urlconnection.java

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/*
 * @(#)URLConnection.java	1.98 03/08/14
 *
 * Copyright  1990-2008 Sun Microsystems, Inc. All Rights Reserved.  
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER  
 *   
 * This program is free software; you can redistribute it and/or  
 * modify it under the terms of the GNU General Public License version  
 * 2 only, as published by the Free Software Foundation.   
 *   
 * This program is distributed in the hope that it will be useful, but  
 * WITHOUT ANY WARRANTY; without even the implied warranty of  
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU  
 * General Public License version 2 for more details (a copy is  
 * included at /legal/license.txt).   
 *   
 * You should have received a copy of the GNU General Public License  
 * version 2 along with this work; if not, write to the Free Software  
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  
 * 02110-1301 USA   
 *   
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa  
 * Clara, CA 95054 or visit www.sun.com if you need additional  
 * information or have any questions. 
 *
 */

package java.net;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Hashtable;
import java.text.DateFormat;
import java.util.StringTokenizer;
import java.util.Collections;
import java.util.Map;
import java.security.Permission;
import java.security.AccessController;
import sun.security.util.SecurityConstants;

/**
 * The abstract class <code>URLConnection</code> is the superclass
 * of all classes that represent a communications link between the
 * application and a URL. Instances of this class can be used both to
 * read from and to write to the resource referenced by the URL. In
 * general, creating a connection to a URL is a multistep process:
 * <p>
 * <center><table border=2 summary="Describes the process of creating a connection to a URL: openConnection() and connect() over time.">
 * <tr><th><code>openConnection()</code></th>
 *     <th><code>connect()</code></th></tr>
 * <tr><td>Manipulate parameters that affect the connection to the remote
 *         resource.</td>
 *     <td>Interact with the resource; query header fields and
 *         contents.</td></tr>
 * </table>
 * ----------------------------&gt;
 * <br>time</center>
 *
 * <ol>
 * <li>The connection object is created by invoking the
 *     <code>openConnection</code> method on a URL.
 * <li>The setup parameters and general request properties are manipulated.
 * <li>The actual connection to the remote object is made, using the
 *    <code>connect</code> method.
 * <li>The remote object becomes available. The header fields and the contents
 *     of the remote object can be accessed.
 * </ol>
 * <p>
 * The setup parameters are modified using the following methods:
 * <ul>
 *   <li><code>setAllowUserInteraction</code>
 *   <li><code>setDoInput</code>
 *   <li><code>setDoOutput</code>
 *   <li><code>setIfModifiedSince</code>
 *   <li><code>setUseCaches</code>
 * </ul>
 * <p>
 * and the general request properties are modified using the method:
 * <ul>
 *   <li><code>setRequestProperty</code>
 * </ul>
 * <p>
 * Default values for the <code>AllowUserInteraction</code> and
 * <code>UseCaches</code> parameters can be set using the methods
 * <code>setDefaultAllowUserInteraction</code> and
 * <code>setDefaultUseCaches</code>.
 * <p>
 * Each of the above <code>set</code> methods has a corresponding
 * <code>get</code> method to retrieve the value of the parameter or
 * general request property. The specific parameters and general
 * request properties that are applicable are protocol specific. 
 * <p>
 * The following methods are used to access the header fields and 
 * the contents after the connection is made to the remote object:
 * <ul>
 *   <li><code>getContent</code>
 *   <li><code>getHeaderField</code>
 *   <li><code>getInputStream</code>
 *   <li><code>getOutputStream</code>
 * </ul>
 * <p>
 * Certain header fields are accessed frequently. The methods:
 * <ul>
 *   <li><code>getContentEncoding</code>
 *   <li><code>getContentLength</code>
 *   <li><code>getContentType</code>
 *   <li><code>getDate</code>
 *   <li><code>getExpiration</code>
 *   <li><code>getLastModifed</code>
 * </ul>
 * <p>
 * provide convenient access to these fields. The 
 * <code>getContentType</code> method is used by the 
 * <code>getContent</code> method to determine the type of the remote 
 * object; subclasses may find it convenient to override the 
 * <code>getContentType</code> method. 
 * <p>
 * In the common case, all of the pre-connection parameters and 
 * general request properties can be ignored: the pre-connection 
 * parameters and request properties default to sensible values. For
 * most clients of this interface, there are only two interesting
 * methods: <code>getInputStream</code> and <code>getContent</code>,
 * which are mirrored in the <code>URL</code> class by convenience methods.
 * <p>
 * More information on the request properties and header fields of
 * an <code>http</code> connection can be found at:
 * <blockquote><pre>
 * <a href="http://www.ietf.org/rfc/rfc2068.txt">http://www.ietf.org/rfc/rfc2068.txt</a>
 * </pre></blockquote>
 *
 * Note about <code>fileNameMap</code>: In versions prior to JDK 1.1.6, 
 * field <code>fileNameMap</code> of <code>URLConnection</code> was public.
 * In JDK 1.1.6 and later, <code>fileNameMap</code> is private; accessor 
 * and mutator methods {@link #getFileNameMap() getFileNameMap} and 
 * {@link #setFileNameMap(java.net.FileNameMap) setFileNameMap} are added
 * to access it.  This change is also described on the <a href=
 * "http://java.sun.com/products/jdk/1.2/compatibility.html#incompatibilities1.2">
 * Compatibility</a> page.
 *
 * Calling the <tt>close()</tt> methods on the <tt>InputStream</tt> or <tt>OutputStream</tt> of an 
 * <tt>URLConnection</tt> after a request may free network resources associated with this 
 * instance, unless particular protocol specifications specify different behaviours 
 * for it.
 *
 * @author  James Gosling
 * @version 1.75, 05/03/00
 * @see     java.net.URL#openConnection()
 * @see     java.net.URLConnection#connect()
 * @see     java.net.URLConnection#getContent()
 * @see     java.net.URLConnection#getContentEncoding()
 * @see     java.net.URLConnection#getContentLength()
 * @see     java.net.URLConnection#getContentType()
 * @see     java.net.URLConnection#getDate()
 * @see     java.net.URLConnection#getExpiration()
 * @see     java.net.URLConnection#getHeaderField(int)
 * @see     java.net.URLConnection#getHeaderField(java.lang.String)
 * @see     java.net.URLConnection#getInputStream()
 * @see     java.net.URLConnection#getLastModified()
 * @see     java.net.URLConnection#getOutputStream()
 * @see     java.net.URLConnection#setAllowUserInteraction(boolean)
 * @see     java.net.URLConnection#setDefaultUseCaches(boolean)
 * @see     java.net.URLConnection#setDoInput(boolean)
 * @see     java.net.URLConnection#setDoOutput(boolean)
 * @see     java.net.URLConnection#setIfModifiedSince(long)
 * @see     java.net.URLConnection#setRequestProperty(java.lang.String, java.lang.String)
 * @see     java.net.URLConnection#setUseCaches(boolean)
 * @since   JDK1.0
 */
public abstract class URLConnection {

