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Java example source code file (SecurityManager.java)

This example Java source code file (SecurityManager.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

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Java - Java tags/keywords

awt, class, classloader, deprecated, filepermission, net, network, nullpointerexception, object, propertypermission, reflection, runtimepermission, security, securityexception, securitymanager, socketpermission, string, threadgroup, util

The SecurityManager.java Java example source code

/*
 * Copyright (c) 1995, 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.lang;

import java.security.*;
import java.io.FileDescriptor;
import java.io.File;
import java.io.FilePermission;
import java.awt.AWTPermission;
import java.util.PropertyPermission;
import java.lang.RuntimePermission;
import java.net.SocketPermission;
import java.net.NetPermission;
import java.util.Hashtable;
import java.net.InetAddress;
import java.lang.reflect.*;
import java.net.URL;

import sun.reflect.CallerSensitive;
import sun.security.util.SecurityConstants;

/**
 * The security manager is a class that allows
 * applications to implement a security policy. It allows an
 * application to determine, before performing a possibly unsafe or
 * sensitive operation, what the operation is and whether
 * it is being attempted in a security context that allows the
 * operation to be performed. The
 * application can allow or disallow the operation.
 * <p>
 * The <code>SecurityManager class contains many methods with
 * names that begin with the word <code>check. These methods
 * are called by various methods in the Java libraries before those
 * methods perform certain potentially sensitive operations. The
 * invocation of such a <code>check method typically looks like this:
 * <blockquote>
 *     SecurityManager security = System.getSecurityManager();
 *     if (security != null) {
 *         security.check<i>XXX(argument,  . . . );
 *     }
 * </pre>
 * <p>
 * The security manager is thereby given an opportunity to prevent
 * completion of the operation by throwing an exception. A security
 * manager routine simply returns if the operation is permitted, but
 * throws a <code>SecurityException if the operation is not
 * permitted. The only exception to this convention is
 * <code>checkTopLevelWindow, which returns a
 * <code>boolean value.
 * <p>
 * The current security manager is set by the
 * <code>setSecurityManager method in class
 * <code>System. The current security manager is obtained
 * by the <code>getSecurityManager method.
 * <p>
 * The special method
 * {@link SecurityManager#checkPermission(java.security.Permission)}
 * determines whether an access request indicated by a specified
 * permission should be granted or denied. The
 * default implementation calls
 *
 * <pre>
 *   AccessController.checkPermission(perm);
 * </pre>
 *
 * <p>
 * If a requested access is allowed,
 * <code>checkPermission returns quietly. If denied, a
 * <code>SecurityException is thrown.
 * <p>
 * As of Java 2 SDK v1.2, the default implementation of each of the other
 * <code>check methods in SecurityManager is to
 * call the <code>SecurityManager checkPermission method
 * to determine if the calling thread has permission to perform the requested
 * operation.
 * <p>
 * Note that the <code>checkPermission method with
 * just a single permission argument always performs security checks
 * within the context of the currently executing thread.
 * Sometimes a security check that should be made within a given context
 * will actually need to be done from within a
 * <i>different context (for example, from within a worker thread).
 * The {@link SecurityManager#getSecurityContext getSecurityContext} method
 * and the {@link SecurityManager#checkPermission(java.security.Permission,
 * java.lang.Object) checkPermission}
 * method that includes a context argument are provided
 * for this situation. The
 * <code>getSecurityContext method returns a "snapshot"
 * of the current calling context. (The default implementation
 * returns an AccessControlContext object.) A sample call is
 * the following:
 *
 * <pre>
 *   Object context = null;
 *   SecurityManager sm = System.getSecurityManager();
 *   if (sm != null) context = sm.getSecurityContext();
 * </pre>
 *
 * <p>
 * The <code>checkPermission method
 * that takes a context object in addition to a permission
 * makes access decisions based on that context,
 * rather than on that of the current execution thread.
 * Code within a different context can thus call that method,
 * passing the permission and the
 * previously-saved context object. A sample call, using the
 * SecurityManager <code>sm obtained as in the previous example,
 * is the following:
 *
 * <pre>
 *   if (sm != null) sm.checkPermission(permission, context);
 * </pre>
 *
 * <p>Permissions fall into these categories: File, Socket, Net,
 * Security, Runtime, Property, AWT, Reflect, and Serializable.
 * The classes managing these various
 * permission categories are <code>java.io.FilePermission,
 * <code>java.net.SocketPermission,
 * <code>java.net.NetPermission,
 * <code>java.security.SecurityPermission,
 * <code>java.lang.RuntimePermission,
 * <code>java.util.PropertyPermission,
 * <code>java.awt.AWTPermission,
 * <code>java.lang.reflect.ReflectPermission, and
 * <code>java.io.SerializablePermission.
 *
 * <p>All but the first two (FilePermission and SocketPermission) are
 * subclasses of <code>java.security.BasicPermission, which itself
 * is an abstract subclass of the
 * top-level class for permissions, which is
 * <code>java.security.Permission. BasicPermission defines the
 * functionality needed for all permissions that contain a name
 * that follows the hierarchical property naming convention
 * (for example, "exitVM", "setFactory", "queuePrintJob", etc).
 * An asterisk
 * may appear at the end of the name, following a ".", or by itself, to
 * signify a wildcard match. For example: "a.*" or "*" is valid,
 * "*a" or "a*b" is not valid.
 *
 * <p>FilePermission and SocketPermission are subclasses of the
 * top-level class for permissions
 * (<code>java.security.Permission). Classes like these
 * that have a more complicated name syntax than that used by
 * BasicPermission subclass directly from Permission rather than from
 * BasicPermission. For example,
 * for a <code>java.io.FilePermission object, the permission name is
 * the path name of a file (or directory).
 *
 * <p>Some of the permission classes have an "actions" list that tells
 * the actions that are permitted for the object.  For example,
 * for a <code>java.io.FilePermission object, the actions list
 * (such as "read, write") specifies which actions are granted for the
 * specified file (or for files in the specified directory).
 *
 * <p>Other permission classes are for "named" permissions -
 * ones that contain a name but no actions list; you either have the
 * named permission or you don't.
 *
 * <p>Note: There is also a java.security.AllPermission
 * permission that implies all permissions. It exists to simplify the work
 * of system administrators who might need to perform multiple
 * tasks that require all (or numerous) permissions.
 * <p>
 * See <a href ="../../../technotes/guides/security/permissions.html">
 * Permissions in the JDK</a> for permission-related information.
 * This document includes, for example, a table listing the various SecurityManager
 * <code>check methods and the permission(s) the default
 * implementation of each such method requires.
 * It also contains a table of all the version 1.2 methods
 * that require permissions, and for each such method tells
 * which permission it requires.
 * <p>
 * For more information about <code>SecurityManager changes made in
 * the JDK and advice regarding porting of 1.1-style security managers,
 * see the <a href="../../../technotes/guides/security/index.html">security documentation.
 *
 * @author  Arthur van Hoff
 * @author  Roland Schemers
 *
 * @see     java.lang.ClassLoader
 * @see     java.lang.SecurityException
 * @see     java.lang.SecurityManager#checkTopLevelWindow(java.lang.Object)
 *  checkTopLevelWindow
 * @see     java.lang.System#getSecurityManager() getSecurityManager
 * @see     java.lang.System#setSecurityManager(java.lang.SecurityManager)
 *  setSecurityManager
 * @see     java.security.AccessController AccessController
 * @see     java.security.AccessControlContext AccessControlContext
 * @see     java.security.AccessControlException AccessControlException
 * @see     java.security.Permission
 * @see     java.security.BasicPermission
 * @see     java.io.FilePermission
 * @see     java.net.SocketPermission
 * @see     java.util.PropertyPermission
 * @see     java.lang.RuntimePermission
 * @see     java.awt.AWTPermission
 * @see     java.security.Policy Policy
 * @see     java.security.SecurityPermission SecurityPermission
 * @see     java.security.ProtectionDomain
 *
 * @since   JDK1.0
 */
public
class SecurityManager {

