/*
 
* 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
 
* or visit www.oracle.com if you need additional information or have any
 
* questions.
 
*/

package java.security;

import sun.security.util.Debug;
import sun.reflect.CallerSensitive;
import sun.reflect.Reflection;

/**
 
* <p> The AccessController class is used for access control operations
 
* and decisions.
 
*
 
* <p> More specifically, the AccessController class is used for
 
* three purposes:
 
*
 
* <ul>
 
* <li> to decide whether an access to a critical system
 
* resource is to be allowed or denied, based on the security policy
 
* currently in effect,
 
* <li>to mark code as being "privileged", thus affecting subsequent
 
* access determinations, and
 
* <li>to obtain a "snapshot" of the current calling context so
 
* access-control decisions from a different context can be made with
 
* respect to the saved context. </ul>
 
*
 
* <p> The {@link #checkPermission(Permission) checkPermission} method
 
* determines whether the access request indicated by a specified
 
* permission should be granted or denied. A sample call appears
 
* below. In this example, {@code checkPermission} will determine
 
* whether or not to grant "read" access to the file named "testFile" in
 
* the "/temp" directory.
 
*
 
* <pre>
 
*
 
* FilePermission perm = new FilePermission("/temp/testFile", "read");
 
* AccessController.checkPermission(perm);
 
*
 
* </pre>
 
*
 
* <p> If a requested access is allowed,
 
* {@code checkPermission} returns quietly. If denied, an
 
* AccessControlException is
 
* thrown. AccessControlException can also be thrown if the requested
 
* permission is of an incorrect type or contains an invalid value.
 
* Such information is given whenever possible.
 
*
 
* Suppose the current thread traversed m callers, in the order of caller 1
 
* to caller 2 to caller m. Then caller m invoked the
 
* {@code checkPermission} method.
 
* The {@code checkPermission} method determines whether access
 
* is granted or denied based on the following algorithm:
 
*
 
*
  
<pre> {@code
 
* for (int i = m; i > 0; i--) {
 
*
 
*
     
if (caller i's domain does not have the permission)
 
*
         
throw AccessControlException
 
*
 
*
     
else if (caller i is marked as privileged) {
 
*
         
if (a context was specified in the call to doPrivileged)
 
*
             
context.checkPermission(permission)
 
*
         
if (limited permissions were specified in the call to doPrivileged) {
 
*
             
for (each limited permission) {
 
*
                 
if (the limited permission implies the requested permission)
 
*
                     
return;
 
*
             
}
 
*
         
} else
 
*
             
return;
 
*
     
}
 
* }
 
*
 
* // Next, check the context inherited when the thread was created.
 
* // Whenever a new thread is created, the AccessControlContext at
 
* // that time is stored and associated with the new thread, as the
 
* // "inherited" context.
 
*
 
* inheritedContext.checkPermission(permission);
 
* }</pre>
 
*
 
* <p> A caller can be marked as being "privileged"
 
* (see {@link #doPrivileged(PrivilegedAction) doPrivileged} and below).
 
* When making access control decisions, the {@code checkPermission}
 
* method stops checking if it reaches a caller that
 
* was marked as "privileged" via a {@code doPrivileged}
 
* call without a context argument (see below for information about a
 
* context argument). If that caller's domain has the
 
* specified permission and at least one limiting permission argument (if any)
 
* implies the requested permission, no further checking is done and
 
* {@code checkPermission}
 
* returns quietly, indicating that the requested access is allowed.
 
* If that domain does not have the specified permission, an exception
 
* is thrown, as usual. If the caller's domain had the specified permission
 
* but it was not implied by any limiting permission arguments given in the call
 
* to {@code doPrivileged} then the permission checking continues
 
* until there are no more callers or another {@code doPrivileged}
 
* call matches the requested permission and returns normally.
 
*
 
* <p> The normal use of the "privileged" feature is as follows. If you
 
* don't need to return a value from within the "privileged" block, do
 
* the following:
 
*
 
*
  
<pre> {@code
 
* somemethod() {
 
*
     
...normal code here...
 
