Improve charset handling in MockHttpServletResponse

This commit adds a getContentAsString(Charset fallbackCharset) method
to MockHttpServletResponse in order to make it easier to get the content
in a specific charset like UTF-8 when the response charset has not been
explicitly set (by default ISO-8859-1 is used).

JsonPathResultMatchers leverages this new feature to support UTF-8
content out of the box.

Closes gh-23219

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

@@ -23,6 +23,7 @@
 import java.io.PrintWriter;
 import java.io.UnsupportedEncodingException;
 import java.io.Writer;
+import java.nio.charset.Charset;
 import java.text.DateFormat;
 import java.text.ParseException;
 import java.text.SimpleDateFormat;
@@ -204,11 +205,32 @@ public byte[] getContentAsByteArray() {
 		return this.content.toByteArray();
 	}
 
+	/**
+	 * Get the content of the response body as a {@code String}, using the configured
+	 * {@linkplain #getCharacterEncoding character encoding}.
+	 * @return the content as a {@code String}
+	 * @throws UnsupportedEncodingException if the character encoding is not supported
+	 * @see #getContentAsString(Charset)
+	 */
 	public String getContentAsString() throws UnsupportedEncodingException {
 		return (this.characterEncoding != null ?
 				this.content.toString(this.characterEncoding) : this.content.toString());
 	}
 
+	/**
+	 * Get the content of the response body as a {@code String}, using the provided
+	 * {@code fallbackCharset} if no charset has been explicitly defined, else using
+	 * using the configured {@linkplain #getCharacterEncoding character encoding}.
+	 * @return the content as a {@code String}
+	 * @throws UnsupportedEncodingException if the character encoding is not supported
+	 * @see #getContentAsString()
+	 */
+	public String getContentAsString(Charset fallbackCharset) throws UnsupportedEncodingException {
+		return isCharset() ?
+				this.content.toString(this.characterEncoding) :
+				this.content.toString(fallbackCharset.name());
+	}
+
 	@Override
 	public void setContentLength(int contentLength) {
 		this.contentLength = contentLength;

spring-test/src/main/java/org/springframework/test/web/servlet/result/JsonPathResultMatchers.java

@@ -17,6 +17,7 @@
 package org.springframework.test.web.servlet.result;
 
 import java.io.UnsupportedEncodingException;
+import java.nio.charset.StandardCharsets;
 
 import com.jayway.jsonpath.JsonPath;
 import org.hamcrest.Matcher;
@@ -235,7 +236,7 @@ public ResultMatcher isMap() {
 	}
 
 	private String getContent(MvcResult result) throws UnsupportedEncodingException {
-		String content = result.getResponse().getContentAsString();
+		String content = result.getResponse().getContentAsString(StandardCharsets.UTF_8);
 		if (StringUtils.hasLength(this.prefix)) {
 			try {
 				String reason = String.format("Expected a JSON payload prefixed with \"%s\" but found: %s",

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

@@ -17,6 +17,7 @@
 package org.springframework.mock.web;
 
 import java.io.IOException;
+import java.nio.charset.StandardCharsets;
 import java.util.Arrays;
 import java.util.Collection;
 import javax.servlet.http.Cookie;
@@ -39,6 +40,7 @@
  * @author Rob Winch
  * @author Sam Brannen
  * @author Brian Clozel
+ * @author Sebastien Deleuze
  * @since 19.02.2006
  */
 public class MockHttpServletResponseTests {
@@ -238,10 +240,11 @@ public void servletWriterCommittedOnWriterClose() throws IOException {
 		assertThat(response.getContentAsByteArray().length).isEqualTo(1);
 	}
 
-	@Test
-	public void servletWriterAutoFlushedForString() throws IOException {
-		response.getWriter().write("X");
-		assertThat(response.getContentAsString()).isEqualTo("X");
+	@Test  // gh-23219
+	public void contentAsUtf8() throws IOException {
+		String content = "Příliš žluťoučký kůň úpěl ďábelské ódy";
+		response.getOutputStream().write(content.getBytes(StandardCharsets.UTF_8));
+		assertThat(response.getContentAsString(StandardCharsets.UTF_8)).isEqualTo(content);
 	}
 
 	@Test
@@ -256,6 +259,12 @@ public void servletWriterAutoFlushedForCharArray() throws IOException {
 		assertThat(response.getContentAsString()).isEqualTo("XY");
 	}
 
+	@Test
+	public void servletWriterAutoFlushedForString() throws IOException {
+		response.getWriter().write("X");
+		assertThat(response.getContentAsString()).isEqualTo("X");
+	}
+
 	@Test
 	public void sendRedirect() throws IOException {
 		String redirectUrl = "/redirect";

spring-test/src/test/java/org/springframework/test/web/servlet/result/JsonPathResultMatchersTests.java

@@ -16,6 +16,8 @@
 
 package org.springframework.test.web.servlet.result;
 
+import java.nio.charset.StandardCharsets;
+
 import org.hamcrest.Matchers;
 import org.junit.Test;
 
@@ -31,11 +33,13 @@
  * @author Craig Andrews
  * @author Sam Brannen
  * @author Brian Clozel
+ * @author Sebastien Deleuze
  */
 public class JsonPathResultMatchersTests {
 
 	private static final String RESPONSE_CONTENT = "{" + //
 			"'str':         'foo',           " + //
+			"'utf8Str':     'Příliš',        " + //
 			"'num':         5,               " + //
 			"'bool':        true,            " + //
 			"'arr':         [42],            " + //
@@ -51,7 +55,7 @@ public class JsonPathResultMatchersTests {
 		try {
 			MockHttpServletResponse response = new MockHttpServletResponse();
 			response.addHeader("Content-Type", "application/json");
-			response.getWriter().print(new String(RESPONSE_CONTENT.getBytes("ISO-8859-1")));
+			response.getOutputStream().write(RESPONSE_CONTENT.getBytes(StandardCharsets.UTF_8));
 			stubMvcResult = new StubMvcResult(null, null, null, null, null, null, response);
 		}
 		catch (Exception e) {
@@ -70,6 +74,11 @@ public void valueWithDirectMatch() throws Exception {
 		new JsonPathResultMatchers("$.str").value("foo").match(stubMvcResult);
 	}
 
+	@Test // gh-23219
+	public void utf8ValueWithDirectMatch() throws Exception {
+		new JsonPathResultMatchers("$.utf8Str").value("Příliš").match(stubMvcResult);
+	}
+
 	@Test // SPR-16587
 	public void valueWithNumberConversion() throws Exception {
 		new JsonPathResultMatchers("$.num").value(5.0f).match(stubMvcResult);