Get content as String for ContentCachingRequestWrapper

This commits adds a getContentAsString method to
ContentCachingRequestWrapper that uses the configured charset without
copying the underlying byte array.

See spring-projectsgh-30709

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

@@ -21,6 +21,7 @@
 import java.io.IOException;
 import java.io.InputStreamReader;
 import java.net.URLEncoder;
+import java.nio.charset.Charset;
 import java.util.Arrays;
 import java.util.Enumeration;
 import java.util.Iterator;
@@ -196,6 +197,14 @@ public byte[] getContentAsByteArray() {
 		return this.cachedContent.toByteArray();
 	}
 
+	/**
+	 * Return the cached request content as a String. The Charset used to decode
+	 * the cached content is the same as returned by getCharacterEncoding.
+	 */
+	public String getContentAsString() {
+		return this.cachedContent.toString(Charset.forName(getCharacterEncoding()));
+	}
+
 	/**
 	 * Template method for handling a content overflow: specifically, a request
 	 * body being read that exceeds the specified content cache limit.