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Java Fundamental Classes Reference

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SecurityManager

Name

SecurityManager

Synopsis

Class Name:

java.lang.SecurityManager

Superclass:

java.lang.Object

Immediate Subclasses:

None

Interfaces Implemented:

None

Availability:

JDK 1.0 or later

Description

The SecurityManager class provides a way of implementing a comprehensive security policy for a Java program. As of this writing, SecurityManager objects are used primarily by Web browsers to establish security policies for applets. However, the use of a SecurityManager object is appropriate in any situation where a hosting environment wants to limit the actions of hosted programs.

The SecurityManager class contains methods that are called by methods in other classes to ask for permission to do something that can affect the security of the system. These permission methods all have names that begin with check. If a check method does not permit an action, it throws a SecurityException or returns a value that indicates the lack of permission. The SecurityManager class provides default implementations of all of the check methods. These default implementations are the most restrictive possible implementations; they simply deny permission to do anything that can affect the security of the system.

The SecurityManager class is an abstract class. A hosting environment should define a subclass of SecurityManager that implements an appropriate security policy. To give the subclass of SecurityManager control over security, the hosting environment creates an instance of the class and installs it by passing it to the setSecurityManager() method of the System class. Once a SecurityManager object is installed, it cannot be changed. If the setSecurityManager() method is called any additional times, it throws a SecurityException.

The methods in other classes that want to ask the SecurityManager for permission to do something are able to access the SecurityManager object by calling the getSecurityManager() method of the System class. This method returns the SecurityManager object, or null to indicate that there is no SecurityManager installed.

Class Summary

public abstract class java.lang.SecurityManager extends java.lang.Object {
    // Constructors
    protected SecurityManager();
    // Variables
    protected boolean inCheck;
    // Instance Methods
    public void checkAccept(String host, int port);
    public void checkAccess(Thread t);
    public void checkAccess(ThreadGroup g);
    public void checkAwtEventQueueAccess();                  // New in 1.1
    public void checkConnect(String host, int port);
    public void checkConnect(String host, int port, Object context);
    public void checkCreateClassLoader();
    public void checkDelete(String file);
    public void checkExec(String cmd);
    public void checkExit(int status);
    public void checkLink(String libname);
    public void checkListen(int port);
    public void checkMemberAccess(Class clazz, int which);   // New in 1.1
    public void checkMulticast(InetAddress maddr);           // New in 1.1
    public void checkMulticast(InetAddress maddr, byte ttl); // New in 1.1
    public void checkPackageAccess();
    public void checkPackageDefinition();
    public void checkPrintJobAccess();                       // New in 1.1
    public void checkPropertiesAccess();
    public void checkPropertyAccess(String key);
    public void checkRead(int fd);
    public void checkRead(String file);
    public void checkRead(String file, Object context);
    public void checkSecurityAccess(String action);          // New in 1.1
    public void checkSetFactory();
    public void checkSystemClipboardAccess();                // New in 1.1
    public boolean checkTopLevelWindow();
    public void checkWrite(int fd);
    public void checkWrite(String file);
    public boolean getInCheck();
    public Object getSecurityContext();                     
    public ThreadGroup getThreadGroup();                     // New in 1.1
    // Protected Instance Methods
    protected int classDepth(String name);
    protected int classLoaderDepth();
    protected ClassLoader currentClassLoader();
    protected Class currentLoadedClass();                    // New in 1.1
    protected Class[] getClassContext();
    protected boolean inClass(String name);
    protected boolean inClassLoader();
}

Variables

inCheck

protected boolean inCheck = false

Description

This variable indicates whether or not a security check is in progress. A subclass of SecurityManager should set this variable to true while a security check is in progress.

This variable can be useful for security checks that require access to resources that a hosted program may not be permitted to access. For example, a security policy might be based on the contents of a permissions file. This means that the various check methods need to read information from a file to decide what to do. Even though a hosted program may not be allowed to read files, the check methods can allow such reads when inCheck is true to support this style of security policy.

Constructors

SecurityManager

protected SecurityManager()

Throws

SecurityException

If a SecurityManager object already exists. In other words, if System.getSecurityManager() returns a value other than null.

Description

Creates a new SecurityManager object. This constructor cannot be called if there is already a current SecurityManager installed for the program.

Public Instance Methods

checkAccept

public void checkAccept(String host, int port)

Parameters

host

The name of the host machine.

port

A port number.

Throws

SecurityException

If the caller does not have permission to accept the connection.

Description

This method decides whether or not to allow a connection from the given host on the given port to be accepted. An implementation of the method should throw a SecurityException to deny permission to accept the connection. The method is called by the accept() method of the java.net.ServerSocket class.

