diff --git a/spring-test/src/main/java/org/springframework/test/web/servlet/htmlunit/HtmlUnitRequestBuilder.java b/spring-test/src/main/java/org/springframework/test/web/servlet/htmlunit/HtmlUnitRequestBuilder.java
index 5544875a889..f46ae7c4570 100644
--- a/spring-test/src/main/java/org/springframework/test/web/servlet/htmlunit/HtmlUnitRequestBuilder.java
+++ b/spring-test/src/main/java/org/springframework/test/web/servlet/htmlunit/HtmlUnitRequestBuilder.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -17,8 +17,10 @@
 package org.springframework.test.web.servlet.htmlunit;
 
 import java.io.UnsupportedEncodingException;
+import java.lang.reflect.Method;
 import java.net.URL;
 import java.net.URLDecoder;
+import java.nio.charset.Charset;
 import java.util.ArrayList;
 import java.util.Enumeration;
 import java.util.List;
@@ -50,7 +52,9 @@ import org.springframework.test.web.servlet.request.MockHttpServletRequestBuilde
 import org.springframework.test.web.servlet.request.MockMvcRequestBuilders;
 import org.springframework.test.web.servlet.request.RequestPostProcessor;
 import org.springframework.util.Assert;
+import org.springframework.util.ClassUtils;
 import org.springframework.util.ObjectUtils;
+import org.springframework.util.ReflectionUtils;
 import org.springframework.util.StringUtils;
 import org.springframework.web.util.UriComponents;
 import org.springframework.web.util.UriComponentsBuilder;
@@ -59,7 +63,7 @@ import org.springframework.web.util.UriComponentsBuilder;
  * Internal class used to transform a {@link WebRequest} into a
  * {@link MockHttpServletRequest} using Spring MVC Test's {@link RequestBuilder}.
  *
- * <p>By default the first path segment of the URL is used as the contextPath.
+ * <p>By default the first path segment of the URL is used as the context path.
  * To override this default see {@link #setContextPath(String)}.
  *
  * @author Rob Winch
@@ -71,6 +75,11 @@ final class HtmlUnitRequestBuilder implements RequestBuilder, Mergeable {
 
 	private static final Pattern LOCALE_PATTERN = Pattern.compile("^\\s*(\\w{2})(?:-(\\w{2}))?(?:;q=(\\d+\\.\\d+))?$");
 
+	private static final Charset DEFAULT_CHARSET = Charset.forName("ISO-8859-1");
+
+
+	private static final Method getCharsetMethod = ClassUtils.getMethodIfAvailable(WebRequest.class, "getCharset");
+
 	private final Map<String, MockHttpSession> sessions;
 
 	private final WebClient webClient;
@@ -98,23 +107,23 @@ final class HtmlUnitRequestBuilder implements RequestBuilder, Mergeable {
 		Assert.notNull(sessions, "Sessions Map must not be null");
 		Assert.notNull(webClient, "WebClient must not be null");
 		Assert.notNull(webRequest, "WebRequest must not be null");
-
 		this.sessions = sessions;
 		this.webClient = webClient;
 		this.webRequest = webRequest;
 	}
 
+
 	public MockHttpServletRequest buildRequest(ServletContext servletContext) {
-		String charset = getCharset();
+		Charset charset = getCharset();
 		String httpMethod = this.webRequest.getHttpMethod().name();
 		UriComponents uriComponents = uriComponents();
 
 		MockHttpServletRequest request = new HtmlUnitMockHttpServletRequest(
 				servletContext, httpMethod, uriComponents.getPath());
 		parent(request, this.parentBuilder);
-		request.setServerName(uriComponents.getHost()); // needs to be first for additional headers
+		request.setServerName(uriComponents.getHost());  // needs to be first for additional headers
 		authType(request);
-		request.setCharacterEncoding(charset);
+		request.setCharacterEncoding(charset.name());
 		content(request, charset);
 		contextPath(request, uriComponents);
 		contentType(request);
@@ -132,6 +141,21 @@ final class HtmlUnitRequestBuilder implements RequestBuilder, Mergeable {
 		return postProcess(request);
 	}
 
+	private Charset getCharset() {
+		if (getCharsetMethod != null) {
+			Object value = ReflectionUtils.invokeMethod(getCharsetMethod, this.webRequest);
+			if (value instanceof Charset) {
+				// HtmlUnit 2.25: a Charset
+				return (Charset) value;
+			}
+			else if (value != null) {
+				// HtmlUnit up until 2.24: a String
+				return Charset.forName(value.toString());
+			}
+		}
+		return DEFAULT_CHARSET;
+	}
+
 	private MockHttpServletRequest postProcess(MockHttpServletRequest request) {
 		if (this.parentPostProcessor != null) {
 			request = this.parentPostProcessor.postProcessRequest(request);
@@ -220,17 +244,12 @@ final class HtmlUnitRequestBuilder implements RequestBuilder, Mergeable {
 		}
 	}
 
-	private void content(MockHttpServletRequest request, String charset) {
+	private void content(MockHttpServletRequest request, Charset charset) {
 		String requestBody = this.webRequest.getRequestBody();
 		if (requestBody == null) {
 			return;
 		}
-		try {
-			request.setContent(requestBody.getBytes(charset));
-		}
-		catch (UnsupportedEncodingException ex) {
-			throw new IllegalStateException(ex);
-		}
+		request.setContent(requestBody.getBytes(charset));
 	}
 
 	private void contentType(MockHttpServletRequest request) {
@@ -256,8 +275,8 @@ final class HtmlUnitRequestBuilder implements RequestBuilder, Mergeable {
 		}
 		else {
 			if (!uriComponents.getPath().startsWith(this.contextPath)) {
-				throw new IllegalArgumentException(uriComponents.getPath() + " should start with contextPath " +
-						this.contextPath);
+				throw new IllegalArgumentException("\"" + uriComponents.getPath() +
+						"\" should start with context path \"" + this.contextPath + "\"");
 			}
 			request.setContextPath(this.contextPath);
 		}
@@ -273,7 +292,7 @@ final class HtmlUnitRequestBuilder implements RequestBuilder, Mergeable {
 				String cookieName = tokens.nextToken().trim();
 				if (!tokens.hasMoreTokens()) {
 					throw new IllegalArgumentException("Expected value for cookie name '" + cookieName +
-							"'. Full cookie was " + cookieHeaderValue);
+							"': full cookie header was [" + cookieHeaderValue + "]");
 				}
 				String cookieValue = tokens.nextToken().trim();
 				processCookie(request, cookies, new Cookie(cookieName, cookieValue));
@@ -305,14 +324,6 @@ final class HtmlUnitRequestBuilder implements RequestBuilder, Mergeable {
 		}
 	}
 
-	private String getCharset() {
-		String charset = this.webRequest.getCharset();
-		if (charset == null) {
-			return "ISO-8859-1";
-		}
-		return charset;
-	}
-
 	private String header(String headerName) {
 		return this.webRequest.getAdditionalHeaders().get(headerName);
 	}
@@ -394,7 +405,7 @@ final class HtmlUnitRequestBuilder implements RequestBuilder, Mergeable {
 	private Locale parseLocale(String locale) {
 		Matcher matcher = LOCALE_PATTERN.matcher(locale);
 		if (!matcher.matches()) {
-			throw new IllegalArgumentException("Invalid locale " + locale);
+			throw new IllegalArgumentException("Invalid locale value [" + locale + "]");
 		}
 		String language = matcher.group(1);
 		String country = matcher.group(2);