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/*
 * 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 jakarta.activation;

import java.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.security.AccessController;
import java.security.PrivilegedAction;

/**
 * @version $Rev$ $Date$
 */
public class CommandInfo {
    private final String commandName;
    private final String commandClass;

    /**
     * Constructor for a CommandInfo
     *
     * @param commandName  the command name
     * @param commandClass the name of the command's implementation class
     */
    public CommandInfo(String commandName, String commandClass) {
        this.commandName = commandName;
        this.commandClass = commandClass;
    }

    /**
     * Return the command name.
     *
     * @return the command name
     */
    public String getCommandName() {
        return commandName;
    }

    /**
     * Return the implementation class name.
     *
     * @return the name of the command's implementation class; may be null
     */
    public String getCommandClass() {
        return commandClass;
    }

    /**
     * Instantiate and return a command JavaBean.
     *
     * If the current runtime environment supports {@code Beans.instantiate},
     * the bean is created using Beans.instantiate(loader, commandClass).
     *
     * Otherwise, use {@link java.lang.Class#forName Class.forName}.
     *
     * If the new bean implements CommandObject then its setCommandContext(String, DataHandler)
     * method is called.
     * Otherwise if it implements Externalizable and the supplied DataHandler is not null
     * then its readExternal(ObjectInputStream) method is called with a stream obtained from
     * DataHandler.getInputStream().
     *
     * @param dh a DataHandler that provides the data to be passed to the command
     * @param loader the ClassLoader to be used to instantiate the command
     * @return a new command instance
     * @throws IOException if there was a problem initializing the command
     * @throws ClassNotFoundException if the command class could not be found
     */
    public Object getCommandObject(DataHandler dh, ClassLoader loader) throws IOException, ClassNotFoundException {
        Object bean = Beans.instantiate(loader, commandClass);
        if (bean instanceof CommandObject) {
            ((CommandObject) bean).setCommandContext(commandName, dh);
        } else if (bean instanceof Externalizable && dh != null) {
            ((Externalizable) bean).readExternal(new ObjectInputStream(dh.getInputStream()));
        }
        return bean;
    }

    /**
     * Helper class to invoke Beans.instantiate if java.desktop is not available.
     */
    private static final class Beans {
        private static final Method instantiateMethod;

        static {
            Method m;
            try {
                Class c = Class.forName("java.beans.Beans");
                m = c.getDeclaredMethod("instantiate", ClassLoader.class, String.class);
            } catch (ClassNotFoundException | NoSuchMethodException e) {
                m = null;
            }
            instantiateMethod = m;

        }

        /**
         * Equivalent to invoking java.beans.Beans.instantiate(loader, cn)
         */
        static Object instantiate(ClassLoader loader, String cn)
                throws IOException, ClassNotFoundException {

            if (instantiateMethod != null) {

                // invoke Beans.instantiate
                try {
                    return instantiateMethod.invoke(null, loader, cn);
                } catch (InvocationTargetException e) {
                    if (e.getCause() instanceof ClassNotFoundException) {
                        throw (ClassNotFoundException) e.getCause();
                    }
                } catch (IllegalAccessException e) {
                    //ignored
                }

            } else {

                SecurityManager security = System.getSecurityManager();
                if (security != null) {
                    // if it's ok with the SecurityManager, it's ok with me.
                    String cname = cn.replace('/', '.');
                    if (cname.startsWith("[")) {
                        int b = cname.lastIndexOf('[') + 2;
                        if (b > 1 && b < cname.length()) {
                            cname = cname.substring(b);
                        }
                    }
                    int i = cname.lastIndexOf('.');
                    if (i != -1) {
                        security.checkPackageAccess(cname.substring(0, i));
                    }
                }

                // Beans.instantiate specified to use SCL when loader is null
                if (loader == null) {
                    loader = (ClassLoader)
                            AccessController.doPrivileged((PrivilegedAction) () -> {
                                ClassLoader cl = null;
                                try {
                                    cl = ClassLoader.getSystemClassLoader();
                                } catch (SecurityException ex) {
                                }
                                return cl;
                            });
                }
                final Class beanClass = Class.forName(cn, true, loader);
                try {
                    return beanClass.getDeclaredConstructor().newInstance();
                } catch (Exception ex) {
                    throw new ClassNotFoundException(beanClass + ": " + ex, ex);
                }

            }
            return null;
        }
    }
}