   /**
     * The URL represents the remote object on the World Wide Web to 
     * which this connection is opened. 
     * <p>
     * The value of this field can be accessed by the 
     * <code>getURL</code> method. 
     * <p>
     * The default value of this variable is the value of the URL 
     * argument in the <code>URLConnection</code> constructor. 
     *
     * @see     java.net.URLConnection#getURL()
     * @see     java.net.URLConnection#url
     */
    protected URL url;

   /**
     * This variable is set by the <code>setDoInput</code> method. Its 
     * value is returned by the <code>getDoInput</code> method. 
     * <p>
     * A URL connection can be used for input and/or output. Setting the 
     * <code>doInput</code> flag to <code>true</code> indicates that 
     * the application intends to read data from the URL connection. 
     * <p>
     * The default value of this field is <code>true</code>. 
     *
     * @see     java.net.URLConnection#getDoInput()
     * @see     java.net.URLConnection#setDoInput(boolean)
     */
    protected boolean doInput = true;

   /**
     * This variable is set by the <code>setDoOutput</code> method. Its 
     * value is returned by the <code>getDoOutput</code> method. 
     * <p>
     * A URL connection can be used for input and/or output. Setting the 
     * <code>doOutput</code> flag to <code>true</code> indicates 
     * that the application intends to write data to the URL connection. 
     * <p>
     * The default value of this field is <code>false</code>. 
     *
     * @see     java.net.URLConnection#getDoOutput()
     * @see     java.net.URLConnection#setDoOutput(boolean)
     */
    protected boolean doOutput = false;

    private static boolean defaultAllowUserInteraction = false;

   /**
     * If <code>true</code>, this <code>URL</code> is being examined in 
     * a context in which it makes sense to allow user interactions such 
     * as popping up an authentication dialog. If <code>false</code>, 
     * then no user interaction is allowed. 
     * <p>
     * The value of this field can be set by the 
     * <code>setAllowUserInteraction</code> method.
     * Its value is returned by the 
     * <code>getAllowUserInteraction</code> method.
     * Its default value is the value of the argument in the last invocation 
     * of the <code>setDefaultAllowUserInteraction</code> method. 
     *
     * @see     java.net.URLConnection#getAllowUserInteraction()
     * @see     java.net.URLConnection#setAllowUserInteraction(boolean)
     * @see     java.net.URLConnection#setDefaultAllowUserInteraction(boolean)
     */
    protected boolean allowUserInteraction = defaultAllowUserInteraction;

    private static boolean defaultUseCaches = true;

