Class AccessController
- java.lang.Object
-
- java.security.AccessController
public final class AccessController extends Object
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.
- Since:
- 1.2
- See Also:
AccessControlContext
Method Summary
Modifier and Type | Method | Description |
---|---|---|
static void | checkPermission(Permission perm) | Determines whether the access request indicated by the specified permission should be allowed or denied, based on the current AccessControlContext and security policy. |
static <T> T | doPrivileged(PrivilegedAction<T> action) | Performs the specified |
static <T> T | doPrivileged(PrivilegedAction<T> action,
AccessControlContext context) | Performs the specified |
static <T> T | doPrivileged(PrivilegedAction<T> action,
AccessControlContext context,
Permission... perms) | Performs the specified |
static <T> T | doPrivileged(PrivilegedExceptionAction<T> action) | Performs the specified |
static <T> T | doPrivileged(PrivilegedExceptionAction<T> action,
AccessControlContext context) | Performs the specified |
static <T> T | doPrivileged(PrivilegedExceptionAction<T> action,
AccessControlContext context,
Permission... perms) | Performs the specified |
static <T> T | doPrivilegedWithCombiner(PrivilegedAction<T> action) | Performs the specified |
static <T> T | doPrivilegedWithCombiner(PrivilegedAction<T> action,
AccessControlContext context,
Permission... perms) | Performs the specified |
static <T> T | doPrivilegedWithCombiner(PrivilegedExceptionAction<T> action) | Performs the specified |
static <T> T | doPrivilegedWithCombiner(PrivilegedExceptionAction<T> action,
AccessControlContext context,
Permission... perms) | Performs the specified |
static AccessControlContext | getContext() | 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. |
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Method Detail
doPrivileged
public static <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.
Note that any DomainCombiner associated with the current AccessControlContext will be ignored while the action is performed.
- Type Parameters:
-
T
- the type of the value returned by the PrivilegedAction'srun
method. - Parameters:
-
action
- the action to be performed. - Returns:
- the value returned by the action's
run
method. - Throws:
-
NullPointerException
- if the action isnull
- See Also:
-
doPrivileged(PrivilegedAction,AccessControlContext)
,doPrivileged(PrivilegedExceptionAction)
,doPrivilegedWithCombiner(PrivilegedAction)
,DomainCombiner
doPrivilegedWithCombiner
public static <T> T doPrivilegedWithCombiner(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.
- Type Parameters:
-
T
- the type of the value returned by the PrivilegedAction'srun
method. - Parameters:
-
action
- the action to be performed. - Returns:
- the value returned by the action's
run
method. - Throws:
-
NullPointerException
- if the action isnull
- Since:
- 1.6
- See Also:
-
doPrivileged(PrivilegedAction)
,DomainCombiner
doPrivileged
public static <T> T doPrivileged(PrivilegedAction<T> action, AccessControlContext context)
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.
- Type Parameters:
-
T
- the type of the value returned by the PrivilegedAction'srun
method. - Parameters:
-
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 isnull
, then no additional restriction is applied. - Returns:
- the value returned by the action's
run
method. - Throws:
-
NullPointerException
- if the action isnull
- See Also:
-
doPrivileged(PrivilegedAction)
,doPrivileged(PrivilegedExceptionAction,AccessControlContext)
doPrivileged
public static <T> T doPrivileged(PrivilegedAction<T> action, AccessControlContext context, Permission... 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.
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.
- Type Parameters:
-
T
- the type of the value returned by the PrivilegedAction'srun
method. - Parameters:
-
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 isnull
, then no additional restriction is applied. -
perms
- thePermission
arguments which limit the scope of the caller's privileges. The number of arguments is variable. - Returns:
- the value returned by the action's
run
method. - Throws:
-
NullPointerException
- if action or perms or any element of perms isnull
- Since:
- 1.8
- See Also:
-
doPrivileged(PrivilegedAction)
,doPrivileged(PrivilegedExceptionAction,AccessControlContext)
doPrivilegedWithCombiner
public static <T> T doPrivilegedWithCombiner(PrivilegedAction<T> action, AccessControlContext context, Permission... 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.
