url.java

来自「《移动Agent技术》一书的所有章节源代码。」· Java 代码 · 共 719 行 · 第 1/2 页

	    i = spec.indexOf('#', start);
	    if (i >= 0) {
		ref = spec.substring(i + 1, limit);
		limit = i;
	    }
	    handler.parseURL(this, spec, start, limit);

	} catch(MalformedURLException e) {
	    throw e;
	} catch(Exception e) {
	    throw new MalformedURLException(original + ": " + e);
	}
    }

    /**
     * Sets the fields of the URL. This is not a public method so that 
     * only URLStreamHandlers can modify URL fields. URLs are 
     * otherwise constant.
     *
     * REMIND: this method will be moved to URLStreamHandler
     *
     * @param protocol the protocol to use
     * @param host the host name to connecto to
     * @param port the protocol port to connect to
     * @param file the specified file name on that host
     * @param ref the reference
     */
    protected void set(String protocol, String host, int port, String file, String ref) {
	this.protocol = protocol;
	this.host = host;
	this.port = port;
	this.file = file;
	this.ref = ref;
    }

    /**
     * Returns the port number of this <code>URL</code>.
     * Returns -1 if the port is not set.
     *
     * @return  the port number
     * @since   JDK1.0
     */
    public int getPort() {
	return port;
    }

    /**
     * Returns the protocol name this <code>URL</code>.
     *
     * @return  the protocol of this <code>URL</code>.
     * @since   JDK1.0
     */
    public String getProtocol() {
	return protocol;
    }

    /**
     * Returns the host name of this <code>URL</code>, if applicable.
     * For "<code>file</code>" protocol, this is an empty string.
     *
     * @return  the host name of this <code>URL</code>.
     * @since   JDK1.0
     */
    public String getHost() {
	return host;
    }

    /**
     * Returns the file name of this <code>URL</code>.
     *
     * @return  the file name of this <code>URL</code>.
     * @since   JDK1.0
     */
    public String getFile() {
	return file;
    }

    /**
     * Returns the anchor (also known as the "reference") of this
     * <code>URL</code>.
     *
     * @return  the anchor (also known as the "reference") of this
     *          <code>URL</code>.
     * @since   JDK1.0
     */
    public String getRef() {
	return ref;
    }

    /**
     * Compares two URLs.
     * The result is <code>true</code> if and only if the argument is 
     * not <code>null</code> and is a <code>URL</code> object that 
     * represents the same <code>URL</code> as this object. Two URL 
     * objects are equal if they have the same protocol and reference the 
     * same host, the same port number on the host, and the same file on 
     * the host. The anchors of the URL objects are not compared. 
     * <p>
     * This method is equivalent to:
     * <ul><code>
     *     (obj instanceof URL) &amp;&amp; sameFile((URL)obj)
     * </code></ul>
     *
     * @param   obj   the URL to compare against.
     * @return  <code>true</code> if the objects are the same;
     *          <code>false</code> otherwise.
     * @since   JDK1.0
     */
    public boolean equals(Object obj) {
	return (ref == null) ? (obj instanceof URL) && sameFile((URL)obj):
	    (obj instanceof URL) && sameFile((URL)obj) && ref.equals(((URL)obj).ref);
    }

    /** 
     * Creates an integer suitable for hash table indexing. 
     *
     * @return  a hash code for this <code>URL</code>.
     * @since   JDK1.0
     */
    public int hashCode() {

	if (hashCode == -1) {
	    hashCode = host.toLowerCase().hashCode() ^ file.hashCode() ^
		protocol.hashCode();
	}

	return hashCode;
    }
	
    /**
     * Compares the host components of two URLs.
     * @param h1 the URL of the first host to compare 
     * @param h2 the URL of the second host to compare 
     * @return	true if and only if they are equal, false otherwise.
     * @exception UnknownHostException If an unknown host is found.
     */
    boolean hostsEqual(String h1, String h2) {
	if (h1.equals(h2)) {
	    return true;
	}
	// Have to resolve addresses before comparing, otherwise
	// names like tachyon and tachyon.eng would compare different
	try {
	    InetAddress a1 = InetAddress.getByName(h1);
	    InetAddress a2 = InetAddress.getByName(h2);
	    return a1.equals(a2);
	} catch(UnknownHostException e) {
	} catch(SecurityException e) {
	}
	return false;
    }

    /**
     * Compares two URLs, excluding the "ref" fields.
     * Returns <code>true</code> if this <code>URL</code> and the 
     * <code>other</code> argument both refer to the same resource.
     * The two <code>URL</code>s might not both contain the same anchor. 
     *
     * @param   other   the <code>URL</code> to compare against.
     * @return  <code>true</code> if they reference the same remote object;
     *          <code>false</code> otherwise.
     * @since   JDK1.0
     */
    public boolean sameFile(URL other) {
	// AVH: should we not user getPort to compare ports?
	return protocol.equals(other.protocol) &&
	       hostsEqual(host, other.host) &&
	       (port == other.port) &&
	       file.equals(other.file);
    }

    /**
     * Constructs a string representation of this <code>URL</code>. The 
     * string is created by calling the <code>toExternalForm</code> 
     * method of the stream protocol handler for this object. 
     *
     * @return  a string representation of this object.
     * @see     java.net.URL#URL(java.lang.String, java.lang.String, int, java.lang.String)
     * @see     java.net.URLStreamHandler#toExternalForm(java.net.URL)
     * @since   JDK1.0
     */
    public String toString() {
	return toExternalForm();
    }

