Module java.base
Package java.lang

Class SecurityManager

java.lang.Object
java.lang.SecurityManager
Direct Known Subclasses:
RMISecurityManager
@Deprecated(since="17",forRemoval=true)public classSecurityManagerextendsObject
Deprecated, for removal: This API element is subject to removal in a future version.
The Security Manager is deprecated and subject to removal in a future release. There is no replacement for the Security Manager. SeeJEP 411 for discussion and alternatives.
The security manager is a class that allows applications to implement a security policy. It allows an application to determine, before performing a possibly unsafe or sensitive operation, what the operation is and whether it is being attempted in a security context that allows the operation to be performed. The application can allow or disallow the operation.

TheSecurityManager class contains many methods with names that begin with the wordcheck. These methods are called by various methods in the Java libraries before those methods perform certain potentially sensitive operations. The invocation of such acheck method typically looks like this:

     SecurityManager security = System.getSecurityManager();     if (security != null) {         security.checkXXX(argument,  . . . );     }

The security manager is thereby given an opportunity to prevent completion of the operation by throwing an exception. A security manager routine simply returns if the operation is permitted, but throws aSecurityException if the operation is not permitted.

Setting a Security Manager

Environments using a security manager will typically set the security manager at startup. In the JDK implementation, this is done by setting the system propertyjava.security.manager on the command line to the class name of the security manager. It can also be set to the empty String ("") or the special token "default" to use the defaultjava.lang.SecurityManager. If a class name is specified, it must bejava.lang.SecurityManager or a public subclass and have a public no-arg constructor. The class is loaded by thebuilt-in system class loader if it is notjava.lang.SecurityManager. If thejava.security.manager system property is not set, the default value isnull, which means a security manager will not be set at startup.

The Java run-time may also allow, but is not required to allow, the security manager to be set dynamically by invoking thesetSecurityManager method. In the JDK implementation, if the Java virtual machine is started with thejava.security.manager system property set to the special token "allow", then a security manager will not be set at startup but can be set dynamically. If the Java virtual machine is started with thejava.security.manager system property not set or set to the special token "disallow", then a security manager will not be set at startup and cannot be set dynamically (thesetSecurityManager method will throw anUnsupportedOperationException). Finally, if thejava.security.manager system property is set to the class name of the security manager, or to the empty String ("") or the special token "default", then a security manager is set at startup (as described previously) and can also be subsequently replaced (or disabled) dynamically (subject to the policy of the currently installed security manager). The following table illustrates the behavior of the JDK implementation for the different settings of thejava.security.manager system property:

property value, the SecurityManager set at startup, can dynamically set a SecurityManager
Property ValueThe SecurityManager set at startupSystem.setSecurityManager run-time behavior
nullNoneThrowsUnsupportedOperationException
empty String ("")java.lang.SecurityManagerSuccess or throwsSecurityException if not permitted by the currently installed security manager
"default"java.lang.SecurityManagerSuccess or throwsSecurityException if not permitted by the currently installed security manager
"disallow"NoneThrowsUnsupportedOperationException
"allow"NoneSuccess or throwsSecurityException if not permitted by the currently installed security manager
a class namethe named classSuccess or throwsSecurityException if not permitted by the currently installed security manager

The current security manager is returned by thegetSecurityManager method.

Checking Permissions

The special methodcheckPermission(java.security.Permission) determines whether an access request indicated by a specified permission should be granted or denied. The default implementation calls
   AccessController.checkPermission(perm);

If a requested access is allowed,checkPermission returns quietly. If denied, aSecurityException is thrown.

The default implementation of each of the othercheck methods inSecurityManager is to call theSecurityManager checkPermission method to determine if the calling thread has permission to perform the requested operation.

Note that thecheckPermission method with just a single permission argument always performs security checks within the context of the currently executing thread. Sometimes a security check that should be made within a given context will actually need to be done from within adifferent context (for example, from within a worker thread). ThegetSecurityContext method and thecheckPermission method that includes a context argument are provided for this situation. ThegetSecurityContext method returns a "snapshot" of the current calling context. (The default implementation returns an AccessControlContext object.) A sample call is the following:

   Object context = null;   SecurityManager sm = System.getSecurityManager();   if (sm != null) context = sm.getSecurityContext();

ThecheckPermission method that takes a context object in addition to a permission makes access decisions based on that context, rather than on that of the current execution thread. Code within a different context can thus call that method, passing the permission and the previously-saved context object. A sample call, using the SecurityManagersm obtained as in the previous example, is the following:

   if (sm != null) sm.checkPermission(permission, context);

Permissions fall into these categories: File, Socket, Net, Security, Runtime, Property, AWT, Reflect, and Serializable. The classes managing these various permission categories arejava.io.FilePermission,java.net.SocketPermission,java.net.NetPermission,java.security.SecurityPermission,java.lang.RuntimePermission,java.util.PropertyPermission,java.awt.AWTPermission,java.lang.reflect.ReflectPermission, andjava.io.SerializablePermission.

All but the first two (FilePermission and SocketPermission) are subclasses ofjava.security.BasicPermission, which itself is an abstract subclass of the top-level class for permissions, which isjava.security.Permission. BasicPermission defines the functionality needed for all permissions that contain a name that follows the hierarchical property naming convention (for example, "exitVM", "setFactory", "queuePrintJob", etc). An asterisk may appear at the end of the name, following a ".", or by itself, to signify a wildcard match. For example: "a.*" or "*" is valid, "*a" or "a*b" is not valid.

FilePermission and SocketPermission are subclasses of the top-level class for permissions (java.security.Permission). Classes like these that have a more complicated name syntax than that used by BasicPermission subclass directly from Permission rather than from BasicPermission. For example, for ajava.io.FilePermission object, the permission name is the path name of a file (or directory).

Some of the permission classes have an "actions" list that tells the actions that are permitted for the object. For example, for ajava.io.FilePermission object, the actions list (such as "read, write") specifies which actions are granted for the specified file (or for files in the specified directory).

Other permission classes are for "named" permissions - ones that contain a name but no actions list; you either have the named permission or you don't.

Note: There is also ajava.security.AllPermission permission that implies all permissions. It exists to simplify the work of system administrators who might need to perform multiple tasks that require all (or numerous) permissions.

SeePermissions in the Java Development Kit (JDK) for permission-related information. This document includes a table listing the various SecurityManagercheck methods and the permission(s) the default implementation of each such method requires. It also contains a table of the methods that require permissions, and for each such method tells which permission it requires.

Since:
1.0
See Also: