Ensure response not closed by MappingJackson2HttpMessageConverter

Closes gh-25987

Author: rstoyanchev

spring-web/src/main/java/org/springframework/http/converter/json/AbstractJackson2HttpMessageConverter.java

@@ -18,6 +18,7 @@
 
 import java.io.IOException;
 import java.io.InputStreamReader;
+import java.io.OutputStream;
 import java.io.Reader;
 import java.lang.reflect.Type;
 import java.nio.charset.Charset;
@@ -55,6 +56,8 @@
 import org.springframework.http.converter.HttpMessageNotWritableException;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
+import org.springframework.util.CollectionUtils;
+import org.springframework.util.StreamUtils;
 import org.springframework.util.TypeUtils;
 
 /**
@@ -308,7 +311,8 @@ protected void writeInternal(Object object, @Nullable Type type, HttpOutputMessa
 		MediaType contentType = outputMessage.getHeaders().getContentType();
 		JsonEncoding encoding = getJsonEncoding(contentType);
 
-		try (JsonGenerator generator = this.objectMapper.getFactory().createGenerator(outputMessage.getBody(), encoding)) {
+		OutputStream outputStream = StreamUtils.nonClosing(outputMessage.getBody());
+		try (JsonGenerator generator = this.objectMapper.getFactory().createGenerator(outputStream, encoding)) {
 			writePrefix(generator, object);
 
 			Object value = object;

spring-web/src/test/java/org/springframework/http/converter/json/MappingJackson2HttpMessageConverterTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -47,6 +47,8 @@
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 import static org.assertj.core.api.Assertions.entry;
 import static org.assertj.core.api.Assertions.within;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.verify;
 
 /**
  * Jackson 2.x converter tests.
@@ -149,6 +151,7 @@ public void write() throws IOException {
 		assertThat(result.contains("\"bool\":true")).isTrue();
 		assertThat(result.contains("\"bytes\":\"AQI=\"")).isTrue();
 		assertThat(outputMessage.getHeaders().getContentType()).as("Invalid content-type").isEqualTo(MediaType.APPLICATION_JSON);
+		verify(outputMessage.getBody(), never()).close();
 	}
 
 	@Test