Shared read-only instances of UrlPathHelper

UrlPathHelper is often created and used without customizations or with
the same customizations. This commit introduces re-usable, instances.
Effectively a backport of commit 23233c.

Closes gh-25690

spring-web/src/main/java/org/springframework/web/filter/ForwardedHeaderFilter.java

@@ -76,20 +76,11 @@ public class ForwardedHeaderFilter extends OncePerRequestFilter {
 	}
 
 
-	private final UrlPathHelper pathHelper;
-
 	private boolean removeOnly;
 
 	private boolean relativeRedirects;
 
 
-	public ForwardedHeaderFilter() {
-		this.pathHelper = new UrlPathHelper();
-		this.pathHelper.setUrlDecode(false);
-		this.pathHelper.setRemoveSemicolonContent(false);
-	}
-
-
 	/**
 	 * Enables mode in which any "Forwarded" or "X-Forwarded-*" headers are
 	 * removed only and the information in them ignored.
@@ -145,7 +136,7 @@ public class ForwardedHeaderFilter extends OncePerRequestFilter {
 			filterChain.doFilter(theRequest, response);
 		}
 		else {
-			HttpServletRequest theRequest = new ForwardedHeaderExtractingRequest(request, this.pathHelper);
+			HttpServletRequest theRequest = new ForwardedHeaderExtractingRequest(request);
 			HttpServletResponse theResponse = (this.relativeRedirects ?
 					RelativeRedirectResponseWrapper.wrapIfNecessary(response, HttpStatus.SEE_OTHER) :
 					new ForwardedHeaderExtractingResponse(response, theRequest));
@@ -221,7 +212,7 @@ public class ForwardedHeaderFilter extends OncePerRequestFilter {
 
 		private final String requestUrl;
 
-		public ForwardedHeaderExtractingRequest(HttpServletRequest request, UrlPathHelper pathHelper) {
+		public ForwardedHeaderExtractingRequest(HttpServletRequest request) {
 			super(request);
 
 			HttpRequest httpRequest = new ServletServerHttpRequest(request);
@@ -235,7 +226,7 @@ public class ForwardedHeaderFilter extends OncePerRequestFilter {
 
 			String prefix = getForwardedPrefix(request);
 			this.contextPath = (prefix != null ? prefix : request.getContextPath());
-			this.requestUri = this.contextPath + pathHelper.getPathWithinApplication(request);
+			this.requestUri = this.contextPath + UrlPathHelper.rawPathInstance.getPathWithinApplication(request);
 			this.requestUrl = this.scheme + "://" + this.host + (port == -1 ? "" : ":" + port) + this.requestUri;
 		}
 

spring-web/src/main/java/org/springframework/web/util/UrlPathHelper.java

@@ -27,6 +27,7 @@ import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 
 import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
 import org.springframework.util.StringUtils;
@@ -69,6 +70,8 @@ public class UrlPathHelper {
 
 	private String defaultEncoding = WebUtils.DEFAULT_CHARACTER_ENCODING;
 
+	private boolean readOnly = false;
+
 
 	/**
 	 * Whether URL lookups should always use the full path within the current
@@ -80,6 +83,7 @@ public class UrlPathHelper {
 	 * <p>By default this is set to "false".
 	 */
 	public void setAlwaysUseFullPath(boolean alwaysUseFullPath) {
+		checkReadOnly();
 		this.alwaysUseFullPath = alwaysUseFullPath;
 	}
 
@@ -102,6 +106,7 @@ public class UrlPathHelper {
 	 * @see java.net.URLDecoder#decode(String, String)
 	 */
 	public void setUrlDecode(boolean urlDecode) {
+		checkReadOnly();
 		this.urlDecode = urlDecode;
 	}
 
@@ -118,6 +123,7 @@ public class UrlPathHelper {
 	 * <p>Default is "true".
 	 */
 	public void setRemoveSemicolonContent(boolean removeSemicolonContent) {
+		checkReadOnly();
 		this.removeSemicolonContent = removeSemicolonContent;
 	}
 
@@ -125,6 +131,7 @@ public class UrlPathHelper {
 	 * Whether configured to remove ";" (semicolon) content from the request URI.
 	 */
 	public boolean shouldRemoveSemicolonContent() {
+		checkReadOnly();
 		return this.removeSemicolonContent;
 	}
 
@@ -142,6 +149,7 @@ public class UrlPathHelper {
 	 * @see WebUtils#DEFAULT_CHARACTER_ENCODING
 	 */
 	public void setDefaultEncoding(String defaultEncoding) {
+		checkReadOnly();
 		this.defaultEncoding = defaultEncoding;
 	}
 
@@ -152,6 +160,17 @@ public class UrlPathHelper {
 		return this.defaultEncoding;
 	}
 
+	/**
+	 * Switch to read-only mode where further configuration changes are not allowed.
+	 */
+	private void setReadOnly() {
+		this.readOnly = true;
+	}
+
+	private void checkReadOnly() {
+		Assert.isTrue(!this.readOnly, "This instance cannot be modified");
+	}
+
 
 	/**
 	 * Return the mapping lookup path for the given request, within the current
@@ -605,4 +624,39 @@ public class UrlPathHelper {
 		return !flagToUse;
 	}
 
+
+	/**
+	 * Shared, read-only instance with defaults. The following apply:
+	 * <ul>
+	 * <li>{@code alwaysUseFullPath=false}
+	 * <li>{@code urlDecode=true}
+	 * <li>{@code removeSemicolon=true}
+	 * <li>{@code defaultEncoding=}{@link WebUtils#DEFAULT_CHARACTER_ENCODING}
+	 * </ul>
+	 */
+	public static final UrlPathHelper defaultInstance = new UrlPathHelper();
+
+	static {
+		defaultInstance.setReadOnly();
+	}
+
+
+	/**
+	 * Shared, read-only instance for the full, encoded path. The following apply:
+	 * <ul>
+	 * <li>{@code alwaysUseFullPath=true}
+	 * <li>{@code urlDecode=false}
+	 * <li>{@code removeSemicolon=false}
+	 * <li>{@code defaultEncoding=}{@link WebUtils#DEFAULT_CHARACTER_ENCODING}
+	 * </ul>
+	 */
+	public static final UrlPathHelper rawPathInstance = new UrlPathHelper();
+
+	static {
+		rawPathInstance.setAlwaysUseFullPath(true);
+		rawPathInstance.setUrlDecode(false);
+		rawPathInstance.setRemoveSemicolonContent(false);
+		rawPathInstance.setReadOnly();
+	}
+
 }