Java tutorial
package bboss.org.apache.velocity.runtime.resource.loader; /* * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you under the Apache License, Version 2.0 (the * "License"); you may not use this file except in compliance * with the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, * software distributed under the License is distributed on an * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY * KIND, either express or implied. See the License for the * specific language governing permissions and limitations * under the License. */ import java.io.InputStream; import java.io.IOException; import java.lang.reflect.Method; import java.net.URL; import java.net.URLConnection; import java.util.HashMap; import org.apache.commons.collections.ExtendedProperties; import org.apache.commons.lang.StringUtils; import bboss.org.apache.velocity.exception.VelocityException; import bboss.org.apache.velocity.exception.ResourceNotFoundException; import bboss.org.apache.velocity.runtime.resource.Resource; /** * This is a simple URL-based loader. * * @author <a href="mailto:geirm@apache.org">Geir Magnusson Jr.</a> * @author <a href="mailto:nbubna@apache.org">Nathan Bubna</a> * @version $Id: URLResourceLoader.java 191743 2005-06-21 23:22:20Z dlr $ * @since 1.5 */ public class URLResourceLoader extends ResourceLoader { private String[] roots = null; protected HashMap templateRoots = null; private int timeout = -1; private Method[] timeoutMethods; /** * @see bboss.org.apache.velocity.runtime.resource.loader.ResourceLoader#init(org.apache.commons.collections.ExtendedProperties) */ public void init(ExtendedProperties configuration) { log.trace("URLResourceLoader : initialization starting."); roots = configuration.getStringArray("root"); if (log.isDebugEnabled()) { for (int i = 0; i < roots.length; i++) { log.debug("URLResourceLoader : adding root '" + roots[i] + "'"); } } timeout = configuration.getInt("timeout", -1); if (timeout > 0) { try { Class[] types = new Class[] { Integer.TYPE }; Method conn = URLConnection.class.getMethod("setConnectTimeout", types); Method read = URLConnection.class.getMethod("setReadTimeout", types); timeoutMethods = new Method[] { conn, read }; log.debug("URLResourceLoader : timeout set to " + timeout); } catch (NoSuchMethodException nsme) { log.debug("URLResourceLoader : Java 1.5+ is required to customize timeout!", nsme); timeout = -1; } } // init the template paths map templateRoots = new HashMap(); log.trace("URLResourceLoader : initialization complete."); } /** * Get an InputStream so that the Runtime can build a * template with it. * * @param name name of template to fetch bytestream of * @return InputStream containing the template * @throws ResourceNotFoundException if template not found * in the file template path. */ public synchronized InputStream getResourceStream(String name) throws ResourceNotFoundException { if (StringUtils.isEmpty(name)) { throw new ResourceNotFoundException("URLResourceLoader : No template name provided"); } InputStream inputStream = null; Exception exception = null; for (int i = 0; i < roots.length; i++) { try { URL u = new URL(roots[i] + name); URLConnection conn = u.openConnection(); tryToSetTimeout(conn); inputStream = conn.getInputStream(); if (inputStream != null) { if (log.isDebugEnabled()) log.debug("URLResourceLoader: Found '" + name + "' at '" + roots[i] + "'"); // save this root for later re-use templateRoots.put(name, roots[i]); break; } } catch (IOException ioe) { if (log.isDebugEnabled()) log.debug("URLResourceLoader: Exception when looking for '" + name + "' at '" + roots[i] + "'", ioe); // only save the first one for later throwing if (exception == null) { exception = ioe; } } } // if we never found the template if (inputStream == null) { String msg; if (exception == null) { msg = "URLResourceLoader : Resource '" + name + "' not found."; } else { msg = exception.getMessage(); } // convert to a general Velocity ResourceNotFoundException throw new ResourceNotFoundException(msg); } return inputStream; } /** * Checks to see if a resource has been deleted, moved or modified. * * @param resource Resource The resource to check for modification * @return boolean True if the resource has been modified, moved, or unreachable */ public boolean isSourceModified(Resource resource) { long fileLastModified = getLastModified(resource); // if the file is unreachable or otherwise changed if (fileLastModified == 0 || fileLastModified != resource.getLastModified()) { return true; } return false; } /** * Checks to see when a resource was last modified * * @param resource Resource the resource to check * @return long The time when the resource was last modified or 0 if the file can't be reached */ public long getLastModified(Resource resource) { // get the previously used root String name = resource.getName(); String root = (String) templateRoots.get(name); try { // get a connection to the URL URL u = new URL(root + name); URLConnection conn = u.openConnection(); tryToSetTimeout(conn); return conn.getLastModified(); } catch (IOException ioe) { // the file is not reachable at its previous address String msg = "URLResourceLoader: '" + name + "' is no longer reachable at '" + root + "'"; log.error(msg, ioe); throw new ResourceNotFoundException(msg, ioe); } } /** * Returns the current, custom timeout setting. If negative, there is no custom timeout. * @since 1.6 */ public int getTimeout() { return timeout; } private void tryToSetTimeout(URLConnection conn) { if (timeout > 0) { Object[] arg = new Object[] { new Integer(timeout) }; try { timeoutMethods[0].invoke(conn, arg); timeoutMethods[1].invoke(conn, arg); } catch (Exception e) { String msg = "Unexpected exception while setting connection timeout for " + conn; log.error(msg, e); throw new VelocityException(msg, e); } } } }