StreamUtils.emptyInput() for consistent empty InputStream exposure

Issue: SPR-13563

Author: jhoeller

spring-context/src/test/java/org/springframework/scripting/support/ResourceScriptSourceTests.java

@@ -16,13 +16,13 @@
 
 package org.springframework.scripting.support;
 
-import java.io.ByteArrayInputStream;
 import java.io.IOException;
 
 import org.junit.Test;
 
 import org.springframework.core.io.ByteArrayResource;
 import org.springframework.core.io.Resource;
+import org.springframework.util.StreamUtils;
 
 import static org.junit.Assert.*;
 import static org.mockito.BDDMockito.*;
@@ -59,7 +59,7 @@ public void lastModifiedWorksWithResourceThatDoesNotSupportFileBasedReading() th
 		// does not support File-based reading; delegates to InputStream-style reading...
 		//resource.getFile();
 		//mock.setThrowable(new FileNotFoundException());
-		given(resource.getInputStream()).willReturn(new ByteArrayInputStream(new byte[0]));
+		given(resource.getInputStream()).willReturn(StreamUtils.emptyInput());
 
 		ResourceScriptSource scriptSource = new ResourceScriptSource(resource);
 		assertTrue("ResourceScriptSource must start off in the 'isModified' state (it obviously isn't).", scriptSource.isModified());

spring-core/src/main/java/org/springframework/util/StreamUtils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2013 the original author or authors.
+ * Copyright 2002-2015 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.
@@ -16,6 +16,7 @@
 
 package org.springframework.util;
 
+import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import java.io.FilterInputStream;
 import java.io.FilterOutputStream;
@@ -43,6 +44,8 @@ public abstract class StreamUtils {
 
 	public static final int BUFFER_SIZE = 4096;
 
+	private static final byte[] EMPTY_CONTENT = new byte[0];
+
 
 	/**
 	 * Copy the contents of the given InputStream into a new byte array.
@@ -129,7 +132,16 @@ public static int copy(InputStream in, OutputStream out) throws IOException {
 	}
 
 	/**
-	 * Returns a variant of the given {@link InputStream} where calling
+	 * Return an efficient empty {@link InputStream}.
+	 * @return a {@link ByteArrayInputStream} based on an empty byte array
+	 * @since 4.2.2
+	 */
+	public static InputStream emptyInput() {
+		return new ByteArrayInputStream(EMPTY_CONTENT);
+	}
+
+	/**
+	 * Return a variant of the given {@link InputStream} where calling
 	 * {@link InputStream#close() close()} has no effect.
 	 * @param in the InputStream to decorate
 	 * @return a version of the InputStream that ignores calls to close
@@ -140,7 +152,7 @@ public static InputStream nonClosing(InputStream in) {
 	}
 
 	/**
-	 * Returns a variant of the given {@link OutputStream} where calling
+	 * Return a variant of the given {@link OutputStream} where calling
 	 * {@link OutputStream#close() close()} has no effect.
 	 * @param out the OutputStream to decorate
 	 * @return a version of the OutputStream that ignores calls to close

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

@@ -39,7 +39,6 @@
 import java.util.Map;
 import java.util.Set;
 import java.util.TimeZone;
-
 import javax.servlet.AsyncContext;
 import javax.servlet.DispatcherType;
 import javax.servlet.RequestDispatcher;
@@ -59,6 +58,7 @@
 import org.springframework.util.LinkedCaseInsensitiveMap;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
+import org.springframework.util.StreamUtils;
 import org.springframework.util.StringUtils;
 
 /**
@@ -122,7 +122,7 @@ public class MockHttpServletRequest implements HttpServletRequest {
 	private static final String CHARSET_PREFIX = "charset=";
 
 	private static final ServletInputStream EMPTY_SERVLET_INPUT_STREAM =
-			new DelegatingServletInputStream(new ByteArrayInputStream(new byte[0]));
+			new DelegatingServletInputStream(StreamUtils.emptyInput());
 
