Fix MockHttpServletRequest.java

In MockHttpServletRequest 'application/json; Modified so that the 'charset=utf-8' format is no longer used.

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

@@ -409,6 +409,10 @@ public void setCharacterEncoding(@Nullable String characterEncoding) {
 
 	private void updateContentTypeHeader() {
 		if (StringUtils.hasLength(this.contentType)) {
+			if (isJsonContentType(this.contentType) {
+				return;	
+			}
+
 			String value = this.contentType;
 			if (StringUtils.hasLength(this.characterEncoding) && !this.contentType.toLowerCase().contains(CHARSET_PREFIX)) {
 				value += ';' + CHARSET_PREFIX + this.characterEncoding;
@@ -417,6 +421,10 @@ private void updateContentTypeHeader() {
 		}
 	}
 
+	private boolean isJsonContentType(String contentType) {
+		return contentType.toLowerCase().startsWith("application/json");
+	}
+
 	/**
 	 * Set the content of the request body as a byte array.
 	 * <p>If the supplied byte array represents text such as XML or JSON, the