Subject

AI-generated Key Takeaways

• The javax.security.auth.Subject class in Java represents a single entity, like a user or service, and their associated security information, including principals (identities) and credentials.

• Subject objects can be set to read-only to prevent modification of their principals and credentials, except for credential destruction.

• Various methods are provided to access and manage principals and credentials, with some requiring specific permissions for security reasons.

• Two Subject instances are considered equal if they have the same principals and public credentials.

• Methods like doAs() and doAsPrivileged() allow code execution with the subject's permissions and privileges.

public final class Subject extends Object
implements Serializable

A Subject represents a grouping of related information for a single entity, such as a person. Such information includes the Subject's identities as well as its security-related attributes (passwords and cryptographic keys, for example).

Subjects may potentially have multiple identities. Each identity is represented as a Principal within the Subject. Principals simply bind names to a Subject. For example, a Subject that happens to be a person, Alice, might have two Principals: one which binds "Alice Bar", the name on her driver license, to the Subject, and another which binds, "999-99-9999", the number on her student identification card, to the Subject. Both Principals refer to the same Subject even though each has a different name.

A Subject may also own security-related attributes, which are referred to as credentials. Sensitive credentials that require special protection, such as private cryptographic keys, are stored within a private credential Set. Credentials intended to be shared, such as public key certificates or Kerberos server tickets are stored within a public credential Set. Different permissions are required to access and modify the different credential Sets.

To retrieve all the Principals associated with a Subject, invoke the getPrincipals method. To retrieve all the public or private credentials belonging to a Subject, invoke the getPublicCredentials method or getPrivateCredentials method, respectively. To modify the returned Set of Principals and credentials, use the methods defined in the Set class. For example:

      Subject subject;
      Principal principal;
      Object credential;

      // add a Principal and credential to the Subject
      subject.getPrincipals().add(principal);
      subject.getPublicCredentials().add(credential);
 

This Subject class implements Serializable. While the Principals associated with the Subject are serialized, the credentials associated with the Subject are not. Note that the java.security.Principal class does not implement Serializable. Therefore all concrete Principal implementations associated with Subjects must implement Serializable.

See Also

• Principal
• DomainCombiner

Public Constructor Summary

	Subject() Create an instance of a Subject with an empty Set of Principals and empty Sets of public and private credentials.
	Subject(boolean readOnly, Set<? extends Principal> principals, Set<?> pubCredentials, Set<?> privCredentials) Create an instance of a Subject with Principals and credentials.

Public Method Summary

static <T> T	doAs(Subject subject, PrivilegedExceptionAction<T> action) Perform work as a particular Subject.
static <T> T	doAs(Subject subject, PrivilegedAction<T> action) Perform work as a particular Subject.
static <T> T	doAsPrivileged(Subject subject, PrivilegedExceptionAction<T> action, AccessControlContext acc) Perform privileged work as a particular Subject.
static <T> T	doAsPrivileged(Subject subject, PrivilegedAction<T> action, AccessControlContext acc) Perform privileged work as a particular Subject.
boolean	equals(Object o) Compares the specified Object with this Subject for equality.
Set<Principal>	getPrincipals() Return the Set of Principals associated with this Subject.
<T extends Principal> Set<T>	getPrincipals(Class<T> c) Return a Set of Principals associated with this Subject that are instances or subclasses of the specified Class.
<T> Set<T>	getPrivateCredentials(Class<T> c) Return a Set of private credentials associated with this Subject that are instances or subclasses of the specified Class.
Set<Object>	getPrivateCredentials() Return the Set of private credentials held by this Subject.
Set<Object>	getPublicCredentials() Return the Set of public credentials held by this Subject.
<T> Set<T>	getPublicCredentials(Class<T> c) Return a Set of public credentials associated with this Subject that are instances or subclasses of the specified Class.
static Subject	getSubject(AccessControlContext acc) Get the Subject associated with the provided AccessControlContext.
int	hashCode() Returns a hashcode for this Subject.
boolean	isReadOnly() Query whether this Subject is read-only.
void	setReadOnly() Set this Subject to be read-only.
String	toString() Return the String representation of this Subject.

Inherited Method Summary

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

Public Constructors

public Subject ()

Create an instance of a Subject with an empty Set of Principals and empty Sets of public and private credentials.

The newly constructed Sets check whether this Subject has been set read-only before permitting subsequent modifications. The newly created Sets also prevent illegal modifications by ensuring that callers have sufficient permissions.

