https://openjdk.java.net/ 
/*
 * Copyright (c) 1997, 2019, 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 jdk.internal.reflect.CallerSensitive;
import jdk.internal.reflect.Reflection;


 The AccessController class is used for access control operations
and decisions.

 More specifically, the AccessController class is used for
three purposes:

    

  •  to decide whether an access to a critical system
resource is to be allowed or denied, based on the security policy
currently in effect,

  • to mark code as being "privileged", thus affecting subsequent
access determinations, and

  • 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. 


 The 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, checkPermission will determine whether or not to grant "read" access to the file named "testFile" in the "/temp" directory. 
FilePermission perm = new FilePermission("/temp/testFile", "read");
AccessController.checkPermission(perm);



 If a requested access is allowed, 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 checkPermission method. The checkPermission method determines whether access is granted or denied based on the following algorithm: 
 
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);



 A caller can be marked as being "privileged" (see doPrivileged and below). When making access control decisions, the checkPermission method stops checking if it reaches a caller that was marked as "privileged" via a 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 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 doPrivileged then the permission checking continues until there are no more callers or another doPrivileged call matches the requested permission and returns normally. 
 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:
 
 
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...
 }


 PrivilegedAction is an interface with a single method, named run. The above example shows creation of an implementation of that interface; a concrete implementation of the run method is supplied. When the call to doPrivileged is made, an instance of the PrivilegedAction implementation is passed to it. The doPrivileged method calls the run method from the PrivilegedAction implementation after enabling privileges, and returns the run method's return value as the doPrivileged return value (which is ignored in this example). 
 If you need to return a value, you can do something like the following:
 
 
somemethod() {
    ...normal code here...
    String user = AccessController.doPrivileged(
        new PrivilegedAction<String>() {
        public String run() {
            return System.getProperty("user.name");
            }
        });
    ...normal code here...
 }


If the action performed in your run method could throw a "checked" exception (those listed in the throws clause of a method), then you need to use the PrivilegedExceptionAction interface instead of the PrivilegedAction interface: 
 
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...
 }


 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 Permission arguments to further limit the scope of the "privilege" (see below). 
 Note that 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 different context (for example, from within a worker thread). The getContext method and AccessControlContext class are provided for this situation. The 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: 
AccessControlContext acc = AccessController.getContext()



 AccessControlContext itself has a checkPermission method that makes access decisions based on the context it 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:

acc.checkPermission(permission)



 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 Permission parameters. 
 
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...
 }


 Passing a limiting Permission argument of an instance of AllPermission is equivalent to calling the equivalent doPrivileged method without limiting Permission arguments. Passing a zero length array of Permission disables the code privileges so that checking always continues beyond the caller of that doPrivileged method. 
Author:Li Gong, Roland Schemers
See Also:
Since:1.2
/**
 * <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
 * @since 1.2
 */

public final class AccessController {

    
Don't allow anyone to instantiate an AccessController

/**
     * Don't allow anyone to instantiate an AccessController
     */
    private AccessController() { }

    
Performs the specified PrivilegedAction with privileges enabled. The action is performed with all of the permissions
possessed by the caller's protection domain.

 If the action's run method throws an (unchecked) exception, it will propagate through this method. 
 Note that any DomainCombiner associated with the current
AccessControlContext will be ignored while the action is performed.

Params:
  • action – the action to be performed.
Type parameters:
  • <T> – the type of the value returned by the PrivilegedAction's run method.
Throws:
See Also:
Returns:the value returned by the action's run method.
/**
     * 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)
     * @see java.security.DomainCombiner
     */

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

    
Performs the specified PrivilegedAction with privileges enabled. The action is performed with all of the permissions
possessed by the caller's protection domain.

 If the action's run method throws an (unchecked) exception, it will propagate through this method. 
 This method preserves the current AccessControlContext's
DomainCombiner (which may be null) while the action is performed.

