https://openjdk.java.net/ 
/*
 * Copyright (c) 1998, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * questions.
 */

package javax.security.auth;

import java.util.*;
import java.io.*;
import java.lang.reflect.*;
import java.text.MessageFormat;
import java.security.AccessController;
import java.security.AccessControlContext;
import java.security.DomainCombiner;
import java.security.Permission;
import java.security.PermissionCollection;
import java.security.Principal;
import java.security.PrivilegedAction;
import java.security.PrivilegedExceptionAction;
import java.security.PrivilegedActionException;
import java.security.ProtectionDomain;
import sun.security.util.ResourcesMgr;


 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:
/**
 * <p> A {@code 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).
 *
 * <p> Subjects may potentially have multiple identities.
 * Each identity is represented as a {@code Principal}
 * within the {@code Subject}.  Principals simply bind names to a
 * {@code Subject}.  For example, a {@code 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 {@code Subject}, and another which binds,
 * "999-99-9999", the number on her student identification card,
 * to the {@code Subject}.  Both Principals refer to the same
 * {@code Subject} even though each has a different name.
 *
 * <p> A {@code 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
 * {@code Set}.  Credentials intended to be shared, such as
 * public key certificates or Kerberos server tickets are stored
 * within a public credential {@code Set}.  Different permissions
 * are required to access and modify the different credential Sets.
 *
 * <p> To retrieve all the Principals associated with a {@code Subject},
 * invoke the {@code getPrincipals} method.  To retrieve
 * all the public or private credentials belonging to a {@code Subject},
 * invoke the {@code getPublicCredentials} method or
 * {@code getPrivateCredentials} method, respectively.
 * To modify the returned {@code Set} of Principals and credentials,
 * use the methods defined in the {@code Set} class.
 * For example:
 * <pre>
 *      Subject subject;
 *      Principal principal;
 *      Object credential;
 *
 *      // add a Principal and credential to the Subject
 *      subject.getPrincipals().add(principal);
 *      subject.getPublicCredentials().add(credential);
 * </pre>
 *
 * <p> This {@code Subject} class implements {@code Serializable}.
 * While the Principals associated with the {@code Subject} are serialized,
 * the credentials associated with the {@code Subject} are not.
 * Note that the {@code java.security.Principal} class
 * does not implement {@code Serializable}.  Therefore all concrete
 * {@code Principal} implementations associated with Subjects
 * must implement {@code Serializable}.
 *
 * @see java.security.Principal
 * @see java.security.DomainCombiner
 */
public final class Subject implements java.io.Serializable {

    private static final long serialVersionUID = -8308522755600156056L;

    
A Set that provides a view of all of this Subject's Principals 


@serialEach element in this set is a java.security.Principal. The set is a Subject.SecureSet.
/**
     * A {@code Set} that provides a view of all of this
     * Subject's Principals
     *
     * <p>
     *
     * @serial Each element in this set is a
     *          {@code java.security.Principal}.
     *          The set is a {@code Subject.SecureSet}.
     */
    Set<Principal> principals;

    
Sets that provide a view of all of this
Subject's Credentials

/**
     * Sets that provide a view of all of this
     * Subject's Credentials
     */
    transient Set<Object> pubCredentials;
    transient Set<Object> privCredentials;

    
Whether this Subject is read-only

@serial
/**
     * Whether this Subject is read-only
     *
     * @serial
     */
    private volatile boolean readOnly = false;

    private static final int PRINCIPAL_SET = 1;
    private static final int PUB_CREDENTIAL_SET = 2;
    private static final int PRIV_CREDENTIAL_SET = 3;

    private static final ProtectionDomain[] NULL_PD_ARRAY
        = new ProtectionDomain[0];

    
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"). 
/**
     * Create an instance of a {@code Subject}
     * with an empty {@code Set} of Principals and empty
     * Sets of public and private credentials.
     *
     * <p> The newly constructed Sets check whether this {@code 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.
     *
     * <p> To modify the Principals Set, the caller must have
     * {@code AuthPermission("modifyPrincipals")}.
     * To modify the public credential Set, the caller must have
     * {@code AuthPermission("modifyPublicCredentials")}.
     * To modify the private credential Set, the caller must have
     * {@code AuthPermission("modifyPrivateCredentials")}.
     */
    public Subject() {

        this.principals = Collections.synchronizedSet
                        (new SecureSet<Principal>(this, PRINCIPAL_SET));
        this.pubCredentials = Collections.synchronizedSet
                        (new SecureSet<Object>(this, PUB_CREDENTIAL_SET));
        this.privCredentials = Collections.synchronizedSet
                        (new SecureSet<Object>(this, PRIV_CREDENTIAL_SET));
    }

    
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"). 


Params:
  • 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:
/**
     * Create an instance of a {@code Subject} with
     * Principals and credentials.
     *
     * <p> The Principals and credentials from the specified Sets
     * are copied into newly constructed Sets.
     * These newly created Sets check whether this {@code 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.
     *
     * <p> To modify the Principals Set, the caller must have
     * {@code AuthPermission("modifyPrincipals")}.
     * To modify the public credential Set, the caller must have
     * {@code AuthPermission("modifyPublicCredentials")}.
     * To modify the private credential Set, the caller must have
     * {@code AuthPermission("modifyPrivateCredentials")}.
     * <p>
     *
     * @param readOnly true if the {@code Subject} is to be read-only,
     *          and false otherwise. <p>
     *
     * @param principals the {@code Set} of Principals
     *          to be associated with this {@code Subject}. <p>
     *
     * @param pubCredentials the {@code Set} of public credentials
     *          to be associated with this {@code Subject}. <p>
     *
     * @param privCredentials the {@code Set} of private credentials
     *          to be associated with this {@code Subject}.
     *
     * @exception NullPointerException if the specified
     *          {@code principals}, {@code pubCredentials},
     *          or {@code privCredentials} are {@code null}.
     */
    public Subject(boolean readOnly, Set<? extends Principal> principals,
                   Set<?> pubCredentials, Set<?> privCredentials)
    {

        if (principals == null ||
            pubCredentials == null ||
            privCredentials == null)
            throw new NullPointerException
                (ResourcesMgr.getString("invalid.null.input.s."));

        this.principals = Collections.synchronizedSet(new SecureSet<Principal>
                                (this, PRINCIPAL_SET, principals));
        this.pubCredentials = Collections.synchronizedSet(new SecureSet<Object>
                                (this, PUB_CREDENTIAL_SET, pubCredentials));
        this.privCredentials = Collections.synchronizedSet(new SecureSet<Object>
                                (this, PRIV_CREDENTIAL_SET, privCredentials));
        this.readOnly = readOnly;
    }

