httpurlconnection.java

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/*
 * 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.InputStream;
import java.io.IOException;
import java.security.Permission;
import java.text.DateFormat;
import java.text.SimpleDateFormat;

/**
 * A URLConnection with support for HTTP-specific features. See
 * <A HREF="http://www.w3.org/pub/WWW/Protocols/"> the spec </A> for
 * details.
 * <p>
 * 
 * Each HttpURLConnection instance is used to make a single request  
 * but the underlying network connection to the HTTP server may be
 * transparently shared by other instances. Calling the close() methods
 * on the InputStream or OutputStream of an HttpURLConnection
 * after a request may free network resources associated with this
 * instance but has no effect on any shared persistent connection.
 * Calling the disconnect() method may close the underlying socket
 * if a persistent connection is otherwise idle at that time.
 * 
 * @see     java.net.HttpURLConnection#disconnect()
 * @since JDK1.1
 */
abstract public class HttpURLConnection extends URLConnection {
    /* instance variables */

    /**
     * The HTTP method (GET,POST,PUT,etc.). 
     */
    protected String method = "GET";

    /**
     * Returns the key for the <code>n</code><sup>th</sup> header field.
     * Some implementations may treat the <code>0</code><sup>th</sup> 
     * header field as special, i.e. as the status line returned by the HTTP
     * server. In this case, {@link #getHeaderField(int) getHeaderField(0)} returns the status 
     * line, but <code>getHeaderFieldKey(0)</code> returns null.
     *
     * @param   n   an index, where n >=0.
     * @return  the key for the <code>n</code><sup>th</sup> header field,
     *          or <code>null</code> if the key does not exist.
     */
    public String getHeaderFieldKey (int n) {
	return null;
    }

    /**
     * Returns the value for the <code>n</code><sup>th</sup> header field. 
     * Some implementations may treat the <code>0</code><sup>th</sup> 
     * header field as special, i.e. as the status line returned by the HTTP
     * server. 
     * <p>
     * This method can be used in conjunction with the 
     * {@link #getHeaderFieldKey getHeaderFieldKey} method to iterate through all 
     * the headers in the message. 
     *
     * @param   n   an index, where n>=0.
     * @return  the value of the <code>n</code><sup>th</sup> header field,
     *		or <code>null</code> if the value does not exist.
     * @see     java.net.HttpURLConnection#getHeaderFieldKey(int)
     */
    public String getHeaderField(int n) {
	return null;
    }

    /**
     * An <code>int</code> representing the three digit HTTP Status-Code.
     * <ul>
     * <li> 1xx: Informational
     * <li> 2xx: Success
     * <li> 3xx: Redirection
     * <li> 4xx: Client Error
     * <li> 5xx: Server Error
     * </ul>
     */
    protected int responseCode = -1;

    /**
     * The HTTP response message.
     */
    protected String responseMessage = null;

    /* static variables */

    /* do we automatically follow redirects? The default is true. */
    private static boolean followRedirects = true;

    /**
     * If <code>true</code>, the protocol will automatically follow redirects.
     * If <code>false</code>, the protocol will not automatically follow 
     * redirects.
     * <p>
     * This field is set by the <code>setInstanceFollowRedirects</code> 
     * method. Its value is returned by the <code>getInstanceFollowRedirects</code> 
     * method.
     * <p>
     * Its default value is based on the value of the static followRedirects 
     * at HttpURLConnection construction time.
     *
     * @see     java.net.HttpURLConnection#setInstanceFollowRedirects(boolean)
     * @see     java.net.HttpURLConnection#getInstanceFollowRedirects()
     * @see     java.net.HttpURLConnection#setFollowRedirects(boolean)
     */
    protected boolean instanceFollowRedirects = followRedirects;

    /* valid HTTP methods */
    private static final String[] methods = {
	"GET", "POST", "HEAD", "OPTIONS", "PUT", "DELETE", "TRACE"
    };

    /**
     * Constructor for the HttpURLConnection.
     * @param u the URL
     */
    protected HttpURLConnection (URL u) {
	super(u);
    }
    
