Support multiple Content-Language values in MockHttpServletResponse

Prior to this commit, if the user supplied a comma-separated list such
as "en, it" as the Content-Language header value to
MockHttpServletResponse's setHeader() method, only the first language
was actually set in the response's Content-Language header (e.g., "en").

This commit ensures that all supplied content languages are set in the
response's Content-Language header.

Closes gh-25281

spring-test/src/main/java/org/springframework/mock/web/MockHttpServletResponse.java

@@ -638,10 +638,15 @@ public class MockHttpServletResponse implements HttpServletResponse {
 			return true;
 		}
 		else if (HttpHeaders.CONTENT_LANGUAGE.equalsIgnoreCase(name)) {
+			String contentLanguages = value.toString();
 			HttpHeaders headers = new HttpHeaders();
-			headers.add(HttpHeaders.CONTENT_LANGUAGE, value.toString());
+			headers.add(HttpHeaders.CONTENT_LANGUAGE, contentLanguages);
 			Locale language = headers.getContentLanguage();
 			setLocale(language != null ? language : Locale.getDefault());
+			// Since setLocale() sets the Content-Language header to the given
+			// single Locale, we have to explicitly set the Content-Language header
+			// to the user-provided value.
+			doAddHeaderValue(HttpHeaders.CONTENT_LANGUAGE, contentLanguages, true);
 			return true;
 		}
 		else if (HttpHeaders.SET_COOKIE.equalsIgnoreCase(name)) {
@@ -660,12 +665,8 @@ public class MockHttpServletResponse implements HttpServletResponse {
 	}
 
 	private void doAddHeaderValue(String name, Object value, boolean replace) {
-		HeaderValueHolder header = this.headers.get(name);
 		Assert.notNull(value, "Header value must not be null");
-		if (header == null) {
-			header = new HeaderValueHolder();
-			this.headers.put(name, header);
-		}
+		HeaderValueHolder header = this.headers.computeIfAbsent(name, key -> new HeaderValueHolder());
 		if (replace) {
 			header.setValue(value);
 		}

spring-test/src/test/java/org/springframework/mock/web/MockHttpServletResponseTests.java

@@ -20,6 +20,7 @@ import java.io.IOException;
 import java.nio.charset.StandardCharsets;
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.Locale;
 
 import javax.servlet.http.Cookie;
 import javax.servlet.http.HttpServletResponse;
@@ -30,6 +31,8 @@ import org.springframework.web.util.WebUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
+import static org.assertj.core.api.SoftAssertions.assertSoftly;
+import static org.springframework.http.HttpHeaders.CONTENT_LANGUAGE;
 import static org.springframework.http.HttpHeaders.CONTENT_LENGTH;
 import static org.springframework.http.HttpHeaders.CONTENT_TYPE;
 import static org.springframework.http.HttpHeaders.LAST_MODIFIED;
@@ -117,6 +120,26 @@ class MockHttpServletResponseTests {
 		assertThat(response.getCharacterEncoding()).isEqualTo("UTF-8");
 	}
 
+	@Test  // gh-25281
+	void contentLanguageHeaderWithSingleValue() {
+		String contentLanguage = "it";
+		response.setHeader(CONTENT_LANGUAGE, contentLanguage);
+		assertSoftly(softly -> {
+			softly.assertThat(response.getHeader(CONTENT_LANGUAGE)).isEqualTo(contentLanguage);
+			softly.assertThat(response.getLocale()).isEqualTo(Locale.ITALIAN);
+		});
+	}
+
+	@Test  // gh-25281
+	void contentLanguageHeaderWithMultipleValues() {
+		String contentLanguage = "it, en";
+		response.setHeader(CONTENT_LANGUAGE, contentLanguage);
+		assertSoftly(softly -> {
+			softly.assertThat(response.getHeader(CONTENT_LANGUAGE)).isEqualTo(contentLanguage);
+			softly.assertThat(response.getLocale()).isEqualTo(Locale.ITALIAN);
+		});
+	}
+
 	@Test
 	void setContentTypeThenCharacterEncoding() {
 		response.setContentType("test/plain");

spring-web/src/testFixtures/java/org/springframework/web/testfixture/servlet/MockHttpServletResponse.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -424,7 +424,7 @@ public class MockHttpServletResponse implements HttpServletResponse {
 
 	/**
 	 * Return the names of all specified headers as a Set of Strings.
-	 * <p>As of Servlet 3.0, this method is also defined HttpServletResponse.
+	 * <p>As of Servlet 3.0, this method is also defined in {@link HttpServletResponse}.
 	 * @return the {@code Set} of header name {@code Strings}, or an empty {@code Set} if none
 	 */
 	@Override
@@ -435,7 +435,7 @@ public class MockHttpServletResponse implements HttpServletResponse {
 	/**
 	 * Return the primary value for the given header as a String, if any.
 	 * Will return the first value in case of multiple values.
-	 * <p>As of Servlet 3.0, this method is also defined in HttpServletResponse.
+	 * <p>As of Servlet 3.0, this method is also defined in {@link HttpServletResponse}.
 	 * As of Spring 3.1, it returns a stringified value for Servlet 3.0 compatibility.
 	 * Consider using {@link #getHeaderValue(String)} for raw Object access.
 	 * @param name the name of the header
@@ -450,7 +450,7 @@ public class MockHttpServletResponse implements HttpServletResponse {
 
 	/**
 	 * Return all values for the given header as a List of Strings.
-	 * <p>As of Servlet 3.0, this method is also defined in HttpServletResponse.
+	 * <p>As of Servlet 3.0, this method is also defined in {@link HttpServletResponse}.
 	 * As of Spring 3.1, it returns a List of stringified values for Servlet 3.0 compatibility.
 	 * Consider using {@link #getHeaderValues(String)} for raw Object access.
 	 * @param name the name of the header
@@ -638,10 +638,15 @@ public class MockHttpServletResponse implements HttpServletResponse {
 			return true;
 		}
 		else if (HttpHeaders.CONTENT_LANGUAGE.equalsIgnoreCase(name)) {
+			String contentLanguages = value.toString();
 			HttpHeaders headers = new HttpHeaders();
-			headers.add(HttpHeaders.CONTENT_LANGUAGE, value.toString());
+			headers.add(HttpHeaders.CONTENT_LANGUAGE, contentLanguages);
 			Locale language = headers.getContentLanguage();
 			setLocale(language != null ? language : Locale.getDefault());
+			// Since setLocale() sets the Content-Language header to the given
+			// single Locale, we have to explicitly set the Content-Language header
+			// to the user-provided value.
+			doAddHeaderValue(HttpHeaders.CONTENT_LANGUAGE, contentLanguages, true);
 			return true;
 		}
 		else if (HttpHeaders.SET_COOKIE.equalsIgnoreCase(name)) {
@@ -660,12 +665,8 @@ public class MockHttpServletResponse implements HttpServletResponse {
 	}
 
 	private void doAddHeaderValue(String name, Object value, boolean replace) {
-		HeaderValueHolder header = this.headers.get(name);
 		Assert.notNull(value, "Header value must not be null");
-		if (header == null) {
-			header = new HeaderValueHolder();
-			this.headers.put(name, header);
-		}
+		HeaderValueHolder header = this.headers.computeIfAbsent(name, key -> new HeaderValueHolder());
 		if (replace) {
 			header.setValue(value);
 		}