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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 org.apache.jasper.servlet;

import static org.apache.jasper.JasperMessages.MESSAGES;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.net.URLClassLoader;
import java.security.AccessControlContext;
import java.security.AccessController;
import java.security.CodeSource;
import java.security.PermissionCollection;
import java.security.PrivilegedExceptionAction;

import org.apache.jasper.Constants;

/**
 * Class loader for loading servlet class files (corresponding to JSP files)
 * and tag handler class files (corresponding to tag files).
 *
 * @author Anil K. Vijendran
 * @author Harish Prabandham
 */
public class JasperLoader extends URLClassLoader {

    private final PermissionCollection permissionCollection;
    private final ClassLoader parent;
    private final SecurityManager securityManager;
    private final CodeSource codeSource;
    private final AccessControlContext acc;

    public JasperLoader(URL[] urls, ClassLoader parent,
                        PermissionCollection permissionCollection, CodeSource codeSource) {
	super(urls, parent);
	    this.permissionCollection = permissionCollection;
	    this.parent = parent;
        this.codeSource = codeSource;
        this.securityManager = System.getSecurityManager();
        this.acc = AccessController.getContext();
    }

     /**
     * Load the class with the specified name.  This method searches for
     * classes in the same manner as loadClass(String, boolean)
     * with false as the second argument.
     *
     * @param name Name of the class to be loaded
     *
     * @exception ClassNotFoundException if the class was not found
     */
    @Override
    public Class loadClass(String name) throws ClassNotFoundException {

        return (loadClass(name, false));
    }

    /**
     * Load the class with the specified name, searching using the following
     * algorithm until it finds and returns the class.  If the class cannot
     * be found, returns ClassNotFoundException.
     * 
     * Call findLoadedClass(String) to check if the
     *     class has already been loaded.  If it has, the same
     *     Class object is returned.
     * If the delegate property is set to true,
     *     call the loadClass() method of the parent class
     *     loader, if any.
     * Call findClass() to find this class in our locally
     *     defined repositories.
     * Call the loadClass() method of our parent
     *     class loader, if any.
     * 
     * If the class was found using the above steps, and the
     * resolve flag is true, this method will then
     * call resolveClass(Class) on the resulting Class object.
     *
     * @param name Name of the class to be loaded
     * @param resolve If true then resolve the class
     *
     * @exception ClassNotFoundException if the class was not found
     */
    @Override
    public synchronized Class loadClass(final String name, boolean resolve)
            throws ClassNotFoundException {

        Class clazz = null;

        // (0) Check our previously loaded class cache
        clazz = findLoadedClass(name);
        if (clazz != null) {
            if (resolve)
                resolveClass(clazz);
            return (clazz);
        }

        // (.5) Permission to access this class when using a SecurityManager
        if (securityManager != null) {
            int dot = name.lastIndexOf('.');
            if (dot >= 0) {
                try {
                    // Do not call the security manager since by default, we grant that package.
                    if (!"org.apache.jasper.runtime".equalsIgnoreCase(name.substring(0,dot))){
                        securityManager.checkPackageAccess(name.substring(0,dot));
                    }
                } catch (SecurityException se) {
                    throw new ClassNotFoundException(MESSAGES.securityExceptionLoadingClass(name), se);
                }
            }
        }

        if( !name.startsWith(Constants.JSP_PACKAGE_NAME + '.') ) {
            // Class is not in org.apache.jsp, therefore, have our
            // parent load it
            clazz = parent.loadClass(name);
            if( resolve )
                resolveClass(clazz);
            return clazz;
        }

        return findClass(name);
    }

    @Override
    protected Class findClass(final String name) throws ClassNotFoundException {
        try {
            return AccessController.doPrivileged(
                    new PrivilegedExceptionAction() {
                        public Class run() throws ClassNotFoundException {
                            String path = name.replace('.', '/').concat(".class");
                            URL res = findResource(path);
                            if (res != null) {
                                try {
                                    byte[] bytes = getBytes(res);
                                    return defineClass(name, bytes, 0, bytes.length, codeSource);
                                } catch (IOException e) {
                                    throw new ClassNotFoundException(name, e);
                                }
                            } else {
                                throw new ClassNotFoundException(name);
                            }
                        }
                    }, acc);
        } catch (java.security.PrivilegedActionException pae) {
            throw (ClassNotFoundException) pae.getException();
        }
    }

    private byte[] getBytes(URL resource)throws IOException{
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();

        try (InputStream stream = resource.openStream()){
            byte[] chunk = new byte[4096];
            int bytesRead;

            while ((bytesRead = stream.read(chunk)) > 0) {
                outputStream.write(chunk, 0, bytesRead);
            }

        }
        return outputStream.toByteArray();
    }

    /**
     * Delegate to parent
     *
     * @see java.lang.ClassLoader#getResourceAsStream(java.lang.String)
     */
    @Override
    public InputStream getResourceAsStream(String name) {
        InputStream is = parent.getResourceAsStream(name);
        if (is == null) {
            URL url = findResource(name);
            if (url != null) {
                try {
                    is = url.openStream();
                } catch (IOException e) {
                    // Ignore
                }
            }
        }
        return is;
    }


    /**
     * Get the Permissions for a CodeSource.
     *
     * Since this ClassLoader is only used for a JSP page in
     * a web application context, we just return our preset
     * PermissionCollection for the web app context.
     *
     * @param codeSource Code source where the code was loaded from
     * @return PermissionCollection for CodeSource
     */
    @Override
    public final PermissionCollection getPermissions(CodeSource codeSource) {
        return permissionCollection;
    }
}