*
     
AccessController.doPrivileged(new PrivilegedAction<Void>() {
 
*
         
public Void run() {
 
*
             
// privileged code goes here, for example:
 
*
             
System.loadLibrary("awt");
 
*
             
return null; // nothing to return
 
*
         
}
 
*
     
});
 
*
     
...normal code here...
 
* }}</pre>
 
*
 
* <p>
 
* PrivilegedAction is an interface with a single method, named
 
* {@code run}.
 
* The above example shows creation of an implementation
 
* of that interface; a concrete implementation of the
 
* {@code run} method is supplied.
 
* When the call to {@code doPrivileged} is made, an
 
* instance of the PrivilegedAction implementation is passed
 
* to it. The {@code doPrivileged} method calls the
 
* {@code run} method from the PrivilegedAction
 
* implementation after enabling privileges, and returns the
 
* {@code run} method's return value as the
 
* {@code doPrivileged} return value (which is
 
* ignored in this example).
 
*
 
* <p> If you need to return a value, you can do something like the following:
 
*
 
*
  
<pre> {@code
 
* somemethod() {
 
*
     
...normal code here...
 
*
     
String user = AccessController.doPrivileged(
 
*
         
new PrivilegedAction<String>() {
 
*
         
public String run() {
 
*
             
return System.getProperty("user.name");
 
*
             
}
 
*
         
});
 
*
     
...normal code here...
 
* }}</pre>
 
*
 
* <p>If the action performed in your {@code run} method could
 
* throw a "checked" exception (those listed in the {@code throws} clause
 
* of a method), then you need to use the
 
* {@code PrivilegedExceptionAction} interface instead of the
 
* {@code PrivilegedAction} interface:
 
*
 
*
  
<pre> {@code
 
* somemethod() throws FileNotFoundException {
 
*
     
...normal code here...
 
*
     
try {
 
*
         
FileInputStream fis = AccessController.doPrivileged(
 
*
         
new PrivilegedExceptionAction<FileInputStream>() {
 
*
             
public FileInputStream run() throws FileNotFoundException {
 
*
                 
return new FileInputStream("someFile");
 
*
             
}
 
*
         
});
 
*
     
} catch (PrivilegedActionException e) {
 
*
         
// e.getException() should be an instance of FileNotFoundException,
 
*
         
// as only "checked" exceptions will be "wrapped" in a
 
*
         
// PrivilegedActionException.
 
*
         
throw (FileNotFoundException) e.getException();
 
*
     
}
 
*
     
...normal code here...
 
*
  
}}</pre>
 
*
 
* <p> Be *very* careful in your use of the "privileged" construct, and
 
* always remember to make the privileged code section as small as possible.
 
* You can pass {@code Permission} arguments to further limit the
 
* scope of the "privilege" (see below).
 
*
 
*
 
* <p> Note that {@code checkPermission} 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</i> context (for example, from within a worker thread).
 
* The {@link #getContext() getContext} method and
 
* AccessControlContext class are provided
 
* for this situation. The {@code getContext} method takes a "snapshot"
 
* of the current calling context, and places
 
* it in an AccessControlContext object, which it returns. A sample call is
 
* the following:
 
*
 
* <pre>
 
*
 
* AccessControlContext acc = AccessController.getContext()
 
*
 
* </pre>
 
*
 
* <p>
 
* AccessControlContext itself has a {@code checkPermission} method
 
* that makes access decisions based on the context <i>it</i> encapsulates,
 
* rather than that of the current execution thread.
 
* Code within a different context can thus call that method on the
 
* previously-saved AccessControlContext object. A sample call is the
 
* following:
 
*
 
* <pre>
 
*
 
* acc.checkPermission(permission)
 
*
 
* </pre>
 
*
 
* <p> There are also times where you don't know a priori which permissions
 
* to check the context against. In these cases you can use the
 
* doPrivileged method that takes a context. You can also limit the scope
 
* of the privileged code by passing additional {@code Permission}
 
* parameters.
 
