Github user ottobackwards commented on a diff in the pull request:
https://github.com/apache/metron/pull/530#discussion_r133061877
--- Diff:
bundles-lib/src/main/java/org/apache/metron/bundles/ExtensionManager.java ---
@@ -0,0 +1,436 @@
+/*
+ * 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.metron.bundles;
+
+
+import org.apache.commons.vfs2.FileObject;
+import org.apache.commons.vfs2.FileSystemException;
+import org.apache.commons.vfs2.FileSystemManager;
+import org.apache.metron.bundles.bundle.Bundle;
+import org.apache.metron.bundles.bundle.BundleCoordinates;
+import org.apache.metron.bundles.bundle.BundleDetails;
+import org.apache.metron.bundles.util.BundleProperties;
+import org.apache.metron.bundles.util.FileUtils;
+import org.apache.metron.bundles.util.StringUtils;
+import
org.apache.metron.bundles.annotation.behavior.RequiresInstanceClassLoading;
+
+import org.atteo.classindex.ClassIndex;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.lang.reflect.Modifier;
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.net.URL;
+import java.net.URLClassLoader;
+import java.util.*;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+/**
+ * Scans through the classpath to load all extension components using the
service provider API and
+ * running through all classloaders (root, BUNDLEs).
+ *
+ * @ThreadSafe - is immutable
+ */
+@SuppressWarnings("rawtypes")
+public class ExtensionManager {
+
+ private static final Logger logger =
LoggerFactory.getLogger(ExtensionManager.class);
+
+ public static final BundleCoordinates SYSTEM_BUNDLE_COORDINATE = new
BundleCoordinates(
+ BundleCoordinates.DEFAULT_GROUP, "system",
BundleCoordinates.DEFAULT_VERSION);
+
+ // Maps a service definition (interface) to those classes that implement
the interface
+ private static final Map<Class, Set<Class>> definitionMap = new
HashMap<>();
+
+ private static final Map<String, List<Bundle>> classNameBundleLookup =
new HashMap<>();
+ private static final Map<BundleCoordinates, Bundle>
bundleCoordinateBundleLookup = new HashMap<>();
+ private static final Map<ClassLoader, Bundle> classLoaderBundleLookup =
new HashMap<>();
+
+ private static final Set<String> requiresInstanceClassLoading = new
HashSet<>();
+ private static final Map<String, ClassLoader> instanceClassloaderLookup
= new ConcurrentHashMap<>();
+
+ private static AtomicBoolean inited = new AtomicBoolean(false);
+
+ // should initialize class definitions
+ public static void initClassDefinitions(final List<Class> classes) {
+ if (classes != null) {
+ for (Class clazz : classes) {
+ definitionMap.put(clazz, new HashSet<>());
+ }
+ }
+ inited.set(true);
+ }
+
+ public static void resetClassDefinitions() {
+ definitionMap.clear();
+ inited.set(false);
+ }
+
+ /**
+ * Loads all extension class types that can be found on the bootstrap
classloader and by creating
+ * classloaders for all BUNDLES found within the classpath.
+ *
+ * @param bundles the bundles to scan through in search of extensions
+ */
+ public static void discoverExtensions(final Bundle systemBundle, final
Set<Bundle> bundles)
+ throws NotInitializedException {
+ checkInitialized();
+ // get the current context class loader
+ ClassLoader currentContextClassLoader =
Thread.currentThread().getContextClassLoader();
+
+ // load the system bundle first so that any extensions found in JARs
directly in lib will be registered as
+ // being from the system bundle and not from all the other Bundles
+ loadExtensions(systemBundle);
+
bundleCoordinateBundleLookup.put(systemBundle.getBundleDetails().getCoordinates(),
systemBundle);
+
+ // consider each bundle class loader
+ for (final Bundle bundle : bundles) {
+ // Must set the context class loader to the bundle classloader itself
+ // so that static initialization techniques that depend on the
context class loader will work properly
+ final ClassLoader ncl = bundle.getClassLoader();
+ Thread.currentThread().setContextClassLoader(ncl);
+ loadExtensions(bundle);
+
+ // Create a look-up from withCoordinates to bundle
+
bundleCoordinateBundleLookup.put(bundle.getBundleDetails().getCoordinates(),
bundle);
+ }
+
+ // restore the current context class loader if appropriate
+ if (currentContextClassLoader != null) {
+
Thread.currentThread().setContextClassLoader(currentContextClassLoader);
+ }
+ }
+
+ /**
+ * Returns a bundle representing the system class loader.
+ *
+ * @param bundleProperties a BundleProperties instance which will be
used to obtain the default
+ * Bundle library path, which will become the working directory of the
returned bundle
+ * @return a bundle for the system class loader
+ */
+ public static Bundle createSystemBundle(final FileSystemManager
fileSystemManager,
+ final BundleProperties bundleProperties) throws FileSystemException,
URISyntaxException {
+ final ClassLoader systemClassLoader =
ClassLoader.getSystemClassLoader();
+
+ final String bundlesLibraryDirectory = bundleProperties
+ .getProperty(BundleProperties.BUNDLE_LIBRARY_DIRECTORY);
+ if (StringUtils.isBlank(bundlesLibraryDirectory)) {
+ throw new IllegalStateException(
+ "Unable to create system bundle because " +
BundleProperties.BUNDLE_LIBRARY_DIRECTORY
+ + " was null or empty");
+ }
+ final URI bundlesLibraryDirURI =
bundleProperties.getBundleLibraryDirectory();
+ FileObject bundleDir =
fileSystemManager.resolveFile(bundlesLibraryDirURI);
+
+ // Test if the source Bundles can be read
+ FileUtils.ensureDirectoryExistAndCanRead(bundleDir);
+
+ final BundleDetails systemBundleDetails = new BundleDetails.Builder()
+ .withBundleFile(bundleDir)
+ .withCoordinates(SYSTEM_BUNDLE_COORDINATE)
+ .build();
+
+ return new Bundle(systemBundleDetails, systemClassLoader);
+ }
+
+ /**
+ * Loads extensions from the specified bundle.
+ *
+ * @param bundle from which to load extensions
+ */
+ @SuppressWarnings("unchecked")
+ private static void loadExtensions(final Bundle bundle) throws
NotInitializedException {
+ checkInitialized();
+ for (final Map.Entry<Class, Set<Class>> entry :
definitionMap.entrySet()) {
+ // this is another extention point
+ // what we care about here is getting the right classes from the
classloader for the bundle
+ // this *could* be as a 'service' itself with different
implementations
+ // The NAR system uses the ServiceLoader, but this chokes on
abstract classes, because for some
+ // reason it feels compelled to instantiate the class,
+ // which there may be in the system.
+ // Changed to ClassIndex
--- End diff --
I think the ClassIndex is a big improvement over the ServiceLoader too.
Easier to use, faster, doesn't try to instantiate abstracts.... safer because
of the compile time generation of the service file.... just great.
I wonder if Nifi would take a PR with VFS / VFSClassloader / ClassIndex get
* better generation on the archetype side
* support for hdfs and other filesystems
* not having to manage the working directories etc
I'll have to talk to @bbende if we ever get done ;)
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