    /**
     * This field is <code>true if there is a security check in
     * progress; <code>false otherwise.
     *
     * @deprecated This type of security checking is not recommended.
     *  It is recommended that the <code>checkPermission
     *  call be used instead.
     */
    @Deprecated
    protected boolean inCheck;

    /*
     * Have we been initialized. Effective against finalizer attacks.
     */
    private boolean initialized = false;


    /**
     * returns true if the current context has been granted AllPermission
     */
    private boolean hasAllPermission()
    {
        try {
            checkPermission(SecurityConstants.ALL_PERMISSION);
            return true;
        } catch (SecurityException se) {
            return false;
        }
    }

    /**
     * Tests if there is a security check in progress.
     *
     * @return the value of the <code>inCheck field. This field
     *          should contain <code>true if a security check is
     *          in progress,
     *          <code>false otherwise.
     * @see     java.lang.SecurityManager#inCheck
     * @deprecated This type of security checking is not recommended.
     *  It is recommended that the <code>checkPermission
     *  call be used instead.
     */
    @Deprecated
    public boolean getInCheck() {
        return inCheck;
    }

    /**
     * Constructs a new <code>SecurityManager.
     *
     * <p> If there is a security manager already installed, this method first
     * calls the security manager's <code>checkPermission method
     * with the <code>RuntimePermission("createSecurityManager")
     * permission to ensure the calling thread has permission to create a new
     * security manager.
     * This may result in throwing a <code>SecurityException.
     *
     * @exception  java.lang.SecurityException if a security manager already
     *             exists and its <code>checkPermission method
     *             doesn't allow creation of a new security manager.
     * @see        java.lang.System#getSecurityManager()
     * @see        #checkPermission(java.security.Permission) checkPermission
     * @see java.lang.RuntimePermission
     */
    public SecurityManager() {
        synchronized(SecurityManager.class) {
            SecurityManager sm = System.getSecurityManager();
            if (sm != null) {
                // ask the currently installed security manager if we
                // can create a new one.
                sm.checkPermission(new RuntimePermission
                                   ("createSecurityManager"));
            }
            initialized = true;
        }
    }

    /**
     * Returns the current execution stack as an array of classes.
     * <p>
     * The length of the array is the number of methods on the execution
     * stack. The element at index <code>0 is the class of the
     * currently executing method, the element at index <code>1 is
     * the class of that method's caller, and so on.
     *
     * @return  the execution stack.
     */
    protected native Class[] getClassContext();

    /**
     * Returns the class loader of the most recently executing method from
     * a class defined using a non-system class loader. A non-system
     * class loader is defined as being a class loader that is not equal to
     * the system class loader (as returned
     * by {@link ClassLoader#getSystemClassLoader}) or one of its ancestors.
     * <p>
     * This method will return
     * <code>null in the following three cases:
     * <ol>
     *   <li>All methods on the execution stack are from classes
     *   defined using the system class loader or one of its ancestors.
     *
     *   <li>All methods on the execution stack up to the first
     *   "privileged" caller
     *   (see {@link java.security.AccessController#doPrivileged})
     *   are from classes
     *   defined using the system class loader or one of its ancestors.
     *
     *   <li> A call to checkPermission with
     *   <code>java.security.AllPermission does not
     *   result in a SecurityException.
     *
     * </ol>
     *
     * @return  the class loader of the most recent occurrence on the stack
     *          of a method from a class defined using a non-system class
     *          loader.
     *
     * @deprecated This type of security checking is not recommended.
     *  It is recommended that the <code>checkPermission
     *  call be used instead.
     *
     * @see  java.lang.ClassLoader#getSystemClassLoader() getSystemClassLoader
     * @see  #checkPermission(java.security.Permission) checkPermission
     */
    @Deprecated
    protected ClassLoader currentClassLoader()
    {
        ClassLoader cl = currentClassLoader0();
        if ((cl != null) && hasAllPermission())
            cl = null;
        return cl;
    }

    private native ClassLoader currentClassLoader0();

    /**
     * Returns the class of the most recently executing method from
     * a class defined using a non-system class loader. A non-system
     * class loader is defined as being a class loader that is not equal to
     * the system class loader (as returned
     * by {@link ClassLoader#getSystemClassLoader}) or one of its ancestors.
     * <p>
     * This method will return
     * <code>null in the following three cases:
     * <ol>
     *   <li>All methods on the execution stack are from classes
     *   defined using the system class loader or one of its ancestors.
     *
     *   <li>All methods on the execution stack up to the first
     *   "privileged" caller
     *   (see {@link java.security.AccessController#doPrivileged})
     *   are from classes
     *   defined using the system class loader or one of its ancestors.
     *
     *   <li> A call to checkPermission with
     *   <code>java.security.AllPermission does not
     *   result in a SecurityException.
     *
     * </ol>
     *
     * @return  the class  of the most recent occurrence on the stack
     *          of a method from a class defined using a non-system class
     *          loader.
     *
     * @deprecated This type of security checking is not recommended.
     *  It is recommended that the <code>checkPermission
     *  call be used instead.
     *
     * @see  java.lang.ClassLoader#getSystemClassLoader() getSystemClassLoader
     * @see  #checkPermission(java.security.Permission) checkPermission
     */
    @Deprecated
    protected Class<?> currentLoadedClass() {
        Class<?> c = currentLoadedClass0();
        if ((c != null) && hasAllPermission())
            c = null;
        return c;
    }

    /**
     * Returns the stack depth of the specified class.
     *
     * @param   name   the fully qualified name of the class to search for.
     * @return  the depth on the stack frame of the first occurrence of a
     *          method from a class with the specified name;
     *          <code>-1 if such a frame cannot be found.
     * @deprecated This type of security checking is not recommended.
     *  It is recommended that the <code>checkPermission
     *  call be used instead.
     *
     */
    @Deprecated
    protected native int classDepth(String name);

