StandardServletMultipartResolver provides strict Servlet compliance option

Closes gh-26826

spring-web/src/main/java/org/springframework/web/multipart/support/StandardServletMultipartResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2021 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 javax.servlet.http.Part;
 
 import org.apache.commons.logging.LogFactory;
 
+import org.springframework.http.MediaType;
 import org.springframework.util.StringUtils;
 import org.springframework.web.multipart.MultipartException;
 import org.springframework.web.multipart.MultipartHttpServletRequest;
@@ -32,6 +33,15 @@ import org.springframework.web.multipart.MultipartResolver;
  * To be added as "multipartResolver" bean to a Spring DispatcherServlet context,
  * without any extra configuration at the bean level (see below).
  *
+ * <p>This resolver variant uses your Servlet container's multipart parser as-is,
+ * potentially exposing the application to container implementation differences.
+ * See {@link org.springframework.web.multipart.commons.CommonsMultipartResolver}
+ * for an alternative implementation using a local Commons FileUpload library
+ * within the application, providing maximum portability across Servlet containers.
+ * Also, see this resolver's configuration option for
+ * {@link #setStrictServletCompliance strict Servlet compliance}, narrowing the
+ * applicability of Spring's {@link MultipartHttpServletRequest} to form data only.
+ *
  * <p><b>Note:</b> In order to use Servlet 3.0 based multipart parsing,
  * you need to mark the affected servlet with a "multipart-config" section in
  * {@code web.xml}, or with a {@link javax.servlet.MultipartConfigElement}
@@ -55,6 +65,7 @@ import org.springframework.web.multipart.MultipartResolver;
  * @author Juergen Hoeller
  * @since 3.1
  * @see #setResolveLazily
+ * @see #setStrictServletCompliance
  * @see HttpServletRequest#getParts()
  * @see org.springframework.web.multipart.commons.CommonsMultipartResolver
  */
@@ -62,6 +73,8 @@ public class StandardServletMultipartResolver implements MultipartResolver {
 
 	private boolean resolveLazily = false;
 
+	private boolean strictServletCompliance = false;
+
 
 	/**
 	 * Set whether to resolve the multipart request lazily at the time of
@@ -76,10 +89,32 @@ public class StandardServletMultipartResolver implements MultipartResolver {
 		this.resolveLazily = resolveLazily;
 	}
 
+	/**
+	 * Specify whether this resolver should strictly comply with the Servlet
+	 * specification, only kicking in for "multipart/form-data" requests.
+	 * <p>Default is "false", trying to process any request with a "multipart/"
+	 * content type as far as the underlying Servlet container supports it
+	 * (which works on e.g. Tomcat but not on Jetty). For consistent portability
+	 * and in particular for consistent custom handling of non-form multipart
+	 * request types outside of Spring's {@link MultipartResolver} mechanism,
+	 * switch this flag to "true": Only "multipart/form-data" requests will be
+	 * wrapped with a {@link MultipartHttpServletRequest} then; other kinds of
+	 * requests will be left as-is, allowing for custom processing in user code.
+	 * <p>Note that Commons FileUpload and therefore
+	 * {@link org.springframework.web.multipart.commons.CommonsMultipartResolver}
+	 * supports any "multipart/" request type. However, it restricts processing
+	 * to POST requests which standard Servlet multipart parsers might not do.
+	 * @since 5.3.9
+	 */
+	public void setStrictServletCompliance(boolean strictServletCompliance) {
+		this.strictServletCompliance = strictServletCompliance;
+	}
+
 
 	@Override
 	public boolean isMultipart(HttpServletRequest request) {
-		return StringUtils.startsWithIgnoreCase(request.getContentType(), "multipart/");
+		return StringUtils.startsWithIgnoreCase(request.getContentType(),
+				(this.strictServletCompliance ? MediaType.MULTIPART_FORM_DATA_VALUE : "multipart/"));
 	}
 
 	@Override

spring-web/src/test/java/org/springframework/web/multipart/support/StandardServletMultipartResolverTests.java

