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25 
26 package java.lang.module;
27 
28 import java.io.IOException;
29 import java.net.URI;
30 import java.util.Objects;
31 import java.util.Optional;
32 
33 
34 /**
35  * A reference to a module's content.
36  *
37  * <p> A module reference is a concrete implementation of this class that
38  * implements the abstract methods defined by this class. It contains the
39  * module's descriptor and its location, if known.  It also has the ability to
40  * create a {@link ModuleReader} in order to access the module's content, which
41  * may be inside the Java run-time system itself or in an artifact such as a
42  * modular JAR file.
43  *
44  * @see ModuleFinder
45  * @see ModuleReader
46  * @since 9
47  */
48 
49 public abstract class ModuleReference {
50 
51     private final ModuleDescriptor descriptor;
52     private final URI location;
53 
54     /**
55      * Constructs a new instance of this class.
56      *
57      * @param descriptor
58      *        The module descriptor
59      * @param location
60      *        The module location or {@code null} if not known
61      */
ModuleReference(ModuleDescriptor descriptor, URI location)62     protected ModuleReference(ModuleDescriptor descriptor, URI location) {
63         this.descriptor = Objects.requireNonNull(descriptor);
64         this.location = location;
65     }
66 
67     /**
68      * Returns the module descriptor.
69      *
70      * @return The module descriptor
71      */
descriptor()72     public final ModuleDescriptor descriptor() {
73         return descriptor;
74     }
75 
76     /**
77      * Returns the location of this module's content, if known.
78      *
79      * <p> This URI, when present, can be used as the {@linkplain
80      * java.security.CodeSource#getLocation location} value of a {@link
81      * java.security.CodeSource CodeSource} so that a module's classes can be
82      * granted specific permissions when loaded by a {@link
83      * java.security.SecureClassLoader SecureClassLoader}.
84      *
85      * @return The location or an empty {@code Optional} if not known
86      */
location()87     public final Optional<URI> location() {
88         return Optional.ofNullable(location);
89     }
90 
91     /**
92      * Opens the module content for reading.
93      *
94      * @return A {@code ModuleReader} to read the module
95      *
96      * @throws IOException
97      *         If an I/O error occurs
98      * @throws SecurityException
99      *         If denied by the security manager
100      */
open()101     public abstract ModuleReader open() throws IOException;
102 }
103