diff --git a/spring-web/src/main/java/org/springframework/http/converter/StringHttpMessageConverter.java b/spring-web/src/main/java/org/springframework/http/converter/StringHttpMessageConverter.java
index 8b8793e277eb..5a408d874976 100644
--- a/spring-web/src/main/java/org/springframework/http/converter/StringHttpMessageConverter.java
+++ b/spring-web/src/main/java/org/springframework/http/converter/StringHttpMessageConverter.java
@@ -93,7 +93,11 @@ public boolean supports(Class<?> clazz) {
 	@Override
 	protected String readInternal(Class<? extends String> clazz, HttpInputMessage inputMessage) throws IOException {
 		Charset charset = getContentTypeCharset(inputMessage.getHeaders().getContentType());
-		return StreamUtils.copyToString(inputMessage.getBody(), charset);
+		long length = inputMessage.getHeaders().getContentLength();
+		byte[] bytes = (length >= 0 && length <= Integer.MAX_VALUE ?
+				inputMessage.getBody().readNBytes((int) length) :
+				inputMessage.getBody().readAllBytes());
+		return new String(bytes, charset);
 	}
 
 	@Override
diff --git a/spring-web/src/main/java/org/springframework/http/server/ServletServerHttpRequest.java b/spring-web/src/main/java/org/springframework/http/server/ServletServerHttpRequest.java
index ee2af3a17e6a..47789cf114f5 100644
--- a/spring-web/src/main/java/org/springframework/http/server/ServletServerHttpRequest.java
+++ b/spring-web/src/main/java/org/springframework/http/server/ServletServerHttpRequest.java
@@ -209,7 +209,7 @@ public InetSocketAddress getRemoteAddress() {
 
 	@Override
 	public InputStream getBody() throws IOException {
-		if (isFormPost(this.servletRequest)) {
+		if (isFormPost(this.servletRequest) && this.servletRequest.getQueryString() == null) {
 			return getBodyFromServletRequestParameters(this.servletRequest);
 		}
 		else {
diff --git a/spring-web/src/test/java/org/springframework/http/server/ServletServerHttpRequestTests.java b/spring-web/src/test/java/org/springframework/http/server/ServletServerHttpRequestTests.java
index d2ccc761e7b0..91eb6c1a1f90 100644
--- a/spring-web/src/test/java/org/springframework/http/server/ServletServerHttpRequestTests.java
+++ b/spring-web/src/test/java/org/springframework/http/server/ServletServerHttpRequestTests.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.
@@ -167,9 +167,8 @@ void getBody() throws IOException {
 		assertThat(result).as("Invalid content returned").isEqualTo(content);
 	}
 
-	@Test
+	@Test // gh-13318
 	void getFormBody() throws IOException {
-		// Charset (SPR-8676)
 		mockRequest.setContentType("application/x-www-form-urlencoded; charset=UTF-8");
 		mockRequest.setMethod("POST");
 		mockRequest.addParameter("name 1", "value 1");
@@ -177,8 +176,7 @@ void getFormBody() throws IOException {
 		mockRequest.addParameter("name 3", (String) null);
 
 		byte[] result = FileCopyUtils.copyToByteArray(request.getBody());
-		byte[] content = "name+1=value+1&name+2=value+2%2B1&name+2=value+2%2B2&name+3".getBytes(
-				StandardCharsets.UTF_8);
+		byte[] content = "name+1=value+1&name+2=value+2%2B1&name+2=value+2%2B2&name+3".getBytes(StandardCharsets.UTF_8);
 		assertThat(result).as("Invalid content returned").isEqualTo(content);
 	}
 
@@ -192,4 +190,18 @@ void getEmptyFormBody() throws IOException {
 		assertThat(result).as("Invalid content returned").isEqualTo(content);
 	}
 
+	@Test // gh-31327
+	void getFormBodyWhenQueryParamsAlsoPresent() throws IOException {
+		mockRequest.setContentType("application/x-www-form-urlencoded; charset=UTF-8");
+		mockRequest.setMethod("POST");
+		mockRequest.setQueryString("q=1");
+		mockRequest.addParameter("q", "1");
+		mockRequest.setContent("foo=bar".getBytes(StandardCharsets.UTF_8));
+		mockRequest.addHeader("Content-Length", 7);
+
+		byte[] result = FileCopyUtils.copyToByteArray(request.getBody());
+		byte[] content = "foo=bar".getBytes(StandardCharsets.UTF_8);
+		assertThat(result).as("Invalid content returned").isEqualTo(content);
+	}
+
 }