    
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.
/**
     * Set this {@code Subject} to be read-only.
     *
     * <p> Modifications (additions and removals) to this Subject's
     * {@code Principal} {@code Set} and
     * credential Sets will be disallowed.
     * The {@code destroy} operation on this Subject's credentials will
     * still be permitted.
     *
     * <p> Subsequent attempts to modify the Subject's {@code Principal}
     * and credential Sets will result in an
     * {@code IllegalStateException} being thrown.
     * Also, once a {@code Subject} is read-only,
     * it can not be reset to being writable again.
     *
     * <p>
     *
     * @exception SecurityException if the caller does not have permission
     *          to set this {@code Subject} to be read-only.
     */
    public void setReadOnly() {
        java.lang.SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            sm.checkPermission(AuthPermissionHolder.SET_READ_ONLY_PERMISSION);
        }

        this.readOnly = true;
    }

    
Query whether this Subject is read-only. 


Returns:true if this Subject is read-only, false otherwise.
/**
     * Query whether this {@code Subject} is read-only.
     *
     * <p>
     *
     * @return true if this {@code Subject} is read-only, false otherwise.
     */
    public boolean isReadOnly() {
        return this.readOnly;
    }

    
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. 


Params:
  • acc – the AccessControlContext from which to retrieve the Subject.
Throws:
Returns: the Subject associated with the provided AccessControlContext, or null if no Subject is associated with the provided AccessControlContext.
/**
     * Get the {@code Subject} associated with the provided
     * {@code AccessControlContext}.
     *
     * <p> The {@code AccessControlContext} may contain many
     * Subjects (from nested {@code doAs} calls).
     * In this situation, the most recent {@code Subject} associated
     * with the {@code AccessControlContext} is returned.
     *
     * <p>
     *
     * @param  acc the {@code AccessControlContext} from which to retrieve
     *          the {@code Subject}.
     *
     * @return  the {@code Subject} associated with the provided
     *          {@code AccessControlContext}, or {@code null}
     *          if no {@code Subject} is associated
     *          with the provided {@code AccessControlContext}.
     *
     * @exception SecurityException if the caller does not have permission
     *          to get the {@code Subject}. <p>
     *
     * @exception NullPointerException if the provided
     *          {@code AccessControlContext} is {@code null}.
     */
    public static Subject getSubject(final AccessControlContext acc) {

        java.lang.SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            sm.checkPermission(AuthPermissionHolder.GET_SUBJECT_PERMISSION);
        }

        if (acc == null) {
            throw new NullPointerException(ResourcesMgr.getString
                ("invalid.null.AccessControlContext.provided"));
        }

        // return the Subject from the DomainCombiner of the provided context
        return AccessController.doPrivileged
            (new java.security.PrivilegedAction<Subject>() {
            public Subject run() {
                DomainCombiner dc = acc.getDomainCombiner();
                if (!(dc instanceof SubjectDomainCombiner))
                    return null;
                SubjectDomainCombiner sdc = (SubjectDomainCombiner)dc;
                return sdc.getSubject();
            }
        });
    }

    
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. 


Params:
  • 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. 
Type parameters:
  • <T> – the type of the value returned by the PrivilegedAction's run method.
Throws:
Returns:the value returned by the PrivilegedAction's run method.
/**
     * Perform work as a particular {@code Subject}.
     *
     * <p> This method first retrieves the current Thread's
     * {@code AccessControlContext} via
     * {@code AccessController.getContext},
     * and then instantiates a new {@code AccessControlContext}
     * using the retrieved context along with a new
     * {@code SubjectDomainCombiner} (constructed using
     * the provided {@code Subject}).
     * Finally, this method invokes {@code AccessController.doPrivileged},
     * passing it the provided {@code PrivilegedAction},
     * as well as the newly constructed {@code AccessControlContext}.
     *
     * <p>
     *
     * @param subject the {@code Subject} that the specified
     *                  {@code action} will run as.  This parameter
     *                  may be {@code null}. <p>
     *
     * @param <T> the type of the value returned by the PrivilegedAction's
     *                  {@code run} method.
     *
     * @param action the code to be run as the specified
     *                  {@code Subject}. <p>
     *
     * @return the value returned by the PrivilegedAction's
     *                  {@code run} method.
     *
     * @exception NullPointerException if the {@code PrivilegedAction}
     *                  is {@code null}. <p>
     *
     * @exception SecurityException if the caller does not have permission
     *                  to invoke this method.
     */
    public static <T> T doAs(final Subject subject,
                        final java.security.PrivilegedAction<T> action) {

        java.lang.SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            sm.checkPermission(AuthPermissionHolder.DO_AS_PERMISSION);
        }
        if (action == null)
            throw new NullPointerException
                (ResourcesMgr.getString("invalid.null.action.provided"));

        // set up the new Subject-based AccessControlContext
        // for doPrivileged
        final AccessControlContext currentAcc = AccessController.getContext();

        // call doPrivileged and push this new context on the stack
        return java.security.AccessController.doPrivileged
                                        (action,
                                        createContext(subject, currentAcc));
    }

    
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. 


