Skip HttpServletResponse.getStatus() on Servlet 2.5

Prior to this commit, ServletWebRequest would call
HttpServletResponse.getStatus(), which is a Servlet 3.x method.

This commit checks if this method is available before calling it, thus
keeping Servlet 2.5 compatibility.

Issue: SPR-13396

Author: bclozel

spring-web/src/main/java/org/springframework/web/context/request/ServletWebRequest.java

@@ -27,6 +27,7 @@
 
 import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpStatus;
+import org.springframework.util.ClassUtils;
 import org.springframework.util.CollectionUtils;
 import org.springframework.util.ObjectUtils;
 import org.springframework.util.StringUtils;
@@ -54,6 +55,10 @@ public class ServletWebRequest extends ServletRequestAttributes implements Nativ
 
 	private static final String METHOD_HEAD = "HEAD";
 
+	/** Checking for Servlet 3.0+ HttpServletResponse.getStatus() */
+	private static final boolean responseGetStatusAvailable =
+			ClassUtils.hasMethod(HttpServletResponse.class, "getStatus");
+
 
 	private boolean notModified = false;
 
@@ -173,7 +178,7 @@ public boolean isSecure() {
 	public boolean checkNotModified(long lastModifiedTimestamp) {
 		HttpServletResponse response = getResponse();
 		if (lastModifiedTimestamp >= 0 && !this.notModified) {
-			if (response == null || HttpStatus.valueOf(response.getStatus()).is2xxSuccessful()) {
+			if (isCompatibleWithConditionalRequests(response)) {
 				this.notModified = isTimestampNotModified(lastModifiedTimestamp);
 				if (response != null) {
 					if (this.notModified && supportsNotModifiedStatus()) {
@@ -188,6 +193,12 @@ public boolean checkNotModified(long lastModifiedTimestamp) {
 		return this.notModified;
 	}
 
+	private boolean isCompatibleWithConditionalRequests(HttpServletResponse response) {
+		return response == null
+				|| !responseGetStatusAvailable
+				|| HttpStatus.valueOf(response.getStatus()).is2xxSuccessful();
+	}
+
 	@SuppressWarnings("deprecation")
 	private boolean isTimestampNotModified(long lastModifiedTimestamp) {
 		long ifModifiedSince = -1;
@@ -215,7 +226,7 @@ private boolean isTimestampNotModified(long lastModifiedTimestamp) {
 	public boolean checkNotModified(String etag) {
 		HttpServletResponse response = getResponse();
 		if (StringUtils.hasLength(etag) && !this.notModified) {
-			if (response == null || HttpStatus.valueOf(response.getStatus()).is2xxSuccessful()) {
+			if (isCompatibleWithConditionalRequests(response)) {
 				etag = addEtagPadding(etag);
 				this.notModified = isETagNotModified(etag);
 				if (response != null) {
@@ -265,7 +276,7 @@ private boolean supportsNotModifiedStatus() {
 	public boolean checkNotModified(String etag, long lastModifiedTimestamp) {
 		HttpServletResponse response = getResponse();
 		if (StringUtils.hasLength(etag) && !this.notModified) {
-			if (response == null || HttpStatus.valueOf(response.getStatus()).is2xxSuccessful()) {
+			if (isCompatibleWithConditionalRequests(response)) {
 				etag = addEtagPadding(etag);
 				this.notModified = isETagNotModified(etag) && isTimestampNotModified(lastModifiedTimestamp);
 				if (response != null) {