   /**
     * If <code>true</code>, the protocol is allowed to use caching 
     * whenever it can. If <code>false</code>, the protocol must always 
     * try to get a fresh copy of the object. 
     * <p>
     * This field is set by the <code>setUseCaches</code> method. Its 
     * value is returned by the <code>getUseCaches</code> method.
     * <p>
     * Its default value is the value given in the last invocation of the 
     * <code>setDefaultUseCaches</code> method. 
     *
     * @see     java.net.URLConnection#setUseCaches(boolean)
     * @see     java.net.URLConnection#getUseCaches()
     * @see     java.net.URLConnection#setDefaultUseCaches(boolean)
     */
    protected boolean useCaches = defaultUseCaches;

   /**
     * Some protocols support skipping the fetching of the object unless 
     * the object has been modified more recently than a certain time. 
     * <p>
     * A nonzero value gives a time as the number of milliseconds since 
     * January 1, 1970, GMT. The object is fetched only if it has been 
     * modified more recently than that time. 
     * <p>
     * This variable is set by the <code>setIfModifiedSince</code> 
     * method. Its value is returned by the 
     * <code>getIfModifiedSince</code> method.
     * <p>
     * The default value of this field is <code>0</code>, indicating 
     * that the fetching must always occur. 
     *
     * @see     java.net.URLConnection#getIfModifiedSince()
     * @see     java.net.URLConnection#setIfModifiedSince(long)
     */
    protected long ifModifiedSince = 0;

   /**
     * If <code>false</code>, this connection object has not created a 
     * communications link to the specified URL. If <code>true</code>, 
     * the communications link has been established. 
     */
    protected boolean connected = false;

   /**
    * @since   JDK1.1
     */
    private static FileNameMap fileNameMap;

    /**
     * @since 1.2.2
     */
    private static boolean fileNameMapLoaded = false;

    /**
     * Loads filename map (a mimetable) from a data file. It will
     * first try to load the user-specific table, defined
     * by &quot;content.types.user.table&quot; property. If that fails,
     * it tries to load the default built-in table at 
     * lib/content-types.properties under java home.
     *
     * @return the FileNameMap
     * @since 1.2
     * @see #setFileNameMap(java.net.FileNameMap)
     */
    public static synchronized FileNameMap getFileNameMap() {
	if ((fileNameMap == null) && !fileNameMapLoaded) {
	    fileNameMap = sun.net.www.MimeTable.loadTable();
	    fileNameMapLoaded = true;
	}

	return new FileNameMap() {
	    private FileNameMap map = fileNameMap;
	    public String getContentTypeFor(String fileName) {
		return map.getContentTypeFor(fileName);
	    }
	};
    }

    /**
     * Sets the FileNameMap.
     * <p>
     * If there is a security manager, this method first calls
     * the security manager's <code>checkSetFactory</code> method 
     * to ensure the operation is allowed. 
     * This could result in a SecurityException.
     *
     * @param map the FileNameMap to be set
     * @exception  SecurityException  if a security manager exists and its  
     *             <code>checkSetFactory</code> method doesn't allow the operation.
     * @see        SecurityManager#checkSetFactory
     * @see #getFileNameMap()
     * @since 1.2
     */
    public static void setFileNameMap(FileNameMap map) {
	SecurityManager sm = System.getSecurityManager();
	if (sm != null) sm.checkSetFactory();
	fileNameMap = map;
    }

    /**
     * Opens a communications link to the resource referenced by this 
     * URL, if such a connection has not already been established. 
     * <p>
     * If the <code>connect</code> method is called when the connection 
     * has already been opened (indicated by the <code>connected</code> 
     * field having the value <code>true</code>), the call is ignored. 
     * <p>
     * URLConnection objects go through two phases: first they are
     * created, then they are connected.  After being created, and
     * before being connected, various options can be specified
     * (e.g., doInput and UseCaches).  After connecting, it is an
     * error to try to set them.  Operations that depend on being
     * connected, like getContentLength, will implicitly perform the
     * connection, if necessary.
     *
     * @exception  IOException  if an I/O error occurs while opening the
     *               connection.
     * @see java.net.URLConnection#connected */
    abstract public void connect() throws IOException;

    /**
     * Constructs a URL connection to the specified URL. A connection to 
     * the object referenced by the URL is not created. 
     *
     * @param   url   the specified URL.
     */
    protected URLConnection(URL url) {
	this.url = url;
    }

    /**
     * Returns the value of this <code>URLConnection</code>'s <code>URL</code>
     * field.
     *
     * @return  the value of this <code>URLConnection</code>'s <code>URL</code>
     *          field.
     * @see     java.net.URLConnection#url
     */
    public URL getURL() {
	return url;
    }

    /**
     * Returns the value of the <code>content-length</code> header field.
     *
     * @return  the content length of the resource that this connection's URL
     *          references, or <code>-1</code> if the content length is
     *          not known.
     */
    public int getContentLength() {
	return getHeaderFieldInt("content-length", -1);
    }

    /**
     * Returns the value of the <code>content-type</code> header field.
     *
     * @return  the content type of the resource that the URL references,
     *          or <code>null</code> if not known.
     * @see     java.net.URLConnection#getHeaderField(java.lang.String)
     */
    public String getContentType() {