# SecurityHandlerFactory.java

    /*
     * 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.pdfbox.pdmodel.encryption;

    import java.lang.reflect.Constructor;
    import java.lang.reflect.InvocationTargetException;
    import java.util.HashMap;
    import java.util.Map;

    /**
     * Manages security handlers for the application.
     * It follows the singleton pattern.
     * To be usable, security managers must be registered in it.
     * Security managers are retrieved by the application when necessary.
     *
     * @author Benoit Guillon
     * @author John Hewson
     */
    public final class SecurityHandlerFactory
    {
        /** Singleton instance */
        public static final SecurityHandlerFactory INSTANCE = new SecurityHandlerFactory();

        private final Map<String, Class<? extends SecurityHandler>> nameToHandler = new HashMap<>();

        private final Map<Class<? extends ProtectionPolicy>,
                          Class<? extends SecurityHandler>> policyToHandler = new HashMap<>();

        private SecurityHandlerFactory()
        {
            registerHandler(StandardSecurityHandler.FILTER,
                            StandardSecurityHandler.class,
                            StandardProtectionPolicy.class);

            registerHandler(PublicKeySecurityHandler.FILTER,
                            PublicKeySecurityHandler.class,
                            PublicKeyProtectionPolicy.class);
        }

        /**
         * Registers a security handler.
         *
         * If the security handler was already registered an exception is thrown.
         * If another handler was previously registered for the same filter name or
         * for the same policy name, an exception is thrown
         *
         * @param name the name of the filter
         * @param securityHandler security handler class to register
         * @param protectionPolicy protection policy class to register
         */
        public void registerHandler(String name,
                                    Class<? extends SecurityHandler> securityHandler,
                                    Class<? extends ProtectionPolicy> protectionPolicy)
        {
            if (nameToHandler.containsKey(name))
            {
                throw new IllegalStateException("The security handler name is already registered");
            }

            nameToHandler.put(name, securityHandler);
            policyToHandler.put(protectionPolicy, securityHandler);
        }

        /**
         * Returns a new security handler for the given protection policy, or null none is available.
         * @param policy the protection policy for which to create a security handler
         * @return a new SecurityHandler instance, or null if none is available
         */
        public SecurityHandler<ProtectionPolicy> newSecurityHandlerForPolicy(ProtectionPolicy policy)
        {
            Class<? extends SecurityHandler> handlerClass = policyToHandler.get(policy.getClass());
            if (handlerClass == null)
            {
                return null;
            }

            Class<?>[] argsClasses = { policy.getClass() };
            Object[] args = { policy };
            return newSecurityHandler(handlerClass, argsClasses, args);
        }

        /**
         * Returns a new security handler for the given Filter name, or null none is available.
         * @param name the Filter name from the PDF encryption dictionary
         * @return a new SecurityHandler instance, or null if none is available
         */
        public SecurityHandler<ProtectionPolicy> newSecurityHandlerForFilter(String name)
        {
            Class<? extends SecurityHandler> handlerClass = nameToHandler.get(name);
            if (handlerClass == null)
            {
                return null;
            }

            Class<?>[] argsClasses = { };
            Object[] args = { };
            return newSecurityHandler(handlerClass, argsClasses, args);
        }

        /* Returns a new security handler for the given parameters, or null none is available.
         *
         * @param handlerClass the handler class.
         * @param argsClasses the parameter array.
         * @param args array of objects to be passed as arguments to the constructor call.
         * @return a new SecurityHandler instance, or null if none is available.
         */
        private SecurityHandler<ProtectionPolicy> newSecurityHandler(Class<? extends SecurityHandler> handlerClass,
                Class<?>[] argsClasses, Object[] args)
        {
            try
            {
                Constructor<? extends SecurityHandler> ctor =
                        handlerClass.getDeclaredConstructor(argsClasses);
                return ctor.newInstance(args);
            }
            catch(NoSuchMethodException | IllegalAccessException | InstantiationException |
                    InvocationTargetException e)
            {
                // should not happen in normal operation
                throw new RuntimeException(e);
            }
        }
    }