Glassfish example source code file (ACLSingletonProvider.java)

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Java - Glassfish tags/keywords

aclsingleton, aclsingleton, classloader, classloader, hashtable, illegalstateexception, privilegedaction, privilegedaction, runtimeexception, security, securitymanager, singleton, t, t, thread's, util

The Glassfish ACLSingletonProvider.java source code

/*
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 *
 * Copyright (c) 2009-2010 Oracle and/or its affiliates. All rights reserved.
 *
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 * and Distribution License("CDDL") (collectively, the "License").  You
 * may not use this file except in compliance with the License.  You can
 * obtain a copy of the License at
 * https://glassfish.dev.java.net/public/CDDL+GPL_1_1.html
 * or packager/legal/LICENSE.txt.  See the License for the specific
 * language governing permissions and limitations under the License.
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 * file and include the License file at packager/legal/LICENSE.txt.
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 * exception as provided by Oracle in the GPL Version 2 section of the License
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 *
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package org.glassfish.weld;

import org.jboss.weld.bootstrap.api.SingletonProvider;
import org.jboss.weld.bootstrap.api.Singleton;
import org.glassfish.javaee.full.deployment.EarLibClassLoader;
import org.glassfish.internal.api.Globals;
import org.glassfish.internal.api.ClassLoaderHierarchy;

import java.util.Map;
import java.util.Hashtable;
import java.security.AccessController;
import java.security.PrivilegedAction;

/**
 * Singleton provider that uses Application ClassLoader to differentiate
 * between applications. It is different from
 * {@link org.jboss.weld.bootstrap.api.helpers.TCCLSingletonProvider}.
 * We can't use TCCLSingletonProvider because thread's context class loader can
 * be different for different modules of a single application (ear).
 * To support Application Scoped beans, Weld needs to be bootstrapped
 * per application as opposed to per module. We rely on the fact that
 * all these module class loaders have a common parent which is per application.
 * We use that parent ApplicationClassLoader to identify the singleton scope.
 *
 * @author Sanjeeb.Sahoo@Sun.COM
 */
public class ACLSingletonProvider extends SingletonProvider
{
    /*
     * See https://glassfish.dev.java.net/issues/show_bug.cgi?id=10192
     * for more details about this class.
     *
     * IMPLEMENTATION NOTE:
     * This class assumes a certain delegation hierarchy of application
     * class loaders. So, deployment team should be aware of this class
     * and change it if application class loader hierarchy changes.
     */

    public <T> ACLSingleton create(Class expectedType)
    {
        return new ACLSingleton<T>();
    }

    private static class ACLSingleton<T> implements Singleton{

        // use Hashtable for concurrent access
        private final Map<ClassLoader, T> store = new Hashtable();
        private ClassLoader ccl = Globals.get(ClassLoaderHierarchy.class).getCommonClassLoader();

        // Can't assume bootstrap loader as null. That's more of a convention.
        // I think either android or IBM JVM does not use null for bootstap loader
        private static ClassLoader bootstrapCL;
        static {
            SecurityManager sm = System.getSecurityManager();
            bootstrapCL = (sm != null) ?
                    AccessController.doPrivileged(new PrivilegedAction<ClassLoader>() {
                        public ClassLoader run()
                        {
                            return Object.class.getClassLoader();
                        }
                    }) : Object.class.getClassLoader();
        }

        public T get()
        {
           ClassLoader acl = getClassLoader();
           T instance = store.get(acl);
           if (instance == null)
           {
              throw new IllegalStateException("Singleton not set for " + acl);
           }
           return instance;
        }

        /**
         * This is the most significant method of this class. This is what
         * distingushes it from TCCLSIngleton. It tries to obtain a class loader
         * that's common to all modules of an application (ear). Since it runs
         * in the context of Java EE, it can assume that Thread's context
         * class loader is always set as application class loader. In GlassFish,
         * the class loader can vary for each module of an Ear. Thread's
         * context class loader is set depending on which module is handling
         * the request. But, fortunately all those embedded module class loaders
         * have a common parent in their delegation chain. That parent
         * is of type EarLibClassLoader. So, this code walks up the delegation
         * chain until it hits either a EarLibClassLoader type of parent or
         * bootstrapClassLoader. If former is the case, it returns that
         * instance of EarLibClassLoader. If latter is the case, it assumes
         * that this is a standalone module and hence it returns the thread's
         * context class loader.
         *
         * @return a class loader that's common to all modules of a Java EE app
         */
        private ClassLoader getClassLoader()
        {
            SecurityManager sm = System.getSecurityManager();
            final ClassLoader tccl = (sm != null) ?
                    AccessController.doPrivileged(new PrivilegedAction<ClassLoader>()
                    {
                        public ClassLoader run()
                        {
                            return Thread.currentThread().getContextClassLoader();
                        }
                    }) : Thread.currentThread().getContextClassLoader();
            if (tccl == null) {
                throw new RuntimeException("Thread's context class loader is null");
            }

            ClassLoader cl = tccl;

            // most of the time, class loader of application (whether it is a
            // standalone module or an ear) has common class loader in their
            // delegation chain. So, we can break the loop early for them.
            // There are exceptions like hybrid app to this rule.
            // So, we have to walk upto bootstrapCL in worst case.
            while (cl != ccl && cl != bootstrapCL) {
                if (cl instanceof EarLibClassLoader) {
//                    System.out.println("ACLSingletonProvider.getClassLoader():\n" +
//                            "Application Class Loader = [ " + cl + "],\n" +
//                            "Thread Context Class Loader = [" + tccl + "]");
                    return cl;
                }
                cl = getParent(cl);
            }
            return tccl;
        }

        private ClassLoader getParent(final ClassLoader cl)
        {
            SecurityManager sm = System.getSecurityManager();
            return sm != null ?
                    AccessController.doPrivileged(new PrivilegedAction<ClassLoader>() {
                        public ClassLoader run()
                        {
                            return cl.getParent();
                        }
                    }) : cl.getParent();
        }

        public void set(T object)
        {
//           System.out.println("Adding singleton for " + getClassLoader());
           store.put(getClassLoader(), object);
        }

        public void clear()
        {
           store.remove(getClassLoader());
        }

        public boolean isSet()
        {
           return store.containsKey(getClassLoader());
        }

    }
}