Params:
  • 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. 
Type parameters:
  • <T> – the type of the value returned by the PrivilegedExceptionAction's run method.
Throws:
Returns:the value returned by the PrivilegedExceptionAction's run method.
/**
     * Perform work as a particular {@code Subject}.
     *
     * <p> This method first retrieves the current Thread's
     * {@code AccessControlContext} via
     * {@code AccessController.getContext},
     * and then instantiates a new {@code AccessControlContext}
     * using the retrieved context along with a new
     * {@code SubjectDomainCombiner} (constructed using
     * the provided {@code Subject}).
     * Finally, this method invokes {@code AccessController.doPrivileged},
     * passing it the provided {@code PrivilegedExceptionAction},
     * as well as the newly constructed {@code AccessControlContext}.
     *
     * <p>
     *
     * @param subject the {@code Subject} that the specified
     *                  {@code action} will run as.  This parameter
     *                  may be {@code null}. <p>
     *
     * @param <T> the type of the value returned by the
     *                  PrivilegedExceptionAction's {@code run} method.
     *
     * @param action the code to be run as the specified
     *                  {@code Subject}. <p>
     *
     * @return the value returned by the
     *                  PrivilegedExceptionAction's {@code run} method.
     *
     * @exception PrivilegedActionException if the
     *                  {@code PrivilegedExceptionAction.run}
     *                  method throws a checked exception. <p>
     *
     * @exception NullPointerException if the specified
     *                  {@code PrivilegedExceptionAction} is
     *                  {@code null}. <p>
     *
     * @exception SecurityException if the caller does not have permission
     *                  to invoke this method.
     */
    public static <T> T doAs(final Subject subject,
                        final java.security.PrivilegedExceptionAction<T> action)
                        throws java.security.PrivilegedActionException {

        java.lang.SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            sm.checkPermission(AuthPermissionHolder.DO_AS_PERMISSION);
        }

        if (action == null)
            throw new NullPointerException
                (ResourcesMgr.getString("invalid.null.action.provided"));

        // set up the new Subject-based AccessControlContext for doPrivileged
        final AccessControlContext currentAcc = AccessController.getContext();

        // call doPrivileged and push this new context on the stack
        return java.security.AccessController.doPrivileged
                                        (action,
                                        createContext(subject, currentAcc));
    }

    
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. 


Params:
  • 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. 
Type parameters:
  • <T> – the type of the value returned by the PrivilegedAction's run method.
Throws:
Returns:the value returned by the PrivilegedAction's run method.
/**
     * Perform privileged work as a particular {@code Subject}.
     *
     * <p> This method behaves exactly as {@code Subject.doAs},
     * except that instead of retrieving the current Thread's
     * {@code AccessControlContext}, it uses the provided
     * {@code AccessControlContext}.  If the provided
     * {@code AccessControlContext} is {@code null},
     * this method instantiates a new {@code AccessControlContext}
     * with an empty collection of ProtectionDomains.
     *
     * <p>
     *
     * @param subject the {@code Subject} that the specified
     *                  {@code action} will run as.  This parameter
     *                  may be {@code null}. <p>
     *
     * @param <T> the type of the value returned by the PrivilegedAction's
     *                  {@code run} method.
     *
     * @param action the code to be run as the specified
     *                  {@code Subject}. <p>
     *
     * @param acc the {@code AccessControlContext} to be tied to the
     *                  specified <i>subject</i> and <i>action</i>. <p>
     *
     * @return the value returned by the PrivilegedAction's
     *                  {@code run} method.
     *
     * @exception NullPointerException if the {@code PrivilegedAction}
     *                  is {@code null}. <p>
     *
     * @exception SecurityException if the caller does not have permission
     *                  to invoke this method.
     */
    public static <T> T doAsPrivileged(final Subject subject,
                        final java.security.PrivilegedAction<T> action,
                        final java.security.AccessControlContext acc) {

        java.lang.SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            sm.checkPermission(AuthPermissionHolder.DO_AS_PRIVILEGED_PERMISSION);
        }

        if (action == null)
            throw new NullPointerException
                (ResourcesMgr.getString("invalid.null.action.provided"));

        // set up the new Subject-based AccessControlContext
        // for doPrivileged
        final AccessControlContext callerAcc =
                (acc == null ?
                new AccessControlContext(NULL_PD_ARRAY) :
                acc);

        // call doPrivileged and push this new context on the stack
        return java.security.AccessController.doPrivileged
                                        (action,
                                        createContext(subject, callerAcc));
    }

    
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. 


Params:
  • 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. 
Type parameters:
  • <T> – the type of the value returned by the PrivilegedExceptionAction's run method.
Throws:
Returns:the value returned by the PrivilegedExceptionAction's run method.
/**
     * Perform privileged work as a particular {@code Subject}.
     *
     * <p> This method behaves exactly as {@code Subject.doAs},
     * except that instead of retrieving the current Thread's
     * {@code AccessControlContext}, it uses the provided
     * {@code AccessControlContext}.  If the provided
     * {@code AccessControlContext} is {@code null},
     * this method instantiates a new {@code AccessControlContext}
     * with an empty collection of ProtectionDomains.
     *
     * <p>
     *
     * @param subject the {@code Subject} that the specified
     *                  {@code action} will run as.  This parameter
     *                  may be {@code null}. <p>
     *
     * @param <T> the type of the value returned by the
     *                  PrivilegedExceptionAction's {@code run} method.
     *
     * @param action the code to be run as the specified
     *                  {@code Subject}. <p>
     *
     * @param acc the {@code AccessControlContext} to be tied to the
     *                  specified <i>subject</i> and <i>action</i>. <p>
     *
     * @return the value returned by the
     *                  PrivilegedExceptionAction's {@code run} method.
     *
     * @exception PrivilegedActionException if the
     *                  {@code PrivilegedExceptionAction.run}
     *                  method throws a checked exception. <p>
     *
     * @exception NullPointerException if the specified
     *                  {@code PrivilegedExceptionAction} is
     *                  {@code null}. <p>
     *
     * @exception SecurityException if the caller does not have permission
     *                  to invoke this method.
     */
    public static <T> T doAsPrivileged(final Subject subject,
                        final java.security.PrivilegedExceptionAction<T> action,
                        final java.security.AccessControlContext acc)
                        throws java.security.PrivilegedActionException {

        java.lang.SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            sm.checkPermission(AuthPermissionHolder.DO_AS_PRIVILEGED_PERMISSION);
        }

        if (action == null)
            throw new NullPointerException
                (ResourcesMgr.getString("invalid.null.action.provided"));