    /**
     * Constructs a string representation of this <code>URL</code>. The 
     * string is created by calling the <code>toExternalForm</code> 
     * method of the stream protocol handler for this object. 
     *
     * @return  a string representation of this object.
     * @see     java.net.URL#URL(java.lang.String, java.lang.String, int, java.lang.String)
     * @see     java.net.URLStreamHandler#toExternalForm(java.net.URL)
     * @since   JDK1.0
     */
    public String toExternalForm() {
	return handler.toExternalForm(this);
    }

    /** 
     * Returns a <code>URLConnection</code> object that represents a 
     * connection to the remote object referred to by the <code>URL</code>.
     * <p>
     * If there is not already an open connection, the connection is 
     * opened by calling the <code>openConnection</code> method of the 
     * protocol handler for this URL. 
     *
     * @return     a <code>URLConnection</code> to the URL.
     * @exception  IOException  if an I/O exception occurs.
     * @see        java.net.URL#URL(java.lang.String, java.lang.String, int, java.lang.String)
     * @see        java.net.URLConnection
     * @see        java.net.URLStreamHandler#openConnection(java.net.URL)
     * @since      JDK1.0
     */
    public URLConnection openConnection()
	throws java.io.IOException
    {
	return handler.openConnection(this);
    }

    /**
     * Opens a connection to this <code>URL</code> and returns an 
     * <code>InputStream</code> for reading from that connection. This 
     * method is a shorthand for:
     * <ul><code>
     *     openConnection().getInputStream()
     * </code></ul>
     *
     * @return     an input stream for reading from the URL connection.
     * @exception  IOException  if an I/O exception occurs.
     * @since      JDK1.0
     */
    public final InputStream openStream() 			// REMIND: drop final
	throws java.io.IOException
    {
	return openConnection().getInputStream();
    }

    /**
     * Returns the contents of this URL. This method is a shorthand for:
     * <ul><code>
     *     openConnection().getContent()
     * </code></ul>
     *
     * @return     the contents of this URL.
     * @exception  IOException  if an I/O exception occurs.
     * @see        java.net.URLConnection#getContent()
     * @since      JDK1.0
     */
    public final Object getContent() 				// REMIND: drop final
	throws java.io.IOException
    {
	return openConnection().getContent();
    }

    /**
     * The URLStreamHandler factory.
     */
    static URLStreamHandlerFactory factory;

    /**
     * Sets an application's <code>URLStreamHandlerFactory</code>.
     * This method can be called at most once by an application. 
     * <p>
     * The <code>URLStreamHandlerFactory</code> instance is used to 
     * construct a stream protocol handler from a protocol name. 
     *
     * @param      fac   the desired factory.
     * @exception  Error  if the application has already set a factory.
     * @see        java.net.URL#URL(java.lang.String, java.lang.String, int, java.lang.String)
     * @see        java.net.URLStreamHandlerFactory
     * @since      JDK1.0
     */
    public static synchronized void setURLStreamHandlerFactory(URLStreamHandlerFactory fac) {
	if (factory != null) {
	    throw new Error("factory already defined");
	}
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	    security.checkSetFactory();
	}
	handlers.clear();
	factory = fac;
    }

    /**
     * A table of protocol handlers.
     */
    static Hashtable handlers = new Hashtable();

    /**
     * Returns the Stream Handler.
     * @param protocol the protocol to use
     */
    static synchronized URLStreamHandler getURLStreamHandler(String protocol) {
	URLStreamHandler handler = (URLStreamHandler)handlers.get(protocol);
	if (handler == null) {
	    // Use the factory (if any)
	    if (factory != null) {
		handler = factory.createURLStreamHandler(protocol);
	    }

	    // Try java protocol handler
	    if (handler == null) {
		String packagePrefixList =
		    System.getProperty(protocolPathProp, "");
		if (packagePrefixList != "") {
		    packagePrefixList += "|";
		}

		// REMIND: decide whether to allow the "null" class prefix
		// or not.
		packagePrefixList += "sun.net.www.protocol";

		StringTokenizer packagePrefixIter =
		    new StringTokenizer(packagePrefixList, "|");

		while (handler == null && packagePrefixIter.hasMoreTokens()) {
		    String packagePrefix = packagePrefixIter.nextToken().trim();
		    try {
			String clname = packagePrefix + "." + protocol
			    + ".Handler";
			handler = (URLStreamHandler)Class.forName(clname).newInstance();
		    } catch (Exception e) {
		    }
		}
	    }
	    if (handler != null) {
		handlers.put(protocol, handler);
	    }
	}
	return handler;
    }

    /**
     * WriteObject is called to save the state of the URL to an ObjectOutputStream
     * The handler is not saved since it is specific to this system.
     */
    private synchronized void writeObject(java.io.ObjectOutputStream s)
        throws IOException
    {
	s.defaultWriteObject();	// write the fields
    }

    /**
     * readObject is called to restore the state of the URL from the stream.
     * It reads the compoents of the URL and finds the local stream handler.
     */
    private synchronized void readObject(java.io.ObjectInputStream s)
         throws IOException, ClassNotFoundException
    {
	s.defaultReadObject();	// read the fields
	if ((handler = getURLStreamHandler(protocol)) == null) {
	    throw new IOException("unknown protocol: " + protocol);
	}
    }
}