Creates a relative url by stripping the common parts of the the url.
import java.io.File;
import java.net.URL;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.StringTokenizer;
/*
* JCommon : a free general purpose class library for the Java(tm) platform
*
*
* (C) Copyright 2000-2005, by Object Refinery Limited and Contributors.
*
* Project Info: http://www.jfree.org/jcommon/index.html
*
* This library is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2.1 of the License, or
* (at your option) any later version.
*
* This library 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 Lesser General Public
* License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
* USA.
*
* [Java is a trademark or registered trademark of Sun Microsystems, Inc.
* in the United States and other countries.]
*
* ------------
* IOUtils.java
* ------------
* (C)opyright 2002-2004, by Thomas Morgner and Contributors.
*
* Original Author: Thomas Morgner;
* Contributor(s): David Gilbert (for Object Refinery Limited);
*
* $Id: IOUtils.java,v 1.8 2009/01/22 08:34:58 taqua Exp $
*
* Changes
* -------
* 26-Jan-2003 : Initial version
* 23-Feb-2003 : Documentation
* 25-Feb-2003 : Fixed Checkstyle issues (DG);
* 29-Apr-2003 : Moved to jcommon
* 04-Jan-2004 : Fixed JDK 1.2.2 issues with createRelativeURL;
* added support for query strings within these urls (TM);
*/
/**
* The IOUtils provide some IO related helper methods.
*
* @author Thomas Morgner.
*/
public class Main {
/**
* Checks, whether the URL uses a file based protocol.
*
* @param url the url.
* @return true, if the url is file based.
*/
private boolean isFileStyleProtocol(final URL url) {
if (url.getProtocol().equals("http")) {
return true;
}
if (url.getProtocol().equals("https")) {
return true;
}
if (url.getProtocol().equals("ftp")) {
return true;
}
if (url.getProtocol().equals("file")) {
return true;
}
if (url.getProtocol().equals("jar")) {
return true;
}
return false;
}
/**
* Transforms the name list back into a single string, separated with "/".
*
* @param name the name list.
* @param query the (optional) query for the URL.
* @return the constructed name.
*/
private String formatName(final List name, final String query) {
final StringBuffer b = new StringBuffer();
final Iterator it = name.iterator();
while (it.hasNext()) {
b.append(it.next());
if (it.hasNext()) {
b.append("/");
}
}
if (query != null) {
b.append('?');
b.append(query);
}
return b.toString();
}
/**
* Checks, whether the URL points to the same service. A service is equal
* if the protocol, host and port are equal.
*
* @param url a url
* @param baseUrl an other url, that should be compared.
* @return true, if the urls point to the same host and port and use the
* same protocol, false otherwise.
*/
private boolean isSameService(final URL url, final URL baseUrl) {
if (!url.getProtocol().equals(baseUrl.getProtocol())) {
return false;
}
if (!url.getHost().equals(baseUrl.getHost())) {
return false;
}
if (url.getPort() != baseUrl.getPort()) {
return false;
}
return true;
}
/**
* Parses the given name and returns the name elements as List of Strings.
*
* @param name the name, that should be parsed.
* @return the parsed name.
*/
private List parseName(final String name) {
final ArrayList list = new ArrayList();
final StringTokenizer strTok = new StringTokenizer(name, "/");
while (strTok.hasMoreElements()) {
final String s = (String) strTok.nextElement();
if (s.length() != 0) {
list.add(s);
}
}
return list;
}
/**
* Compares both name lists, and returns the last common index shared
* between the two lists.
*
* @param baseName the name created using the base url.
* @param urlName the target url name.
* @return the number of shared elements.
*/
private int startsWithUntil(final List baseName, final List urlName) {
final int minIdx = Math.min(urlName.size(), baseName.size());
for (int i = 0; i < minIdx; i++) {
final String baseToken = (String) baseName.get(i);
final String urlToken = (String) urlName.get(i);
if (!baseToken.equals(urlToken)) {
return i;
}
}
return minIdx;
}
/**
* Returns <code>true</code> if the URL represents a path, and
* <code>false</code> otherwise.
*
* @param baseURL the URL.
*
* @return A boolean.
*/
private boolean isPath(final URL baseURL) {
if (getPath(baseURL).endsWith("/")) {
return true;
}
else if (baseURL.getProtocol().equals("file")) {
final File f = new File(getPath(baseURL));
try {
if (f.isDirectory()) {
return true;
}
}
catch (SecurityException se) {
// ignored ...
}
}
return false;
}
/**
* Implements the JDK 1.3 method URL.getPath(). The path is defined
* as URL.getFile() minus the (optional) query.
*
* @param url the URL
* @return the path
*/
private String getQuery (final URL url) {
final String file = url.getFile();
final int queryIndex = file.indexOf('?');
if (queryIndex == -1) {
return null;
}
return file.substring(queryIndex + 1);
}
/**
* Implements the JDK 1.3 method URL.getPath(). The path is defined
* as URL.getFile() minus the (optional) query.
*
* @param url the URL
* @return the path
*/
private String getPath (final URL url) {
final String file = url.getFile();
final int queryIndex = file.indexOf('?');
if (queryIndex == -1) {
return file;
}
return file.substring(0, queryIndex);
}
/**
* Creates a relative url by stripping the common parts of the the url.
*
* @param url the to be stripped url
* @param baseURL the base url, to which the <code>url</code> is relative
* to.
* @return the relative url, or the url unchanged, if there is no relation
* beween both URLs.
*/
public String createRelativeURL(final URL url, final URL baseURL) {
if (url == null) {
throw new NullPointerException("content url must not be null.");
}
if (baseURL == null) {
throw new NullPointerException("baseURL must not be null.");
}
if (isFileStyleProtocol(url) && isSameService(url, baseURL)) {
// If the URL contains a query, ignore that URL; do not
// attemp to modify it...
final List urlName = parseName(getPath(url));
final List baseName = parseName(getPath(baseURL));
final String query = getQuery(url);
if (!isPath(baseURL)) {
baseName.remove(baseName.size() - 1);
}
// if both urls are identical, then return the plain file name...
if (url.equals(baseURL)) {
return (String) urlName.get(urlName.size() - 1);
}
int commonIndex = startsWithUntil(urlName, baseName);
if (commonIndex == 0) {
return url.toExternalForm();
}
if (commonIndex == urlName.size()) {
// correct the base index if there is some weird mapping
// detected,
// fi. the file url is fully included in the base url:
//
// base: /file/test/funnybase
// file: /file/test
//
// this could be a valid configuration whereever virtual
// mappings are allowed.
commonIndex -= 1;
}
final ArrayList retval = new ArrayList();
if (baseName.size() >= urlName.size()) {
final int levels = baseName.size() - commonIndex;
for (int i = 0; i < levels; i++) {
retval.add("..");
}
}
retval.addAll(urlName.subList(commonIndex, urlName.size()));
return formatName(retval, query);
}
return url.toExternalForm();
}
}
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