*
 
*
  
<pre> {@code
 
* somemethod() {
 
*
     
AccessController.doPrivileged(new PrivilegedAction<Object>() {
 
*
         
public Object run() {
 
*
             
// Code goes here. Any permission checks within this
 
*
             
// run method will require that the intersection of the
 
*
             
// caller's protection domain and the snapshot's
 
*
             
// context have the desired permission. If a requested
 
*
             
// permission is not implied by the limiting FilePermission
 
*
             
// argument then checking of the thread continues beyond the
 
*
             
// caller of doPrivileged.
 
*
         
}
 
*
     
}, acc, new FilePermission("/temp/*", read));
 
*
     
...normal code here...
 
* }}</pre>
 
* <p> Passing a limiting {@code Permission} argument of an instance of
 
* {@code AllPermission} is equivalent to calling the equivalent
 
* {@code doPrivileged} method without limiting {@code Permission}
 
* arguments. Passing a zero length array of {@code Permission} disables
 
* the code privileges so that checking always continues beyond the caller of
 
* that {@code doPrivileged} method.
 
*
 
* @see AccessControlContext
 
*
 
* @author Li Gong
 
* @author Roland Schemers
 
*/


public final class AccessController {

    
/**
     
* Don't allow anyone to instantiate an AccessController
     
*/

    
private AccessController() { }

    
/**
     
* Performs the specified {@code PrivilegedAction} with privileges
     
* enabled. The action is performed with <i>all</i> of the permissions
     
* possessed by the caller's protection domain.
     
*
     
* <p> If the action's {@code run} method throws an (unchecked)
     
* exception, it will propagate through this method.
     
*
     
* <p> Note that any DomainCombiner associated with the current
     
* AccessControlContext will be ignored while the action is performed.
     
*
     
* @param <T> the type of the value returned by the PrivilegedAction's
     
*
                  
{@code run} method.
     
*
     
* @param action the action to be performed.
     
*
     
* @return the value returned by the action's {@code run} method.
     
*
     
* @exception NullPointerException if the action is {@code null}
     
*
     
* @see #doPrivileged(PrivilegedAction,AccessControlContext)
     
* @see #doPrivileged(PrivilegedExceptionAction)
     
* @see #doPrivilegedWithCombiner(PrivilegedAction)
     
*
 

     
*/


    
@CallerSensitive
    
public static native <T> T doPrivileged(PrivilegedAction<T> action);

    
/**
     
* Performs the specified {@code PrivilegedAction} with privileges
     
* enabled. The action is performed with <i>all</i> of the permissions
     
* possessed by the caller's protection domain.
     
*
     
* <p> If the action's {@code run} method throws an (unchecked)
     
* exception, it will propagate through this method.
     
*
     
* <p> This method preserves the current AccessControlContext's
     
* DomainCombiner (which may be null) while the action is performed.
     
*
     
* @param <T> the type of the value returned by the PrivilegedAction's
     
*
                  
{@code run} method.
     
*
     
* @param action the action to be performed.
     
*
     
* @return the value returned by the action's {@code run} method.
     
*
     
* @exception NullPointerException if the action is {@code null}
     
*
     
* @see #doPrivileged(PrivilegedAction)
     
*
 

     
*
     
* @since 1.6
     
*/

    
@CallerSensitive
    
public static <T> T doPrivilegedWithCombiner(PrivilegedAction<T> action) {
        
AccessControlContext acc = getStackAccessControlContext();
        
if (acc == null) {
            
return AccessController.doPrivileged(action);
        
}
        
DomainCombiner dc = acc.getAssignedCombiner();
        
return AccessController.doPrivileged(action,
                                             
preserveCombiner(dc, Reflection.getCallerClass()));
    
}


    
/**
     
* Performs the specified {@code PrivilegedAction} with privileges
     
* enabled and restricted by the specified {@code AccessControlContext}.
     
* The action is performed with the intersection of the permissions
     
* possessed by the caller's protection domain, and those possessed
     
* by the domains represented by the specified {@code AccessControlContext}.
     