    /**
     * Returns the stack depth of the most recently executing method
     * from a class defined using a non-system class loader.  A non-system
     * class loader is defined as being a class loader that is not equal to
     * the system class loader (as returned
     * by {@link ClassLoader#getSystemClassLoader}) or one of its ancestors.
     * <p>
     * This method will return
     * -1 in the following three cases:
     * <ol>
     *   <li>All methods on the execution stack are from classes
     *   defined using the system class loader or one of its ancestors.
     *
     *   <li>All methods on the execution stack up to the first
     *   "privileged" caller
     *   (see {@link java.security.AccessController#doPrivileged})
     *   are from classes
     *   defined using the system class loader or one of its ancestors.
     *
     *   <li> A call to checkPermission with
     *   <code>java.security.AllPermission does not
     *   result in a SecurityException.
     *
     * </ol>
     *
     * @return the depth on the stack frame of the most recent occurrence of
     *          a method from a class defined using a non-system class loader.
     *
     * @deprecated This type of security checking is not recommended.
     *  It is recommended that the <code>checkPermission
     *  call be used instead.
     *
     * @see   java.lang.ClassLoader#getSystemClassLoader() getSystemClassLoader
     * @see   #checkPermission(java.security.Permission) checkPermission
     */
    @Deprecated
    protected int classLoaderDepth()
    {
        int depth = classLoaderDepth0();
        if (depth != -1) {
            if (hasAllPermission())
                depth = -1;
            else
                depth--; // make sure we don't include ourself
        }
        return depth;
    }

    private native int classLoaderDepth0();

    /**
     * Tests if a method from a class with the specified
     *         name is on the execution stack.
     *
     * @param  name   the fully qualified name of the class.
     * @return <code>true if a method from a class with the specified
     *         name is on the execution stack; <code>false otherwise.
     * @deprecated This type of security checking is not recommended.
     *  It is recommended that the <code>checkPermission
     *  call be used instead.
     */
    @Deprecated
    protected boolean inClass(String name) {
        return classDepth(name) >= 0;
    }

    /**
     * Basically, tests if a method from a class defined using a
     *          class loader is on the execution stack.
     *
     * @return  <code>true if a call to currentClassLoader
     *          has a non-null return value.
     *
     * @deprecated This type of security checking is not recommended.
     *  It is recommended that the <code>checkPermission
     *  call be used instead.
     * @see        #currentClassLoader() currentClassLoader
     */
    @Deprecated
    protected boolean inClassLoader() {
        return currentClassLoader() != null;
    }

    /**
     * Creates an object that encapsulates the current execution
     * environment. The result of this method is used, for example, by the
     * three-argument <code>checkConnect method and by the
     * two-argument <code>checkRead method.
     * These methods are needed because a trusted method may be called
     * on to read a file or open a socket on behalf of another method.
     * The trusted method needs to determine if the other (possibly
     * untrusted) method would be allowed to perform the operation on its
     * own.
     * <p> The default implementation of this method is to return
     * an <code>AccessControlContext object.
     *
     * @return  an implementation-dependent object that encapsulates
     *          sufficient information about the current execution environment
     *          to perform some security checks later.
     * @see     java.lang.SecurityManager#checkConnect(java.lang.String, int,
     *   java.lang.Object) checkConnect
     * @see     java.lang.SecurityManager#checkRead(java.lang.String,
     *   java.lang.Object) checkRead
     * @see     java.security.AccessControlContext AccessControlContext
     */
    public Object getSecurityContext() {
        return AccessController.getContext();
    }

    /**
     * Throws a <code>SecurityException if the requested
     * access, specified by the given permission, is not permitted based
     * on the security policy currently in effect.
     * <p>
     * This method calls <code>AccessController.checkPermission
     * with the given permission.
     *
     * @param     perm   the requested permission.
     * @exception SecurityException if access is not permitted based on
     *            the current security policy.
     * @exception NullPointerException if the permission argument is
     *            <code>null.
     * @since     1.2
     */
    public void checkPermission(Permission perm) {
        java.security.AccessController.checkPermission(perm);
    }

    /**
     * Throws a <code>SecurityException if the
     * specified security context is denied access to the resource
     * specified by the given permission.
     * The context must be a security
     * context returned by a previous call to
     * <code>getSecurityContext and the access control
     * decision is based upon the configured security policy for
     * that security context.
     * <p>
     * If <code>context is an instance of
     * <code>AccessControlContext then the
     * <code>AccessControlContext.checkPermission method is
     * invoked with the specified permission.
     * <p>
     * If <code>context is not an instance of
     * <code>AccessControlContext then a
     * <code>SecurityException is thrown.
     *
     * @param      perm      the specified permission
     * @param      context   a system-dependent security context.
     * @exception  SecurityException  if the specified security context
     *             is not an instance of <code>AccessControlContext
     *             (e.g., is <code>null), or is denied access to the
     *             resource specified by the given permission.
     * @exception  NullPointerException if the permission argument is
     *             <code>null.
     * @see        java.lang.SecurityManager#getSecurityContext()
     * @see java.security.AccessControlContext#checkPermission(java.security.Permission)
     * @since      1.2
     */
    public void checkPermission(Permission perm, Object context) {
        if (context instanceof AccessControlContext) {
            ((AccessControlContext)context).checkPermission(perm);
        } else {
            throw new SecurityException();
        }
    }

    /**
     * Throws a <code>SecurityException if the
     * calling thread is not allowed to create a new class loader.
     * <p>
     * This method calls <code>checkPermission with the
     * <code>RuntimePermission("createClassLoader")
     * permission.
     * <p>
     * If you override this method, then you should make a call to
     * <code>super.checkCreateClassLoader
     * at the point the overridden method would normally throw an
     * exception.
     *
     * @exception SecurityException if the calling thread does not
     *             have permission
     *             to create a new class loader.
     * @see        java.lang.ClassLoader#ClassLoader()
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    public void checkCreateClassLoader() {
        checkPermission(SecurityConstants.CREATE_CLASSLOADER_PERMISSION);
    }

    /**
     * reference to the root thread group, used for the checkAccess
     * methods.
     */

    private static ThreadGroup rootGroup = getRootGroup();

    private static ThreadGroup getRootGroup() {
        ThreadGroup root =  Thread.currentThread().getThreadGroup();
        while (root.getParent() != null) {
            root = root.getParent();
        }
        return root;
    }