The checkAccept() method of SecurityManager always throws a SecurityException.

checkAccess

public void checkAccess(Thread g)

Parameters

g

A reference to a Thread object.

Throws

SecurityException

If the current thread does not have permission to modify the specified thread.

Description

This method decides whether or not to allow the current thread to modify the specified Thread. An implementation of the method should throw a SecurityException to deny permission to modify the thread. Methods of the Thread class that call this method include stop(), suspend(), resume(), setPriority(), setName(), and setDaemon().

The checkAccess() method of SecurityManager always throws a SecurityException.

public void checkAccess(ThreadGroup g)

Parameters

g

A reference to a ThreadGroup object.

Throws

SecurityException

If the current thread does not have permission to modify the specified thread group.

Description

This method decides whether or not to allow the current thread to modify the specified ThreadGroup. An implementation of the method should throw a SecurityException to deny permission to modify the thread group. Methods of the ThreadGroup class that call this method include setDaemon(), setMaxPriority(), stop(), suspend(), resume(), and destroy().

The checkAccess() method of SecurityManager always throws a SecurityException.

checkAwtEventQueueAccess

public void checkAwtEventQueueAccess()

Availability

New as of JDK 1.1

Throws

SecurityException

If the caller does not have permission to access the AWT event queue.

Description

This method decides whether or not to allow access to the AWT event queue. An implementation of the method should throw a SecurityException to deny permission to access the event queue. The method is called by the getSystemEventQueue() method of the java.awt.Toolkit class.

The checkAwtEventQueueAccess() method of SecurityManager always throws a SecurityException.

checkConnect

public void checkConnect(String host, int port)

Parameters

host

The name of the host.

port

A port number. A value of -1 indicates an attempt to determine the IP address of given hostname.

Throws

SecurityException

If the caller does not have permission to open the socket connection.

Description

This method decides whether or not to allow a socket connection to the given host on the given port to be opened. An implementation of the method should throw a SecurityException to deny permission to open the connection. The method is called by the constructors of the java.net.Socket class, the send() and receive() methods of the java.net.DatagramSocket class, and the getByName() and getAllByName() methods of the java.net.InetAddress class.

The checkConnect() method of SecurityManager always throws a SecurityException.

 public void checkConnect(String host, int port, Object context) 

Parameters

host

The name of the host.

port

A port number. A value of -1 indicates an attempt to determine the IP address of given host name.

context

A security context object returned by this object's getSecurityContext() method.

Throws

SecurityException

If the specified security context does not have permission to open the socket connection.

Description

This method decides whether or not to allow a socket connection to the given host on the given port to be opened for the specified security context. An implementation of the method should throw a SecurityException to deny permission to open the connection.

The checkConnect() method of SecurityManager always throws a SecurityException.

checkCreateClassLoader

public void checkCreateClassLoader()

Throws

SecurityException

If the caller does not have permission to create a ClassLoader object.

Description

This method decides whether or not to allow a ClassLoader object to be created. An implementation of the method should throw a SecurityException to deny permission to create a ClassLoader. The method is called by the constructor of the ClassLoader class.

The checkCreateClassLoader() method of SecurityManager always throws a SecurityException.

checkDelete

public void checkDelete(String file)

Parameters

file

The name of a file.

Throws

SecurityException

If the caller does not have permission to delete the specified file.

Description

This method decides whether or not to allow a file to be deleted. An implementation of the method should throw a SecurityException to deny permission to delete the specified file. The method is called by the delete() method of the java.io.File class.

The checkDelete() method of SecurityManager always throws a SecurityException.

checkExec

public void checkExec(String cmd)

Parameters

cmd

The name of an external command.

Throws

SecurityException

If the caller does not have permission to execute the specified command.

Description

This method decides whether or not to allow an external command to be executed. An implementation of the method should throw a SecurityException to deny permission to execute the specified command. The method is called by the exec() methods of the Runtime and System classes.

The checkExec() method of SecurityManager always throws a SecurityException.

checkExit

public void checkExit(int status)

Parameters

status

An exit status code.

Throws

SecurityException

If the caller does not have permission to exit the Java virtual machine with the given status code.

Description

This method decides whether or not to allow the Java virtual machine to exit with the given status code. An implementation of the method should throw a SecurityException to deny permission to exit with the specified status code. The method is called by the exit() methods of the Runtime and System classes.

The checkExit() method of SecurityManager always throws a SecurityException.

checkLink

public void checkLink(String lib)

Parameters

lib

The name of a library.

