[GitHub] metron pull request #530: METRON-777 Metron Extension System and Parser Exte...

[ottobackwards]

Github user ottobackwards commented on a diff in the pull request:

    https://github.com/apache/metron/pull/530#discussion_r132820881
  
    --- Diff: 
bundles-lib/src/main/java/org/apache/metron/bundles/VFSBundleClassLoader.java 
---
    @@ -0,0 +1,515 @@
    +/*
    + * 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.io.IOException;
    +import java.net.URL;
    +import java.security.CodeSource;
    +import java.security.Permission;
    +import java.security.PermissionCollection;
    +import java.security.Permissions;
    +import java.security.SecureClassLoader;
    +import java.security.cert.Certificate;
    +import java.util.ArrayList;
    +import java.util.Collections;
    +import java.util.Enumeration;
    +import java.util.Iterator;
    +import java.util.List;
    +import java.util.jar.Attributes;
    +import java.util.jar.Attributes.Name;
    +import org.apache.commons.vfs2.FileObject;
    +import org.apache.commons.vfs2.FileSystemException;
    +import org.apache.commons.vfs2.FileSystemManager;
    +import org.apache.commons.vfs2.NameScope;
    +import org.slf4j.Logger;
    +import org.slf4j.LoggerFactory;
    +
    +
    +/**
    + * <p>
    + * A <tt>ClassLoader</tt> for loading BUNDLES (plugin archives). BUNDLEs 
are designed to
    + * allow isolating bundles of code (comprising one-or-more
    + * plugin classes and their
    + * dependencies) from other such bundles; this allows for dependencies and
    + * processors that require conflicting, incompatible versions of the same
    + * dependency to run in a single instance of a given process.</p>
    + *
    + * <p>
    + * <tt>BundleClassLoader</tt> follows the delegation model described in
    + * {@link ClassLoader#findClass(java.lang.String) 
ClassLoader.findClass(...)};
    + * classes are first loaded from the parent <tt>ClassLoader</tt>, and only 
if
    + * they cannot be found there does the <tt>BundleClassLoader</tt> provide a
    + * definition. Specifically, this means that resources are loaded from the 
application's
    + * <tt>conf</tt>
    + * and <tt>lib</tt> directories first, and if they cannot be found there, 
are
    + * loaded from the BUNDLE.</p>
    + *
    + * <p>
    + * The packaging of a BUNDLE is such that it is a ZIP file with the 
following
    + * directory structure:
    + *
    + * <pre>
    + *   +META-INF/
    + *   +-- bundled-dependencies/
    + *   +-- &lt;JAR files&gt;
    + *   +-- MANIFEST.MF
    + * </pre>
    + * </p>
    + *
    + * <p>
    + * The MANIFEST.MF file contains the same information as a typical JAR 
file but
    + * also includes two additional bundle properties: {@code Bundle-Id} and
    + * {@code Bundle-Dependency-Id}.
    + * </p>
    + *
    + * <p>
    + * The {@code Bundle-Id} provides a unique identifier for this BUNDLE.
    + * </p>
    + *
    + * <p>
    + * The {@code Bundle-Dependency-Id} is optional. If provided, it indicates 
that
    + * this BUNDLE should inherit all of the dependencies of the BUNDLE with 
the provided
    + * ID. Often times, the BUNDLE that is depended upon is referred to as the 
Parent.
    + * This is because its ClassLoader will be the parent ClassLoader of the
    + * dependent BUNDLE.
    + * </p>
    + *
    + * <p>
    + * If a BUNDLE is built using the Bundles Maven Plugin, the {@code 
Bundle-Id} property
    + * will be set to the artifactId of the BUNDLE. The {@code 
Bundle-Dependency-Id} will
    + * be set to the artifactId of the BUNDLE that is depended upon. For 
example, if
    + * BUNDLE A is defined as such:
    + *
    + * <pre>
    + * ...
    + * &lt;artifactId&gt;bundle-a&lt;/artifactId&gt;
    + * &lt;packaging&gt;bundle&lt;/packaging&gt;
    + * ...
    + * &lt;dependencies&gt;
    + *   &lt;dependency&gt;
    + *     &lt;groupId&gt;group&lt;/groupId&gt;
    + *     &lt;artifactId&gt;bundle-z&lt;/artifactId&gt;
    + *     <b>&lt;type&gt;bundle&lt;/type&gt;</b>
    + *   &lt;/dependency&gt;
    + * &lt;/dependencies&gt;
    + * </pre>
    + * </p>
    + *
    + *
    + * <p>
    + * Then the MANIFEST.MF file that is created for Bundle A will have the 
following
    + * properties set:
    + * <ul>
    + * <li>{@code {Foo}-Id: bundle-a}</li>
    + * <li>{@code {Foo}-Dependency-Id: bundle-z}</li>
    + * </ul>
    + * Where is configurable by BundleProperty META_ID_PREFIX [ default Bundle 
]
    + * </p>
    + *
    + * <p>
    + * Note, above, that the {@code type} of the dependency is set to {@code 
foo}.
    + * </p>
    + *
    + * <p>
    + * If the Bundle has more than one dependency of {@code type} {@code Foo}, 
then the
    + * Maven Bundle plugin will fail to build the Bundle.
    + * </p>
    + *
    + * This classloader is Metron Bundle aware, in that it understands that 
the passed in root
    + * FileObjects may be Bundles,
    + * This class is adapted from Apache Commons VFS
    + * VFSClassLoader class v.2.1
    + * And the Apache Nifi NarClassLoader v. 1.2
    + *
    + * @see FileSystemManager#createFileSystem
    + */
    +public class VFSBundleClassLoader extends SecureClassLoader {
    --- End diff --
    
    Thanks!


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