Fixes #5521 ResourceCollection NPE (#5527)

* Fixes #5521 ResourceCollection NPE

Fix constructor and addPath so that all resources in a RC must exist when created.

* Fixes #5521 ResourceCollection NPE

Cleanup the vestiges of non existent directories detected by resource ending in /

* Fixes #5521 ResourceCollection NPE

Revert adding paths ending in / as jar:file resource needs them

* feedback from review

improved javadoc.

jetty-util/src/main/java/org/eclipse/jetty/util/resource/JarFileResource.java

@@ -144,7 +144,7 @@ public boolean exists()
             String fileUrl = _urlString.substring(4, _urlString.length() - 2);
             try
             {
-                return newResource(fileUrl).exists();
+                return _directory = newResource(fileUrl).exists();
             }
             catch (Exception e)
             {
@@ -236,15 +236,10 @@ else if (entry.isDirectory())
         return _exists;
     }
 
-    /**
-     * Returns true if the represented resource is a container/directory.
-     * If the resource is not a file, resources ending with "/" are
-     * considered directories.
-     */
     @Override
     public boolean isDirectory()
     {
-        return _urlString.endsWith("/") || exists() && _directory;
+        return exists() && _directory;
     }
 
     /**

jetty-util/src/main/java/org/eclipse/jetty/util/resource/Resource.java

@@ -320,8 +320,6 @@ public static boolean isContainedIn(Resource r, Resource containingResource) thr
 
     /**
      * @return true if the represented resource is a container/directory.
-     * if the resource is not a file, resources ending with "/" are
-     * considered directories.
      */
     public abstract boolean isDirectory();
 
@@ -412,7 +410,7 @@ public abstract boolean renameTo(Resource dest)
 
     /**
      * Returns the resource contained inside the current resource with the
-     * given name.
+     * given name, which may or may not exist.
      *
      * @param path The path segment to add, which is not encoded
      * @return the Resource for the resolved path within this Resource, never null

jetty-util/src/main/java/org/eclipse/jetty/util/resource/ResourceCollection.java

@@ -62,8 +62,19 @@ public ResourceCollection()
      * @param resources the resources to be added to collection
      */
     public ResourceCollection(Resource... resources)
+    {
+        this(Arrays.asList(resources));
+    }
+
+    /**
+     * Instantiates a new resource collection.
+     *
+     * @param resources the resources to be added to collection
+     */
+    public ResourceCollection(Collection<Resource> resources)
     {
         _resources = new ArrayList<>();
+
         for (Resource r : resources)
         {
             if (r == null)
@@ -82,17 +93,6 @@ public ResourceCollection(Resource... resources)
         }
     }
 
-    /**
-     * Instantiates a new resource collection.
-     *
-     * @param resources the resources to be added to collection
-     */
-    public ResourceCollection(Collection<Resource> resources)
-    {
-        _resources = new ArrayList<>();
-        _resources.addAll(resources);
-    }
-
     /**
      * Instantiates a new resource collection.
      *
@@ -226,8 +226,16 @@ public void setResources(String resources) throws IOException
     }
 
     /**
+     * Add a path to the resource collection.
      * @param path The path segment to add
-     * @return The contained resource (found first) in the collection of resources
+     * @return The resulting resource(s) :
+     * <ul>
+     *   <li>is a file that exists in at least one of the collection, then the first one found is returned</li>
+     *   <li>is a directory that exists in at exactly one of the collection, then that directory resource is returned </li>
+     *   <li>is a directory that exists in several of the collection, then a ResourceCollection of those directories is returned</li>
+     *   <li>do not exist in any of the collection, then a new non existent resource relative to the first in the collection is returned.</li>
+     * </ul>
+     * @throws MalformedURLException if the resolution of the path fails because the input path parameter is malformed against any of the collection
      */
     @Override
     public Resource addPath(String path) throws IOException
@@ -247,27 +255,28 @@ public Resource addPath(String path) throws IOException
         ArrayList<Resource> resources = null;
 