 	/**
 	 * Date formats as specified in the HTTP RFC

spring-web/src/main/java/org/springframework/http/converter/json/Jackson2ObjectMapperBuilder.java

@@ -16,7 +16,6 @@
 
 package org.springframework.http.converter.json;
 
-import java.io.ByteArrayInputStream;
 import java.text.DateFormat;
 import java.text.SimpleDateFormat;
 import java.util.Arrays;
@@ -54,6 +53,7 @@
 import org.springframework.context.ApplicationContext;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
+import org.springframework.util.StreamUtils;
 import org.springframework.util.StringUtils;
 
 /**
@@ -761,7 +761,7 @@ public ObjectMapper create() {
 		private static final XMLResolver NO_OP_XML_RESOLVER = new XMLResolver() {
 			@Override
 			public Object resolveEntity(String publicID, String systemID, String base, String ns) {
-				return new ByteArrayInputStream(new byte[0]);
+				return StreamUtils.emptyInput();
 			}
 		};
 	}

spring-web/src/main/java/org/springframework/http/converter/xml/Jaxb2CollectionHttpMessageConverter.java

@@ -16,7 +16,6 @@
 
 package org.springframework.http.converter.xml;
 
-import java.io.ByteArrayInputStream;
 import java.io.IOException;
 import java.lang.reflect.ParameterizedType;
 import java.lang.reflect.Type;
@@ -46,6 +45,7 @@
 import org.springframework.http.converter.HttpMessageConversionException;
 import org.springframework.http.converter.HttpMessageNotReadableException;
 import org.springframework.http.converter.HttpMessageNotWritableException;
+import org.springframework.util.StreamUtils;
 
 /**
  * An {@code HttpMessageConverter} that can read XML collections using JAXB2.
@@ -256,7 +256,7 @@ protected XMLInputFactory createXmlInputFactory() {
 	private static final XMLResolver NO_OP_XML_RESOLVER = new XMLResolver() {
 		@Override
 		public Object resolveEntity(String publicID, String systemID, String base, String ns) {
-			return new ByteArrayInputStream(new byte[0]);
+			return StreamUtils.emptyInput();
 		}
 	};
 

spring-web/src/main/java/org/springframework/http/converter/xml/SourceHttpMessageConverter.java

@@ -289,7 +289,7 @@ public InputSource resolveEntity(String publicId, String systemId) {
 	private static final XMLResolver NO_OP_XML_RESOLVER = new XMLResolver() {
 		@Override
 		public Object resolveEntity(String publicID, String systemID, String base, String ns) {
-			return new ByteArrayInputStream(new byte[0]);
+			return StreamUtils.emptyInput();
 		}
 	};
 

spring-web/src/main/java/org/springframework/web/multipart/commons/CommonsMultipartFile.java

@@ -16,7 +16,6 @@
 
 package org.springframework.web.multipart.commons;
 
-import java.io.ByteArrayInputStream;
 import java.io.File;
 import java.io.IOException;
 import java.io.InputStream;
@@ -28,10 +27,11 @@
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 
+import org.springframework.util.StreamUtils;
 import org.springframework.web.multipart.MultipartFile;
 
 /**
- * MultipartFile implementation for Apache Commons FileUpload.
+ * {@link MultipartFile} implementation for Apache Commons FileUpload.
  *
  * @author Trevor D. Cook
  * @author Juergen Hoeller
@@ -124,7 +124,7 @@ public InputStream getInputStream() throws IOException {
 			throw new IllegalStateException("File has been moved - cannot be read again");
 		}
 		InputStream inputStream = this.fileItem.getInputStream();
-		return (inputStream != null ? inputStream : new ByteArrayInputStream(new byte[0]));
+		return (inputStream != null ? inputStream : StreamUtils.emptyInput());
 	}
 
