Ensure that WebAppClassLoader.addJars considers classpath entries in a deterministic order.

Signed-off-by: Jesse Glick <jglick@cloudbees.com>

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

@@ -447,8 +447,8 @@ public abstract class Resource implements ResourceFactory, Closeable
     /* ------------------------------------------------------------ */
     /**
      * list of resource names contained in the given resource.
-     * 
+     * Ordering is unspecified, so callers may wish to sort the return value to ensure deterministic behavior.
-     * @return a list of resource names contained in the given resource.
+     * @return a list of resource names contained in the given resource, or null.
      * Note: The resource names are not URL encoded.
      */
     public abstract String[] list();

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

@@ -438,7 +438,7 @@ public class ResourceCollection extends Resource
                 set.add(s);
         }
         String[] result=set.toArray(new String[set.size()]);
-        Arrays.sort(result);
+        Arrays.sort(result); // TODO still necessary?
         return result;
     }
     

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

@@ -29,6 +29,7 @@ import java.security.CodeSource;
 import java.security.PermissionCollection;
 import java.security.PrivilegedExceptionAction;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.Enumeration;
 import java.util.HashSet;
@@ -324,10 +325,15 @@ public class WebAppClassLoader extends URLClassLoader
      */
     public void addJars(Resource lib)
     {
-        if (lib.exists() && lib.isDirectory())
+        if (lib.exists() && lib.isDirectory()) // TODO perhaps redundant given null check from list()?
         {
             String[] files=lib.list();
-            for (int f=0;files!=null && f<files.length;f++)
+            if (files == null)
+            {
+                return;
+            }
+            Arrays.sort(files);
+            for (int f=0;f<files.length;f++)
             {
                 try 
                 {

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

@@ -716,6 +716,7 @@ public class WebInfConfiguration extends AbstractConfiguration
         Resource web_inf_lib = web_inf.addPath("/lib");
         if (web_inf_lib.exists() && web_inf_lib.isDirectory())
         {
+            // TODO should files be sorted? What is the interaction with Ordering?
             String[] files=web_inf_lib.list();
             for (int f=0;files!=null && f<files.length;f++)
             {

jetty-webapp/src/test/java/org/eclipse/jetty/webapp/WebAppClassLoaderTest.java

@@ -22,10 +22,13 @@ import static org.eclipse.jetty.toolchain.test.ExtraMatchers.ordered;
 import static org.hamcrest.Matchers.contains;
 import static org.hamcrest.Matchers.notNullValue;
 import static org.hamcrest.Matchers.nullValue;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertThat;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assume.assumeThat;
 
+import java.io.InputStream;
 import java.lang.instrument.ClassFileTransformer;
 import java.lang.instrument.IllegalClassFormatException;
 import java.net.URI;
@@ -34,9 +37,11 @@ import java.nio.file.Path;
 import java.security.ProtectionDomain;
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.Enumeration;
 import java.util.List;
 
 import org.eclipse.jetty.toolchain.test.MavenTestingUtils;
+import org.eclipse.jetty.util.IO;
 import org.eclipse.jetty.util.resource.PathResource;
 import org.eclipse.jetty.util.resource.Resource;
 import org.junit.Before;
@@ -323,4 +328,23 @@ public class WebAppClassLoaderTest
         
     }
 
+    @Test
+    public void ordering() throws Exception
+    {
+        Enumeration<URL> resources = _loader.getResources("org/acme/clashing.txt");
+        assertTrue(resources.hasMoreElements());
+        URL resource = resources.nextElement();
+        try (InputStream data = resource.openStream())
+        {
+            assertEquals("correct contents of " + resource, "alpha", IO.toString(data));
+        }
+        assertTrue(resources.hasMoreElements());
+        resource = resources.nextElement();
+        try (InputStream data = resource.openStream())
+        {
+            assertEquals("correct contents of " + resource, "omega", IO.toString(data));
+        }
+        assertFalse(resources.hasMoreElements());
+    }
+
 }