        // set up the new Subject-based AccessControlContext for doPrivileged
        final AccessControlContext callerAcc =
                (acc == null ?
                new AccessControlContext(NULL_PD_ARRAY) :
                acc);

        // call doPrivileged and push this new context on the stack
        return java.security.AccessController.doPrivileged
                                        (action,
                                        createContext(subject, callerAcc));
    }

    private static AccessControlContext createContext(final Subject subject,
                                        final AccessControlContext acc) {


        return java.security.AccessController.doPrivileged
            (new java.security.PrivilegedAction<AccessControlContext>() {
            public AccessControlContext run() {
                if (subject == null)
                    return new AccessControlContext(acc, null);
                else
                    return new AccessControlContext
                                        (acc,
                                        new SubjectDomainCombiner(subject));
            }
        });
    }

    
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.
/**
     * Return the {@code Set} of Principals associated with this
     * {@code Subject}.  Each {@code Principal} represents
     * an identity for this {@code Subject}.
     *
     * <p> The returned {@code Set} is backed by this Subject's
     * internal {@code Principal} {@code Set}.  Any modification
     * to the returned {@code Set} affects the internal
     * {@code Principal} {@code Set} as well.
     *
     * <p>
     *
     * @return  The {@code Set} of Principals associated with this
     *          {@code Subject}.
     */
    public Set<Principal> getPrincipals() {

        // always return an empty Set instead of null
        // so LoginModules can add to the Set if necessary
        return principals;
    }

    
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. 


Params:
  • c – the returned Set of Principals will all be instances of this class.
Type parameters:
  • <T> – the type of the class modeled by c
Throws:
Returns:a Set of Principals that are instances of the specified Class.
/**
     * Return a {@code Set} of Principals associated with this
     * {@code Subject} that are instances or subclasses of the specified
     * {@code Class}.
     *
     * <p> The returned {@code Set} is not backed by this Subject's
     * internal {@code Principal} {@code Set}.  A new
     * {@code Set} is created and returned for each method invocation.
     * Modifications to the returned {@code Set}
     * will not affect the internal {@code Principal} {@code Set}.
     *
     * <p>
     *
     * @param <T> the type of the class modeled by {@code c}
     *
     * @param c the returned {@code Set} of Principals will all be
     *          instances of this class.
     *
     * @return a {@code Set} of Principals that are instances of the
     *          specified {@code Class}.
     *
     * @exception NullPointerException if the specified {@code Class}
     *                  is {@code null}.
     */
    public <T extends Principal> Set<T> getPrincipals(Class<T> c) {

        if (c == null)
            throw new NullPointerException
                (ResourcesMgr.getString("invalid.null.Class.provided"));

        // always return an empty Set instead of null
        // so LoginModules can add to the Set if necessary
        return new ClassSet<T>(PRINCIPAL_SET, c);
    }

    
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.
/**
     * Return the {@code Set} of public credentials held by this
     * {@code Subject}.
     *
     * <p> The returned {@code Set} is backed by this Subject's
     * internal public Credential {@code Set}.  Any modification
     * to the returned {@code Set} affects the internal public
     * Credential {@code Set} as well.
     *
     * <p>
     *
     * @return  A {@code Set} of public credentials held by this
     *          {@code Subject}.
     */
    public Set<Object> getPublicCredentials() {

        // always return an empty Set instead of null
        // so LoginModules can add to the Set if necessary
        return pubCredentials;
    }

    
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.
/**
     * Return the {@code Set} of private credentials held by this
     * {@code Subject}.
     *
     * <p> The returned {@code Set} is backed by this Subject's
     * internal private Credential {@code Set}.  Any modification
     * to the returned {@code Set} affects the internal private
     * Credential {@code Set} as well.
     *
     * <p> A caller requires permissions to access the Credentials
     * in the returned {@code Set}, or to modify the
     * {@code Set} itself.  A {@code SecurityException}
     * is thrown if the caller does not have the proper permissions.
     *
     * <p> While iterating through the {@code Set},
     * a {@code SecurityException} is thrown
     * if the caller does not have permission to access a
     * particular Credential.  The {@code Iterator}
     * is nevertheless advanced to next element in the {@code Set}.
     *
     * <p>
     *
     * @return  A {@code Set} of private credentials held by this
     *          {@code Subject}.
     */
    public Set<Object> getPrivateCredentials() {

        // XXX
        // we do not need a security check for
        // AuthPermission(getPrivateCredentials)
        // because we already restrict access to private credentials
        // via the PrivateCredentialPermission.  all the extra AuthPermission
        // would do is protect the set operations themselves
        // (like size()), which don't seem security-sensitive.

        // always return an empty Set instead of null
        // so LoginModules can add to the Set if necessary
        return privCredentials;
    }

    
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. 


