RestTemplate adds duplicate accept header information

spring-web/src/main/java/org/springframework/web/client/RestTemplate.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -20,6 +20,7 @@
 import java.lang.reflect.Type;
 import java.net.URI;
 import java.util.ArrayList;
+import java.util.LinkedHashSet;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
@@ -767,7 +768,7 @@ public void doWithRequest(ClientHttpRequest request) throws IOException {
 				if (this.responseType instanceof Class) {
 					responseClass = (Class<?>) this.responseType;
 				}
-				List<MediaType> allSupportedMediaTypes = new ArrayList<MediaType>();
+				Set<MediaType> allSupportedMediaTypes = new LinkedHashSet<MediaType>();
 				for (HttpMessageConverter<?> converter : getMessageConverters()) {
 					if (responseClass != null) {
 						if (converter.canRead(responseClass, null)) {
@@ -782,11 +783,12 @@ else if (converter instanceof GenericHttpMessageConverter) {
 					}
 				}
 				if (!allSupportedMediaTypes.isEmpty()) {
-					MediaType.sortBySpecificity(allSupportedMediaTypes);
+					List<MediaType> result = new ArrayList<MediaType>(allSupportedMediaTypes);
+					MediaType.sortBySpecificity(result);
 					if (logger.isDebugEnabled()) {
 						logger.debug("Setting request Accept header to " + allSupportedMediaTypes);
 					}
-					request.getHeaders().setAccept(allSupportedMediaTypes);
+					request.getHeaders().setAccept(result);
 				}
 			}
 		}

spring-web/src/test/java/org/springframework/web/client/RestTemplateTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -19,6 +19,8 @@
 import java.io.ByteArrayInputStream;
 import java.io.IOException;
 import java.net.URI;
+import java.nio.charset.StandardCharsets;
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.EnumSet;
 import java.util.HashMap;
@@ -43,6 +45,8 @@
 import org.springframework.http.client.ClientHttpResponse;
 import org.springframework.http.converter.GenericHttpMessageConverter;
 import org.springframework.http.converter.HttpMessageConverter;
+import org.springframework.http.converter.StringHttpMessageConverter;
+import org.springframework.util.StringUtils;
 import org.springframework.web.util.DefaultUriTemplateHandler;
 
 import static org.hamcrest.MatcherAssert.assertThat;
@@ -878,4 +882,24 @@ public void requestInterceptorCanAddExistingHeaderValueWithBody() throws Excepti
 		verify(response).close();
 	}
 
+	@Test
+	public void acceptHeaderValueShouldBeNotDuplicated() throws Exception {
+		final StringHttpMessageConverter utf8HttpMessageConverter = new StringHttpMessageConverter(StandardCharsets.UTF_8);
+		final StringHttpMessageConverter iso88591HttpMessageConverter = new StringHttpMessageConverter(StandardCharsets.ISO_8859_1);
+
+		final RestTemplate multipleEncodingTemplate = new RestTemplate(Arrays.asList(utf8HttpMessageConverter, iso88591HttpMessageConverter));
+		multipleEncodingTemplate.setRequestFactory(requestFactory);
+		given(requestFactory.createRequest(new URI("http://example.com"), GET)).willReturn(request);
+
+		final HttpHeaders requestHeaders = new HttpHeaders();
+		given(request.getHeaders()).willReturn(requestHeaders);
+		given(request.execute()).willReturn(response);
+
+		final HttpHeaders responseHeaders = new HttpHeaders();
+		given(response.getHeaders()).willReturn(responseHeaders);
+
+		multipleEncodingTemplate.getForObject("http://example.com", String.class);
+		assertEquals("text/plain, */*", StringUtils.collectionToDelimitedString(request.getHeaders().get("accept"), ","));
+	}
+
 }