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25
26 /**
27 * Provides the classes for implementing networking applications.
28 *
29 * <p> The java.net package can be roughly divided in two sections:</p>
30 * <ul>
31 * <li><p><i>A Low Level API</i>, which deals with the
32 * following abstractions:</p>
33 * <ul>
34 * <li><p><i>Addresses</i>, which are networking identifiers,
35 * like IP addresses.</p></li>
36 * <li><p><i>Sockets</i>, which are basic bidirectional data communication
37 * mechanisms.</p></li>
38 * <li><p><i>Interfaces</i>, which describe network interfaces. </p></li>
39 * </ul></li>
40 * <li> <p><i>A High Level API</i>, which deals with the following
41 * abstractions:</p>
42 * <ul>
43 * <li><p><i>URIs</i>, which represent
44 * Universal Resource Identifiers.</p></li>
45 * <li><p><i>URLs</i>, which represent
46 * Universal Resource Locators.</p></li>
47 * <li><p><i>Connections</i>, which represents connections to the resource
48 * pointed to by <i>URLs</i>.</p></li>
49 * </ul></li>
50 * </ul>
51 * <h2>Addresses</h2>
52 * <p>Addresses are used throughout the java.net APIs as either host
53 * identifiers, or socket endpoint identifiers.</p>
54 * <p>The {@link java.net.InetAddress} class is the abstraction representing an
55 * IP (Internet Protocol) address. It has two subclasses:
56 * <ul>
57 * <li>{@link java.net.Inet4Address} for IPv4 addresses.</li>
58 * <li>{@link java.net.Inet6Address} for IPv6 addresses.</li>
59 * </ul>
60 * <p>But, in most cases, there is no need to deal directly with the subclasses,
61 * as the InetAddress abstraction should cover most of the needed
62 * functionality.</p>
63 * <h3><b>About IPv6</b></h3>
64 * <p>Not all systems have support for the IPv6 protocol, and while the Java
65 * networking stack will attempt to detect it and use it transparently when
66 * available, it is also possible to disable its use with a system property.
67 * In the case where IPv6 is not available, or explicitly disabled,
68 * Inet6Address are not valid arguments for most networking operations any
69 * more. While methods like {@link java.net.InetAddress#getByName} are
70 * guaranteed not to return an Inet6Address when looking up host names, it
71 * is possible, by passing literals, to create such an object. In which
72 * case, most methods, when called with an Inet6Address will throw an
73 * Exception.</p>
74 * <h2>Sockets</h2>
75 * <p>Sockets are means to establish a communication link between machines over
76 * the network. The java.net package provides 4 kinds of Sockets:</p>
77 * <ul>
78 * <li>{@link java.net.Socket} is a TCP client API, and will typically
79 * be used to {@linkplain java.net.Socket#connect(SocketAddress)
80 * connect} to a remote host.</li>
81 * <li>{@link java.net.ServerSocket} is a TCP server API, and will
82 * typically {@linkplain java.net.ServerSocket#accept accept}
83 * connections from client sockets.</li>
84 * <li>{@link java.net.DatagramSocket} is a UDP endpoint API and is used
85 * to {@linkplain java.net.DatagramSocket#send send} and
86 * {@linkplain java.net.DatagramSocket#receive receive}
87 * {@linkplain java.net.DatagramPacket datagram packets}.</li>
88 * <li>{@link java.net.MulticastSocket} is a subclass of
89 * {@code DatagramSocket} used when dealing with multicast
90 * groups.</li>
91 * </ul>
92 * <p>Sending and receiving with TCP sockets is done through InputStreams and
93 * OutputStreams which can be obtained via the
94 * {@link java.net.Socket#getInputStream} and
95 * {@link java.net.Socket#getOutputStream} methods.</p>
96 * <h2>Interfaces</h2>
97 * <p>The {@link java.net.NetworkInterface} class provides APIs to browse and
98 * query all the networking interfaces (e.g. ethernet connection or PPP
99 * endpoint) of the local machine. It is through that class that you can
100 * check if any of the local interfaces is configured to support IPv6.</p>
101 * <p>Note, all conforming implementations must support at least one
102 * {@code NetworkInterface} object, which must either be connected to a
103 * network, or be a "loopback" interface that can only communicate with
104 * entities on the same machine.</p>
105 *
106 * <h2>High level API</h2>
107 * <p>A number of classes in the java.net package do provide for a much higher
108 * level of abstraction and allow for easy access to resources on the
109 * network. The classes are:
110 * <ul>
111 * <li>{@link java.net.URI} is the class representing a
112 * Universal Resource Identifier, as specified in RFC 2396.
113 * As the name indicates, this is just an Identifier and doesn't
114 * provide directly the means to access the resource.</li>
115 * <li>{@link java.net.URL} is the class representing a
116 * Universal Resource Locator, which is both an older concept for
117 * URIs and a means to access the resources.</li>
118 * <li>{@link java.net.URLConnection} is created from a URL and is the
119 * communication link used to access the resource pointed by the
120 * URL. This abstract class will delegate most of the work to the
121 * underlying protocol handlers like http or https.</li>
122 * <li>{@link java.net.HttpURLConnection} is a subclass of URLConnection
123 * and provides some additional functionalities specific to the
124 * HTTP protocol.</li>
125 * </ul>
126 * <p>The recommended usage is to use {@link java.net.URI} to identify
127 * resources, then convert it into a {@link java.net.URL} when it is time to
128 * access the resource. From that URL, you can either get the
129 * {@link java.net.URLConnection} for fine control, or get directly the
130 * InputStream.
131 * <p>Here is an example:</p>
132 * <pre>
133 * URI uri = new URI("http://java.sun.com/");
134 * URL url = uri.toURL();
135 * InputStream in = url.openStream();
136 * </pre>
137 * <h2>Protocol Handlers</h2>
138 * As mentioned, URL and URLConnection rely on protocol handlers which must be
139 * present, otherwise an Exception is thrown. This is the major difference with
140 * URIs which only identify resources, and therefore don't need to have access
141 * to the protocol handler. So, while it is possible to create an URI with any
142 * kind of protocol scheme (e.g. {@code myproto://myhost.mydomain/resource/}),
143 * a similar URL will try to instantiate the handler for the specified protocol;
144 * if it doesn't exist an exception will be thrown.
145 * <p>By default the protocol handlers are loaded dynamically from the default
146 * location. It is, however, possible to add to the search path by setting
147 * the {@code java.protocol.handler.pkgs} system property. For instance if
148 * it is set to {@code myapp.protocols}, then the URL code will try, in the
149 * case of http, first to load {@code myapp.protocols.http.Handler}, then,
150 * if this fails, {@code http.Handler} from the default location.
151 * <p>Note that the Handler class <b>has to</b> be a subclass of the abstract
152 * class {@link java.net.URLStreamHandler}.</p>
153 * <h2>Additional Specification</h2>
154 * <ul>
155 * <li><a href="doc-files/net-properties.html">
156 * Networking System Properties</a></li>
157 * </ul>
158 *
159 * @since 1.0
160 */
161 package java.net;