* <p>
     
* If the action's {@code run} method throws an (unchecked) exception,
     
* it will propagate through this method.
     
* <p>
     
* If a security manager is installed and the specified
     
* {@code AccessControlContext} was not created by system code and the
     
* caller's {@code ProtectionDomain} has not been granted the
     
* {@literal "createAccessControlContext"}
     
*
 
, then the action is performed
     
* with no permissions.
     
*
     
* @param <T> the type of the value returned by the PrivilegedAction's
     
*
                  
{@code run} method.
     
* @param action the action to be performed.
     
* @param context an <i>access control context</i>
     
*
                
representing the restriction to be applied to the
     
*
                
caller's domain's privileges before performing
     
*
                
the specified action.
  
If the context is
     
*
                
{@code null}, then no additional restriction is applied.
     
*
     
* @return the value returned by the action's {@code run} method.
     
*
     
* @exception NullPointerException if the action is {@code null}
     
*
     
* @see #doPrivileged(PrivilegedAction)
     
* @see #doPrivileged(PrivilegedExceptionAction,AccessControlContext)
     
*/

    
@CallerSensitive
    
public static native <T> T doPrivileged(PrivilegedAction<T> action,
                                            
AccessControlContext context);


    
/**
     
* Performs the specified {@code PrivilegedAction} with privileges
     
* enabled and restricted by the specified
     
* {@code AccessControlContext} and with a privilege scope limited
     
* by specified {@code Permission} arguments.
     
*
     
* The action is performed with the intersection of the permissions
     
* possessed by the caller's protection domain, and those possessed
     
* by the domains represented by the specified
     
* {@code AccessControlContext}.
     
* <p>
     
* If the action's {@code run} method throws an (unchecked) exception,
     
* it will propagate through this method.
     
* <p>
     
* If a security manager is installed and the specified
     
* {@code AccessControlContext} was not created by system code and the
     
* caller's {@code ProtectionDomain} has not been granted the
     
* {@literal "createAccessControlContext"}
     
*
 
, then the action is performed
     
* with no permissions.
     
*
     
* @param <T> the type of the value returned by the PrivilegedAction's
     
*
                  
{@code run} method.
     
* @param action the action to be performed.
     
* @param context an <i>access control context</i>
     
*
                
representing the restriction to be applied to the
     
*
                
caller's domain's privileges before performing
     
*
                
the specified action.
  
If the context is
     
*
                
{@code null},
     
*
                
then no additional restriction is applied.
     
* @param perms the {@code Permission} arguments which limit the
     
*
              
scope of the caller's privileges. The number of arguments
     
*
              
is variable.
     
*
     
* @return the value returned by the action's {@code run} method.
     
*
     
* @throws NullPointerException if action or perms or any element of
     
*
         
perms is {@code null}
     
*
     
* @see #doPrivileged(PrivilegedAction)
     
* @see #doPrivileged(PrivilegedExceptionAction,AccessControlContext)
     
*
     
* @since 1.8
     
*/

    
@CallerSensitive
    
public static <T> T doPrivileged(PrivilegedAction<T> action,
        
AccessControlContext context, Permission... perms) {

        
AccessControlContext parent = getContext();
        
if (perms == null) {
            
throw new NullPointerException("null permissions parameter");
        
}
        
Class <?> caller = Reflection.getCallerClass();
        
return AccessController.doPrivileged(action, createWrapper(null,
            
caller, parent, context, perms));
    
}


    
/**
     
* Performs the specified {@code PrivilegedAction} with privileges
     
* enabled and restricted by the specified
     
* {@code AccessControlContext} and with a privilege scope limited
     
* by specified {@code Permission} arguments.
     
*
     
* The action is performed with the intersection of the permissions
     
* possessed by the caller's protection domain, and those possessed
     
* by the domains represented by the specified
     
* {@code AccessControlContext}.
     
* <p>
     
* If the action's {@code run} method throws an (unchecked) exception,
     
* it will propagate through this method.
     
*
     
* <p> This method preserves the current AccessControlContext's
     
* DomainCombiner (which may be null) while the action is performed.
     