Params:
  • c – the returned Set of public credentials will all be instances of this class.
Type parameters:
  • <T> – the type of the class modeled by c
Throws:
Returns:a Set of public credentials that are instances of the specified Class.
/**
     * Return a {@code Set} of public credentials associated with this
     * {@code Subject} that are instances or subclasses of the specified
     * {@code Class}.
     *
     * <p> The returned {@code Set} is not backed by this Subject's
     * internal public Credential {@code Set}.  A new
     * {@code Set} is created and returned for each method invocation.
     * Modifications to the returned {@code Set}
     * will not affect the internal public Credential {@code Set}.
     *
     * <p>
     *
     * @param <T> the type of the class modeled by {@code c}
     *
     * @param c the returned {@code Set} of public credentials will all be
     *          instances of this class.
     *
     * @return a {@code Set} of public credentials that are instances
     *          of the  specified {@code Class}.
     *
     * @exception NullPointerException if the specified {@code Class}
     *          is {@code null}.
     */
    public <T> Set<T> getPublicCredentials(Class<T> c) {

        if (c == null)
            throw new NullPointerException
                (ResourcesMgr.getString("invalid.null.Class.provided"));

        // always return an empty Set instead of null
        // so LoginModules can add to the Set if necessary
        return new ClassSet<T>(PUB_CREDENTIAL_SET, 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. 


Params:
  • c – the returned Set of private credentials will all be instances of this class.
Type parameters:
  • <T> – the type of the class modeled by c
Throws:
Returns:a Set of private credentials that are instances of the specified Class.
/**
     * Return a {@code Set} of private credentials associated with this
     * {@code Subject} that are instances or subclasses of the specified
     * {@code Class}.
     *
     * <p> The caller must have permission to access all of the
     * requested Credentials, or a {@code SecurityException}
     * will be thrown.
     *
     * <p> The returned {@code Set} is not backed by this Subject's
     * internal private Credential {@code Set}.  A new
     * {@code Set} is created and returned for each method invocation.
     * Modifications to the returned {@code Set}
     * will not affect the internal private Credential {@code Set}.
     *
     * <p>
     *
     * @param <T> the type of the class modeled by {@code c}
     *
     * @param c the returned {@code Set} of private credentials will all be
     *          instances of this class.
     *
     * @return a {@code Set} of private credentials that are instances
     *          of the  specified {@code Class}.
     *
     * @exception NullPointerException if the specified {@code Class}
     *          is {@code null}.
     */
    public <T> Set<T> getPrivateCredentials(Class<T> c) {

        // XXX
        // we do not need a security check for
        // AuthPermission(getPrivateCredentials)
        // because we already restrict access to private credentials
        // via the PrivateCredentialPermission.  all the extra AuthPermission
        // would do is protect the set operations themselves
        // (like size()), which don't seem security-sensitive.

        if (c == null)
            throw new NullPointerException
                (ResourcesMgr.getString("invalid.null.Class.provided"));

        // always return an empty Set instead of null
        // so LoginModules can add to the Set if necessary
        return new ClassSet<T>(PRIV_CREDENTIAL_SET, c);
    }

    
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. 


Params:
  • o – Object to be compared for equality with 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.
Returns:true if the specified Object is equal to this Subject.
/**
     * Compares the specified Object with this {@code Subject}
     * for equality.  Returns true if the given object is also a Subject
     * and the two {@code Subject} instances are equivalent.
     * More formally, two {@code Subject} instances are
     * equal if their {@code Principal} and {@code Credential}
     * Sets are equal.
     *
     * <p>
     *
     * @param o Object to be compared for equality with this
     *          {@code Subject}.
     *
     * @return true if the specified Object is equal to this
     *          {@code Subject}.
     *
     * @exception SecurityException if the caller does not have permission
     *          to access the private credentials for this {@code Subject},
     *          or if the caller does not have permission to access the
     *          private credentials for the provided {@code Subject}.
     */
    public boolean equals(Object o) {

        if (o == null)
            return false;

        if (this == o)
            return true;

        if (o instanceof Subject) {

            final Subject that = (Subject)o;

            // check the principal and credential sets
            Set<Principal> thatPrincipals;
            synchronized(that.principals) {
                // avoid deadlock from dual locks
                thatPrincipals = new HashSet<Principal>(that.principals);
            }
            if (!principals.equals(thatPrincipals)) {
                return false;
            }

            Set<Object> thatPubCredentials;
            synchronized(that.pubCredentials) {
                // avoid deadlock from dual locks
                thatPubCredentials = new HashSet<Object>(that.pubCredentials);
            }
            if (!pubCredentials.equals(thatPubCredentials)) {
                return false;
            }

            Set<Object> thatPrivCredentials;
            synchronized(that.privCredentials) {
                // avoid deadlock from dual locks
                thatPrivCredentials = new HashSet<Object>(that.privCredentials);
            }
            if (!privCredentials.equals(thatPrivCredentials)) {
                return false;
            }
            return true;
        }
        return false;
    }

    
Return the String representation of this Subject. 


Returns:the String representation of this Subject.
/**
     * Return the String representation of this {@code Subject}.
     *
     * <p>
     *
     * @return the String representation of this {@code Subject}.
     */
    public String toString() {
        return toString(true);
    }

    
package private convenience method to print out the Subject
without firing off a security check when trying to access
the Private Credentials

/**
     * package private convenience method to print out the Subject
     * without firing off a security check when trying to access
     * the Private Credentials
     */
    String toString(boolean includePrivateCredentials) {

        String s = ResourcesMgr.getString("Subject.");
        String suffix = "";

        synchronized(principals) {
            Iterator<Principal> pI = principals.iterator();
            while (pI.hasNext()) {
                Principal p = pI.next();
                suffix = suffix + ResourcesMgr.getString(".Principal.") +
                        p.toString() + ResourcesMgr.getString("NEWLINE");
            }
        }

        synchronized(pubCredentials) {
            Iterator<Object> pI = pubCredentials.iterator();
            while (pI.hasNext()) {
                Object o = pI.next();
                suffix = suffix +
                        ResourcesMgr.getString(".Public.Credential.") +
                        o.toString() + ResourcesMgr.getString("NEWLINE");
            }
        }

        if (includePrivateCredentials) {
            synchronized(privCredentials) {
                Iterator<Object> pI = privCredentials.iterator();
                while (pI.hasNext()) {
                    try {
                        Object o = pI.next();
                        suffix += ResourcesMgr.getString
                                        (".Private.Credential.") +
                                        o.toString() +
                                        ResourcesMgr.getString("NEWLINE");
                    } catch (SecurityException se) {
                        suffix += ResourcesMgr.getString
                                (".Private.Credential.inaccessible.");
                        break;
                    }
                }
            }
        }
        return s + suffix;
    }

    
Returns a hashcode for this Subject. 


