diff --git a/java/org/apache/catalina/servlets/DefaultServlet.java b/java/org/apache/catalina/servlets/DefaultServlet.java
index b1541a91f..88668aaca 100644
--- a/java/org/apache/catalina/servlets/DefaultServlet.java
+++ b/java/org/apache/catalina/servlets/DefaultServlet.java
@@ -61,6 +61,7 @@
 
 import org.apache.catalina.Globals;
 import org.apache.catalina.connector.RequestFacade;
+import org.apache.catalina.util.FileUtil;
 import org.apache.catalina.util.RequestUtil;
 import org.apache.catalina.util.ServerInfo;
 import org.apache.catalina.util.StringManager;
@@ -1709,7 +1710,7 @@ private File validateGlobalXsltFile(File base) {
 
         // First check that the resulting path is under the provided base
         try {
-            if (!candidate.getCanonicalPath().startsWith(base.getCanonicalPath())) {
+            if (!(new FileUtil(base)).isParentOf(candidate)) {
                 return null;
             }
         } catch (IOException ioe) {
diff --git a/java/org/apache/catalina/session/FileStore.java b/java/org/apache/catalina/session/FileStore.java
index 5086a0964..0ae142113 100644
--- a/java/org/apache/catalina/session/FileStore.java
+++ b/java/org/apache/catalina/session/FileStore.java
@@ -32,6 +32,7 @@
 import org.apache.catalina.Globals;
 import org.apache.catalina.Loader;
 import org.apache.catalina.Session;
+import org.apache.catalina.util.FileUtil;
 import org.apache.juli.logging.Log;
 import org.apache.juli.logging.LogFactory;
 import org.apache.tomcat.util.res.StringManager;
@@ -400,9 +401,10 @@ private File file(String id) throws IOException {
         }
         String filename = id + FILE_EXT;
         File file = new File(storageDir, filename);
+        FileUtil storageDirUtil = new FileUtil(storageDir);
 
         // Check the file is within the storage directory
-        if (!file.getCanonicalPath().startsWith(storageDir.getCanonicalPath())) {
+        if (!storageDirUtil.isParentOf(file)) {
             log.warn(sm.getString("fileStore.invalid", file.getPath(), id));
             return null;
         }
diff --git a/java/org/apache/catalina/startup/ContextConfig.java b/java/org/apache/catalina/startup/ContextConfig.java
index 5cb9b1c2f..e48bf8947 100644
--- a/java/org/apache/catalina/startup/ContextConfig.java
+++ b/java/org/apache/catalina/startup/ContextConfig.java
@@ -58,6 +58,7 @@
 import org.xml.sax.ErrorHandler;
 import org.xml.sax.InputSource;
 import org.xml.sax.SAXParseException;
+import org.apache.catalina.util.FileUtil;
 
 /**
  * Startup event listener for a <b>Context</b> that configures the properties
@@ -912,7 +913,7 @@ protected void fixDocBase()
             }
         }
 
-        if (docBase.startsWith(canonicalAppBase.getPath() + File.separatorChar)) {
+        if ((new FileUtil(canonicalAppBase)).isParentOf(docBase)) {
             docBase = docBase.substring(canonicalAppBase.getPath().length());
             docBase = docBase.replace(File.separatorChar, '/');
             if (docBase.startsWith("/")) {
diff --git a/java/org/apache/catalina/startup/ExpandWar.java b/java/org/apache/catalina/startup/ExpandWar.java
index 133053f2a..735be7bb6 100644
--- a/java/org/apache/catalina/startup/ExpandWar.java
+++ b/java/org/apache/catalina/startup/ExpandWar.java
@@ -32,6 +32,7 @@
 import java.util.jar.JarFile;
 
 import org.apache.catalina.Host;
+import org.apache.catalina.util.FileUtil;
 import org.apache.catalina.util.StringManager;
 import org.apache.juli.logging.Log;
 import org.apache.juli.logging.LogFactory;
@@ -136,10 +137,7 @@ public static String expand(Host host, URL war, String pathname)
             throw new IOException(sm.getString("expandWar.createFailed", docBase));
 