    /**
     * Throws a <code>SecurityException if the
     * calling thread is not allowed to modify the thread argument.
     * <p>
     * This method is invoked for the current security manager by the
     * <code>stop, suspend, resume,
     * <code>setPriority, setName, and
     * <code>setDaemon methods of class Thread.
     * <p>
     * If the thread argument is a system thread (belongs to
     * the thread group with a <code>null parent) then
     * this method calls <code>checkPermission with the
     * <code>RuntimePermission("modifyThread") permission.
     * If the thread argument is <i>not a system thread,
     * this method just returns silently.
     * <p>
     * Applications that want a stricter policy should override this
     * method. If this method is overridden, the method that overrides
     * it should additionally check to see if the calling thread has the
     * <code>RuntimePermission("modifyThread") permission, and
     * if so, return silently. This is to ensure that code granted
     * that permission (such as the JDK itself) is allowed to
     * manipulate any thread.
     * <p>
     * If this method is overridden, then
     * <code>super.checkAccess should
     * be called by the first statement in the overridden method, or the
     * equivalent security check should be placed in the overridden method.
     *
     * @param      t   the thread to be checked.
     * @exception  SecurityException  if the calling thread does not have
     *             permission to modify the thread.
     * @exception  NullPointerException if the thread argument is
     *             <code>null.
     * @see        java.lang.Thread#resume() resume
     * @see        java.lang.Thread#setDaemon(boolean) setDaemon
     * @see        java.lang.Thread#setName(java.lang.String) setName
     * @see        java.lang.Thread#setPriority(int) setPriority
     * @see        java.lang.Thread#stop() stop
     * @see        java.lang.Thread#suspend() suspend
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    public void checkAccess(Thread t) {
        if (t == null) {
            throw new NullPointerException("thread can't be null");
        }
        if (t.getThreadGroup() == rootGroup) {
            checkPermission(SecurityConstants.MODIFY_THREAD_PERMISSION);
        } else {
            // just return
        }
    }
    /**
     * Throws a <code>SecurityException if the
     * calling thread is not allowed to modify the thread group argument.
     * <p>
     * This method is invoked for the current security manager when a
     * new child thread or child thread group is created, and by the
     * <code>setDaemon, setMaxPriority,
     * <code>stop, suspend, resume, and
     * <code>destroy methods of class ThreadGroup.
     * <p>
     * If the thread group argument is the system thread group (
     * has a <code>null parent) then
     * this method calls <code>checkPermission with the
     * <code>RuntimePermission("modifyThreadGroup") permission.
     * If the thread group argument is <i>not the system thread group,
     * this method just returns silently.
     * <p>
     * Applications that want a stricter policy should override this
     * method. If this method is overridden, the method that overrides
     * it should additionally check to see if the calling thread has the
     * <code>RuntimePermission("modifyThreadGroup") permission, and
     * if so, return silently. This is to ensure that code granted
     * that permission (such as the JDK itself) is allowed to
     * manipulate any thread.
     * <p>
     * If this method is overridden, then
     * <code>super.checkAccess should
     * be called by the first statement in the overridden method, or the
     * equivalent security check should be placed in the overridden method.
     *
     * @param      g   the thread group to be checked.
     * @exception  SecurityException  if the calling thread does not have
     *             permission to modify the thread group.
     * @exception  NullPointerException if the thread group argument is
     *             <code>null.
     * @see        java.lang.ThreadGroup#destroy() destroy
     * @see        java.lang.ThreadGroup#resume() resume
     * @see        java.lang.ThreadGroup#setDaemon(boolean) setDaemon
     * @see        java.lang.ThreadGroup#setMaxPriority(int) setMaxPriority
     * @see        java.lang.ThreadGroup#stop() stop
     * @see        java.lang.ThreadGroup#suspend() suspend
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    public void checkAccess(ThreadGroup g) {
        if (g == null) {
            throw new NullPointerException("thread group can't be null");
        }
        if (g == rootGroup) {
            checkPermission(SecurityConstants.MODIFY_THREADGROUP_PERMISSION);
        } else {
            // just return
        }
    }

    /**
     * Throws a <code>SecurityException if the
     * calling thread is not allowed to cause the Java Virtual Machine to
     * halt with the specified status code.
     * <p>
     * This method is invoked for the current security manager by the
     * <code>exit method of class Runtime. A status
     * of <code>0 indicates success; other values indicate various
     * errors.
     * <p>
     * This method calls <code>checkPermission with the
     * <code>RuntimePermission("exitVM."+status) permission.
     * <p>
     * If you override this method, then you should make a call to
     * <code>super.checkExit
     * at the point the overridden method would normally throw an
     * exception.
     *
     * @param      status   the exit status.
     * @exception SecurityException if the calling thread does not have
     *              permission to halt the Java Virtual Machine with
     *              the specified status.
     * @see        java.lang.Runtime#exit(int) exit
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    public void checkExit(int status) {
        checkPermission(new RuntimePermission("exitVM."+status));
    }

    /**
     * Throws a <code>SecurityException if the
     * calling thread is not allowed to create a subprocess.
     * <p>
     * This method is invoked for the current security manager by the
     * <code>exec methods of class Runtime.
     * <p>
     * This method calls <code>checkPermission with the
     * <code>FilePermission(cmd,"execute") permission
     * if cmd is an absolute path, otherwise it calls
     * <code>checkPermission with
     * <code>FilePermission("<<ALL FILES>>","execute").
     * <p>
     * If you override this method, then you should make a call to
     * <code>super.checkExec
     * at the point the overridden method would normally throw an
     * exception.
     *
     * @param      cmd   the specified system command.
     * @exception  SecurityException if the calling thread does not have
     *             permission to create a subprocess.
     * @exception  NullPointerException if the <code>cmd argument is
     *             <code>null.
     * @see     java.lang.Runtime#exec(java.lang.String)
     * @see     java.lang.Runtime#exec(java.lang.String, java.lang.String[])
     * @see     java.lang.Runtime#exec(java.lang.String[])
     * @see     java.lang.Runtime#exec(java.lang.String[], java.lang.String[])
     * @see     #checkPermission(java.security.Permission) checkPermission
     */
    public void checkExec(String cmd) {
        File f = new File(cmd);
        if (f.isAbsolute()) {
            checkPermission(new FilePermission(cmd,
                SecurityConstants.FILE_EXECUTE_ACTION));
        } else {
            checkPermission(new FilePermission("<",
                SecurityConstants.FILE_EXECUTE_ACTION));
        }
    }

    /**
     * Throws a <code>SecurityException if the
     * calling thread is not allowed to dynamic link the library code
     * specified by the string argument file. The argument is either a
     * simple library name or a complete filename.
     * <p>
     * This method is invoked for the current security manager by
     * methods <code>load and loadLibrary of class
     * <code>Runtime.
     * <p>
     * This method calls <code>checkPermission with the
     * <code>RuntimePermission("loadLibrary."+lib) permission.
     * <p>
     * If you override this method, then you should make a call to
     * <code>super.checkLink
     * at the point the overridden method would normally throw an
     * exception.
     *
     * @param      lib   the name of the library.
     * @exception  SecurityException if the calling thread does not have
     *             permission to dynamically link the library.
     * @exception  NullPointerException if the <code>lib argument is
     *             <code>null.
     * @see        java.lang.Runtime#load(java.lang.String)
     * @see        java.lang.Runtime#loadLibrary(java.lang.String)
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    public void checkLink(String lib) {
        if (lib == null) {
            throw new NullPointerException("library can't be null");
        }
        checkPermission(new RuntimePermission("loadLibrary."+lib));
    }

    /**
     * Throws a <code>SecurityException if the
     * calling thread is not allowed to read from the specified file
     * descriptor.
     * <p>
     * This method calls <code>checkPermission with the
     * <code>RuntimePermission("readFileDescriptor")
     * permission.
     * <p>
     * If you override this method, then you should make a call to
     * <code>super.checkRead
     * at the point the overridden method would normally throw an
     * exception.
     *
     * @param      fd   the system-dependent file descriptor.
     * @exception  SecurityException  if the calling thread does not have
     *             permission to access the specified file descriptor.
     * @exception  NullPointerException if the file descriptor argument is
     *             <code>null.
     * @see        java.io.FileDescriptor
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    public void checkRead(FileDescriptor fd) {
        if (fd == null) {
            throw new NullPointerException("file descriptor can't be null");
        }
        checkPermission(new RuntimePermission("readFileDescriptor"));
    }

    /**
     * Throws a <code>SecurityException if the
     * calling thread is not allowed to read the file specified by the
     * string argument.
     * <p>
     * This method calls <code>checkPermission with the
     * <code>FilePermission(file,"read") permission.
     * <p>
     * If you override this method, then you should make a call to
     * <code>super.checkRead
     * at the point the overridden method would normally throw an
     * exception.
     *
     * @param      file   the system-dependent file name.
     * @exception  SecurityException if the calling thread does not have
     *             permission to access the specified file.
     * @exception  NullPointerException if the <code>file argument is
     *             <code>null.
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    public void checkRead(String file) {
        checkPermission(new FilePermission(file,
            SecurityConstants.FILE_READ_ACTION));
    }