To modify the Principals Set, the caller must have AuthPermission("modifyPrincipals"). To modify the public credential Set, the caller must have AuthPermission("modifyPublicCredentials"). To modify the private credential Set, the caller must have AuthPermission("modifyPrivateCredentials").

public Subject (boolean readOnly, Set<? extends Principal> principals, Set<?> pubCredentials, Set<?> privCredentials)

Create an instance of a Subject with Principals and credentials.

The Principals and credentials from the specified Sets are copied into newly constructed Sets. These newly created Sets check whether this Subject has been set read-only before permitting subsequent modifications. The newly created Sets also prevent illegal modifications by ensuring that callers have sufficient permissions.

To modify the Principals Set, the caller must have AuthPermission("modifyPrincipals"). To modify the public credential Set, the caller must have AuthPermission("modifyPublicCredentials"). To modify the private credential Set, the caller must have AuthPermission("modifyPrivateCredentials").

Parameters

readOnly	true if the Subject is to be read-only, and false otherwise.
principals	the Set of Principals to be associated with this Subject.
pubCredentials	the Set of public credentials to be associated with this Subject.
privCredentials	the Set of private credentials to be associated with this Subject.

Throws

NullPointerException	if the specified principals, pubCredentials, or privCredentials are null.

Public Methods

public static T doAs (Subject subject, PrivilegedExceptionAction<T> action)

Perform work as a particular Subject.

This method first retrieves the current Thread's AccessControlContext via AccessController.getContext, and then instantiates a new AccessControlContext using the retrieved context along with a new SubjectDomainCombiner (constructed using the provided Subject). Finally, this method invokes AccessController.doPrivileged, passing it the provided PrivilegedExceptionAction, as well as the newly constructed AccessControlContext.

Parameters

subject	the Subject that the specified action will run as. This parameter may be null.
action	the code to be run as the specified Subject.

Returns

• the value returned by the PrivilegedExceptionAction's run method.

Throws

PrivilegedActionException	if the PrivilegedExceptionAction.run method throws a checked exception.
NullPointerException	if the specified PrivilegedExceptionAction is null.
SecurityException	if the caller does not have permission to invoke this method.

public static T doAs (Subject subject, PrivilegedAction<T> action)

Perform work as a particular Subject.

This method first retrieves the current Thread's AccessControlContext via AccessController.getContext, and then instantiates a new AccessControlContext using the retrieved context along with a new SubjectDomainCombiner (constructed using the provided Subject). Finally, this method invokes AccessController.doPrivileged, passing it the provided PrivilegedAction, as well as the newly constructed AccessControlContext.

Parameters

subject	the Subject that the specified action will run as. This parameter may be null.
action	the code to be run as the specified Subject.

Returns

• the value returned by the PrivilegedAction's run method.

Throws

NullPointerException	if the PrivilegedAction is null.
SecurityException	if the caller does not have permission to invoke this method.

public static T doAsPrivileged (Subject subject, PrivilegedExceptionAction<T> action, AccessControlContext acc)

Perform privileged work as a particular Subject.

This method behaves exactly as Subject.doAs, except that instead of retrieving the current Thread's AccessControlContext, it uses the provided AccessControlContext. If the provided AccessControlContext is null, this method instantiates a new AccessControlContext with an empty collection of ProtectionDomains.

Parameters

subject	the Subject that the specified action will run as. This parameter may be null.
action	the code to be run as the specified Subject.
acc	the AccessControlContext to be tied to the specified subject and action.

Returns

• the value returned by the PrivilegedExceptionAction's run method.

Throws

PrivilegedActionException	if the PrivilegedExceptionAction.run method throws a checked exception.
NullPointerException	if the specified PrivilegedExceptionAction is null.
SecurityException	if the caller does not have permission to invoke this method.

public static T doAsPrivileged (Subject subject, PrivilegedAction<T> action, AccessControlContext acc)

Perform privileged work as a particular Subject.

This method behaves exactly as Subject.doAs, except that instead of retrieving the current Thread's AccessControlContext, it uses the provided AccessControlContext. If the provided AccessControlContext is null, this method instantiates a new AccessControlContext with an empty collection of ProtectionDomains.

Parameters

subject	the Subject that the specified action will run as. This parameter may be null.
action	the code to be run as the specified Subject.
acc	the AccessControlContext to be tied to the specified subject and action.

Returns

• the value returned by the PrivilegedAction's run method.