- Type Parameters:
-
T
- the type of the value returned by the PrivilegedAction'srun
method. - Parameters:
-
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 isnull
, then no additional restriction is applied. -
perms
- thePermission
arguments which limit the scope of the caller's privileges. The number of arguments is variable. - Returns:
- the value returned by the action's
run
method. - Throws:
-
NullPointerException
- if action or perms or any element of perms isnull
- Since:
- 1.8
- See Also:
-
doPrivileged(PrivilegedAction)
,doPrivileged(PrivilegedExceptionAction,AccessControlContext)
,DomainCombiner
doPrivileged
public static <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.
Note that any DomainCombiner associated with the current AccessControlContext will be ignored while the action is performed.
- Type Parameters:
-
T
- the type of the value returned by the PrivilegedExceptionAction'srun
method. - Parameters:
-
action
- the action to be performed - Returns:
- the value returned by the action's
run
method - Throws:
-
PrivilegedActionException
- if the specified action'srun
method threw a checked exception -
NullPointerException
- if the action isnull
- See Also:
-
doPrivileged(PrivilegedAction)
,doPrivileged(PrivilegedExceptionAction,AccessControlContext)
,doPrivilegedWithCombiner(PrivilegedExceptionAction)
,DomainCombiner
doPrivilegedWithCombiner
public static <T> T doPrivilegedWithCombiner(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.
- Type Parameters:
-
T
- the type of the value returned by the PrivilegedExceptionAction'srun
method. - Parameters:
-
action
- the action to be performed. - Returns:
- the value returned by the action's
run
method - Throws:
-
PrivilegedActionException
- if the specified action'srun
method threw a checked exception -
NullPointerException
- if the action isnull
- Since:
- 1.6
- See Also:
-
doPrivileged(PrivilegedAction)
,doPrivileged(PrivilegedExceptionAction,AccessControlContext)
,DomainCombiner
doPrivileged
public static <T> T doPrivileged(PrivilegedExceptionAction<T> action, AccessControlContext context) throws PrivilegedActionException
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.
- Type Parameters:
-
T
- the type of the value returned by the PrivilegedExceptionAction'srun
method. - Parameters:
-
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 isnull
, then no additional restriction is applied. - Returns:
- the value returned by the action's
run
method - Throws:
-
PrivilegedActionException
- if the specified action'srun
method threw a checked exception -
NullPointerException
- if the action isnull
- See Also:
-
doPrivileged(PrivilegedAction)
,doPrivileged(PrivilegedAction,AccessControlContext)
doPrivileged
public static <T> T doPrivileged(PrivilegedExceptionAction<T> action, AccessControlContext context, Permission... perms) 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.
- Type Parameters:
-
T
- the type of the value returned by the PrivilegedExceptionAction'srun
method. - Parameters:
-
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 isnull
, then no additional restriction is applied. -
perms
- thePermission
arguments which limit the scope of the caller's privileges. The number of arguments is variable. - Returns:
- the value returned by the action's
run
method. - Throws:
-
PrivilegedActionException
- if the specified action'srun
method threw a checked exception -
NullPointerException
- if action or perms or any element of perms isnull
- Since:
- 1.8
- See Also:
-
doPrivileged(PrivilegedAction)
,doPrivileged(PrivilegedAction,AccessControlContext)
doPrivilegedWithCombiner
public static <T> T doPrivilegedWithCombiner(PrivilegedExceptionAction<T> action, AccessControlContext context, Permission... perms) 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.
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.
- Type Parameters:
-
T
- the type of the value returned by the PrivilegedExceptionAction'srun
method. - Parameters:
-
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 isnull
, then no additional restriction is applied. -
perms
- thePermission
arguments which limit the scope of the caller's privileges. The number of arguments is variable. - Returns:
- the value returned by the action's
run
method. - Throws:
-
PrivilegedActionException
- if the specified action'srun
method threw a checked exception -
NullPointerException
- if action or perms or any element of perms isnull
- Since:
- 1.8
- See Also:
-
doPrivileged(PrivilegedAction)
,doPrivileged(PrivilegedAction,AccessControlContext)
,DomainCombiner
getContext
public static AccessControlContext getContext()
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.
- Returns:
- the AccessControlContext based on the current context.
- See Also:
AccessControlContext
checkPermission
public static void checkPermission(Permission perm) throws AccessControlException
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.
- Parameters:
-
perm
- the requested permission. - Throws:
-
AccessControlException
- if the specified permission is not permitted, based on the current security policy. -
NullPointerException
- if the specified permission isnull
and is checked based on the security policy currently in effect.