    /**
     * Throws a <code>SecurityException if the
     * specified security context is not allowed to read the file
     * specified by the string argument. The context must be a security
     * context returned by a previous call to
     * <code>getSecurityContext.
     * <p> If context is an instance of
     * <code>AccessControlContext then the
     * <code>AccessControlContext.checkPermission method will
     * be invoked with the <code>FilePermission(file,"read") permission.
     * <p> If context is not an instance of
     * <code>AccessControlContext then a
     * <code>SecurityException is thrown.
     * <p>
     * If you override this method, then you should make a call to
     * <code>super.checkRead
     * at the point the overridden method would normally throw an
     * exception.
     *
     * @param      file      the system-dependent filename.
     * @param      context   a system-dependent security context.
     * @exception  SecurityException  if the specified security context
     *             is not an instance of <code>AccessControlContext
     *             (e.g., is <code>null), or does not have permission
     *             to read the specified file.
     * @exception  NullPointerException if the <code>file argument is
     *             <code>null.
     * @see        java.lang.SecurityManager#getSecurityContext()
     * @see        java.security.AccessControlContext#checkPermission(java.security.Permission)
     */
    public void checkRead(String file, Object context) {
        checkPermission(
            new FilePermission(file, SecurityConstants.FILE_READ_ACTION),
            context);
    }

    /**
     * Throws a <code>SecurityException if the
     * calling thread is not allowed to write to the specified file
     * descriptor.
     * <p>
     * This method calls <code>checkPermission with the
     * <code>RuntimePermission("writeFileDescriptor")
     * permission.
     * <p>
     * If you override this method, then you should make a call to
     * <code>super.checkWrite
     * at the point the overridden method would normally throw an
     * exception.
     *
     * @param      fd   the system-dependent file descriptor.
     * @exception SecurityException  if the calling thread does not have
     *             permission to access the specified file descriptor.
     * @exception  NullPointerException if the file descriptor argument is
     *             <code>null.
     * @see        java.io.FileDescriptor
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    public void checkWrite(FileDescriptor fd) {
        if (fd == null) {
            throw new NullPointerException("file descriptor can't be null");
        }
        checkPermission(new RuntimePermission("writeFileDescriptor"));

    }

    /**
     * Throws a <code>SecurityException if the
     * calling thread is not allowed to write to the file specified by
     * the string argument.
     * <p>
     * This method calls <code>checkPermission with the
     * <code>FilePermission(file,"write") permission.
     * <p>
     * If you override this method, then you should make a call to
     * <code>super.checkWrite
     * at the point the overridden method would normally throw an
     * exception.
     *
     * @param      file   the system-dependent filename.
     * @exception  SecurityException  if the calling thread does not
     *             have permission to access the specified file.
     * @exception  NullPointerException if the <code>file argument is
     *             <code>null.
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    public void checkWrite(String file) {
        checkPermission(new FilePermission(file,
            SecurityConstants.FILE_WRITE_ACTION));
    }

    /**
     * Throws a <code>SecurityException if the
     * calling thread is not allowed to delete the specified file.
     * <p>
     * This method is invoked for the current security manager by the
     * <code>delete method of class File.
     * <p>
     * This method calls <code>checkPermission with the
     * <code>FilePermission(file,"delete") permission.
     * <p>
     * If you override this method, then you should make a call to
     * <code>super.checkDelete
     * at the point the overridden method would normally throw an
     * exception.
     *
     * @param      file   the system-dependent filename.
     * @exception  SecurityException if the calling thread does not
     *             have permission to delete the file.
     * @exception  NullPointerException if the <code>file argument is
     *             <code>null.
     * @see        java.io.File#delete()
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    public void checkDelete(String file) {
        checkPermission(new FilePermission(file,
            SecurityConstants.FILE_DELETE_ACTION));
    }

    /**
     * Throws a <code>SecurityException if the
     * calling thread is not allowed to open a socket connection to the
     * specified host and port number.
     * <p>
     * A port number of <code>-1 indicates that the calling
     * method is attempting to determine the IP address of the specified
     * host name.
     * <p>
     * This method calls <code>checkPermission with the
     * <code>SocketPermission(host+":"+port,"connect") permission if
     * the port is not equal to -1. If the port is equal to -1, then
     * it calls <code>checkPermission with the
     * <code>SocketPermission(host,"resolve") permission.
     * <p>
     * If you override this method, then you should make a call to
     * <code>super.checkConnect
     * at the point the overridden method would normally throw an
     * exception.
     *
     * @param      host   the host name port to connect to.
     * @param      port   the protocol port to connect to.
     * @exception  SecurityException  if the calling thread does not have
     *             permission to open a socket connection to the specified
     *               <code>host and port.
     * @exception  NullPointerException if the <code>host argument is
     *             <code>null.
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    public void checkConnect(String host, int port) {
        if (host == null) {
            throw new NullPointerException("host can't be null");
        }
        if (!host.startsWith("[") && host.indexOf(':') != -1) {
            host = "[" + host + "]";
        }
        if (port == -1) {
            checkPermission(new SocketPermission(host,
                SecurityConstants.SOCKET_RESOLVE_ACTION));
        } else {
            checkPermission(new SocketPermission(host+":"+port,
                SecurityConstants.SOCKET_CONNECT_ACTION));
        }
    }

    /**
     * Throws a <code>SecurityException if the
     * specified security context is not allowed to open a socket
     * connection to the specified host and port number.
     * <p>
     * A port number of <code>-1 indicates that the calling
     * method is attempting to determine the IP address of the specified
     * host name.
     * <p> If context is not an instance of
     * <code>AccessControlContext then a
     * <code>SecurityException is thrown.
     * <p>
     * Otherwise, the port number is checked. If it is not equal
     * to -1, the <code>context's checkPermission
     * method is called with a
     * <code>SocketPermission(host+":"+port,"connect") permission.
     * If the port is equal to -1, then
     * the <code>context's checkPermission method
     * is called with a
     * <code>SocketPermission(host,"resolve") permission.
     * <p>
     * If you override this method, then you should make a call to
     * <code>super.checkConnect
     * at the point the overridden method would normally throw an
     * exception.
     *
     * @param      host      the host name port to connect to.
     * @param      port      the protocol port to connect to.
     * @param      context   a system-dependent security context.
     * @exception  SecurityException if the specified security context
     *             is not an instance of <code>AccessControlContext
     *             (e.g., is <code>null), or does not have permission
     *             to open a socket connection to the specified
     *             <code>host and port.
     * @exception  NullPointerException if the <code>host argument is
     *             <code>null.
     * @see        java.lang.SecurityManager#getSecurityContext()
     * @see        java.security.AccessControlContext#checkPermission(java.security.Permission)
     */
    public void checkConnect(String host, int port, Object context) {
        if (host == null) {
            throw new NullPointerException("host can't be null");
        }
        if (!host.startsWith("[") && host.indexOf(':') != -1) {
            host = "[" + host + "]";
        }
        if (port == -1)
            checkPermission(new SocketPermission(host,
                SecurityConstants.SOCKET_RESOLVE_ACTION),
                context);
        else
            checkPermission(new SocketPermission(host+":"+port,
                SecurityConstants.SOCKET_CONNECT_ACTION),
                context);
    }

