Add allowHeader property to WebContentGenerator

The WebContentGenerator now maintains an additional property that
sub-classes can use for an "Allow" header in response to an HTTP
OPTIONS request. This property is pre-initialized once at startup
and does not have to rely on getSupportedMethods in addition to
adding HTTP OPTIONS if not explicitly listed.

Issue: SPR-13130

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

@@ -16,7 +16,9 @@
 
 package org.springframework.web.servlet.support;
 
+import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collection;
 import java.util.LinkedHashSet;
 import java.util.Set;
 import java.util.concurrent.TimeUnit;
@@ -25,6 +27,8 @@ import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 
 import org.springframework.http.CacheControl;
+import org.springframework.http.HttpMethod;
+import org.springframework.util.ObjectUtils;
 import org.springframework.util.StringUtils;
 import org.springframework.web.HttpRequestMethodNotSupportedException;
 import org.springframework.web.HttpSessionRequiredException;
@@ -51,6 +55,7 @@ import org.springframework.web.context.support.WebApplicationObjectSupport;
  * @author Rod Johnson
  * @author Juergen Hoeller
  * @author Brian Clozel
+ * @author Rossen Stoyanchev
  * @see #setCacheSeconds
  * @see #setCacheControl
  * @see #setRequireSession
@@ -76,6 +81,8 @@ public abstract class WebContentGenerator extends WebApplicationObjectSupport {
 	/** Set of supported HTTP methods */
 	private Set<String> supportedMethods;
 
+	private String allowHeader;
+
 	private boolean requireSession = false;
 
 	private CacheControl cacheControl;
@@ -115,6 +122,7 @@ public abstract class WebContentGenerator extends WebApplicationObjectSupport {
 			this.supportedMethods.add(METHOD_HEAD);
 			this.supportedMethods.add(METHOD_POST);
 		}
+		initAllowHeader();
 	}
 
 	/**
@@ -122,7 +130,28 @@ public abstract class WebContentGenerator extends WebApplicationObjectSupport {
 	 * @param supportedMethods the supported HTTP methods for this content generator
 	 */
 	public WebContentGenerator(String... supportedMethods) {
-		this.supportedMethods = new LinkedHashSet<String>(Arrays.asList(supportedMethods));
+		setSupportedMethods(supportedMethods);
+	}
+
+	private void initAllowHeader() {
+		Collection<String> allowedMethods;
+		if (this.supportedMethods == null) {
+			allowedMethods = new ArrayList<String>(HttpMethod.values().length - 1);
+			for (HttpMethod method : HttpMethod.values()) {
+				if (!HttpMethod.TRACE.equals(method)) {
+					allowedMethods.add(method.name());
+				}
+			}
+		}
+		else if (this.supportedMethods.contains(HttpMethod.OPTIONS.name())) {
+			allowedMethods = this.supportedMethods;
+		}
+		else {
+			allowedMethods = new ArrayList<String>(this.supportedMethods);
+			allowedMethods.add(HttpMethod.OPTIONS.name());
+
+		}
+		this.allowHeader = StringUtils.collectionToCommaDelimitedString(allowedMethods);
 	}
 
 
@@ -132,12 +161,13 @@ public abstract class WebContentGenerator extends WebApplicationObjectSupport {
 	 * unrestricted for general controllers and interceptors.
 	 */
 	public final void setSupportedMethods(String... methods) {
-		if (methods != null) {
+		if (!ObjectUtils.isEmpty(methods)) {
 			this.supportedMethods = new LinkedHashSet<String>(Arrays.asList(methods));
 		}
 		else {
 			this.supportedMethods = null;
 		}
+		initAllowHeader();
 	}
 
 	/**
@@ -147,6 +177,19 @@ public abstract class WebContentGenerator extends WebApplicationObjectSupport {
 		return StringUtils.toStringArray(this.supportedMethods);
 	}
 
+	/**
+	 * Return the "Allow" header value to use in response to an HTTP OPTIONS
+	 * request based on the configured {@link #setSupportedMethods supported
+	 * methods} also automatically adding "OPTIONS" to the list even if not
+	 * present as a supported method. This means sub-classes don't have to
+	 * explicitly list "OPTIONS" as a supported method as long as HTTP OPTIONS
+	 * requests are handled before making a call to
+	 * {@link #checkRequest(HttpServletRequest)}.
+	 */
+	protected String getAllowHeader() {
+		return this.allowHeader;
+	}
+
 	/**
 	 * Set whether a session should be required to handle requests.
 	 */