Add getResource to MultipartFile

Issue: SPR-16808

spring-web/src/main/java/org/springframework/web/multipart/MultipartFile.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -21,6 +21,7 @@ import java.io.IOException;
 import java.io.InputStream;
 
 import org.springframework.core.io.InputStreamSource;
+import org.springframework.core.io.Resource;
 import org.springframework.lang.Nullable;
 
 /**
@@ -93,6 +94,17 @@ public interface MultipartFile extends InputStreamSource {
 	@Override
 	InputStream getInputStream() throws IOException;
 
+	/**
+	 * Return a Resource representation of this MultipartFile. This can be used
+	 * as input to the {@code RestTemplate} or the {@code WebClient} to expose
+	 * content length and the filename along with the InputStream.
+	 * @return this MultipartFile adapted to the Resource contract
+	 * @since 5.1
+	 */
+	default Resource getResource() {
+		return new MultipartFileResource(this);
+	}
+
 	/**
 	 * Transfer the received file to the given destination file.
 	 * <p>This may either move the file in the filesystem, copy the file in the

spring-web/src/main/java/org/springframework/web/multipart/MultipartFileResource.java

@@ -0,0 +1,99 @@
+/*
+ * Copyright 2002-2018 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.web.multipart;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+import org.springframework.core.io.AbstractResource;
+import org.springframework.util.Assert;
+
+/**
+ * Adapt {@link MultipartFile} to {@link org.springframework.core.io.Resource},
+ * exposing the content as {@code InputStream} and also overriding
+ * {@link #contentLength()} as well as {@link #getFilename()}.
+ *
+ * @author Rossen Stoyanchev
+ * @since 5.1
+ */
+class MultipartFileResource extends AbstractResource {
+
+	private final MultipartFile multipartFile;
+
+
+	public MultipartFileResource(MultipartFile multipartFile) {
+		Assert.notNull(multipartFile, "MultipartFile must not be null.");
+		this.multipartFile = multipartFile;
+	}
+
+
+	/**
+	 * This implementation always returns {@code true}.
+	 */
+	@Override
+	public boolean exists() {
+		return true;
+	}
+
+	/**
+	 * This implementation always returns {@code true}.
+	 */
+	@Override
+	public boolean isOpen() {
+		return true;
+	}
+
+	@Override
+	public long contentLength() {
+		return this.multipartFile.getSize();
+	}
+
+	@Override
+	public String getFilename() {
+		return this.multipartFile.getOriginalFilename();
+	}
+
+	/**
+	 * This implementation throws IllegalStateException if attempting to
+	 * read the underlying stream multiple times.
+	 */
+	@Override
+	public InputStream getInputStream() throws IOException, IllegalStateException {
+		return this.multipartFile.getInputStream();
+	}
+
+	/**
+	 * This implementation returns a description that has the Multipart name.
+	 */
+	@Override
+	public String getDescription() {
+		return "MultipartFile resource [" + this.multipartFile.getName() + "]";
+	}
+
+
+	@Override
+	public boolean equals(Object obj) {
+		return (obj == this ||
+				(obj instanceof MultipartFileResource &&
+						((MultipartFileResource) obj).multipartFile.equals(this.multipartFile)));
+	}
+
+	@Override
+	public int hashCode() {
+		return this.multipartFile.hashCode();
+	}
+
+}