    /**
     * Throws a <code>SecurityException if the
     * calling thread is not allowed to wait for a connection request on
     * the specified local port number.
     * <p>
     * This method calls <code>checkPermission with the
     * <code>SocketPermission("localhost:"+port,"listen").
     * <p>
     * If you override this method, then you should make a call to
     * <code>super.checkListen
     * at the point the overridden method would normally throw an
     * exception.
     *
     * @param      port   the local port.
     * @exception  SecurityException  if the calling thread does not have
     *             permission to listen on the specified port.
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    public void checkListen(int port) {
        checkPermission(new SocketPermission("localhost:"+port,
            SecurityConstants.SOCKET_LISTEN_ACTION));
    }

    /**
     * Throws a <code>SecurityException if the
     * calling thread is not permitted to accept a socket connection from
     * the specified host and port number.
     * <p>
     * This method is invoked for the current security manager by the
     * <code>accept method of class ServerSocket.
     * <p>
     * This method calls <code>checkPermission with the
     * <code>SocketPermission(host+":"+port,"accept") permission.
     * <p>
     * If you override this method, then you should make a call to
     * <code>super.checkAccept
     * at the point the overridden method would normally throw an
     * exception.
     *
     * @param      host   the host name of the socket connection.
     * @param      port   the port number of the socket connection.
     * @exception  SecurityException  if the calling thread does not have
     *             permission to accept the connection.
     * @exception  NullPointerException if the <code>host argument is
     *             <code>null.
     * @see        java.net.ServerSocket#accept()
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    public void checkAccept(String host, int port) {
        if (host == null) {
            throw new NullPointerException("host can't be null");
        }
        if (!host.startsWith("[") && host.indexOf(':') != -1) {
            host = "[" + host + "]";
        }
        checkPermission(new SocketPermission(host+":"+port,
            SecurityConstants.SOCKET_ACCEPT_ACTION));
    }

    /**
     * Throws a <code>SecurityException if the
     * calling thread is not allowed to use
     * (join/leave/send/receive) IP multicast.
     * <p>
     * This method calls <code>checkPermission with the
     * <code>java.net.SocketPermission(maddr.getHostAddress(),
     * "accept,connect")</code> permission.
     * <p>
     * If you override this method, then you should make a call to
     * <code>super.checkMulticast
     * at the point the overridden method would normally throw an
     * exception.
     *
     * @param      maddr  Internet group address to be used.
     * @exception  SecurityException  if the calling thread is not allowed to
     *  use (join/leave/send/receive) IP multicast.
     * @exception  NullPointerException if the address argument is
     *             <code>null.
     * @since      JDK1.1
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    public void checkMulticast(InetAddress maddr) {
        String host = maddr.getHostAddress();
        if (!host.startsWith("[") && host.indexOf(':') != -1) {
            host = "[" + host + "]";
        }
        checkPermission(new SocketPermission(host,
            SecurityConstants.SOCKET_CONNECT_ACCEPT_ACTION));
    }

    /**
     * Throws a <code>SecurityException if the
     * calling thread is not allowed to use
     * (join/leave/send/receive) IP multicast.
     * <p>
     * This method calls <code>checkPermission with the
     * <code>java.net.SocketPermission(maddr.getHostAddress(),
     * "accept,connect")</code> permission.
     * <p>
     * If you override this method, then you should make a call to
     * <code>super.checkMulticast
     * at the point the overridden method would normally throw an
     * exception.
     *
     * @param      maddr  Internet group address to be used.
     * @param      ttl        value in use, if it is multicast send.
     * Note: this particular implementation does not use the ttl
     * parameter.
     * @exception  SecurityException  if the calling thread is not allowed to
     *  use (join/leave/send/receive) IP multicast.
     * @exception  NullPointerException if the address argument is
     *             <code>null.
     * @since      JDK1.1
     * @deprecated Use #checkPermission(java.security.Permission) instead
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    @Deprecated
    public void checkMulticast(InetAddress maddr, byte ttl) {
        String host = maddr.getHostAddress();
        if (!host.startsWith("[") && host.indexOf(':') != -1) {
            host = "[" + host + "]";
        }
        checkPermission(new SocketPermission(host,
            SecurityConstants.SOCKET_CONNECT_ACCEPT_ACTION));
    }

    /**
     * Throws a <code>SecurityException if the
     * calling thread is not allowed to access or modify the system
     * properties.
     * <p>
     * This method is used by the <code>getProperties and
     * <code>setProperties methods of class System.
     * <p>
     * This method calls <code>checkPermission with the
     * <code>PropertyPermission("*", "read,write") permission.
     * <p>
     * If you override this method, then you should make a call to
     * <code>super.checkPropertiesAccess
     * at the point the overridden method would normally throw an
     * exception.
     * <p>
     *
     * @exception  SecurityException  if the calling thread does not have
     *             permission to access or modify the system properties.
     * @see        java.lang.System#getProperties()
     * @see        java.lang.System#setProperties(java.util.Properties)
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    public void checkPropertiesAccess() {
        checkPermission(new PropertyPermission("*",
            SecurityConstants.PROPERTY_RW_ACTION));
    }

    /**
     * Throws a <code>SecurityException if the
     * calling thread is not allowed to access the system property with
     * the specified <code>key name.
     * <p>
     * This method is used by the <code>getProperty method of
     * class <code>System.
     * <p>
     * This method calls <code>checkPermission with the
     * <code>PropertyPermission(key, "read") permission.
     * <p>
     * If you override this method, then you should make a call to
     * <code>super.checkPropertyAccess
     * at the point the overridden method would normally throw an
     * exception.
     *
     * @param      key   a system property key.
     *
     * @exception  SecurityException  if the calling thread does not have
     *             permission to access the specified system property.
     * @exception  NullPointerException if the <code>key argument is
     *             <code>null.
     * @exception  IllegalArgumentException if <code>key is empty.
     *
     * @see        java.lang.System#getProperty(java.lang.String)
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    public void checkPropertyAccess(String key) {
        checkPermission(new PropertyPermission(key,
            SecurityConstants.PROPERTY_READ_ACTION));
    }

