162 lines
8.3 KiB
Java
162 lines
8.3 KiB
Java
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/*
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* Copyright (c) 1998, 2013, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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/**
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* Provides the classes for implementing networking applications.
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*
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* <p> The java.net package can be roughly divided in two sections:</p>
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* <ul>
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* <li><p><i>A Low Level API</i>, which deals with the
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* following abstractions:</p>
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* <ul>
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* <li><p><i>Addresses</i>, which are networking identifiers,
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* like IP addresses.</p></li>
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* <li><p><i>Sockets</i>, which are basic bidirectional data communication
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* mechanisms.</p></li>
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* <li><p><i>Interfaces</i>, which describe network interfaces. </p></li>
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* </ul></li>
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* <li> <p><i>A High Level API</i>, which deals with the following
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* abstractions:</p>
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* <ul>
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* <li><p><i>URIs</i>, which represent
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* Universal Resource Identifiers.</p></li>
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* <li><p><i>URLs</i>, which represent
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* Universal Resource Locators.</p></li>
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* <li><p><i>Connections</i>, which represents connections to the resource
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* pointed to by <i>URLs</i>.</p></li>
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* </ul></li>
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* </ul>
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* <h2>Addresses</h2>
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* <p>Addresses are used throughout the java.net APIs as either host
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* identifiers, or socket endpoint identifiers.</p>
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* <p>The {@link java.net.InetAddress} class is the abstraction representing an
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* IP (Internet Protocol) address. It has two subclasses:
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* <ul>
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* <li>{@link java.net.Inet4Address} for IPv4 addresses.</li>
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* <li>{@link java.net.Inet6Address} for IPv6 addresses.</li>
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* </ul>
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* <p>But, in most cases, there is no need to deal directly with the subclasses,
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* as the InetAddress abstraction should cover most of the needed
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* functionality.</p>
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* <h3><b>About IPv6</b></h3>
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* <p>Not all systems have support for the IPv6 protocol, and while the Java
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* networking stack will attempt to detect it and use it transparently when
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* available, it is also possible to disable its use with a system property.
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* In the case where IPv6 is not available, or explicitly disabled,
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* Inet6Address are not valid arguments for most networking operations any
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* more. While methods like {@link java.net.InetAddress#getByName} are
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* guaranteed not to return an Inet6Address when looking up host names, it
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* is possible, by passing literals, to create such an object. In which
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* case, most methods, when called with an Inet6Address will throw an
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* Exception.</p>
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* <h2>Sockets</h2>
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* <p>Sockets are means to establish a communication link between machines over
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* the network. The java.net package provides 4 kinds of Sockets:</p>
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* <ul>
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* <li>{@link java.net.Socket} is a TCP client API, and will typically
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* be used to {@linkplain java.net.Socket#connect(SocketAddress)
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* connect} to a remote host.</li>
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* <li>{@link java.net.ServerSocket} is a TCP server API, and will
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* typically {@linkplain java.net.ServerSocket#accept accept}
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* connections from client sockets.</li>
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* <li>{@link java.net.DatagramSocket} is a UDP endpoint API and is used
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* to {@linkplain java.net.DatagramSocket#send send} and
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* {@linkplain java.net.DatagramSocket#receive receive}
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* {@linkplain java.net.DatagramPacket datagram packets}.</li>
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* <li>{@link java.net.MulticastSocket} is a subclass of
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* {@code DatagramSocket} used when dealing with multicast
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* groups.</li>
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* </ul>
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* <p>Sending and receiving with TCP sockets is done through InputStreams and
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* OutputStreams which can be obtained via the
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* {@link java.net.Socket#getInputStream} and
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* {@link java.net.Socket#getOutputStream} methods.</p>
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* <h2>Interfaces</h2>
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* <p>The {@link java.net.NetworkInterface} class provides APIs to browse and
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* query all the networking interfaces (e.g. ethernet connection or PPP
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* endpoint) of the local machine. It is through that class that you can
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* check if any of the local interfaces is configured to support IPv6.</p>
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* <p>Note, all conforming implementations must support at least one
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* {@code NetworkInterface} object, which must either be connected to a
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* network, or be a "loopback" interface that can only communicate with
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* entities on the same machine.</p>
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*
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* <h2>High level API</h2>
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* <p>A number of classes in the java.net package do provide for a much higher
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* level of abstraction and allow for easy access to resources on the
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* network. The classes are:
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* <ul>
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* <li>{@link java.net.URI} is the class representing a
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* Universal Resource Identifier, as specified in RFC 2396.
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* As the name indicates, this is just an Identifier and doesn't
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* provide directly the means to access the resource.</li>
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* <li>{@link java.net.URL} is the class representing a
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* Universal Resource Locator, which is both an older concept for
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* URIs and a means to access the resources.</li>
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* <li>{@link java.net.URLConnection} is created from a URL and is the
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* communication link used to access the resource pointed by the
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* URL. This abstract class will delegate most of the work to the
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* underlying protocol handlers like http or https.</li>
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* <li>{@link java.net.HttpURLConnection} is a subclass of URLConnection
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* and provides some additional functionalities specific to the
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* HTTP protocol.</li>
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* </ul>
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* <p>The recommended usage is to use {@link java.net.URI} to identify
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* resources, then convert it into a {@link java.net.URL} when it is time to
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* access the resource. From that URL, you can either get the
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* {@link java.net.URLConnection} for fine control, or get directly the
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* InputStream.
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* <p>Here is an example:</p>
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* <pre>
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* URI uri = new URI("http://java.sun.com/");
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* URL url = uri.toURL();
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* InputStream in = url.openStream();
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* </pre>
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* <h2>Protocol Handlers</h2>
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* As mentioned, URL and URLConnection rely on protocol handlers which must be
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* present, otherwise an Exception is thrown. This is the major difference with
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* URIs which only identify resources, and therefore don't need to have access
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* to the protocol handler. So, while it is possible to create an URI with any
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* kind of protocol scheme (e.g. {@code myproto://myhost.mydomain/resource/}),
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* a similar URL will try to instantiate the handler for the specified protocol;
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* if it doesn't exist an exception will be thrown.
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* <p>By default the protocol handlers are loaded dynamically from the default
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* location. It is, however, possible to add to the search path by setting
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* the {@code java.protocol.handler.pkgs} system property. For instance if
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* it is set to {@code myapp.protocols}, then the URL code will try, in the
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* case of http, first to load {@code myapp.protocols.http.Handler}, then,
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* if this fails, {@code http.Handler} from the default location.
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* <p>Note that the Handler class <b>has to</b> be a subclass of the abstract
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* class {@link java.net.URLStreamHandler}.</p>
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* <h2>Additional Specification</h2>
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* <ul>
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* <li><a href="doc-files/net-properties.html">
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* Networking System Properties</a></li>
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* </ul>
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*
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* @since JDK1.0
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*/
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package java.net;
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