Throws

SecurityException

If the caller does not have permission to load the specified library.

Description

This method decides whether to allow the specified library to be loaded. An implementation of the method should throw a SecurityException to deny permission to load the specified library. The method is called by the load() and loadLibrary() methods of the Runtime and System classes.

The checkLink() method of SecurityManager always throws a SecurityException.

checkListen

public void checkListen(int port)

Parameters

port

A port number.

Throws

SecurityException

If the caller does not have permission to listen on the specified port.

Description

This method decides whether or not to allow the caller to listen on the specified port. An implementation of the method should throw a SecurityException to deny permission to listen on the specified port. The method is called by the constructors of the java.net.ServerSocket class and by the constructor of the java.net.DatagramSocket class that takes one argument.

The checkListen() method of SecurityManager always throws a SecurityException.

checkMemberAccess

public void checkMemberAccess(Class clazz, int which)

Availability

New as of JDK 1.1

Parameters

clazz

A Class object.

which

The value Member.PUBLIC for the set of all public members including inherited members or the value Member.DECLARED for the set of all declared members of the specified class or interface.

Throws

SecurityException

If the caller does not have permission to access the members of the specified class or interface.

Description

This method decides whether or not to allow access to the members of the specified Class object. An implementation of the method should throw a SecurityException to deny permission to access the members. Methods of the Class class that call this method include getField(), getFields(), getDeclaredField(), getDeclaredFields(), getMethod(), getMethods(), getDeclaredMethod(), getDeclaredMethods(), getConstructor(), getConstructors(), getDeclaredConstructor(), getDeclaredConstructors(), and getDeclaredClasses().

The checkMemberAccess() method of SecurityManager always throws a SecurityException.

checkMulticast

public void checkMulticast(InetAddress maddr)

Availability

New as of JDK 1.1

Parameters

maddr

An InetAddress object that represents a multicast address.

Throws

SecurityException

If the current thread does not have permission to use the specified multicast address.

Description

This method decides whether or not to allow the current thread to use the specified multicast InetAddress. An implementation of the method should throw a SecurityException to deny permission to use the multicast address. The method is called by the send() method of java.net.DatagramSocket if the packet is being sent to a multicast address. The method is also called by the joinGroup() and leaveGroup() methods of java.net.MulticastSocket.

The checkMulticast() method of SecurityManager always throws a SecurityException.

public void checkMulticast(InetAddress maddr, byte ttl)

Availability

New as of JDK 1.1

Parameters

maddr

An InetAddress object that represents a multicast address.

ttl

The time-to-live (TTL) value.

Throws

SecurityException

If the current thread does not have permission to use the specified multicast address and TTL value.

Description

This method decides whether or not to allow the current thread to use the specified multicast InetAddress and TTL value. An implementation of the method should throw a SecurityException to deny permission to use the multicast address. The method is called by the send() method of java.net.MulticastSocket.

The checkMulticast() method of SecurityManager always throws a SecurityException.

checkPackageAccess

public void checkPackageAccess(String pkg)

Parameters

pkg

The name of a package.

Throws

SecurityException

If the caller does not have permission to access the specified package.

Description

This method decides whether or not to allow the specified package to be accessed. An implementation of the method should throw a SecurityException to deny permission to access the specified package. The method is intended to be called by implementations of the loadClass() method in subclasses of the ClassLoader class.

The checkPackageAccess() method of SecurityManager always throws a SecurityException.

checkPackageDefinition

public void checkPackageDefinition(String pkg)

Parameters

pkg

The name of a package.

Throws

SecurityException

If the caller does not have permission to define classes in the specified package.

Description

This method decides whether or not to allow the caller to define classes in the specified package. An implementation of the method should throw a SecurityException to deny permission to create classes in the specified package. The method is intended to be called by implementations of the loadClass() method in subclasses of the ClassLoader class.

The checkPackageDefinition() method of SecurityManager always throws a SecurityException.

checkPrintJobAccess

public void checkPrintJobAccess()

Availability

New as of JDK 1.1

Throws

SecurityException

If the caller does not have permission to initiate a print job request.

Description

This method decides whether or not to allow the caller to initiate a print job request. An implementation of the method should throw a SecurityException to deny permission to initiate the request.

The checkPrintJobAccess() method of SecurityManager always throws a SecurityException.

checkPropertiesAccess

public void checkPropertiesAccess()

Throws

SecurityException

If the caller does not have permission to access the system properties.

Description

This method decides whether or not to allow the caller to access and modify the system properties. An implementation of the method should throw a SecurityException to deny permission to access and modify the properties. Methods of the System class that call this method include getProperties() and setProperties().