Params:
  • action – the action to be performed.
Type parameters:
  • <T> – the type of the value returned by the PrivilegedAction's run method.
Throws:
See Also:
Returns:the value returned by the action's run method.
Since:1.6
/**
     * 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)
     * @see java.security.DomainCombiner
     *
     * @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 PrivilegedAction with privileges enabled and restricted by the specified 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 AccessControlContext. 
 If the action's run method throws an (unchecked) exception, it will propagate through this method. 
 If a security manager is installed and the specified AccessControlContext was not created by system code and the caller's ProtectionDomain has not been granted the "createAccessControlContext" SecurityPermission, then the action is performed with no permissions. 
Params:
  • action – the action to be performed.
  • context – an access control context representing the restriction to be applied to the caller's domain's privileges before performing the specified action. If the context is null, then no additional restriction is applied.
Type parameters:
  • <T> – the type of the value returned by the PrivilegedAction's run method.
Throws:
See Also:
Returns:the value returned by the action's run method.
/**
     * 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"}
     * {@link java.security.SecurityPermission}, 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 PrivilegedAction with privileges enabled and restricted by the specified AccessControlContext and with a privilege scope limited by specified 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 AccessControlContext. 
 If the action's run method throws an (unchecked) exception, it will propagate through this method. 
 If a security manager is installed and the specified AccessControlContext was not created by system code and the caller's ProtectionDomain has not been granted the "createAccessControlContext" SecurityPermission, then the action is performed with no permissions. 
Params:
  • action – the action to be performed.
  • context – an access control context representing the restriction to be applied to the caller's domain's privileges before performing the specified action. If the context is null, then no additional restriction is applied.
  • perms – the Permission arguments which limit the scope of the caller's privileges. The number of arguments is variable.
Type parameters:
  • <T> – the type of the value returned by the PrivilegedAction's run method.
Throws:
See Also:
Returns:the value returned by the action's run method.
Since:1.8
/**
     * 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"}
     * {@link java.security.SecurityPermission}, 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();
        DomainCombiner dc = (context == null) ? null : context.getCombiner();
        return AccessController.doPrivileged(action, createWrapper(dc,
            caller, parent, context, perms));
    }


    
Performs the specified PrivilegedAction with privileges enabled and restricted by the specified AccessControlContext and with a privilege scope limited by specified 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 AccessControlContext. 
 If the action's run method throws an (unchecked) exception, it will propagate through this method. 
 This method preserves the current AccessControlContext's
DomainCombiner (which may be null) while the action is performed.

 If a security manager is installed and the specified AccessControlContext was not created by system code and the caller's ProtectionDomain has not been granted the "createAccessControlContext" SecurityPermission, then the action is performed with no permissions. 
Params:
  • action – the action to be performed.
  • context – an access control context representing the restriction to be applied to the caller's domain's privileges before performing the specified action. If the context is null, then no additional restriction is applied.
  • perms – the Permission arguments which limit the scope of the caller's privileges. The number of arguments is variable.
Type parameters:
  • <T> – the type of the value returned by the PrivilegedAction's run method.
Throws:
See Also:
Returns:the value returned by the action's run method.
Since:1.8
/**
     * 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"}
     * {@link java.security.SecurityPermission}, 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)
     * @see java.security.DomainCombiner
     *
     * @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 PrivilegedExceptionAction with privileges enabled. The action is performed with all of the
permissions possessed by the caller's protection domain.

 If the action's run method throws an unchecked
exception, it will propagate through this method.

 Note that any DomainCombiner associated with the current
AccessControlContext will be ignored while the action is performed.

Params:
  • action – the action to be performed
Type parameters:
  • <T> – the type of the value returned by the PrivilegedExceptionAction's run method.
Throws:
See Also:
Returns:the value returned by the action's run method
/**
     * 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)
     * @see java.security.DomainCombiner
     */
    @CallerSensitive
    public static native <T> T
        doPrivileged(PrivilegedExceptionAction<T> action)
        throws PrivilegedActionException;


    
Performs the specified PrivilegedExceptionAction with privileges enabled. The action is performed with all of the
permissions possessed by the caller's protection domain.

 If the action's run method throws an unchecked
exception, it will propagate through this method.

 This method preserves the current AccessControlContext's
DomainCombiner (which may be null) while the action is performed.

Params:
  • action – the action to be performed.
Type parameters:
  • <T> – the type of the value returned by the PrivilegedExceptionAction's run method.
Throws:
See Also:
Returns:the value returned by the action's run method
Since:1.6
/**
     * 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)
     * @see java.security.DomainCombiner
     *
     * @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

/**
     * 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.