    /**
     * Sets whether HTTP redirects  (requests with response code 3xx) should 
     * be automatically followed by this class.  True by default.  Applets
     * cannot change this variable.
     * <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 set a <code>boolean</code> indicating whether or not
     * to follow HTTP redirects.
     * @exception  SecurityException  if a security manager exists and its  
     *             <code>checkSetFactory</code> method doesn't 
     *             allow the operation.
     * @see        SecurityManager#checkSetFactory
     * @see #getFollowRedirects()
     */
    public static void setFollowRedirects(boolean set) {
	SecurityManager sec = System.getSecurityManager();
	if (sec != null) {
	    // seems to be the best check here...
	    sec.checkSetFactory();
	}
	followRedirects = set;
    }

    /**
     * Returns a <code>boolean</code> indicating
     * whether or not HTTP redirects (3xx) should
     * be automatically followed.
     *
     * @return <code>true</code> if HTTP redirects should
     * be automatically followed, <tt>false</tt> if not.
     * @see #setFollowRedirects(boolean)
     */
    public static boolean getFollowRedirects() {
	return followRedirects;
    }

    /**
     * Sets whether HTTP redirects (requests with response code 3xx) should
     * be automatically followed by this <code>HttpURLConnection</code> 
     * instance.
     * <p>
     * The default value comes from followRedirects, which defaults to
     * true.
     *
     * @param followRedirects a <code>boolean</code> indicating 
     * whether or not to follow HTTP redirects.
     *
     * @see    java.net.HttpURLConnection#instanceFollowRedirects
     * @see #getInstanceFollowRedirects
     */
     public void setInstanceFollowRedirects(boolean followRedirects) {
 	instanceFollowRedirects = followRedirects;
     }

     /**
     * Returns the value of this <code>HttpURLConnection</code>'s
     * <code>instanceFollowRedirects</code> field.
     *
     * @return  the value of this <code>HttpURLConnection</code>'s
     *          <code>instanceFollowRedirects</code> field.
     * @see     java.net.HttpURLConnection#instanceFollowRedirects
     * @see #setInstanceFollowRedirects(boolean)
     */
     public boolean getInstanceFollowRedirects() {
         return instanceFollowRedirects;
     }

    /**
     * Set the method for the URL request, one of:
     * <UL>
     *  <LI>GET
     *  <LI>POST
     *  <LI>HEAD
     *  <LI>OPTIONS
     *  <LI>PUT
     *  <LI>DELETE
     *  <LI>TRACE
     * </UL> are legal, subject to protocol restrictions.  The default
     * method is GET.
     * 
     * @param method the HTTP method
     * @exception ProtocolException if the method cannot be reset or if
     *              the requested method isn't valid for HTTP.
     * @see #getRequestMethod()
     */
    public void setRequestMethod(String method) throws ProtocolException {
	if (connected) {
	    throw new ProtocolException("Can't reset method: already connected");
	}
	// This restriction will prevent people from using this class to 
	// experiment w/ new HTTP methods using java.  But it should 
	// be placed for security - the request String could be
	// arbitrarily long.

	for (int i = 0; i < methods.length; i++) {
	    if (methods[i].equals(method)) {
		this.method = method;
		return;
	    }
	}
	throw new ProtocolException("Invalid HTTP method: " + method);
    }

    /**
     * Get the request method.
     * @return the HTTP request method
     * @see #setRequestMethod(java.lang.String)
     */
    public String getRequestMethod() {
	return method;
    }
    
    /**
     * Gets the status code from an HTTP response message.
     * For example, in the case of the following status lines:
     * <PRE>
     * HTTP/1.0 200 OK
     * HTTP/1.0 401 Unauthorized
     * </PRE>
     * It will return 200 and 401 respectively.
     * Returns -1 if no code can be discerned
     * from the response (i.e., the response is not valid HTTP).
     * @throws IOException if an error occurred connecting to the server.
     * @return the HTTP Status-Code, or -1
     */
    public int getResponseCode() throws IOException {
	/*
	 * We're got the response code already
	 */
	if (responseCode != -1) {
	    return responseCode;
	}

	/*
	 * Ensure that we have connected to the server. Record
	 * exception as we need to re-throw it if there isn't
	 * a status line.
	 */
	Exception exc = null;
	try {
            getInputStream();
	} catch (Exception e) {
	    exc = e;
	}

	/*
 	 * If we can't a status-line then re-throw any exception
	 * that getInputStream threw.
	 */
	String statusLine = getHeaderField(0);
	if (statusLine == null) {
	    if (exc != null) {
		if (exc instanceof RuntimeException)
                    throw (RuntimeException)exc;
                else
                    throw (IOException)exc;
	    }
	    return -1;
	}