Polish "Get content as String for ContentCachingRequestWrapper"

See gh-30709

spring-web/src/main/java/org/springframework/web/util/ContentCachingRequestWrapper.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -198,8 +198,14 @@ public class ContentCachingRequestWrapper extends HttpServletRequestWrapper {
 	}
 
 	/**
-	 * Return the cached request content as a String. The Charset used to decode
-	 * the cached content is the same as returned by getCharacterEncoding.
+	 * Return the cached request content as a String, using the configured
+	 * {@link Charset}.
+	 * <p><strong>Note:</strong> The String returned from this method
+	 * reflects the amount of content that has been read at the time when it
+	 * is called. If the application does not read the content, this method
+	 * returns an empty String.
+	 * @since 6.1
+	 * @see #getContentAsByteArray()
 	 */
 	public String getContentAsString() {
 		return this.cachedContent.toString(Charset.forName(getCharacterEncoding()));