Throws:
  • SecurityException – if the caller does not have permission
         to access this Subject's private credentials.
Returns:a hashcode for this Subject.
/**
     * Returns a hashcode for this {@code Subject}.
     *
     * <p>
     *
     * @return a hashcode for this {@code Subject}.
     *
     * @exception SecurityException if the caller does not have permission
     *          to access this Subject's private credentials.
     */
    public int hashCode() {

        /**
         * The hashcode is derived exclusive or-ing the
         * hashcodes of this Subject's Principals and credentials.
         *
         * If a particular credential was destroyed
         * ({@code credential.hashCode()} throws an
         * {@code IllegalStateException}),
         * the hashcode for that credential is derived via:
         * {@code credential.getClass().toString().hashCode()}.
         */

        int hashCode = 0;

        synchronized(principals) {
            Iterator<Principal> pIterator = principals.iterator();
            while (pIterator.hasNext()) {
                Principal p = pIterator.next();
                hashCode ^= p.hashCode();
            }
        }

        synchronized(pubCredentials) {
            Iterator<Object> pubCIterator = pubCredentials.iterator();
            while (pubCIterator.hasNext()) {
                hashCode ^= getCredHashCode(pubCIterator.next());
            }
        }
        return hashCode;
    }

    
get a credential's hashcode

/**
     * get a credential's hashcode
     */
    private int getCredHashCode(Object o) {
        try {
            return o.hashCode();
        } catch (IllegalStateException ise) {
            return o.getClass().toString().hashCode();
        }
    }

    
Writes this object out to a stream (i.e., serializes it).

/**
     * Writes this object out to a stream (i.e., serializes it).
     */
    private void writeObject(java.io.ObjectOutputStream oos)
                throws java.io.IOException {
        synchronized(principals) {
            oos.defaultWriteObject();
        }
    }

    
Reads this object from a stream (i.e., deserializes it)

/**
     * Reads this object from a stream (i.e., deserializes it)
     */
    @SuppressWarnings("unchecked")
    private void readObject(java.io.ObjectInputStream s)
                throws java.io.IOException, ClassNotFoundException {

        ObjectInputStream.GetField gf = s.readFields();

        readOnly = gf.get("readOnly", false);

        Set<Principal> inputPrincs = (Set<Principal>)gf.get("principals", null);

        // Rewrap the principals into a SecureSet
        if (inputPrincs == null) {
            throw new NullPointerException
                (ResourcesMgr.getString("invalid.null.input.s."));
        }
        try {
            principals = Collections.synchronizedSet(new SecureSet<Principal>
                                (this, PRINCIPAL_SET, inputPrincs));
        } catch (NullPointerException npe) {
            // Sometimes people deserialize the principals set only.
            // Subject is not accessible, so just don't fail.
            principals = Collections.synchronizedSet
                        (new SecureSet<Principal>(this, PRINCIPAL_SET));
        }

        // The Credential {@code Set} is not serialized, but we do not
        // want the default deserialization routine to set it to null.
        this.pubCredentials = Collections.synchronizedSet
                        (new SecureSet<Object>(this, PUB_CREDENTIAL_SET));
        this.privCredentials = Collections.synchronizedSet
                        (new SecureSet<Object>(this, PRIV_CREDENTIAL_SET));
    }

    
Prevent modifications unless caller has permission.

@serialinclude
/**
     * Prevent modifications unless caller has permission.
     *
     * @serial include
     */
    private static class SecureSet<E>
        extends AbstractSet<E>
        implements java.io.Serializable {

        private static final long serialVersionUID = 7911754171111800359L;

        
@serialFieldthis$0 Subject The outer Subject instance.
@serialFieldelements LinkedList The elements in this set.
/**
         * @serialField this$0 Subject The outer Subject instance.
         * @serialField elements LinkedList The elements in this set.
         */
        private static final ObjectStreamField[] serialPersistentFields = {
            new ObjectStreamField("this$0", Subject.class),
            new ObjectStreamField("elements", LinkedList.class),
            new ObjectStreamField("which", int.class)
        };

        Subject subject;
        LinkedList<E> elements;

        
@serialAn integer identifying the type of objects contained in this set. If which == 1, this is a Principal set and all the elements are of type java.security.Principal. If which == 2, this is a public credential set and all the elements are of type Object. If which == 3, this is a private credential set and all the elements are of type Object.
/**
         * @serial An integer identifying the type of objects contained
         *      in this set.  If {@code which == 1},
         *      this is a Principal set and all the elements are
         *      of type {@code java.security.Principal}.
         *      If {@code which == 2}, this is a public credential
         *      set and all the elements are of type {@code Object}.
         *      If {@code which == 3}, this is a private credential
         *      set and all the elements are of type {@code Object}.
         */
        private int which;

        SecureSet(Subject subject, int which) {
            this.subject = subject;
            this.which = which;
            this.elements = new LinkedList<E>();
        }

