springframework.core.ResolvableType.*;
 
 /**
  * @author Arjen Poutsma
@@ -44,25 +42,22 @@ public class ResourceDecoderTests extends AbstractDataBufferAllocatingTestCase {
 	private final ResourceDecoder decoder = new ResourceDecoder();
 
 	@Test
-	public void canDecode() throws Exception {
-		assertTrue(this.decoder.canDecode(ResolvableType.forClass(InputStreamResource.class),
-				MimeTypeUtils.TEXT_PLAIN));
-		assertTrue(this.decoder.canDecode(ResolvableType.forClass(ByteArrayResource.class),
-				MimeTypeUtils.TEXT_PLAIN));
-		assertTrue(this.decoder.canDecode(ResolvableType.forClass(Resource.class),
-				MimeTypeUtils.TEXT_PLAIN));
-		assertTrue(this.decoder.canDecode(ResolvableType.forClass(InputStreamResource.class),
-				MimeTypeUtils.APPLICATION_JSON));
+	public void canDecode() {
+		assertTrue(this.decoder.canDecode(forClass(InputStreamResource.class), MimeTypeUtils.TEXT_PLAIN));
+		assertTrue(this.decoder.canDecode(forClass(ByteArrayResource.class), MimeTypeUtils.TEXT_PLAIN));
+		assertTrue(this.decoder.canDecode(forClass(Resource.class), MimeTypeUtils.TEXT_PLAIN));
+		assertTrue(this.decoder.canDecode(forClass(InputStreamResource.class), MimeTypeUtils.APPLICATION_JSON));
+		assertFalse(this.decoder.canDecode(forClass(Object.class), MimeTypeUtils.APPLICATION_JSON));
 	}
 
 	@Test
-	public void decode() throws Exception {
+	public void decode() {
 		DataBuffer fooBuffer = stringBuffer("foo");
 		DataBuffer barBuffer = stringBuffer("bar");
 		Flux<DataBuffer> source = Flux.just(fooBuffer, barBuffer);
 
 		Flux<Resource> result = this.decoder
-				.decode(source, ResolvableType.forClass(Resource.class), null, Collections.emptyMap());
+				.decode(source, forClass(Resource.class), null, Collections.emptyMap());
 
 		StepVerifier.create(result)
 				.consumeNextWith(resource -> {

spring-web/src/main/java/org/springframework/http/converter/ResourceHttpMessageConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -86,7 +86,7 @@ public class ResourceHttpMessageConverter extends AbstractHttpMessageConverter<R
 				}
 			};
 		}
-		else if (clazz.isAssignableFrom(ByteArrayResource.class)) {
+		else if (Resource.class == clazz || ByteArrayResource.class.isAssignableFrom(clazz)) {
 			byte[] body = StreamUtils.copyToByteArray(inputMessage.getBody());
 			return new ByteArrayResource(body) {
 				@Override