         // Expand the WAR into the new document base directory
-        String canonicalDocBasePrefix = docBase.getCanonicalPath();
-        if (!canonicalDocBasePrefix.endsWith(File.separator)) {
-            canonicalDocBasePrefix += File.separator;
-        }
+        FileUtil docBaseUtil = new FileUtil(docBase);
         JarURLConnection juc = (JarURLConnection) war.openConnection();
         juc.setUseCaches(false);
         JarFile jarFile = null;
@@ -152,8 +150,7 @@ public static String expand(Host host, URL war, String pathname)
                 JarEntry jarEntry = (JarEntry) jarEntries.nextElement();
                 String name = jarEntry.getName();
                 File expandedFile = new File(docBase, name);
-                if (!expandedFile.getCanonicalPath().startsWith(
-                        canonicalDocBasePrefix)) {
+                if (!docBaseUtil.isParentOf(expandedFile)) {
                     // Trying to expand outside the docBase
                     // Throw an exception to stop the deployment
                     throw new IllegalArgumentException(
@@ -241,10 +238,7 @@ public static void validate(Host host, URL war, String pathname)
         File docBase = new File(appBase, pathname);
 
         // Calculate the document base directory
-        String canonicalDocBasePrefix = docBase.getCanonicalPath();
-        if (!canonicalDocBasePrefix.endsWith(File.separator)) {
-            canonicalDocBasePrefix += File.separator;
-        }
+        FileUtil docBaseUtil = new FileUtil(docBase);
         JarURLConnection juc = (JarURLConnection) war.openConnection();
         juc.setUseCaches(false);
         JarFile jarFile = null;
@@ -255,8 +249,7 @@ public static void validate(Host host, URL war, String pathname)
                 JarEntry jarEntry = jarEntries.nextElement();
                 String name = jarEntry.getName();
                 File expandedFile = new File(docBase, name);
-                if (!expandedFile.getCanonicalPath().startsWith(
-                        canonicalDocBasePrefix)) {
+                if (!docBaseUtil.isParentOf(expandedFile)) {
                     // Entry located outside the docBase
                     // Throw an exception to stop the deployment
                     throw new IllegalArgumentException(
diff --git a/java/org/apache/catalina/startup/HostConfig.java b/java/org/apache/catalina/startup/HostConfig.java
index 31fcefe25..0403caafe 100644
--- a/java/org/apache/catalina/startup/HostConfig.java
+++ b/java/org/apache/catalina/startup/HostConfig.java
@@ -48,6 +48,7 @@
 import org.apache.catalina.LifecycleListener;
 import org.apache.catalina.core.ContainerBase;
 import org.apache.catalina.core.StandardHost;
+import org.apache.catalina.util.FileUtil;
 import org.apache.catalina.util.IOTools;
 import org.apache.catalina.util.StringManager;
 import org.apache.tomcat.util.digester.Digester;
@@ -656,8 +657,8 @@ protected void deployDescriptor(String contextPath, File contextXml, String file
                     docBase = new File(appBase(), context.getDocBase());
                 }
                 // If external docBase, register .xml as redeploy first
-                if (!docBase.getCanonicalPath().startsWith(
-                        appBase().getAbsolutePath() + File.separator)) {
+                FileUtil appBaseUtil = new FileUtil(appBase());
+                if (!appBaseUtil.isParentOf(docBase)) {
                     isExternal = true;
                     deployedApp.redeployResources.put
                         (contextXml.getAbsolutePath(), new Long(contextXml.lastModified()));
diff --git a/java/org/apache/catalina/util/FileUtil.java b/java/org/apache/catalina/util/FileUtil.java
new file mode 100644
index 000000000..10a2e3049
--- /dev/null
+++ b/java/org/apache/catalina/util/FileUtil.java
@@ -0,0 +1,50 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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
+ *
+ *      http://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.apache.catalina.util;
+
+import java.io.File;
+import java.io.IOException;
+
+public class FileUtil {
+
+    private final String canonicalPath;
+
+    public FileUtil(File f) throws IOException {
+        String path = f.getCanonicalPath();
+        if (!path.endsWith(File.pathSeparator)) {
+            path += File.pathSeparatorChar;
+        }
+
+        canonicalPath = path;
+    }
+
+
+    public String getCanonicalPath() {
+        return canonicalPath;
+    }
+
+
+    public boolean isParentOf(File child) throws IOException {
+        return isParentOf(child.getCanonicalPath());
+    }
+
+
+    public boolean isParentOf(String childPath) {
+        return childPath.startsWith(canonicalPath);
+    }
+}
\ No newline at end of file
diff --git a/webapps/docs/changelog.xml b/webapps/docs/changelog.xml
index 87b16dd59..c8c6e97ec 100644
--- a/webapps/docs/changelog.xml
+++ b/webapps/docs/changelog.xml
@@ -120,6 +120,10 @@
         Ensure the ASF logo image is correctly displayed in ROOT, docs and
         host-manager applications. (violetagg)
       </fix>
+      <scode>
+          Test for one directory being a sub-directory of another in a consistent
+          way. (markt)
+      </scode>
     </changelog>
   </subsection>
 </section>