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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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
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 * 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
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 * accompanied this code).
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 *
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 */

package java.security;

import sun.security.util.Debug;
import sun.reflect.CallerSensitive;
import sun.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)
        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, 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.

 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.

 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:
 
 
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
            // callers protection domain and the snapshot's
            // context have the desired permission.
        }
    }, acc);
    ...normal code here...
 }


Author:Li Gong, Roland Schemers
See Also:
/**
 * <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,<p>
 * <li>to mark code as being "privileged", thus affecting subsequent
 * access determinations, and<p>
 * <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</code> 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</code> 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</code> method.
 * The <code>checkPermission </code>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)
 *         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</code>
 * method stops checking if it reaches a caller that
 * was marked as "privileged" via a <code>doPrivileged</code>
 * call without a context argument (see below for information about a
 * context argument). If that caller's domain has the
 * specified permission, no further checking is done and
 * <code>checkPermission</code>
 * returns quietly, indicating that the requested access is allowed.
 * If that domain does not have the specified permission, an exception
 * is thrown, as usual.
 *
 * <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</code>.
 * The above example shows creation of an implementation
 * of that interface; a concrete implementation of the
 * <code>run</code> method is supplied.
 * When the call to <code>doPrivileged</code> is made, an
 * instance of the PrivilegedAction implementation is passed
 * to it. The <code>doPrivileged</code> method calls the
 * <code>run</code> method from the PrivilegedAction
 * implementation after enabling privileges, and returns the
 * <code>run</code> method's return value as the
 * <code>doPrivileged</code> 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</code> method could
 * throw a "checked" exception (those listed in the <code>throws</code> clause
 * of a method), then you need to use the
 * <code>PrivilegedExceptionAction</code> interface instead of the
 * <code>PrivilegedAction</code> 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.
 *
 * <p> Note that <code>checkPermission</code> 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</code> 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</code> 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:
 *
 *  <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
 *             // callers protection domain and the snapshot's
 *             // context have the desired permission.
 *         }
 *     }, acc);
 *     ...normal code here...
 * }}</pre>
 *
 * @see AccessControlContext
 *
 * @author Li Gong
 * @author Roland Schemers
 */

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.
Throws:
See Also:
Returns:the value returned by the action's run method.
/**
     * Performs the specified <code>PrivilegedAction</code> 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</code> 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 action the action to be performed.
     *
     * @return the value returned by the action's <code>run</code> method.
     *
     * @exception NullPointerException if the action is <code>null</code>
     *
     * @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.
Throws:
See Also:
Returns:the value returned by the action's run method.
Since:1.6
/**
     * Performs the specified <code>PrivilegedAction</code> 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</code> 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 action the action to be performed.
     *
     * @return the value returned by the action's <code>run</code> method.
     *
     * @exception NullPointerException if the action is <code>null</code>
     *
     * @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.

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.
Throws:
See Also:
Returns:the value returned by the action's run method.
/**
     * Performs the specified <code>PrivilegedAction</code> with privileges
     * enabled and restricted by the specified
     * <code>AccessControlContext</code>.
     * 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</code>.
     * <p>
     * If the action's <code>run</code> method throws an (unchecked) exception,
     * it will propagate through this 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</code>,
     *                then no additional restriction is applied.
     *
     * @return the value returned by the action's <code>run</code> method.
     *
     * @exception NullPointerException if the action is <code>null</code>
     *
     * @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.

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.
Throws:
See Also:
Returns:the value returned by the action's run method.
Since:1.8
/**
     * Performs the specified <code>PrivilegedAction</code> with privileges
     * enabled and restricted by the specified
     * <code>AccessControlContext</code> and with a privilege scope limited
     * by specified <code>Permission</code> 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</code>.
     * <p>
     * If the action's <code>run</code> method throws an (unchecked) exception,
     * it will propagate through this 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</code>,
     *                then no additional restriction is applied.
     * @param perms the <code>Permission</code> 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</code> method.
     *
     * @throws NullPointerException if action or perms or any element of
     *         perms is <code>null</code>
     *
     * @see #doPrivileged(PrivilegedAction)
     * @see #doPrivileged(PrivilegedExceptionAction,AccessControlContext)
     *
     * @since 1.8
     */
    @CallerSensitive
    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 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
Throws:
See Also:
Returns:the value returned by the action's run method
/**
     * Performs the specified <code>PrivilegedExceptionAction</code> 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</code> 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 action the action to be performed
     *
     * @return the value returned by the action's <code>run</code> method
     *
     * @exception PrivilegedActionException if the specified action's
     *         <code>run</code> method threw a <i>checked</i> exception
     * @exception NullPointerException if the action is <code>null</code>
     *
     * @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.
Throws:
See Also:
Returns:the value returned by the action's run method
Since:1.6
/**
     * Performs the specified <code>PrivilegedExceptionAction</code> 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</code> 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 action the action to be performed.
     *
     * @return the value returned by the action's <code>run</code> method
     *
     * @exception PrivilegedActionException if the specified action's
     *         <code>run</code> method threw a <i>checked</i> exception
     * @exception NullPointerException if the action is <code>null</code>
     *
     * @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,
                                                         final 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())
        {
            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 PrivilegedExceptionAction with
privileges enabled and restricted by the specified
AccessControlContext.  The action is performed with the
intersection of the 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.

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.
Throws:
See Also:
Returns:the value returned by the action's run method
/**
     * Performs the specified <code>PrivilegedExceptionAction</code> with
     * privileges enabled and restricted by the specified
     * <code>AccessControlContext</code>.  The action is performed with the
     * intersection of the the permissions possessed by the caller's
     * protection domain, and those possessed by the domains represented by the
     * specified <code>AccessControlContext</code>.
     * <p>
     * If the action's <code>run</code> method throws an <i>unchecked</i>
     * exception, it will propagate through this 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</code>,
     *                then no additional restriction is applied.
     *
     * @return the value returned by the action's <code>run</code> method
     *
     * @exception PrivilegedActionException if the specified action's
     *         <code>run</code> method
     *         threw a <i>checked</i> exception
     * @exception NullPointerException if the action is <code>null</code>
     *
     * @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
    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));
    }

    
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 a suitable AccessControlException otherwise.

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 a suitable AccessControlException otherwise.
     *
     * @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</code> 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);
    }
}