Github user ottobackwards commented on a diff in the pull request:
https://github.com/apache/metron/pull/530#discussion_r131943632
--- Diff:
bundles-lib/src/main/java/org/apache/metron/bundles/BundleClassLoaders.java ---
@@ -0,0 +1,353 @@
+/*
+ * 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 java.net.URISyntaxException;
+import java.util.*;
+
+import org.apache.commons.collections.CollectionUtils;
+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.BundleCoordinate;
+import org.apache.metron.bundles.bundle.BundleDetails;
+import org.apache.metron.bundles.util.BundleProperties;
+import org.apache.metron.bundles.util.BundleSelector;
+import org.apache.metron.bundles.util.FileUtils;
+import org.apache.metron.bundles.util.BundleUtil;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * A singleton class used to initialize the extension and framework
classloaders.
+ */
+public final class BundleClassLoaders {
+
+ private static volatile BundleClassLoaders bundleClassLoaders;
+ private volatile InitContext initContext;
+ private static final Logger logger =
LoggerFactory.getLogger(BundleClassLoaders.class);
+
+ private final static class InitContext {
+
+ private final List<FileObject> extensionDirs;
+ private final Map<String, Bundle> bundles;
+
+ private InitContext(
+ final List<FileObject> extensionDirs,
+ final Map<String, Bundle> bundles) {
+ this.extensionDirs = extensionDirs;
+ this.bundles = bundles;
+ }
+ }
+
+ private BundleClassLoaders() {
+ }
+
+ /**
+ * @return The singleton instance of the BundleClassLoaders
+ */
+ public static BundleClassLoaders getInstance() {
+ BundleClassLoaders result = bundleClassLoaders;
+ if (result == null) {
+ synchronized (BundleClassLoaders.class) {
+ result = bundleClassLoaders;
+ if (result == null) {
+ bundleClassLoaders = result = new BundleClassLoaders();
+ }
+ }
+ }
+ return result;
+ }
+
+ public static void reset() {
+ getInstance().unInit();
+ }
+
+ private void unInit() {
+ synchronized (this) {
+ initContext = null;
+ }
+ }
+
+ /**
+ * Initializes and loads the BundleClassLoaders. This method must be
called before the rest of the
+ * methods to access the classloaders are called and it can be safely
called any number of times
+ * provided the same framework and extension working dirs are used.
+ *
+ * @param fileSystemManager the FileSystemManager
+ * @param extensionsDirs where to find extension artifacts
+ * @param props BundleProperties
+ * @throws FileSystemException if any issue occurs while exploding
bundle working directories.
+ * @throws java.lang.ClassNotFoundException if unable to load class
definition
+ * @throws IllegalStateException already initialized with a given pair
of directories cannot
+ * reinitialize or use a different pair of directories.
+ */
+ public void init(final FileSystemManager fileSystemManager, final
List<FileObject> extensionsDirs,
+ BundleProperties props)
+ throws FileSystemException, ClassNotFoundException,
URISyntaxException {
+ if (extensionsDirs == null || fileSystemManager == null) {
+ throw new NullPointerException("cannot have empty arguments");
+ }
+ InitContext ic = initContext;
+ if (ic == null) {
+ synchronized (this) {
+ ic = initContext;
+ if (ic == null) {
+ initContext = ic = load(fileSystemManager, extensionsDirs,
props);
+ }
+ }
+ } else {
+ boolean matching = CollectionUtils
+ .isEqualCollection(initContext.extensionDirs, extensionsDirs);
+ if (!matching) {
+ throw new IllegalStateException(
+ "Cannot reinitialize and extension/framework directories
cannot change");
+ }
+ }
+ }
+
+ /**
+ * Should be called at most once.
+ */
+ private InitContext load(final FileSystemManager fileSystemManager,
+ final List<FileObject> extensionsDirs, BundleProperties props)
+ throws FileSystemException, ClassNotFoundException,
URISyntaxException {
+ // get the system classloader
+ final ClassLoader systemClassLoader =
ClassLoader.getSystemClassLoader();
+
+ // find all bundle files and create class loaders for them.
--- End diff --
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