@@ -0,0 +1,90 @@
+/*
+ * Copyright 2002-2021 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
+ *
+ *      https://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.support;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.http.MediaType;
+import org.springframework.web.testfixture.servlet.MockHttpServletRequest;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * @author Juergen Hoeller
+ */
+public class StandardServletMultipartResolverTests {
+
+	@Test
+	public void isMultipartWithDefaultSetting() {
+		StandardServletMultipartResolver resolver = new StandardServletMultipartResolver();
+
+		MockHttpServletRequest request = new MockHttpServletRequest("POST", "/");
+		assertThat(resolver.isMultipart(request)).isFalse();
+
+		request.setContentType(MediaType.MULTIPART_FORM_DATA_VALUE);
+		assertThat(resolver.isMultipart(request)).isTrue();
+
+		request.setContentType(MediaType.MULTIPART_MIXED_VALUE);
+		assertThat(resolver.isMultipart(request)).isTrue();
+
+		request.setContentType(MediaType.MULTIPART_RELATED_VALUE);
+		assertThat(resolver.isMultipart(request)).isTrue();
+
+		request = new MockHttpServletRequest("PUT", "/");
+		assertThat(resolver.isMultipart(request)).isFalse();
+
+		request.setContentType(MediaType.MULTIPART_FORM_DATA_VALUE);
+		assertThat(resolver.isMultipart(request)).isTrue();
+
+		request.setContentType(MediaType.MULTIPART_MIXED_VALUE);
+		assertThat(resolver.isMultipart(request)).isTrue();
+
+		request.setContentType(MediaType.MULTIPART_RELATED_VALUE);
+		assertThat(resolver.isMultipart(request)).isTrue();
+	}
+
+	@Test
+	public void isMultipartWithStrictSetting() {
+		StandardServletMultipartResolver resolver = new StandardServletMultipartResolver();
+		resolver.setStrictServletCompliance(true);
+
+		MockHttpServletRequest request = new MockHttpServletRequest("POST", "/");
+		assertThat(resolver.isMultipart(request)).isFalse();
+
+		request.setContentType(MediaType.MULTIPART_FORM_DATA_VALUE);
+		assertThat(resolver.isMultipart(request)).isTrue();
+
+		request.setContentType(MediaType.MULTIPART_MIXED_VALUE);
+		assertThat(resolver.isMultipart(request)).isFalse();
+
+		request.setContentType(MediaType.MULTIPART_RELATED_VALUE);
+		assertThat(resolver.isMultipart(request)).isFalse();
+
+		request = new MockHttpServletRequest("PUT", "/");
+		assertThat(resolver.isMultipart(request)).isFalse();
+
+		request.setContentType(MediaType.MULTIPART_FORM_DATA_VALUE);
+		assertThat(resolver.isMultipart(request)).isTrue();
+
+		request.setContentType(MediaType.MULTIPART_MIXED_VALUE);
+		assertThat(resolver.isMultipart(request)).isFalse();
+
+		request.setContentType(MediaType.MULTIPART_RELATED_VALUE);
+		assertThat(resolver.isMultipart(request)).isFalse();
+	}
+
+}

src/docs/asciidoc/web/webmvc.adoc

@@ -1140,18 +1140,30 @@ another based on Servlet 3.0 multipart request parsing.
 
 To enable multipart handling, you need to declare a `MultipartResolver` bean in your
 `DispatcherServlet` Spring configuration with a name of `multipartResolver`.
-The `DispatcherServlet` detects it and applies it to the incoming request. When a POST with
-content-type of `multipart/form-data` is received, the resolver parses the content and
-wraps the current `HttpServletRequest` as `MultipartHttpServletRequest` to
-provide access to resolved parts in addition to exposing them as request parameters.
+The `DispatcherServlet` detects it and applies it to the incoming request. When a POST
+with a content type of `multipart/form-data` is received, the resolver parses the
+content wraps the current `HttpServletRequest` as a `MultipartHttpServletRequest` to
+provide access to resolved files in addition to exposing parts as request parameters.
 
 
 [[mvc-multipart-resolver-commons]]
 ==== Apache Commons `FileUpload`
 
 To use Apache Commons `FileUpload`, you can configure a bean of type
-`CommonsMultipartResolver` with a name of `multipartResolver`. You also need to
-have `commons-fileupload` as a dependency on your classpath.
+`CommonsMultipartResolver` with a name of `multipartResolver`. You also need to have
+the `commons-fileupload` jar as a dependency on your classpath.
+
+This resolver variant delegates to a local library within the application, providing
+maximum portability across Servlet containers. As an alternative, consider standard
+Servlet multipart resolution through the container's own parser as discussed below.
+
+[NOTE]
+====
+Commons FileUpload traditionally applies to POST requests only but accepts any
+`multipart/` content type. See the
+{api-spring-framework}/web/multipart/commons/CommonsMultipartResolver.html[`CommonsMultipartResolver`]
+javadoc for details and configuration options.
+====
 
 
 [[mvc-multipart-resolver-standard]]
@@ -1200,6 +1212,16 @@ The following example shows how to set a `MultipartConfigElement` on the Servlet
 Once the Servlet 3.0 configuration is in place, you can add a bean of type
 `StandardServletMultipartResolver` with a name of `multipartResolver`.
 
+[NOTE]
+====
+This resolver variant uses your Servlet container's multipart parser as-is,
+potentially exposing the application to container implementation differences.
+By default, it will try to parse any `multipart/` content type with any HTTP
+method but this may not be supported across all Servlet containers. See the
+{api-spring-framework}/web/multipart/support/StandardServletMultipartResolver.html[`StandardServletMultipartResolver`]
+javadoc for details and configuration options.
+====
+
 
 
 [[mvc-logging]]