The checkPropertiesAccess() method of SecurityManager always throws a SecurityException.

checkPropertyAccess

public void checkPropertyAccess(String key)

Parameters

key

The name of an individual system property.

Throws

SecurityException

If the caller does not have permission to access the specified system property.

Description

This method decides whether or not to allow the caller to access the specified system property. An implementation of the method should throw a SecurityException to deny permission to access the property. The method is called by the getProperty() method of the System class.

The checkPropertyAccess() method of SecurityManager always throws a SecurityException.

checkRead

public void checkRead(FileDescriptor fd)

Parameters

fd

A reference to a FileDescriptor object.

Throws

SecurityException

If the caller does not have permission to read from the given file descriptor.

Description

This method decides whether or not to allow the caller to read from the specified file descriptor. An implementation of the method should throw a SecurityException to deny permission to read from the file descriptor. The method is called by the constructor of the java.io.FileInputStream class that takes a FileDescriptor argument.

The checkRead() method of SecurityManager always throws a SecurityException.

public void checkRead(String file)

Parameters

file

The name of a file.

Throws

SecurityException

If the caller does not have permission to read from the named file.

Description

This method decides whether or not to allow the caller to read from the named file. An implementation of the method should throw a SecurityException to deny permission to read from the file. The method is called by constructors of the java.io.FileInputStream and java.io.RandomAccessFile classes, as well as by the canRead(), exists(), isDirectory(), isFile(), lastModified(), length(), and list() methods of the java.io.File class.

The checkRead() method of SecurityManager always throws a SecurityException.

public void checkRead(String file, Object context)

Parameters

file

The name of a file.

context

A security context object returned by this object's getSecurityContext() method.

Throws

SecurityException

If the specified security context does not have permission to read from the named file.

Description

This method decides whether or not to allow the specified security context to read from the named file. An implementation of the method should throw a SecurityException to deny permission to read from the file.

The checkRead() method of SecurityManager always throws a SecurityException.

checkSecurityAccess

public void checkSecurityAccess(String action)

Availability

New as of JDK 1.1

Parameters

action

A string that specifies a security action.

Throws

SecurityException

If the caller does not have permission to perform the specified security action.

Description

This method decides whether to allow the caller to perform the specified security action. An implementation of the method should throw a SecurityException to deny permission to perform the action. The method is called by many of the methods in the java.security.Identity and java.security.Security classes.

The checkSecurityAccess() method of SecurityManager always throws a SecurityException.

checkSetFactory

public void checkSetFactory()

Throws

SecurityException

If the caller does not have permission to set the factory class to be used by another class.

Description

This method decides whether to allow the caller to set the factory class to be used by another class. An implementation of the method should throw a SecurityException to deny permission to set the factory class. The method is called by the setSocketFactory() method of the java.net.ServerSocket class, the setSocketImplFactory() method of the java.net.Socket class, the setURLStreamHandlerFactory() method of the java.net.URL class, and the setContentHandlerFactory() method of the java.net.URLConnection class.

The checkSetFactory() method of SecurityManager always throws a SecurityException.

checkSystemClipboardAccess

public void checkSystemClipboardAccess()

Availability

New as of JDK 1.1

Throws

SecurityException

If the caller does not have permission to access the system clipboard.

Description

This method decides whether or not to allow the caller to access the system clipboard. An implementation of the method should throw a SecurityException to deny permission to access the system clipboard.

The checkSystemClipboardAccess() method of SecurityManager always throws a SecurityException.

checkTopLevelWindow

public boolean checkTopLevelWindow(Object window)

Parameters

window

A window object.

Returns

true if the caller is trusted to put up the specified top-level window; otherwise false.

Description

This method decides whether or not to trust the caller to put up the specified top-level window. An implementation of the method should return false to indicate that the caller is not trusted. In this case, the hosting environment can still decide to display the window, but the window should include a visual indication that it is not trusted. If the caller is trusted, the method should return true, and the window can be displayed without any special indication.

The checkTopLevelWindow() method of SecurityManager always returns false.

checkWrite

public void checkWrite(FileDescriptor fd)

Parameters

fd

A FileDescriptor object.

Throws

SecurityException

If the caller does not have permission to write to the given file descriptor.

Description

This method decides whether or not to allow the caller to write to the specified file descriptor. An implementation of the method should throw a SecurityException to deny permission to write to the file descriptor. The method is called by the constructor of the java.io.FileOutputStream class that takes a FileDescriptor argument.

