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   * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
   * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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   */
  
  package java.security;
  
  import java.util.HashMap;
  import java.util.ArrayList;
  import java.net.URL;
  
  import sun.security.util.Debug;
  
  /**
   * This class extends ClassLoader with additional support for defining
   * classes with an associated code source and permissions which are
   * retrieved by the system policy by default.
   *
   * @author  Li Gong
   * @author  Roland Schemers
   */
  public class SecureClassLoader extends ClassLoader {
      /*
       * If initialization succeed this is set to true and security checks will
       * succeed. Otherwise the object is not initialized and the object is
       * useless.
       */
      private final boolean initialized;
  
      // HashMap that maps CodeSource to ProtectionDomain
      // @GuardedBy("pdcache")
      private final HashMap<CodeSource, ProtectionDomain> pdcache =
                          new HashMap<>(11);
  
      private static final Debug debug = Debug.getInstance("scl");
  
      static {
          ClassLoader.registerAsParallelCapable();
      }
  
      /**
       * Creates a new SecureClassLoader using the specified parent
       * class loader for delegation.
       *
       * <p>If there is a security manager, this method first
       * calls the security manager's {@code checkCreateClassLoader}
       * method  to ensure creation of a class loader is allowed.
       * <p>
       * @param parent the parent ClassLoader
       * @exception  SecurityException  if a security manager exists and its
       *             {@code checkCreateClassLoader} method doesn't allow
       *             creation of a class loader.
       * @see SecurityManager#checkCreateClassLoader
       */
      protected SecureClassLoader(ClassLoader parent) {
          super(parent);
          // this is to make the stack depth consistent with 1.1
          SecurityManager security = System.getSecurityManager();
          if (security != null) {
              security.checkCreateClassLoader();
          }
          initialized = true;
      }
  
      /**
       * Creates a new SecureClassLoader using the default parent class
       * loader for delegation.
       *
       * <p>If there is a security manager, this method first
       * calls the security manager's {@code checkCreateClassLoader}
       * method  to ensure creation of a class loader is allowed.
       *
       * @exception  SecurityException  if a security manager exists and its
       *             {@code checkCreateClassLoader} method doesn't allow
       *             creation of a class loader.
       * @see SecurityManager#checkCreateClassLoader
       */
      protected SecureClassLoader() {
          super();
          // this is to make the stack depth consistent with 1.1
          SecurityManager security = System.getSecurityManager();
          if (security != null) {
              security.checkCreateClassLoader();
          }
          initialized = true;
      }
  
      /**
       * Converts an array of bytes into an instance of class Class,
       * with an optional CodeSource. Before the
       * class can be used it must be resolved.
       * <p>
       * If a non-null CodeSource is supplied a ProtectionDomain is
       * constructed and associated with the class being defined.
       * <p>
       * @param      name the expected name of the class, or {@code null}
       *                  if not known, using '.' and not '/' as the separator
       *                  and without a trailing ".class" suffix.
       * @param      b    the bytes that make up the class data. The bytes in
       *             positions {@code off} through {@code off+len-1}
       *             should have the format of a valid class file as defined by
       *             <cite>The Java&trade; Virtual Machine Specification</cite>.
       * @param      off  the start offset in {@code b} of the class data
       * @param      len  the length of the class data
       * @param      cs   the associated CodeSource, or {@code null} if none
       * @return the {@code Class} object created from the data,
       *         and optional CodeSource.
       * @exception  ClassFormatError if the data did not contain a valid class
       * @exception  IndexOutOfBoundsException if either {@code off} or
       *             {@code len} is negative, or if
       *             {@code off+len} is greater than {@code b.length}.
       *
       * @exception  SecurityException if an attempt is made to add this class
       *             to a package that contains classes that were signed by
       *             a different set of certificates than this class, or if
       *             the class name begins with "java.".
       */
      protected final Class<?> defineClass(String name,
                                           byte[] b, int off, int len,
                                           CodeSource cs)
      {
          return defineClass(name, b, off, len, getProtectionDomain(cs));
      }
  
      /**
       * Converts a {@link java.nio.ByteBuffer ByteBuffer}
       * into an instance of class {@code Class}, with an optional CodeSource.
       * Before the class can be used it must be resolved.
       * <p>
       * If a non-null CodeSource is supplied a ProtectionDomain is
       * constructed and associated with the class being defined.
       * <p>
       * @param      name the expected name of the class, or {@code null}
       *                  if not known, using '.' and not '/' as the separator
       *                  and without a trailing ".class" suffix.
       * @param      b    the bytes that make up the class data.  The bytes from positions
       *                  {@code b.position()} through {@code b.position() + b.limit() -1}
       *                  should have the format of a valid class file as defined by
       *                  <cite>The Java&trade; Virtual Machine Specification</cite>.
       * @param      cs   the associated CodeSource, or {@code null} if none
       * @return the {@code Class} object created from the data,
       *         and optional CodeSource.
       * @exception  ClassFormatError if the data did not contain a valid class
       * @exception  SecurityException if an attempt is made to add this class
       *             to a package that contains classes that were signed by
       *             a different set of certificates than this class, or if
       *             the class name begins with "java.".
       *
       * @since  1.5
       */
      protected final Class<?> defineClass(String name, java.nio.ByteBuffer b,
                                           CodeSource cs)
      {
          return defineClass(name, b, getProtectionDomain(cs));
      }
  
      /**
       * Returns the permissions for the given CodeSource object.
       * <p>
       * This method is invoked by the defineClass method which takes
       * a CodeSource as an argument when it is constructing the
       * ProtectionDomain for the class being defined.
       * <p>
       * @param codesource the codesource.
       *
       * @return the permissions granted to the codesource.
       *
       */
      protected PermissionCollection getPermissions(CodeSource codesource)
      {
          check();
          return new Permissions(); // ProtectionDomain defers the binding
      }
  
      /*
       * Returned cached ProtectionDomain for the specified CodeSource.
       */
      private ProtectionDomain getProtectionDomain(CodeSource cs) {
          if (cs == null)
              return null;
  
          ProtectionDomain pd = null;
          synchronized (pdcache) {
              pd = pdcache.get(cs);
              if (pd == null) {
                  PermissionCollection perms = getPermissions(cs);
                  pd = new ProtectionDomain(cs, perms, this, null);
                  pdcache.put(cs, pd);
                  if (debug != null) {
                      debug.println(" getPermissions "+ pd);
                      debug.println("");
                  }
              }
          }
          return pd;
      }
  
      /*
       * Check to make sure the class loader has been initialized.
       */
      private void check() {
          if (!initialized) {
              throw new SecurityException("ClassLoader object not initialized");
          }
      }
  
  }
  