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package java.security;

import java.util.*;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;


Abstract class representing a collection of Permission objects.

With a PermissionCollection, you can:

    

  •  add a permission to the collection using the add method. 
  •  check to see if a particular permission is implied in the collection, using the implies method. 
  •  enumerate all the permissions, using the elements method. 


When it is desirable to group together a number of Permission objects of the same type, the newPermissionCollection method on that particular type of Permission object should first be called. The default behavior (from the Permission class) is to simply return null. Subclasses of class Permission override the method if they need to store their permissions in a particular PermissionCollection object in order to provide the correct semantics when the PermissionCollection.implies method is called. If a non-null value is returned, that PermissionCollection must be used. If null is returned, then the caller of newPermissionCollection is free to store permissions of the given type in any PermissionCollection they choose (one that uses a Hashtable, one that uses a Vector, etc). 
The PermissionCollection returned by the Permission.newPermissionCollection method is a homogeneous collection, which stores only Permission objects for a given Permission type. A PermissionCollection may also be heterogeneous. For example, Permissions is a PermissionCollection subclass that represents a collection of PermissionCollections. That is, its members are each a homogeneous PermissionCollection. For example, a Permissions object might have a FilePermissionCollection for all the FilePermission objects, a SocketPermissionCollection for all the SocketPermission objects, and so on. Its add method adds a permission to the appropriate collection. 
Whenever a permission is added to a heterogeneous PermissionCollection such as Permissions, and the PermissionCollection doesn't yet contain a PermissionCollection of the specified permission's type, the PermissionCollection should call the newPermissionCollection method on the permission's class to see if it requires a special PermissionCollection. If newPermissionCollection returns null, the PermissionCollection is free to store the permission in any type of PermissionCollection it desires (one using a Hashtable, one using a Vector, etc.). For example, the Permissions object uses a default PermissionCollection implementation that stores the permission objects in a Hashtable. 
 Subclass implementations of PermissionCollection should assume that they may be called simultaneously from multiple threads, and therefore should be synchronized properly. Furthermore, Enumerations returned via the elements method are not fail-fast.  Modifications to a collection should not be
performed while enumerating over that collection.

Author:Roland Schemers
See Also:
Since:1.2
/**
 * Abstract class representing a collection of Permission objects.
 *
 * <p>With a PermissionCollection, you can:
 * <UL>
 * <LI> add a permission to the collection using the {@code add} method.
 * <LI> check to see if a particular permission is implied in the
 *      collection, using the {@code implies} method.
 * <LI> enumerate all the permissions, using the {@code elements} method.
 * </UL>
 *
 * <p>When it is desirable to group together a number of Permission objects
 * of the same type, the {@code newPermissionCollection} method on that
 * particular type of Permission object should first be called. The default
 * behavior (from the Permission class) is to simply return null.
 * Subclasses of class Permission override the method if they need to store
 * their permissions in a particular PermissionCollection object in order
 * to provide the correct semantics when the
 * {@code PermissionCollection.implies} method is called.
 * If a non-null value is returned, that PermissionCollection must be used.
 * If null is returned, then the caller of {@code newPermissionCollection}
 * is free to store permissions of the
 * given type in any PermissionCollection they choose
 * (one that uses a Hashtable, one that uses a Vector, etc).
 *
 * <p>The PermissionCollection returned by the
 * {@code Permission.newPermissionCollection}
 * method is a homogeneous collection, which stores only Permission objects
 * for a given Permission type.  A PermissionCollection may also be
 * heterogeneous.  For example, Permissions is a PermissionCollection
 * subclass that represents a collection of PermissionCollections.
 * That is, its members are each a homogeneous PermissionCollection.
 * For example, a Permissions object might have a FilePermissionCollection
 * for all the FilePermission objects, a SocketPermissionCollection for all the
 * SocketPermission objects, and so on. Its {@code add} method adds a
 * permission to the appropriate collection.
 *
 * <p>Whenever a permission is added to a heterogeneous PermissionCollection
 * such as Permissions, and the PermissionCollection doesn't yet contain a
 * PermissionCollection of the specified permission's type, the
 * PermissionCollection should call
 * the {@code newPermissionCollection} method on the permission's class
 * to see if it requires a special PermissionCollection. If
 * {@code newPermissionCollection}
 * returns null, the PermissionCollection
 * is free to store the permission in any type of PermissionCollection it
 * desires (one using a Hashtable, one using a Vector, etc.). For example,
 * the Permissions object uses a default PermissionCollection implementation
 * that stores the permission objects in a Hashtable.
 *
 * <p> Subclass implementations of PermissionCollection should assume
 * that they may be called simultaneously from multiple threads,
 * and therefore should be synchronized properly.  Furthermore,
 * Enumerations returned via the {@code elements} method are
 * not <em>fail-fast</em>.  Modifications to a collection should not be
 * performed while enumerating over that collection.
 *
 * @see Permission
 * @see Permissions
 *
 *
 * @author Roland Schemers
 * @since 1.2
 */

public abstract class PermissionCollection implements java.io.Serializable {

    private static final long serialVersionUID = -6727011328946861783L;

    // when set, add will throw an exception.
    private volatile boolean readOnly;

    
Adds a permission object to the current collection of permission objects.