* <p>
     
* If a security manager is installed and the specified
     
* {@code AccessControlContext} was not created by system code and the
     
* caller's {@code ProtectionDomain} has not been granted the
     
* {@literal "createAccessControlContext"}
     
*
 
, then the action is performed
     
* with no permissions.
     
*
     
* @param <T> the type of the value returned by the PrivilegedAction's
     
*
                  
{@code run} method.
     
* @param action the action to be performed.
     
* @param context an <i>access control context</i>
     
*
                
representing the restriction to be applied to the
     
*
                
caller's domain's privileges before performing
     
*
                
the specified action.
  
If the context is
     
*
                
{@code null},
     
*
                
then no additional restriction is applied.
     
* @param perms the {@code Permission} arguments which limit the
     
*
              
scope of the caller's privileges. The number of arguments
     
*
              
is variable.
     
*
     
* @return the value returned by the action's {@code run} method.
     
*
     
* @throws NullPointerException if action or perms or any element of
     
*
         
perms is {@code null}
     
*
     
* @see #doPrivileged(PrivilegedAction)
     
* @see #doPrivileged(PrivilegedExceptionAction,AccessControlContext)
     
*
 

     
*
     
* @since 1.8
     
*/

    
@CallerSensitive
    
public static <T> T doPrivilegedWithCombiner(PrivilegedAction<T> action,
        
AccessControlContext context, Permission... perms) {

        
AccessControlContext parent = getContext();
        
DomainCombiner dc = parent.getCombiner();
        
if (dc == null && context != null) {
            
dc = context.getCombiner();
        
}
        
if (perms == null) {
            
throw new NullPointerException("null permissions parameter");
        
}
        
Class <?> caller = Reflection.getCallerClass();
        
return AccessController.doPrivileged(action, createWrapper(dc, caller,
            
parent, context, perms));
    
}

    
/**
     
* Performs the specified {@code PrivilegedExceptionAction} with
     
* privileges enabled.
  
The action is performed with <i>all</i> of the
     
* permissions possessed by the caller's protection domain.
     
*
     
* <p> If the action's {@code run} method throws an <i>unchecked</i>
     
* exception, it will propagate through this method.
     
*
     
* <p> Note that any DomainCombiner associated with the current
     
* AccessControlContext will be ignored while the action is performed.
     
*
     
* @param <T> the type of the value returned by the
     
*
                  
PrivilegedExceptionAction's {@code run} method.
     
*
     
* @param action the action to be performed
     
*
     
* @return the value returned by the action's {@code run} method
     
*
     
* @exception PrivilegedActionException if the specified action's
     
*
         
{@code run} method threw a <i>checked</i> exception
     
* @exception NullPointerException if the action is {@code null}
     
*
     
* @see #doPrivileged(PrivilegedAction)
     
* @see #doPrivileged(PrivilegedExceptionAction,AccessControlContext)
     
* @see #doPrivilegedWithCombiner(PrivilegedExceptionAction)
     
*
 

     
*/

    
@CallerSensitive
    
public static native <T> T
        
doPrivileged
(PrivilegedExceptionAction<T> action)
        
throws PrivilegedActionException;


    
/**
     
* Performs the specified {@code PrivilegedExceptionAction} with
     
* privileges enabled.
  
The action is performed with <i>all</i> of the
     
* permissions possessed by the caller's protection domain.
     
*
     
* <p> If the action's {@code run} method throws an <i>unchecked</i>
     
* exception, it will propagate through this method.
     
*
     
* <p> This method preserves the current AccessControlContext's
     
* DomainCombiner (which may be null) while the action is performed.
     
*
     
* @param <T> the type of the value returned by the
     
*
                  
PrivilegedExceptionAction's {@code run} method.
     
*
     
* @param action the action to be performed.
     
