Java tutorial
/* * Copyright 2004 Clinton Begin * * Licensed 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.*; import java.net.URL; import java.net.URLConnection; import java.nio.charset.Charset; import java.util.Properties; /** * A class to simplify access to resources through the classloader. */ public class Resources extends Object { private static ClassLoader defaultClassLoader; /** * Charset to use when calling getResourceAsReader. * null means use the system default. */ private static Charset charset; private Resources() { } /** * Returns the default classloader (may be null). * * @return The default classloader */ public static ClassLoader getDefaultClassLoader() { return defaultClassLoader; } /** * Sets the default classloader * * @param defaultClassLoader - the new default ClassLoader */ public static void setDefaultClassLoader(ClassLoader defaultClassLoader) { Resources.defaultClassLoader = defaultClassLoader; } /** * Returns the URL of the resource on the classpath * * @param resource The resource to find * @return The resource * @throws IOException If the resource cannot be found or read */ public static URL getResourceURL(String resource) throws IOException { return getResourceURL(getClassLoader(), resource); } /** * Returns the URL of the resource on the classpath * * @param loader The classloader used to load the resource * @param resource The resource to find * @return The resource * @throws IOException If the resource cannot be found or read */ public static URL getResourceURL(ClassLoader loader, String resource) throws IOException { URL url = null; if (loader != null) url = loader.getResource(resource); if (url == null) url = ClassLoader.getSystemResource(resource); if (url == null) throw new IOException("Could not find resource " + resource); return url; } /** * Returns a resource on the classpath as a Stream object * * @param resource The resource to find * @return The resource * @throws IOException If the resource cannot be found or read */ public static InputStream getResourceAsStream(String resource) throws IOException { return getResourceAsStream(getClassLoader(), resource); } /** * Returns a resource on the classpath as a Stream object * * @param loader The classloader used to load the resource * @param resource The resource to find * @return The resource * @throws IOException If the resource cannot be found or read */ public static InputStream getResourceAsStream(ClassLoader loader, String resource) throws IOException { InputStream in = null; if (loader != null) in = loader.getResourceAsStream(resource); if (in == null) in = ClassLoader.getSystemResourceAsStream(resource); if (in == null) throw new IOException("Could not find resource " + resource); return in; } /** * Returns a resource on the classpath as a Properties object * * @param resource The resource to find * @return The resource * @throws IOException If the resource cannot be found or read */ public static Properties getResourceAsProperties(String resource) throws IOException { Properties props = new Properties(); InputStream in = null; String propfile = resource; in = getResourceAsStream(propfile); props.load(in); in.close(); return props; } /** * Returns a resource on the classpath as a Properties object * * @param loader The classloader used to load the resource * @param resource The resource to find * @return The resource * @throws IOException If the resource cannot be found or read */ public static Properties getResourceAsProperties(ClassLoader loader, String resource) throws IOException { Properties props = new Properties(); InputStream in = null; String propfile = resource; in = getResourceAsStream(loader, propfile); props.load(in); in.close(); return props; } /** * Returns a resource on the classpath as a Reader object * * @param resource The resource to find * @return The resource * @throws IOException If the resource cannot be found or read */ public static Reader getResourceAsReader(String resource) throws IOException { Reader reader; if (charset == null) { reader = new InputStreamReader(getResourceAsStream(resource)); } else { reader = new InputStreamReader(getResourceAsStream(resource), charset); } return reader; } /** * Returns a resource on the classpath as a Reader object * * @param loader The classloader used to load the resource * @param resource The resource to find * @return The resource * @throws IOException If the resource cannot be found or read */ public static Reader getResourceAsReader(ClassLoader loader, String resource) throws IOException { Reader reader; if (charset == null) { reader = new InputStreamReader(getResourceAsStream(loader, resource)); } else { reader = new InputStreamReader(getResourceAsStream(loader, resource), charset); } return reader; } /** * Returns a resource on the classpath as a File object * * @param resource The resource to find * @return The resource * @throws IOException If the resource cannot be found or read */ public static File getResourceAsFile(String resource) throws IOException { return new File(getResourceURL(resource).getFile()); } /** * Returns a resource on the classpath as a File object * * @param loader - the classloader used to load the resource * @param resource - the resource to find * @return The resource * @throws IOException If the resource cannot be found or read */ public static File getResourceAsFile(ClassLoader loader, String resource) throws IOException { return new File(getResourceURL(loader, resource).getFile()); } /** * Gets a URL as an input stream * * @param urlString - the URL to get * @return An input stream with the data from the URL * @throws IOException If the resource cannot be found or read */ public static InputStream getUrlAsStream(String urlString) throws IOException { URL url = new URL(urlString); URLConnection conn = url.openConnection(); return conn.getInputStream(); } /** * Gets a URL as a Reader * * @param urlString - the URL to get * @return A Reader with the data from the URL * @throws IOException If the resource cannot be found or read */ public static Reader getUrlAsReader(String urlString) throws IOException { return new InputStreamReader(getUrlAsStream(urlString)); } /** * Gets a URL as a Properties object * * @param urlString - the URL to get * @return A Properties object with the data from the URL * @throws IOException If the resource cannot be found or read */ public static Properties getUrlAsProperties(String urlString) throws IOException { Properties props = new Properties(); InputStream in = null; String propfile = urlString; in = getUrlAsStream(propfile); props.load(in); in.close(); return props; } /** * Loads a class * * @param className - the class to load * @return The loaded class * @throws ClassNotFoundException If the class cannot be found (duh!) */ public static Class classForName(String className) throws ClassNotFoundException { Class clazz = null; try { clazz = getClassLoader().loadClass(className); } catch (Exception e) { // Ignore. Failsafe below. } if (clazz == null) { clazz = Class.forName(className); } return clazz; } /** * Creates an instance of a class * * @param className - the class to create * @return An instance of the class * @throws ClassNotFoundException If the class cannot be found (duh!) * @throws InstantiationException If the class cannot be instantiaed * @throws IllegalAccessException If the class is not public, or other access problems arise */ public static Object instantiate(String className) throws ClassNotFoundException, InstantiationException, IllegalAccessException { return instantiate(classForName(className)); } /** * Creates an instance of a class * * @param clazz - the class to create * @return An instance of the class * @throws InstantiationException If the class cannot be instantiaed * @throws IllegalAccessException If the class is not public, or other access problems arise */ public static Object instantiate(Class clazz) throws InstantiationException, IllegalAccessException { try { return clazz.newInstance(); } catch (Exception e) { // Try alternative...theoretically should fail for the exact same // reason, but in case of a weird security manager, this will help // some cases. //return clazz.newInstance(); return clazz.newInstance(); } } private static ClassLoader getClassLoader() { if (defaultClassLoader != null) { return defaultClassLoader; } else { return Thread.currentThread().getContextClassLoader(); } } public static Charset getCharset() { return charset; } /** * Use this method to set the Charset to be used when * calling the getResourceAsReader methods. This will * allow iBATIS to function properly when the system default * encoding doesn't deal well with unicode (IBATIS-340, IBATIS-349) * * @param charset */ public static void setCharset(Charset charset) { Resources.charset = charset; } }