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25 
26 package java.security;
27 
28 /**
29  * A GuardedObject is an object that is used to protect access to
30  * another object.
31  *
32  * <p>A GuardedObject encapsulates a target object and a Guard object,
33  * such that access to the target object is possible
34  * only if the Guard object allows it.
35  * Once an object is encapsulated by a GuardedObject,
36  * access to that object is controlled by the {@code getObject}
37  * method, which invokes the
38  * {@code checkGuard} method on the Guard object that is
39  * guarding access. If access is not allowed,
40  * an exception is thrown.
41  *
42  * @see Guard
43  * @see Permission
44  *
45  * @author Roland Schemers
46  * @author Li Gong
47  * @since 1.2
48  */
49 
50 public class GuardedObject implements java.io.Serializable {
51 
52     private static final long serialVersionUID = -5240450096227834308L;
53 
54     private Object object; // the object we are guarding
55     private Guard guard;   // the guard
56 
57     /**
58      * Constructs a GuardedObject using the specified object and guard.
59      * If the Guard object is null, then no restrictions will
60      * be placed on who can access the object.
61      *
62      * @param object the object to be guarded.
63      *
64      * @param guard the Guard object that guards access to the object.
65      */
66 
GuardedObject(Object object, Guard guard)67     public GuardedObject(Object object, Guard guard)
68     {
69         this.guard = guard;
70         this.object = object;
71     }
72 
73     /**
74      * Retrieves the guarded object, or throws an exception if access
75      * to the guarded object is denied by the guard.
76      *
77      * @return the guarded object.
78      *
79      * @exception SecurityException if access to the guarded object is
80      * denied.
81      */
getObject()82     public Object getObject()
83         throws SecurityException
84     {
85         if (guard != null)
86             guard.checkGuard(object);
87 
88         return object;
89     }
90 
91     /**
92      * Writes this object out to a stream (i.e., serializes it).
93      * We check the guard if there is one.
94      */
writeObject(java.io.ObjectOutputStream oos)95     private void writeObject(java.io.ObjectOutputStream oos)
96         throws java.io.IOException
97     {
98         if (guard != null)
99             guard.checkGuard(object);
100 
101         oos.defaultWriteObject();
102     }
103 }
104