*
     
* @return the value returned by the action's {@code run} method
     
*
     
* @exception PrivilegedActionException if the specified action's
     
*
         
{@code run} method threw a <i>checked</i> exception
     
* @exception NullPointerException if the action is {@code null}
     
*
     
* @see #doPrivileged(PrivilegedAction)
     
* @see #doPrivileged(PrivilegedExceptionAction,AccessControlContext)
     
*
 

     
*
     
* @since 1.6
     
*/

    
@CallerSensitive
    
public static <T> T doPrivilegedWithCombiner(PrivilegedExceptionAction<T> action)
        
throws PrivilegedActionException
    
{
        
AccessControlContext acc = getStackAccessControlContext();
        
if (acc == null) {
            
return AccessController.doPrivileged(action);
        
}
        
DomainCombiner dc = acc.getAssignedCombiner();
        
return AccessController.doPrivileged(action,
                                             
preserveCombiner(dc, Reflection.getCallerClass()));
    
}

    
/**
     
* preserve the combiner across the doPrivileged call
     
*/
    
private static AccessControlContext preserveCombiner(DomainCombiner combiner,
                                                         
Class<?> caller)
    
{
        
return createWrapper(combiner, caller, null, null, null);
    
}

    
/**
     
* Create a wrapper to contain the limited privilege scope data.
     
*/

    
private static AccessControlContext
        
createWrapper
(DomainCombiner combiner, Class<?> caller,
                      
AccessControlContext parent, AccessControlContext context,
                      
Permission[] perms)
    
{
        
ProtectionDomain callerPD = getCallerPD(caller);
        
// check if caller is authorized to create context
        
if (context != null && !context.isAuthorized() &&
            
System.getSecurityManager() != null &&
            
!callerPD.impliesCreateAccessControlContext())
        
{
            
ProtectionDomain nullPD = new ProtectionDomain(null, null);
            
return new AccessControlContext(new ProtectionDomain[] { nullPD });
        
} else {
            
return new AccessControlContext(callerPD, combiner, parent,
                                            
context, perms);
        
}
    
}

    
private static ProtectionDomain getCallerPD(final Class <?> caller) {
        
ProtectionDomain callerPd = doPrivileged
            
(new PrivilegedAction<ProtectionDomain>() {
            
public ProtectionDomain run() {
                
return caller.getProtectionDomain();
            
}
        
});

        
return callerPd;
    
}

    
/**
     
* Performs the specified {@code PrivilegedExceptionAction} with
     
* privileges enabled and restricted by the specified
     
* {@code AccessControlContext}.
  
The action is performed with the
     
* intersection of the permissions possessed by the caller's
     
* protection domain, and those possessed by the domains represented by the
     
* specified {@code AccessControlContext}.
     
* <p>
     
* If the action's {@code run} method throws an <i>unchecked</i>
     
* exception, it will propagate through this method.
     
* <p>
     
* If a security manager is installed and the specified
     
* {@code AccessControlContext} was not created by system code and the
     
* caller's {@code ProtectionDomain} has not been granted the
     
* {@literal "createAccessControlContext"}
     
*
 
, then the action is performed
     
* with no permissions.
     
*
     
* @param <T> the type of the value returned by the
     
*
                  
PrivilegedExceptionAction's {@code run} method.
     
* @param action the action to be performed
     
* @param context an <i>access control context</i>
     
*
                
representing the restriction to be applied to the
     
*
                
caller's domain's privileges before performing
     
*
                
the specified action.
  
If the context is
     
*
                
{@code null}, then no additional restriction is applied.
     
*
     
* @return the value returned by the action's {@code run} method
     
*
     
* @exception PrivilegedActionException if the specified action's
     
*
         
{@code run} method threw a <i>checked</i> exception
     
* @exception NullPointerException if the action is {@code null}
     
*
     
* @see #doPrivileged(PrivilegedAction)
     
* @see #doPrivileged(PrivilegedAction,AccessControlContext)
     
*/

    
@CallerSensitive
    
public static native <T> T
        
doPrivileged
(PrivilegedExceptionAction<T> action,
                     
AccessControlContext context)
        
throws PrivilegedActionException;


    
/**
     
* Performs the specified {@code PrivilegedExceptionAction} with
     
* privileges enabled and restricted by the specified
     
* {@code AccessControlContext} and with a privilege scope limited by
     
* specified {@code Permission} arguments.
     
