java.lang

Class SecurityManager

java.lang.Object

java.lang.SecurityManager

Direct Known Subclasses:

KernelSecurityManager, KernelSecurityPolicyManager

public class SecurityManager
extends Object

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.

The SecurityManager class contains many methods with names that begin with the word check. These methods are called by various methods in the Java libraries before those methods perform certain potentially sensitive operations. The invocation of such a check 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 a SecurityException if the operation is not permitted. The only exception to this convention is checkTopLevelWindow, which returns a boolean value.

The current security manager is set by the setSecurityManager method in class System. The current security manager is obtained by the getSecurityManager method.

The special method checkPermission(java.security.Permission) determines whether an access request indicated by a specified permission should be granted or denied.

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

As of Java 2 SDK v1.2, the default implementation of each of the other check methods in SecurityManager is to call the SecurityManager checkPermission method to determine if the calling thread has permission to perform the requested operation.

Note that the checkPermission method with just a single permission argument always performs security checks within the context of the currently executing thread.

Permissions fall into these categories: Runtime and Property. The classes managing these various permission categories are java.lang.RuntimePermission, java.util.PropertyPermission,

Some of the permission classes have an "actions" list that tells the actions that are permitted for the object.

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.

See Also:

SecurityException, getSecurityManager, setSecurityManager, Permission, BasicPermission

Constructor Summary

Constructors

Constructor and Description
SecurityManager() Constructs a new SecurityManager.

Method Summary

Modifier and Type	Method and Description
void	checkAccess(Thread t) Throws a SecurityException if the calling thread is not allowed to modify the thread argument.
void	checkPermission(Permission perm) Throws a SecurityException if the requested access, specified by the given permission, is not permitted based on the security policy currently in effect.

Methods inherited from class java.lang.Object

clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

SecurityManager

public SecurityManager()

Constructs a new SecurityManager.

If there is a security manager already installed, this method first calls the security manager's checkPermission method with the RuntimePermission("createSecurityManager") permission to ensure the calling thread has permission to create a new security manager. This may result in throwing a SecurityException.

Throws:

SecurityException - if a security manager already exists and its checkPermission method doesn't allow creation of a new security manager.

See Also:

System.getSecurityManager(), checkPermission, RuntimePermission

Method Detail

checkAccess

public void checkAccess(Thread t)

Throws a SecurityException if the calling thread is not allowed to modify the thread argument.

This method is invoked for the current security manager by the setPriority and setName methods of class Thread.

If the thread argument is a system thread then this method calls checkPermission with the RuntimePermission("modifyThread") permission. If the thread argument is not a system thread, this method just returns silently.

Applications that want a stricter policy should override this method. If this method is overridden, the method that overrides it should additionally check to see if the calling thread has the RuntimePermission("modifyThread") permission, and if so, return silently. This is to ensure that code granted that permission is allowed to manipulate any thread.

If this method is overridden, then super.checkAccess should be called by the first statement in the overridden method, or the equivalent security check should be placed in the overridden method.

Parameters:

t - the thread to be checked.

Throws:

SecurityException - if the calling thread does not have permission to modify the thread.

NullPointerException - if the thread argument is null.

See Also:

setName, setPriority, checkPermission

checkPermission

public void checkPermission(Permission perm)

Throws a SecurityException if the requested access, specified by the given permission, is not permitted based on the security policy currently in effect.

Parameters:

perm - the requested permission.

Throws:

SecurityException - if access is not permitted based on the current security policy.

NullPointerException - if the permission argument is null.