Merge pull request #1034 from config25

* gh-1034:
  Fix URL decoding charset mismatch in MockMvcRequestConverter

Closes gh-1034

Author: wilkinsona

spring-restdocs-mockmvc/src/main/java/org/springframework/restdocs/mockmvc/MockMvcRequestConverter.java

@@ -280,7 +280,7 @@ private static void processParameter(String parameter, MultiValueMap<String, Str
 	}
 
 	private static String decode(String encoded) {
-		return URLDecoder.decode(encoded, StandardCharsets.US_ASCII);
+		return URLDecoder.decode(encoded, StandardCharsets.UTF_8);
 	}
 
 }

spring-restdocs-mockmvc/src/test/java/org/springframework/restdocs/mockmvc/MockMvcRequestConverterTests.java

@@ -158,6 +158,17 @@ public void postRequestWithParametersAndQueryStringCreatesFormUrlEncodedContentW
 		assertThat(request.getHeaders().getContentType()).isEqualTo(MediaType.APPLICATION_FORM_URLENCODED);
 	}
 
+	@Test
+	public void postRequestWithNonAsciiParametersAndQueryStringCreatesFormUrlEncodedContentWithoutDuplication() {
+		OperationRequest request = createOperationRequest(MockMvcRequestBuilders.post("/foo?name=\uD64D\uAE38\uB3D9")
+			.param("name", "\uD64D\uAE38\uB3D9")
+			.param("other", "\uD64D\uAE38\uB3D9"));
+		assertThat(request.getUri()).isEqualTo(URI.create("http://localhost/foo?name=%ED%99%8D%EA%B8%B8%EB%8F%99"));
+		assertThat(request.getMethod()).isEqualTo(HttpMethod.POST);
+		assertThat(request.getContentAsString()).isEqualTo("other=%ED%99%8D%EA%B8%B8%EB%8F%99");
+		assertThat(request.getHeaders().getContentType()).isEqualTo(MediaType.APPLICATION_FORM_URLENCODED);
+	}
+
 	@Test
 	public void mockMultipartFileUpload() {
 		OperationRequest request = createOperationRequest(MockMvcRequestBuilders.multipart("/foo")