        SecureSet(Subject subject, int which, Set<? extends E> set) {
            this.subject = subject;
            this.which = which;
            this.elements = new LinkedList<E>(set);
        }

        public int size() {
            return elements.size();
        }

        public Iterator<E> iterator() {
            final LinkedList<E> list = elements;
            return new Iterator<E>() {
                ListIterator<E> i = list.listIterator(0);

                public boolean hasNext() {return i.hasNext();}

                public E next() {
                    if (which != Subject.PRIV_CREDENTIAL_SET) {
                        return i.next();
                    }

                    SecurityManager sm = System.getSecurityManager();
                    if (sm != null) {
                        try {
                            sm.checkPermission(new PrivateCredentialPermission
                                (list.get(i.nextIndex()).getClass().getName(),
                                subject.getPrincipals()));
                        } catch (SecurityException se) {
                            i.next();
                            throw (se);
                        }
                    }
                    return i.next();
                }

                public void remove() {

                    if (subject.isReadOnly()) {
                        throw new IllegalStateException(ResourcesMgr.getString
                                ("Subject.is.read.only"));
                    }

                    java.lang.SecurityManager sm = System.getSecurityManager();
                    if (sm != null) {
                        switch (which) {
                        case Subject.PRINCIPAL_SET:
                            sm.checkPermission(AuthPermissionHolder.MODIFY_PRINCIPALS_PERMISSION);
                            break;
                        case Subject.PUB_CREDENTIAL_SET:
                            sm.checkPermission(AuthPermissionHolder.MODIFY_PUBLIC_CREDENTIALS_PERMISSION);
                            break;
                        default:
                            sm.checkPermission(AuthPermissionHolder.MODIFY_PRIVATE_CREDENTIALS_PERMISSION);
                            break;
                        }
                    }
                    i.remove();
                }
            };
        }

        public boolean add(E o) {

            if (subject.isReadOnly()) {
                throw new IllegalStateException
                        (ResourcesMgr.getString("Subject.is.read.only"));
            }

            java.lang.SecurityManager sm = System.getSecurityManager();
            if (sm != null) {
                switch (which) {
                case Subject.PRINCIPAL_SET:
                    sm.checkPermission(AuthPermissionHolder.MODIFY_PRINCIPALS_PERMISSION);
                    break;
                case Subject.PUB_CREDENTIAL_SET:
                    sm.checkPermission(AuthPermissionHolder.MODIFY_PUBLIC_CREDENTIALS_PERMISSION);
                    break;
                default:
                    sm.checkPermission(AuthPermissionHolder.MODIFY_PRIVATE_CREDENTIALS_PERMISSION);
                    break;
                }
            }

            switch (which) {
            case Subject.PRINCIPAL_SET:
                if (!(o instanceof Principal)) {
                    throw new SecurityException(ResourcesMgr.getString
                        ("attempting.to.add.an.object.which.is.not.an.instance.of.java.security.Principal.to.a.Subject.s.Principal.Set"));
                }
                break;
            default:
                // ok to add Objects of any kind to credential sets
                break;
            }

            // check for duplicates
            if (!elements.contains(o))
                return elements.add(o);
            else
                return false;
        }

        public boolean remove(Object o) {

            final Iterator<E> e = iterator();
            while (e.hasNext()) {
                E next;
                if (which != Subject.PRIV_CREDENTIAL_SET) {
                    next = e.next();
                } else {
                    next = java.security.AccessController.doPrivileged
                        (new java.security.PrivilegedAction<E>() {
                        public E run() {
                            return e.next();
                        }
                    });
                }

                if (next == null) {
                    if (o == null) {
                        e.remove();
                        return true;
                    }
                } else if (next.equals(o)) {
                    e.remove();
                    return true;
                }
            }
            return false;
        }

        public boolean contains(Object o) {
            final Iterator<E> e = iterator();
            while (e.hasNext()) {
                E next;
                if (which != Subject.PRIV_CREDENTIAL_SET) {
                    next = e.next();
                } else {

                    // For private credentials:
                    // If the caller does not have read permission for
                    // for o.getClass(), we throw a SecurityException.
                    // Otherwise we check the private cred set to see whether
                    // it contains the Object

                    SecurityManager sm = System.getSecurityManager();
                    if (sm != null) {
                        sm.checkPermission(new PrivateCredentialPermission
                                                (o.getClass().getName(),
                                                subject.getPrincipals()));
                    }
                    next = java.security.AccessController.doPrivileged
                        (new java.security.PrivilegedAction<E>() {
                        public E run() {
                            return e.next();
                        }
                    });
                }

                if (next == null) {
                    if (o == null) {
                        return true;
                    }
                } else if (next.equals(o)) {
                    return true;
                }
            }
            return false;
        }

        public boolean removeAll(Collection<?> c) {
            Objects.requireNonNull(c);
            boolean modified = false;
            final Iterator<E> e = iterator();
            while (e.hasNext()) {
                E next;
                if (which != Subject.PRIV_CREDENTIAL_SET) {
                    next = e.next();
                } else {
                    next = java.security.AccessController.doPrivileged
                        (new java.security.PrivilegedAction<E>() {
                        public E run() {
                            return e.next();
                        }
                    });
                }

                Iterator<?> ce = c.iterator();
                while (ce.hasNext()) {
                    Object o = ce.next();
                    if (next == null) {
                        if (o == null) {
                            e.remove();
                            modified = true;
                            break;
                        }
                    } else if (next.equals(o)) {
                        e.remove();
                        modified = true;
                        break;
                    }
                }
            }
            return modified;
        }

        public boolean retainAll(Collection<?> c) {
            Objects.requireNonNull(c);
            boolean modified = false;
            boolean retain = false;
            final Iterator<E> e = iterator();
            while (e.hasNext()) {
                retain = false;
                E next;
                if (which != Subject.PRIV_CREDENTIAL_SET) {
                    next = e.next();
                } else {
                    next = java.security.AccessController.doPrivileged
                        (new java.security.PrivilegedAction<E>() {
                        public E run() {
                            return e.next();
                        }
                    });
                }

                Iterator<?> ce = c.iterator();
                while (ce.hasNext()) {
                    Object o = ce.next();
                    if (next == null) {
                        if (o == null) {
                            retain = true;
                            break;
                        }
                    } else if (next.equals(o)) {
                        retain = true;
                        break;
                    }
                }

                if (!retain) {
                    e.remove();
                    retain = false;
                    modified = true;
                }
            }
            return modified;
        }

        public void clear() {
            final Iterator<E> e = iterator();
            while (e.hasNext()) {
                E next;
                if (which != Subject.PRIV_CREDENTIAL_SET) {
                    next = e.next();
                } else {
                    next = java.security.AccessController.doPrivileged
                        (new java.security.PrivilegedAction<E>() {
                        public E run() {
                            return e.next();
                        }
                    });
                }
                e.remove();
            }
        }

        
Writes this object out to a stream (i.e., serializes it).