Params:
  • permission – the Permission object to add.
Throws:
  • SecurityException – -  if this PermissionCollection object
                                has been marked readonly
  • IllegalArgumentException – - if this PermissionCollection
               object is a homogeneous collection and the permission
               is not of the correct type.
/**
     * Adds a permission object to the current collection of permission objects.
     *
     * @param permission the Permission object to add.
     *
     * @exception SecurityException -  if this PermissionCollection object
     *                                 has been marked readonly
     * @exception IllegalArgumentException - if this PermissionCollection
     *                object is a homogeneous collection and the permission
     *                is not of the correct type.
     */
    public abstract void add(Permission permission);

    
Checks to see if the specified permission is implied by
the collection of Permission objects held in this PermissionCollection.

Params:
  • permission – the Permission object to compare.
Returns:true if "permission" is implied by the  permissions in
the collection, false if not.
/**
     * Checks to see if the specified permission is implied by
     * the collection of Permission objects held in this PermissionCollection.
     *
     * @param permission the Permission object to compare.
     *
     * @return true if "permission" is implied by the  permissions in
     * the collection, false if not.
     */
    public abstract boolean implies(Permission permission);

    
Returns an enumeration of all the Permission objects in the collection.

See Also:
Returns:an enumeration of all the Permissions.
/**
     * Returns an enumeration of all the Permission objects in the collection.
     *
     * @return an enumeration of all the Permissions.
     * @see #elementsAsStream()
     */
    public abstract Enumeration<Permission> elements();

    
Returns a stream of all the Permission objects in the collection.

 The collection should not be modified (see add) during the execution of the terminal stream operation. Otherwise, the result of the terminal stream operation is undefined. 
Implementation Requirements: The default implementation creates a stream whose source is derived from the enumeration returned from a call to elements().
Returns:a stream of all the Permissions.
Since:9
/**
     * Returns a stream of all the Permission objects in the collection.
     *
     * <p> The collection should not be modified (see {@link #add}) during the
     * execution of the terminal stream operation. Otherwise, the result of the
     * terminal stream operation is undefined.
     *
     * @implSpec
     * The default implementation creates a stream whose source is derived from
     * the enumeration returned from a call to {@link #elements()}.
     *
     * @return a stream of all the Permissions.
     * @since 9
     */
    public Stream<Permission> elementsAsStream() {
        int characteristics = isReadOnly()
                ? Spliterator.NONNULL | Spliterator.IMMUTABLE
                : Spliterator.NONNULL;
        return StreamSupport.stream(
                Spliterators.spliteratorUnknownSize(
                        elements().asIterator(), characteristics),
                false);
    }

    
Marks this PermissionCollection object as "readonly". After a PermissionCollection object is marked as readonly, no new Permission objects can be added to it using add. 
/**
     * Marks this PermissionCollection object as "readonly". After
     * a PermissionCollection object
     * is marked as readonly, no new Permission objects can be added to it
     * using {@code add}.
     */
    public void setReadOnly() {
        readOnly = true;
    }

    
Returns true if this PermissionCollection object is marked as readonly. If it is readonly, no new Permission objects can be added to it using add. 
By default, the object is not readonly. It can be set to readonly by a call to setReadOnly. 
Returns:true if this PermissionCollection object is marked as readonly,
false otherwise.
/**
     * Returns true if this PermissionCollection object is marked as readonly.
     * If it is readonly, no new Permission objects can be added to it
     * using {@code add}.
     *
     * <p>By default, the object is <i>not</i> readonly. It can be set to
     * readonly by a call to {@code setReadOnly}.
     *
     * @return true if this PermissionCollection object is marked as readonly,
     * false otherwise.
     */
    public boolean isReadOnly() {
        return readOnly;
    }

    
Returns a string describing this PermissionCollection object,
providing information about all the permissions it contains.
The format is:

super.toString() (
  // enumerate all the Permission
  // objects and call toString() on them,
  // one per line..
)
 super.toString is a call to the toString method of this object's superclass, which is Object. The result is this PermissionCollection's type name followed by this object's hashcode, thus enabling clients to differentiate different PermissionCollections object, even if they contain the same permissions. 
Returns:information about this PermissionCollection object,
        as described above.
/**
     * Returns a string describing this PermissionCollection object,
     * providing information about all the permissions it contains.
     * The format is:
     * <pre>
     * super.toString() (
     *   // enumerate all the Permission
     *   // objects and call toString() on them,
     *   // one per line..
     * )</pre>
     *
     * {@code super.toString} is a call to the {@code toString}
     * method of this
     * object's superclass, which is Object. The result is
     * this PermissionCollection's type name followed by this object's
     * hashcode, thus enabling clients to differentiate different
     * PermissionCollections object, even if they contain the same permissions.
     *
     * @return information about this PermissionCollection object,
     *         as described above.
     *
     */
    public String toString() {
        Enumeration<Permission> enum_ = elements();
        StringBuilder sb = new StringBuilder();
        sb.append(super.toString()+" (\n");
        while (enum_.hasMoreElements()) {
            try {
                sb.append(" ");
                sb.append(enum_.nextElement().toString());
                sb.append("\n");
            } catch (NoSuchElementException e){
                // ignore
            }
        }
        sb.append(")\n");
        return sb.toString();
    }
}