Support CharSequence for response body

Issue: SPR-13423

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/AbstractMessageConverterMethodProcessor.java

@@ -170,6 +170,13 @@ public abstract class AbstractMessageConverterMethodProcessor extends AbstractMe
 
 		Class<?> returnValueClass = getReturnValueType(returnValue, returnType);
 		Type returnValueType = getGenericType(returnType);
+
+		if (returnValue != null && returnValue instanceof CharSequence) {
+			returnValueClass = String.class;
+			returnValueType = String.class;
+			returnValue = (T) returnValue.toString();
+		}
+
 		HttpServletRequest servletRequest = inputMessage.getServletRequest();
 		List<MediaType> requestedMediaTypes = getAcceptableMediaTypes(servletRequest);
 		List<MediaType> producibleMediaTypes = getProducibleMediaTypes(servletRequest, returnValueClass, returnValueType);

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/HttpEntityMethodProcessorTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2016 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.
@@ -19,7 +19,6 @@ package org.springframework.web.servlet.mvc.method.annotation;
 import java.io.Serializable;
 import java.lang.reflect.Method;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 
@@ -31,7 +30,10 @@ import org.junit.Test;
 import org.springframework.core.MethodParameter;
 import org.springframework.http.HttpEntity;
 import org.springframework.http.MediaType;
+import org.springframework.http.ResponseEntity;
+import org.springframework.http.converter.ByteArrayHttpMessageConverter;
 import org.springframework.http.converter.HttpMessageConverter;
+import org.springframework.http.converter.StringHttpMessageConverter;
 import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
 import org.springframework.mock.web.test.MockHttpServletRequest;
 import org.springframework.mock.web.test.MockHttpServletResponse;
@@ -45,7 +47,10 @@ import org.springframework.web.context.request.ServletWebRequest;
 import org.springframework.web.method.HandlerMethod;
 import org.springframework.web.method.support.ModelAndViewContainer;
 
-import static org.junit.Assert.*;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
 
 /**
  * Test fixture with {@link HttpEntityMethodProcessor} delegating to
@@ -182,11 +187,35 @@ public class HttpEntityMethodProcessorTests {
 		assertTrue(content.contains("\"type\":\"bar\""));
 	}
 
+	// SPR-13423
+
+	@Test
+	public void handleReturnValueCharSequence() throws Exception {
+		List<HttpMessageConverter<?>>converters = new ArrayList<>();
+		converters.add(new ByteArrayHttpMessageConverter());
+		converters.add(new StringHttpMessageConverter());
+
+		Method method = getClass().getDeclaredMethod("handle");
+		MethodParameter returnType = new MethodParameter(method, -1);
+		ResponseEntity<StringBuilder> returnValue = ResponseEntity.ok(new StringBuilder("Foo"));
+
+		HttpEntityMethodProcessor processor = new HttpEntityMethodProcessor(converters);
+		processor.handleReturnValue(returnValue, returnType, mavContainer, webRequest);
+
+		assertEquals("text/plain;charset=ISO-8859-1", servletResponse.getHeader("Content-Type"));
+		assertEquals("Foo", servletResponse.getContentAsString());
+	}
+
+
 
 	@SuppressWarnings("unused")
 	public void handle(HttpEntity<List<SimpleBean>> arg1, HttpEntity<SimpleBean> arg2) {
 	}
 
+	ResponseEntity<CharSequence> handle() {
+		return null;
+	}
+
 	@SuppressWarnings("unused")
 	private static abstract class MyParameterizedController<DTO extends Identifiable> {
 

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/RequestResponseBodyMethodProcessorTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2016 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.
@@ -290,6 +290,24 @@ public class RequestResponseBodyMethodProcessorTests {
 		assertEquals("Foo", servletResponse.getContentAsString());
 	}
 
+	// SPR-13423
+	
+	@Test
+	public void handleReturnValueCharSequence() throws Exception {
+		List<HttpMessageConverter<?>>converters = new ArrayList<>();
+		converters.add(new ByteArrayHttpMessageConverter());
+		converters.add(new StringHttpMessageConverter());
+
+		Method method = ResponseBodyController.class.getMethod("handleWithCharSequence");
+		MethodParameter returnType = new MethodParameter(method, -1);
+
+		RequestResponseBodyMethodProcessor processor = new RequestResponseBodyMethodProcessor(converters);
+		processor.handleReturnValue(new StringBuilder("Foo"), returnType, mavContainer, webRequest);
+
+		assertEquals("text/plain;charset=ISO-8859-1", servletResponse.getHeader("Content-Type"));
+		assertEquals("Foo", servletResponse.getContentAsString());
+	}
+
 	@Test
 	public void handleReturnValueStringAcceptCharset() throws Exception {
 		this.servletRequest.addHeader("Accept", "text/plain;charset=UTF-8");
@@ -739,6 +757,11 @@ public class RequestResponseBodyMethodProcessorTests {
 		public String handle() {
 			return "hello";
 		}
+
+		@RequestMapping
+		public CharSequence handleWithCharSequence() {
+			return null;
+		}
 	}