@serialDataIf this is a private credential set,
     a security check is performed to ensure that
     the caller has permission to access each credential
     in the set.  If the security check passes,
     the set is serialized.
/**
         * Writes this object out to a stream (i.e., serializes it).
         *
         * <p>
         *
         * @serialData If this is a private credential set,
         *      a security check is performed to ensure that
         *      the caller has permission to access each credential
         *      in the set.  If the security check passes,
         *      the set is serialized.
         */
        private void writeObject(java.io.ObjectOutputStream oos)
                throws java.io.IOException {

            if (which == Subject.PRIV_CREDENTIAL_SET) {
                // check permissions before serializing
                Iterator<E> i = iterator();
                while (i.hasNext()) {
                    i.next();
                }
            }
            ObjectOutputStream.PutField fields = oos.putFields();
            fields.put("this$0", subject);
            fields.put("elements", elements);
            fields.put("which", which);
            oos.writeFields();
        }

        @SuppressWarnings("unchecked")
        private void readObject(ObjectInputStream ois)
            throws IOException, ClassNotFoundException
        {
            ObjectInputStream.GetField fields = ois.readFields();
            subject = (Subject) fields.get("this$0", null);
            which = fields.get("which", 0);

            LinkedList<E> tmp = (LinkedList<E>) fields.get("elements", null);
            if (tmp.getClass() != LinkedList.class) {
                elements = new LinkedList<E>(tmp);
            } else {
                elements = tmp;
            }
        }
    }

    
This class implements a Set which returns only members that are an instance of a specified Class. 
/**
     * This class implements a {@code Set} which returns only
     * members that are an instance of a specified Class.
     */
    private class ClassSet<T> extends AbstractSet<T> {

        private int which;
        private Class<T> c;
        private Set<T> set;

        ClassSet(int which, Class<T> c) {
            this.which = which;
            this.c = c;
            set = new HashSet<T>();

            switch (which) {
            case Subject.PRINCIPAL_SET:
                synchronized(principals) { populateSet(); }
                break;
            case Subject.PUB_CREDENTIAL_SET:
                synchronized(pubCredentials) { populateSet(); }
                break;
            default:
                synchronized(privCredentials) { populateSet(); }
                break;
            }
        }

        @SuppressWarnings("unchecked")     /*To suppress warning from line 1374*/
        private void populateSet() {
            final Iterator<?> iterator;
            switch(which) {
            case Subject.PRINCIPAL_SET:
                iterator = Subject.this.principals.iterator();
                break;
            case Subject.PUB_CREDENTIAL_SET:
                iterator = Subject.this.pubCredentials.iterator();
                break;
            default:
                iterator = Subject.this.privCredentials.iterator();
                break;
            }

            // Check whether the caller has permisson to get
            // credentials of Class c

            while (iterator.hasNext()) {
                Object next;
                if (which == Subject.PRIV_CREDENTIAL_SET) {
                    next = java.security.AccessController.doPrivileged
                        (new java.security.PrivilegedAction<Object>() {
                        public Object run() {
                            return iterator.next();
                        }
                    });
                } else {
                    next = iterator.next();
                }
                if (c.isAssignableFrom(next.getClass())) {
                    if (which != Subject.PRIV_CREDENTIAL_SET) {
                        set.add((T)next);
                    } else {
                        // Check permission for private creds
                        SecurityManager sm = System.getSecurityManager();
                        if (sm != null) {
                            sm.checkPermission(new PrivateCredentialPermission
                                                (next.getClass().getName(),
                                                Subject.this.getPrincipals()));
                        }
                        set.add((T)next);
                    }
                }
            }
        }

        public int size() {
            return set.size();
        }

        public Iterator<T> iterator() {
            return set.iterator();
        }

        public boolean add(T o) {

            if (!o.getClass().isAssignableFrom(c)) {
                MessageFormat form = new MessageFormat(ResourcesMgr.getString
                        ("attempting.to.add.an.object.which.is.not.an.instance.of.class"));
                Object[] source = {c.toString()};
                throw new SecurityException(form.format(source));
            }

            return set.add(o);
        }
    }

    static class AuthPermissionHolder {
        static final AuthPermission DO_AS_PERMISSION =
            new AuthPermission("doAs");

        static final AuthPermission DO_AS_PRIVILEGED_PERMISSION =
            new AuthPermission("doAsPrivileged");

        static final AuthPermission SET_READ_ONLY_PERMISSION =
            new AuthPermission("setReadOnly");

        static final AuthPermission GET_SUBJECT_PERMISSION =
            new AuthPermission("getSubject");

        static final AuthPermission MODIFY_PRINCIPALS_PERMISSION =
            new AuthPermission("modifyPrincipals");

        static final AuthPermission MODIFY_PUBLIC_CREDENTIALS_PERMISSION =
            new AuthPermission("modifyPublicCredentials");

        static final AuthPermission MODIFY_PRIVATE_CREDENTIALS_PERMISSION =
            new AuthPermission("modifyPrivateCredentials");
    }
}