/**
     * 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())
        {
            return getInnocuousAcc();
        } else {
            return new AccessControlContext(callerPD, combiner, parent,
                                            context, perms);
        }
    }

    private static class AccHolder {
        // An AccessControlContext with no granted permissions.
        // Only initialized on demand when getInnocuousAcc() is called.
        static final AccessControlContext innocuousAcc =
            new AccessControlContext(new ProtectionDomain[] {
                                     new ProtectionDomain(null, null) });
    }
    private static AccessControlContext getInnocuousAcc() {
        return AccHolder.innocuousAcc;
    }

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

        return callerPd;
    }

    
Performs the specified PrivilegedExceptionAction with privileges enabled and restricted by the specified 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 AccessControlContext. 
 If the action's run method throws an unchecked
exception, it will propagate through this method.

 If a security manager is installed and the specified AccessControlContext was not created by system code and the caller's ProtectionDomain has not been granted the "createAccessControlContext" SecurityPermission, then the action is performed with no permissions. 
Params:
  • action – the action to be performed
  • context – an access control context representing the restriction to be applied to the caller's domain's privileges before performing the specified action. If the context is null, then no additional restriction is applied.
Type parameters:
  • <T> – the type of the value returned by the PrivilegedExceptionAction's run method.
Throws:
See Also:
Returns:the value returned by the action's run method
/**
     * 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"}
     * {@link java.security.SecurityPermission}, 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 PrivilegedExceptionAction with privileges enabled and restricted by the specified AccessControlContext and with a privilege scope limited by specified 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 AccessControlContext. 
 If the action's run method throws an (unchecked) exception, it will propagate through this method. 
 If a security manager is installed and the specified AccessControlContext was not created by system code and the caller's ProtectionDomain has not been granted the "createAccessControlContext" SecurityPermission, then the action is performed with no permissions. 
Params:
  • action – the action to be performed.
  • context – an access control context representing the restriction to be applied to the caller's domain's privileges before performing the specified action. If the context is null, then no additional restriction is applied.
  • perms – the Permission arguments which limit the scope of the caller's privileges. The number of arguments is variable.
Type parameters:
  • <T> – the type of the value returned by the PrivilegedExceptionAction's run method.
Throws:
See Also:
Returns:the value returned by the action's run method.
Since:1.8
/**
     * 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"}
     * {@link java.security.SecurityPermission}, 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();
        DomainCombiner dc = (context == null) ? null : context.getCombiner();
        return AccessController.doPrivileged(action, createWrapper(dc, caller, parent, context, perms));
    }


    
Performs the specified PrivilegedExceptionAction with privileges enabled and restricted by the specified AccessControlContext and with a privilege scope limited by specified 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 AccessControlContext. 
 If the action's run method throws an (unchecked) exception, it will propagate through this method. 
 This method preserves the current AccessControlContext's
DomainCombiner (which may be null) while the action is performed.

 If a security manager is installed and the specified AccessControlContext was not created by system code and the caller's ProtectionDomain has not been granted the "createAccessControlContext" SecurityPermission, then the action is performed with no permissions. 
Params:
  • action – the action to be performed.
  • context – an access control context representing the restriction to be applied to the caller's domain's privileges before performing the specified action. If the context is null, then no additional restriction is applied.
  • perms – the Permission arguments which limit the scope of the caller's privileges. The number of arguments is variable.
Type parameters:
  • <T> – the type of the value returned by the PrivilegedExceptionAction's run method.
Throws:
See Also:
Returns:the value returned by the action's run method.
Since:1.8
/**
     * 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"}
     * {@link java.security.SecurityPermission}, 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)
     * @see java.security.DomainCombiner
     *
     * @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.

Returns:the access control context based on the current stack or
        null if there was only privileged system code.
/**
     * 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.

/**
     * 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 Also:
  • AccessControlContext
Returns:the AccessControlContext based on the current context.
/**
     * 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 perm Permission object instance. 
Params:
  • perm – the requested permission.
Throws:
  • AccessControlException – if the specified permission
           is not permitted, based on the current security policy.
  • NullPointerException – if the specified permission is null and is checked based on the security policy currently in effect.
/**
     * 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);
    }
}