         // Attempt a simple (single) Resource lookup that exists
+        Resource addedResource = null;
         for (Resource res : _resources)
         {
-            Resource r = res.addPath(path);
-            if (!r.isDirectory() && r.exists())
-            {
-                // Return simple (non-directory) Resource
-                return r;
-            }
-
+            addedResource = res.addPath(path);
+            if (!addedResource.exists())
+                continue;
+            if (!addedResource.isDirectory())
+                return addedResource; // Return simple (non-directory) Resource
             if (resources == null)
-            {
                 resources = new ArrayList<>();
-            }
+            resources.add(addedResource);
+        }
 
-            resources.add(r);
+        if (resources == null)
+        {
+            if (addedResource != null)
+                return addedResource; // This will not exist
+            return EmptyResource.INSTANCE;
         }
 
         if (resources.size() == 1)
-        {
             return resources.get(0);
-        }
 
         return new ResourceCollection(resources);
     }
@@ -384,7 +393,6 @@ public URI getURI()
     public boolean isDirectory()
     {
         assertResourcesSet();
-
         return true;
     }
 

jetty-util/src/main/java/org/eclipse/jetty/util/resource/URLResource.java

@@ -128,11 +128,6 @@ public boolean exists()
         return _in != null;
     }
 
-    /**
-     * Returns true if the represented resource is a container/directory.
-     * If the resource is not a file, resources ending with "/" are
-     * considered directories.
-     */
     @Override
     public boolean isDirectory()
     {

jetty-util/src/test/java/org/eclipse/jetty/util/resource/ResourceCollectionTest.java

@@ -35,7 +35,6 @@
 
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.contains;
-import static org.hamcrest.Matchers.emptyArray;
 import static org.hamcrest.Matchers.is;
 import static org.hamcrest.Matchers.nullValue;
 import static org.junit.jupiter.api.Assertions.assertEquals;
@@ -189,7 +188,7 @@ public void testList() throws Exception
 
         assertThat(Arrays.asList(rc1.list()), contains("1.txt", "2.txt", "3.txt", "dir/"));
         assertThat(Arrays.asList(rc1.addPath("dir").list()), contains("1.txt", "2.txt", "3.txt"));
-        assertThat(rc1.addPath("unknown").list(), emptyArray());
+        assertThat(rc1.addPath("unknown").list(), nullValue());
     }
 
     @Test

jetty-util/src/test/java/org/eclipse/jetty/util/resource/ResourceTest.java

@@ -215,15 +215,15 @@ public static Stream<Arguments> scenarios() throws Exception
         cases.addCase(new Scenario(tdata1, "alphabet.txt", EXISTS, !DIR, "ABCDEFGHIJKLMNOPQRSTUVWXYZ"));
         cases.addCase(new Scenario(tdata2, "alphabet.txt", EXISTS, !DIR, "ABCDEFGHIJKLMNOPQRSTUVWXYZ"));
 
-        cases.addCase(new Scenario("jar:file:/somejar.jar!/content/", !EXISTS, DIR));
-        cases.addCase(new Scenario("jar:file:/somejar.jar!/", !EXISTS, DIR));
+        cases.addCase(new Scenario("jar:file:/somejar.jar!/content/", !EXISTS, !DIR));
+        cases.addCase(new Scenario("jar:file:/somejar.jar!/", !EXISTS, !DIR));
 
         String urlRef = cases.uriRef.toASCIIString();
         Scenario zdata = new Scenario("jar:" + urlRef + "TestData/test.zip!/", EXISTS, DIR);
         cases.addCase(zdata);
 
         cases.addCase(new Scenario(zdata, "Unknown", !EXISTS, !DIR));
-        cases.addCase(new Scenario(zdata, "/Unknown/", !EXISTS, DIR));
+        cases.addCase(new Scenario(zdata, "/Unknown/", !EXISTS, !DIR));
 
         cases.addCase(new Scenario(zdata, "subdir", EXISTS, DIR));
         cases.addCase(new Scenario(zdata, "/subdir/", EXISTS, DIR));

jetty-webapp/src/main/java/org/eclipse/jetty/webapp/WebAppContext.java

@@ -31,7 +31,6 @@
 import java.util.EventListener;
 import java.util.HashMap;
 import java.util.HashSet;
-import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;