 	@Override

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

@@ -39,7 +39,6 @@
 import java.util.Map;
 import java.util.Set;
 import java.util.TimeZone;
-
 import javax.servlet.AsyncContext;
 import javax.servlet.DispatcherType;
 import javax.servlet.RequestDispatcher;
@@ -59,6 +58,7 @@
 import org.springframework.util.LinkedCaseInsensitiveMap;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
+import org.springframework.util.StreamUtils;
 import org.springframework.util.StringUtils;
 
 /**
@@ -122,7 +122,7 @@ public class MockHttpServletRequest implements HttpServletRequest {
 	private static final String CHARSET_PREFIX = "charset=";
 
 	private static final ServletInputStream EMPTY_SERVLET_INPUT_STREAM =
-			new DelegatingServletInputStream(new ByteArrayInputStream(new byte[0]));
+			new DelegatingServletInputStream(StreamUtils.emptyInput());
 
 	/**
 	 * Date formats as specified in the HTTP RFC

spring-web/src/test/java/org/springframework/web/filter/ShallowEtagHeaderFilterTests.java

@@ -16,16 +16,15 @@
 
 package org.springframework.web.filter;
 
-import java.io.ByteArrayInputStream;
 import javax.servlet.FilterChain;
 import javax.servlet.http.HttpServletResponse;
 
-import org.junit.Before;
 import org.junit.Test;
 
 import org.springframework.mock.web.test.MockHttpServletRequest;
 import org.springframework.mock.web.test.MockHttpServletResponse;
 import org.springframework.util.FileCopyUtils;
+import org.springframework.util.StreamUtils;
 
 import static org.junit.Assert.*;
 
@@ -36,27 +35,23 @@
  */
 public class ShallowEtagHeaderFilterTests {
 
-	private ShallowEtagHeaderFilter filter;
+	private final ShallowEtagHeaderFilter filter = new ShallowEtagHeaderFilter();
 
-	@Before
-	public void createFilter() throws Exception {
-		filter = new ShallowEtagHeaderFilter();
-	}
 
 	@Test
 	public void isEligibleForEtag() {
 		MockHttpServletRequest request = new MockHttpServletRequest("GET", "/hotels");
 		MockHttpServletResponse response = new MockHttpServletResponse();
 
-		assertTrue(filter.isEligibleForEtag(request, response, 200, new ByteArrayInputStream(new byte[0])));
-		assertFalse(filter.isEligibleForEtag(request, response, 300, new ByteArrayInputStream(new byte[0])));
+		assertTrue(filter.isEligibleForEtag(request, response, 200, StreamUtils.emptyInput()));
+		assertFalse(filter.isEligibleForEtag(request, response, 300, StreamUtils.emptyInput()));
 
 		request = new MockHttpServletRequest("POST", "/hotels");
-		assertFalse(filter.isEligibleForEtag(request, response, 200, new ByteArrayInputStream(new byte[0])));
+		assertFalse(filter.isEligibleForEtag(request, response, 200, StreamUtils.emptyInput()));
 
 		request = new MockHttpServletRequest("POST", "/hotels");
 		request.addHeader("Cache-Control","must-revalidate, no-store");
-		assertFalse(filter.isEligibleForEtag(request, response, 200, new ByteArrayInputStream(new byte[0])));
+		assertFalse(filter.isEligibleForEtag(request, response, 200, StreamUtils.emptyInput()));
 	}
 
 	@Test
@@ -120,9 +115,7 @@ public void filterWriter() throws Exception {
 		assertArrayEquals("Invalid content", new byte[0], response.getContentAsByteArray());
 	}
 
-	// SPR-12960
-
-	@Test
+	@Test  // SPR-12960
 	public void filterWriterWithDisabledCaching() throws Exception {
 		final MockHttpServletRequest request = new MockHttpServletRequest("GET", "/hotels");
 		MockHttpServletResponse response = new MockHttpServletResponse();