The checkWrite() method of SecurityManager always throws a SecurityException.

public void checkWrite(String file)

Parameters

file

The name of a file.

Throws

SecurityException

If the caller does not have permission to read from the named file.

Description

This method decides whether or not to allow the caller to write to the named file. An implementation of the method should throw a SecurityException to deny permission to write to the file. The method is called by constructors of the java.io.FileOutputStream and java.io.RandomAccessFile classes, as well as by the canWrite(), mkdir(), and renameTo() methods of the java.io.File class.

The checkWrite() method of SecurityManager always throws a SecurityException.

getInCheck

public boolean getInCheck()

Returns

true if a security check is in progress; otherwise false.

Description

This method returns the value of the SecurityManager object's inCheck variable, which is true if a security check is in progress and false otherwise.

getSecurityContext

public Object getSecurityContext()

Returns

An implementation-dependent object that contains enough information about the current execution environment to perform security checks at a later time.

Description

This method is meant to create an object that encapsulates information about the current execution environment. The resulting security context object is used by specific versions of the checkConnect() and checkRead() methods. The intent is that such a security context object can be used by a trusted method to determine whether or not another, untrusted method can perform a particular operation.

The getSecurityContext() method of SecurityManager simply returns null. This method should be overridden to return an appropriate security context object for the security policy that is being implemented.

getThreadGroup

public ThreadGroup getThreadGroup()

Availability

New as of JDK 1.1

Returns

A ThreadGroup in which to place any threads that are created when this method is called.

Description

This method returns the appropriate parent ThreadGroup for any threads that are created when the method is called. The getThreadGroup() method of SecurityManager simply returns the ThreadGroup of the current thread. This method should be overridden to return an appropriate ThreadGroup.

Protected Instance Methods

classDepth

protected native int classDepth(String name)

Parameters

name

The fully qualified name of a class.

Returns

The number of pending method invocations from the top of the stack to a call to a method of the given class; -1 if no stack frame in the current thread is associated with a call to a method in the given class.

Description

This method returns the number of pending method invocations between this method invocation and an invocation of a method associated with the named class.

classLoaderDepth

protected native int classLoaderDepth()

Returns

The number of pending method invocations from the top of the stack to a call to a method that is associated with a class that was loaded by a ClassLoader object; -1 if no stack frame in the current thread is associated with a call to such a method.

Description

This method returns the number of pending method invocations between this method invocation and an invocation of a method associated with a class that was loaded by a ClassLoader object.

currentClassLoader

protected native ClassLoader currentClassLoader()

Returns

The most recent ClassLoader object executing on the stack.

Description

This method finds the most recent pending invocation of a method associated with a class that was loaded by a ClassLoader object. The method then returns the ClassLoader object that loaded that class.

currentLoadedClass

protected Class currentLoadedClass()

Availability

New as of JDK 1.1

Returns

The most recent Class object loaded by a ClassLoader.

Description

This method finds the most recent pending invocation of a method associated with a class that was loaded by a ClassLoader object. The method then returns the Class object for that class.

getClassContext

protected native Class[] getClassContext()

Returns

An array of Class objects that represents the current execution stack.

Description

This method returns an array of Class objects that represents the current execution stack. The length of the array is the number of pending method calls on the current thread's stack, not including the call to getClassContext(). Each element of the array references a Class object that describes the class associated with the corresponding method call. The first element of the array corresponds to the most recently called method, the second element is that method's caller, and so on.

inClass

protected boolean inClass(String name)

Parameters

name

The fully qualified name of a class.

Returns

true if there is a pending method invocation on the stack for a method of the given class; otherwise false.

Description

This method determines whether or not there is a pending method invocation that is associated with the named class.

inClassLoader

protected boolean inClassLoader()

Returns

true if there is a pending method invocation on the stack for a method of a class that was loaded by a ClassLoader object; otherwise false.

Description

This method determines whether or not there is a pending method invocation that is associated with a class that was loaded by a ClassLoader object. The method returns true only if the currentClassLoader() method does not return null.

Inherited Methods

Method

Inherited From

Method

Inherited From

clone()

Object

equals(Object)

Object

finalize()

Object

getClass()

Object

hashCode()

Object

notify()

Object

notifyAll()

Object

toString()

Object

wait()

Object

wait(long)

Object

wait(long, int)

Object

   

See Also

Class, ClassLoader, DatagramSocket, File, FileDescriptor, FileInputStream, FileOutputStream, InetAddress, MulticastSocket, Object, RandomAccessFile, Runtime, SecurityException, ServerSocket, Socket, System, Thread, ThreadGroup, Toolkit, URL, URLConnection


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