    /**
     * Returns <code>false if the calling
     * thread is not trusted to bring up the top-level window indicated
     * by the <code>window argument. In this case, the caller can
     * still decide to show the window, but the window should include
     * some sort of visual warning. If the method returns
     * <code>true, then the window can be shown without any
     * special restrictions.
     * <p>
     * See class <code>Window for more information on trusted and
     * untrusted windows.
     * <p>
     * This method calls
     * <code>checkPermission with the
     * <code>AWTPermission("showWindowWithoutWarningBanner") permission,
     * and returns <code>true if a SecurityException is not thrown,
     * otherwise it returns <code>false.
     * In the case of subset Profiles of Java SE that do not include the
     * {@code java.awt} package, {@code checkPermission} is instead called
     * to check the permission {@code java.security.AllPermission}.
     * <p>
     * If you override this method, then you should make a call to
     * <code>super.checkTopLevelWindow
     * at the point the overridden method would normally return
     * <code>false, and the value of
     * <code>super.checkTopLevelWindow should
     * be returned.
     *
     * @param      window   the new window that is being created.
     * @return     <code>true if the calling thread is trusted to put up
     *             top-level windows; <code>false otherwise.
     * @exception  NullPointerException if the <code>window argument is
     *             <code>null.
     * @deprecated The dependency on {@code AWTPermission} creates an
     *             impediment to future modularization of the Java platform.
     *             Users of this method should instead invoke
     *             {@link #checkPermission} directly.
     *             This method will be changed in a future release to check
     *             the permission {@code java.security.AllPermission}.
     * @see        java.awt.Window
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    @Deprecated
    public boolean checkTopLevelWindow(Object window) {
        if (window == null) {
            throw new NullPointerException("window can't be null");
        }
        Permission perm = SecurityConstants.AWT.TOPLEVEL_WINDOW_PERMISSION;
        if (perm == null) {
            perm = SecurityConstants.ALL_PERMISSION;
        }
        try {
            checkPermission(perm);
            return true;
        } catch (SecurityException se) {
            // just return false
        }
        return false;
    }

    /**
     * Throws a <code>SecurityException if the
     * calling thread is not allowed to initiate a print job request.
     * <p>
     * This method calls
     * <code>checkPermission with the
     * <code>RuntimePermission("queuePrintJob") permission.
     * <p>
     * If you override this method, then you should make a call to
     * <code>super.checkPrintJobAccess
     * at the point the overridden method would normally throw an
     * exception.
     * <p>
     *
     * @exception  SecurityException  if the calling thread does not have
     *             permission to initiate a print job request.
     * @since   JDK1.1
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    public void checkPrintJobAccess() {
        checkPermission(new RuntimePermission("queuePrintJob"));
    }

    /**
     * Throws a <code>SecurityException if the
     * calling thread is not allowed to access the system clipboard.
     * <p>
     * This method calls <code>checkPermission with the
     * <code>AWTPermission("accessClipboard")
     * permission.
     * In the case of subset Profiles of Java SE that do not include the
     * {@code java.awt} package, {@code checkPermission} is instead called
     * to check the permission {@code java.security.AllPermission}.
     * <p>
     * If you override this method, then you should make a call to
     * <code>super.checkSystemClipboardAccess
     * at the point the overridden method would normally throw an
     * exception.
     *
     * @since   JDK1.1
     * @exception  SecurityException  if the calling thread does not have
     *             permission to access the system clipboard.
     * @deprecated The dependency on {@code AWTPermission} creates an
     *             impediment to future modularization of the Java platform.
     *             Users of this method should instead invoke
     *             {@link #checkPermission} directly.
     *             This method will be changed in a future release to check
     *             the permission {@code java.security.AllPermission}.
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    @Deprecated
    public void checkSystemClipboardAccess() {
        Permission perm = SecurityConstants.AWT.ACCESS_CLIPBOARD_PERMISSION;
        if (perm == null) {
            perm = SecurityConstants.ALL_PERMISSION;
        }
        checkPermission(perm);
    }

    /**
     * Throws a <code>SecurityException if the
     * calling thread is not allowed to access the AWT event queue.
     * <p>
     * This method calls <code>checkPermission with the
     * <code>AWTPermission("accessEventQueue") permission.
     * In the case of subset Profiles of Java SE that do not include the
     * {@code java.awt} package, {@code checkPermission} is instead called
     * to check the permission {@code java.security.AllPermission}.
     *
     * <p>
     * If you override this method, then you should make a call to
     * <code>super.checkAwtEventQueueAccess
     * at the point the overridden method would normally throw an
     * exception.
     *
     * @since   JDK1.1
     * @exception  SecurityException  if the calling thread does not have
     *             permission to access the AWT event queue.
     * @deprecated The dependency on {@code AWTPermission} creates an
     *             impediment to future modularization of the Java platform.
     *             Users of this method should instead invoke
     *             {@link #checkPermission} directly.
     *             This method will be changed in a future release to check
     *             the permission {@code java.security.AllPermission}.
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    @Deprecated
    public void checkAwtEventQueueAccess() {
        Permission perm = SecurityConstants.AWT.CHECK_AWT_EVENTQUEUE_PERMISSION;
        if (perm == null) {
            perm = SecurityConstants.ALL_PERMISSION;
        }
        checkPermission(perm);
    }

    /*
     * We have an initial invalid bit (initially false) for the class
     * variables which tell if the cache is valid.  If the underlying
     * java.security.Security property changes via setProperty(), the
     * Security class uses reflection to change the variable and thus
     * invalidate the cache.
     *
     * Locking is handled by synchronization to the
     * packageAccessLock/packageDefinitionLock objects.  They are only
     * used in this class.
     *
     * Note that cache invalidation as a result of the property change
     * happens without using these locks, so there may be a delay between
     * when a thread updates the property and when other threads updates
     * the cache.
     */
    private static boolean packageAccessValid = false;
    private static String[] packageAccess;
    private static final Object packageAccessLock = new Object();

    private static boolean packageDefinitionValid = false;
    private static String[] packageDefinition;
    private static final Object packageDefinitionLock = new Object();

    private static String[] getPackages(String p) {
        String packages[] = null;
        if (p != null && !p.equals("")) {
            java.util.StringTokenizer tok =
                new java.util.StringTokenizer(p, ",");
            int n = tok.countTokens();
            if (n > 0) {
                packages = new String[n];
                int i = 0;
                while (tok.hasMoreElements()) {
                    String s = tok.nextToken().trim();
                    packages[i++] = s;
                }
            }
        }

        if (packages == null)
            packages = new String[0];
        return packages;
    }

    /**
     * Throws a <code>SecurityException if the
     * calling thread is not allowed to access the package specified by
     * the argument.
     * <p>
     * This method is used by the <code>loadClass method of class
     * loaders.
     * <p>
     * This method first gets a list of
     * restricted packages by obtaining a comma-separated list from
     * a call to
     * <code>java.security.Security.getProperty("package.access"),
     * and checks to see if <code>pkg starts with or equals
     * any of the restricted packages. If it does, then
     * <code>checkPermission gets called with the
     * <code>RuntimePermission("accessClassInPackage."+pkg)
     * permission.
     * <p>
     * If this method is overridden, then
     * <code>super.checkPackageAccess should be called
     * as the first line in the overridden method.
     *
     * @param      pkg   the package name.
     * @exception  SecurityException  if the calling thread does not have
     *             permission to access the specified package.
     * @exception  NullPointerException if the package name argument is
     *             <code>null.
     * @see        java.lang.ClassLoader#loadClass(java.lang.String, boolean)
     *  loadClass
     * @see        java.security.Security#getProperty getProperty
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    public void checkPackageAccess(String pkg) {
        if (pkg == null) {
            throw new NullPointerException("package name can't be null");
        }

        String[] pkgs;
        synchronized (packageAccessLock) {
            /*
             * Do we need to update our property array?
             */
            if (!packageAccessValid) {
                String tmpPropertyStr =
                    AccessController.doPrivileged(
                        new PrivilegedAction<String>() {
                            public String run() {
                                return java.security.Security.getProperty(
                                    "package.access");
                            }
                        }
                    );
                packageAccess = getPackages(tmpPropertyStr);
                packageAccessValid = true;
            }

