Do not use Servlet 3.0 API in doOptions()

Refactor FrameworkServlet.doOptions() to capture the "Allow" header
by using a HttpServletResponseWrapper.

Prior to this commit the HttpServletResponse.getHeader() method was
used which is only available in Servlet 3.0 environments.

Issue: SPR-10341

spring-webmvc/src/main/java/org/springframework/web/servlet/FrameworkServlet.java

@@ -26,6 +26,7 @@ import javax.servlet.ServletContext;
 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
+import javax.servlet.http.HttpServletResponseWrapper;
 
 import org.springframework.beans.BeanUtils;
 import org.springframework.context.ApplicationContext;
@@ -866,10 +867,18 @@ public abstract class FrameworkServlet extends HttpServletBean {
 				return;
 			}
 		}
-		super.doOptions(request, response);
-		String allowedMethods = response.getHeader("Allow");
-		allowedMethods += ", " + RequestMethod.PATCH.name();
-		response.setHeader("Allow", allowedMethods);
+
+		// Use response wrapper for Servlet 2.5 compatibility where
+		// the getHeader() method does not exist
+		super.doOptions(request, new HttpServletResponseWrapper(response) {
+			@Override
+			public void setHeader(String name, String value) {
+				if("Allow".equals(name)) {
+					value = (StringUtils.hasLength(value) ? value + ", " : "") + RequestMethod.PATCH.name();
+				}
+				super.setHeader(name, value);
+			}
+		});
 	}
 
 	/**

spring-webmvc/src/test/java/org/springframework/web/servlet/DispatcherServletTests.java

@@ -61,6 +61,8 @@ import org.springframework.web.util.WebUtils;
 
 import static org.hamcrest.CoreMatchers.*;
 import static org.junit.Assert.*;
+import static org.mockito.Matchers.*;
+import static org.mockito.Mockito.*;
 
 /**
  * @author Rod Johnson
@@ -857,9 +859,10 @@ public class DispatcherServletTests extends TestCase {
 
 	public void testAllowedOptionsIncludesPatchMethod() throws Exception {
 		MockHttpServletRequest request = new MockHttpServletRequest(getServletContext(), "OPTIONS", "/foo");
-		MockHttpServletResponse response = new MockHttpServletResponse();
+		MockHttpServletResponse response = spy(new MockHttpServletResponse());
 		DispatcherServlet servlet = new DispatcherServlet();
 		servlet.service(request, response);
+		verify(response, never()).getHeader(anyString()); // SPR-10341
 		assertThat(response.getHeader("Allow"), equalTo("GET, HEAD, POST, PUT, DELETE, TRACE, OPTIONS, PATCH"));
 	}