*
     
* The action is performed with the intersection of the permissions
     
* possessed by the caller's protection domain, and those possessed
     
* by the domains represented by the specified
     
* {@code AccessControlContext}.
     
* <p>
     
* If the action's {@code run} method throws an (unchecked) exception,
     
* it will propagate through this method.
     
* <p>
     
* If a security manager is installed and the specified
     
* {@code AccessControlContext} was not created by system code and the
     
* caller's {@code ProtectionDomain} has not been granted the
     
* {@literal "createAccessControlContext"}
     
*
 
, then the action is performed
     
* with no permissions.
     
*
     
* @param <T> the type of the value returned by the
     
*
                  
PrivilegedExceptionAction's {@code run} method.
     
* @param action the action to be performed.
     
* @param context an <i>access control context</i>
     
*
                
representing the restriction to be applied to the
     
*
                
caller's domain's privileges before performing
     
*
                
the specified action.
  
If the context is
     
*
                
{@code null},
     
*
                
then no additional restriction is applied.
     
* @param perms the {@code Permission} arguments which limit the
     
*
              
scope of the caller's privileges. The number of arguments
     
*
              
is variable.
     
*
     
* @return the value returned by the action's {@code run} method.
     
*
     
* @throws PrivilegedActionException if the specified action's
     
*
         
{@code run} method threw a <i>checked</i> exception
     
* @throws NullPointerException if action or perms or any element of
     
*
         
perms is {@code null}
     
*
     
* @see #doPrivileged(PrivilegedAction)
     
* @see #doPrivileged(PrivilegedAction,AccessControlContext)
     
*
     
* @since 1.8
     
*/

    
@CallerSensitive
    
public static <T> T doPrivileged(PrivilegedExceptionAction<T> action,
                                     
AccessControlContext context, Permission... perms)
        
throws PrivilegedActionException
    
{
        
AccessControlContext parent = getContext();
        
if (perms == null) {
            
throw new NullPointerException("null permissions parameter");
        
}
        
Class <?> caller = Reflection.getCallerClass();
        
return AccessController.doPrivileged(action, createWrapper(null, caller, parent, context, perms));
    
}


    
/**
     
* Performs the specified {@code PrivilegedExceptionAction} with
     
* privileges enabled and restricted by the specified
     
* {@code AccessControlContext} and with a privilege scope limited by
     
* specified {@code Permission} arguments.
     
*
     
* The action is performed with the intersection of the permissions
     
* possessed by the caller's protection domain, and those possessed
     
* by the domains represented by the specified
     
* {@code AccessControlContext}.
     
* <p>
     
* If the action's {@code run} method throws an (unchecked) exception,
     
* it will propagate through this method.
     
*
     
* <p> This method preserves the current AccessControlContext's
     
* DomainCombiner (which may be null) while the action is performed.
     
* <p>
     
* If a security manager is installed and the specified
     
* {@code AccessControlContext} was not created by system code and the
     
* caller's {@code ProtectionDomain} has not been granted the
     
* {@literal "createAccessControlContext"}
     
*
 
, then the action is performed
     
* with no permissions.
     
*
     
* @param <T> the type of the value returned by the
     
*
                  
PrivilegedExceptionAction's {@code run} method.
     
* @param action the action to be performed.
     
* @param context an <i>access control context</i>
     
*
                
representing the restriction to be applied to the
     
*
                
caller's domain's privileges before performing
     
*
                
the specified action.
  
If the context is
     
*
                
{@code null},
     
*
                
then no additional restriction is applied.
     
* @param perms the {@code Permission} arguments which limit the
     
*
              
scope of the caller's privileges. The number of arguments
     
*
              
is variable.
     
*
     
* @return the value returned by the action's {@code run} method.
     
