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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  * @spec JPMS
48  */
49 
50 public abstract class ModuleReference {
51 
52     private final ModuleDescriptor descriptor;
53     private final URI location;
54 
55     /**
56      * Constructs a new instance of this class.
57      *
58      * @param descriptor
59      *        The module descriptor
60      * @param location
61      *        The module location or {@code null} if not known
62      */
ModuleReference(ModuleDescriptor descriptor, URI location)63     protected ModuleReference(ModuleDescriptor descriptor, URI location) {
64         this.descriptor = Objects.requireNonNull(descriptor);
65         this.location = location;
66     }
67 
68     /**
69      * Returns the module descriptor.
70      *
71      * @return The module descriptor
72      */
descriptor()73     public final ModuleDescriptor descriptor() {
74         return descriptor;
75     }
76 
77     /**
78      * Returns the location of this module's content, if known.
79      *
80      * <p> This URI, when present, can be used as the {@linkplain
81      * java.security.CodeSource#getLocation location} value of a {@link
82      * java.security.CodeSource CodeSource} so that a module's classes can be
83      * granted specific permissions when loaded by a {@link
84      * java.security.SecureClassLoader SecureClassLoader}.
85      *
86      * @return The location or an empty {@code Optional} if not known
87      */
location()88     public final Optional<URI> location() {
89         return Optional.ofNullable(location);
90     }
91 
92     /**
93      * Opens the module content for reading.
94      *
95      * @return A {@code ModuleReader} to read the module
96      *
97      * @throws IOException
98      *         If an I/O error occurs
99      * @throws SecurityException
100      *         If denied by the security manager
101      */
open()102     public abstract ModuleReader open() throws IOException;
103 }
104