            // Using a snapshot of packageAccess -- don't care if static field
            // changes afterwards; array contents won't change.
            pkgs = packageAccess;
        }

        /*
         * Traverse the list of packages, check for any matches.
         */
        for (int i = 0; i < pkgs.length; i++) {
            if (pkg.startsWith(pkgs[i]) || pkgs[i].equals(pkg + ".")) {
                checkPermission(
                    new RuntimePermission("accessClassInPackage."+pkg));
                break;  // No need to continue; only need to check this once
            }
        }
    }

    /**
     * Throws a <code>SecurityException if the
     * calling thread is not allowed to define classes in the package
     * specified by the argument.
     * <p>
     * This method is used by the <code>loadClass method of some
     * class loaders.
     * <p>
     * This method first gets a list of restricted packages by
     * obtaining a comma-separated list from a call to
     * <code>java.security.Security.getProperty("package.definition"),
     * and checks to see if <code>pkg starts with or equals
     * any of the restricted packages. If it does, then
     * <code>checkPermission gets called with the
     * <code>RuntimePermission("defineClassInPackage."+pkg)
     * permission.
     * <p>
     * If this method is overridden, then
     * <code>super.checkPackageDefinition should be called
     * as the first line in the overridden method.
     *
     * @param      pkg   the package name.
     * @exception  SecurityException  if the calling thread does not have
     *             permission to define classes in the specified package.
     * @see        java.lang.ClassLoader#loadClass(java.lang.String, boolean)
     * @see        java.security.Security#getProperty getProperty
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    public void checkPackageDefinition(String pkg) {
        if (pkg == null) {
            throw new NullPointerException("package name can't be null");
        }

        String[] pkgs;
        synchronized (packageDefinitionLock) {
            /*
             * Do we need to update our property array?
             */
            if (!packageDefinitionValid) {
                String tmpPropertyStr =
                    AccessController.doPrivileged(
                        new PrivilegedAction<String>() {
                            public String run() {
                                return java.security.Security.getProperty(
                                    "package.definition");
                            }
                        }
                    );
                packageDefinition = getPackages(tmpPropertyStr);
                packageDefinitionValid = true;
            }
            // Using a snapshot of packageDefinition -- don't care if static
            // field changes afterwards; array contents won't change.
            pkgs = packageDefinition;
        }

        /*
         * Traverse the list of packages, check for any matches.
         */
        for (int i = 0; i < pkgs.length; i++) {
            if (pkg.startsWith(pkgs[i]) || pkgs[i].equals(pkg + ".")) {
                checkPermission(
                    new RuntimePermission("defineClassInPackage."+pkg));
                break; // No need to continue; only need to check this once
            }
        }
    }

    /**
     * Throws a <code>SecurityException if the
     * calling thread is not allowed to set the socket factory used by
     * <code>ServerSocket or Socket, or the stream
     * handler factory used by <code>URL.
     * <p>
     * This method calls <code>checkPermission with the
     * <code>RuntimePermission("setFactory") permission.
     * <p>
     * If you override this method, then you should make a call to
     * <code>super.checkSetFactory
     * at the point the overridden method would normally throw an
     * exception.
     * <p>
     *
     * @exception  SecurityException  if the calling thread does not have
     *             permission to specify a socket factory or a stream
     *             handler factory.
     *
     * @see        java.net.ServerSocket#setSocketFactory(java.net.SocketImplFactory) setSocketFactory
     * @see        java.net.Socket#setSocketImplFactory(java.net.SocketImplFactory) setSocketImplFactory
     * @see        java.net.URL#setURLStreamHandlerFactory(java.net.URLStreamHandlerFactory) setURLStreamHandlerFactory
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    public void checkSetFactory() {
        checkPermission(new RuntimePermission("setFactory"));
    }

    /**
     * Throws a <code>SecurityException if the
     * calling thread is not allowed to access members.
     * <p>
     * The default policy is to allow access to PUBLIC members, as well
     * as access to classes that have the same class loader as the caller.
     * In all other cases, this method calls <code>checkPermission
     * with the <code>RuntimePermission("accessDeclaredMembers")
     * </code> permission.
     * <p>
     * If this method is overridden, then a call to
     * <code>super.checkMemberAccess cannot be made,
     * as the default implementation of <code>checkMemberAccess
     * relies on the code being checked being at a stack depth of
     * 4.
     *
     * @param clazz the class that reflection is to be performed on.
     *
     * @param which type of access, PUBLIC or DECLARED.
     *
     * @exception  SecurityException if the caller does not have
     *             permission to access members.
     * @exception  NullPointerException if the <code>clazz argument is
     *             <code>null.
     *
     * @deprecated This method relies on the caller being at a stack depth
     *             of 4 which is error-prone and cannot be enforced by the runtime.
     *             Users of this method should instead invoke {@link #checkPermission}
     *             directly.  This method will be changed in a future release
     *             to check the permission {@code java.security.AllPermission}.
     *
     * @see java.lang.reflect.Member
     * @since JDK1.1
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    @Deprecated
    @CallerSensitive
    public void checkMemberAccess(Class<?> clazz, int which) {
        if (clazz == null) {
            throw new NullPointerException("class can't be null");
        }
        if (which != Member.PUBLIC) {
            Class<?> stack[] = getClassContext();
            /*
             * stack depth of 4 should be the caller of one of the
             * methods in java.lang.Class that invoke checkMember
             * access. The stack should look like:
             *
             * someCaller                        [3]
             * java.lang.Class.someReflectionAPI [2]
             * java.lang.Class.checkMemberAccess [1]
             * SecurityManager.checkMemberAccess [0]
             *
             */
            if ((stack.length<4) ||
                (stack[3].getClassLoader() != clazz.getClassLoader())) {
                checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
            }
        }
    }

    /**
     * Determines whether the permission with the specified permission target
     * name should be granted or denied.
     *
     * <p> If the requested permission is allowed, this method returns
     * quietly. If denied, a SecurityException is raised.
     *
     * <p> This method creates a SecurityPermission object for
     * the given permission target name and calls <code>checkPermission
     * with it.
     *
     * <p> See the documentation for
     * <code>{@link java.security.SecurityPermission} for
     * a list of possible permission target names.
     *
     * <p> If you override this method, then you should make a call to
     * <code>super.checkSecurityAccess
     * at the point the overridden method would normally throw an
     * exception.
     *
     * @param target the target name of the <code>SecurityPermission.
     *
     * @exception SecurityException if the calling thread does not have
     * permission for the requested access.
     * @exception NullPointerException if <code>target is null.
     * @exception IllegalArgumentException if <code>target is empty.
     *
     * @since   JDK1.1
     * @see        #checkPermission(java.security.Permission) checkPermission
     */
    public void checkSecurityAccess(String target) {
        checkPermission(new SecurityPermission(target));
    }

    private native Class<?> currentLoadedClass0();

    /**
     * Returns the thread group into which to instantiate any new
     * thread being created at the time this is being called.
     * By default, it returns the thread group of the current
     * thread. This should be overridden by a specific security
     * manager to return the appropriate thread group.
     *
     * @return  ThreadGroup that new threads are instantiated into
     * @since   JDK1.1
     * @see     java.lang.ThreadGroup
     */
    public ThreadGroup getThreadGroup() {
        return Thread.currentThread().getThreadGroup();
    }

}

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