*
     
* @throws PrivilegedActionException if the specified action's
     
*
         
{@code run} method threw a <i>checked</i> exception
     
* @throws NullPointerException if action or perms or any element of
     
*
         
perms is {@code null}
     
*
     
* @see #doPrivileged(PrivilegedAction)
     
* @see #doPrivileged(PrivilegedAction,AccessControlContext)
     
*
 

     
*
     
* @since 1.8
     
*/

    
@CallerSensitive
    
public static <T> T doPrivilegedWithCombiner(PrivilegedExceptionAction<T> action,
                                                 
AccessControlContext context,
                                                 
Permission... perms)
        
throws PrivilegedActionException
    
{
        
AccessControlContext parent = getContext();
        
DomainCombiner dc = parent.getCombiner();
        
if (dc == null && context != null) {
            
dc = context.getCombiner();
        
}
        
if (perms == null) {
            
throw new NullPointerException("null permissions parameter");
        
}
        
Class <?> caller = Reflection.getCallerClass();
        
return AccessController.doPrivileged(action, createWrapper(dc, caller,
            
parent, context, perms));
    
}

    
/**
     
* Returns the AccessControl context. i.e., it gets
     
* the protection domains of all the callers on the stack,
     
* starting at the first class with a non-null
     
* ProtectionDomain.
     
*
     
* @return the access control context based on the current stack or
     
*
         
null if there was only privileged system code.
     
*/


    
private static native AccessControlContext getStackAccessControlContext();


    
/**
     
* Returns the "inherited" AccessControl context. This is the context
     
* that existed when the thread was created. Package private so
     
* AccessControlContext can use it.
     
*/


    
static native AccessControlContext getInheritedAccessControlContext();

    
/**
     
* This method takes a "snapshot" of the current calling context, which
     
* includes the current Thread's inherited AccessControlContext and any
     
* limited privilege scope, and places it in an AccessControlContext object.
     
* This context may then be checked at a later point, possibly in another thread.
     
*
     
* @see AccessControlContext
     
*
     
* @return the AccessControlContext based on the current context.
     
*/


    
public static AccessControlContext getContext()
    
{
        
AccessControlContext acc = getStackAccessControlContext();
        
if (acc == null) {
            
// all we had was privileged system code. We don't want
            
// to return null though, so we construct a real ACC.
            
return new AccessControlContext(null, true);
        
} else {
            
return acc.optimize();
        
}
    
}

    
/**
     
* Determines whether the access request indicated by the
     
* specified permission should be allowed or denied, based on
     
* the current AccessControlContext and security policy.
     
* This method quietly returns if the access request
     
* is permitted, or throws an AccessControlException otherwise. The
     
* getPermission method of the AccessControlException returns the
     
* {@code perm} Permission object instance.
     
*
     
* @param perm the requested permission.
     
*
     
* @exception AccessControlException if the specified permission
     
*
            
is not permitted, based on the current security policy.
     
* @exception NullPointerException if the specified permission
     
*
            
is {@code null} and is checked based on the
     
*
            
security policy currently in effect.
     
*/


    
public static void checkPermission(Permission perm)
        
throws AccessControlException
    
{
        
//System.err.println("checkPermission "+perm);
        
//Thread.currentThread().dumpStack();

        
if (perm == null) {
            
throw new NullPointerException("permission can't be null");
        
}

        
AccessControlContext stack = getStackAccessControlContext();
        
// if context is null, we had privileged system code on the stack.
        
if (stack == null) {
            
Debug debug = AccessControlContext.getDebug();
            
boolean dumpDebug = false;
            
if (debug != null) {
                
dumpDebug = !Debug.isOn("codebase=");
                
dumpDebug &= !Debug.isOn("permission=") ||
                    
Debug.isOn("permission=" + perm.getClass().getCanonicalName());
            
}

            
if (dumpDebug && Debug.isOn("stack")) {
                
Thread.dumpStack();
            
}

            
if (dumpDebug && Debug.isOn("domain")) {
                
debug.println("domain (context is null)");
            
}

            
if (dumpDebug) {
                
debug.println("access allowed "+perm);
            
}
            
return;
        
}

        
AccessControlContext acc = stack.optimize();
        
acc.checkPermission(perm);
    
}
}