Throws

NullPointerException	if the PrivilegedAction is null.
SecurityException	if the caller does not have permission to invoke this method.

public boolean equals (Object o)

Compares the specified Object with this Subject for equality. Returns true if the given object is also a Subject and the two Subject instances are equivalent. More formally, two Subject instances are equal if their Principal and Credential Sets are equal.

Parameters

o	Object to be compared for equality with this Subject.

Returns

• true if the specified Object is equal to this Subject.

Throws

SecurityException	if the caller does not have permission to access the private credentials for this Subject, or if the caller does not have permission to access the private credentials for the provided Subject.

public Set<Principal> getPrincipals ()

Return the Set of Principals associated with this Subject. Each Principal represents an identity for this Subject.

The returned Set is backed by this Subject's internal Principal Set. Any modification to the returned Set affects the internal Principal Set as well.

Returns

• The Set of Principals associated with this Subject.

public Set<T> getPrincipals (Class<T> c)

Return a Set of Principals associated with this Subject that are instances or subclasses of the specified Class.

The returned Set is not backed by this Subject's internal Principal Set. A new Set is created and returned for each method invocation. Modifications to the returned Set will not affect the internal Principal Set.

Parameters

c	the returned Set of Principals will all be instances of this class.

Returns

• a Set of Principals that are instances of the specified Class.

Throws

NullPointerException	if the specified Class is null.

public Set<T> getPrivateCredentials (Class<T> c)

Return a Set of private credentials associated with this Subject that are instances or subclasses of the specified Class.

The caller must have permission to access all of the requested Credentials, or a SecurityException will be thrown.

The returned Set is not backed by this Subject's internal private Credential Set. A new Set is created and returned for each method invocation. Modifications to the returned Set will not affect the internal private Credential Set.

Parameters

c	the returned Set of private credentials will all be instances of this class.

Returns

• a Set of private credentials that are instances of the specified Class.

Throws

NullPointerException	if the specified Class is null.

public Set<Object> getPrivateCredentials ()

Return the Set of private credentials held by this Subject.

The returned Set is backed by this Subject's internal private Credential Set. Any modification to the returned Set affects the internal private Credential Set as well.

A caller requires permissions to access the Credentials in the returned Set, or to modify the Set itself. A SecurityException is thrown if the caller does not have the proper permissions.

While iterating through the Set, a SecurityException is thrown if the caller does not have permission to access a particular Credential. The Iterator is nevertheless advanced to next element in the Set.

Returns

• A Set of private credentials held by this Subject.

public Set<Object> getPublicCredentials ()

Return the Set of public credentials held by this Subject.

The returned Set is backed by this Subject's internal public Credential Set. Any modification to the returned Set affects the internal public Credential Set as well.

Returns

• A Set of public credentials held by this Subject.

public Set<T> getPublicCredentials (Class<T> c)

Return a Set of public credentials associated with this Subject that are instances or subclasses of the specified Class.

The returned Set is not backed by this Subject's internal public Credential Set. A new Set is created and returned for each method invocation. Modifications to the returned Set will not affect the internal public Credential Set.

Parameters

c	the returned Set of public credentials will all be instances of this class.

Returns

• a Set of public credentials that are instances of the specified Class.

Throws

NullPointerException	if the specified Class is null.

public static Subject getSubject (AccessControlContext acc)

Get the Subject associated with the provided AccessControlContext.

The AccessControlContext may contain many Subjects (from nested doAs calls). In this situation, the most recent Subject associated with the AccessControlContext is returned.

Parameters

acc	the AccessControlContext from which to retrieve the Subject.

Returns

• the Subject associated with the provided AccessControlContext, or null if no Subject is associated with the provided AccessControlContext.

Throws

SecurityException	if the caller does not have permission to get the Subject.
NullPointerException	if the provided AccessControlContext is null.

public int hashCode ()

Returns a hashcode for this Subject.

Returns

• a hashcode for this Subject.

Throws

SecurityException	if the caller does not have permission to access this Subject's private credentials.

public boolean isReadOnly ()

Query whether this Subject is read-only.

Returns

• true if this Subject is read-only, false otherwise.

public void setReadOnly ()

Set this Subject to be read-only.

Modifications (additions and removals) to this Subject's Principal Set and credential Sets will be disallowed. The destroy operation on this Subject's credentials will still be permitted.

Subsequent attempts to modify the Subject's Principal and credential Sets will result in an IllegalStateException being thrown. Also, once a Subject is read-only, it can not be reset to being writable again.

Throws

SecurityException	if the caller does not have permission to set this Subject to be read-only.

public String toString ()

Return the String representation of this Subject.

Returns

• the String representation of this Subject.