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| 1 | /* | ||
| 2 | * Copyright (c) 1999, 2003, Oracle and/or its affiliates. All rights reserved. | ||
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | ||
| 4 | * | ||
| 5 | * This code is free software; you can redistribute it and/or modify it | ||
| 6 | * under the terms of the GNU General Public License version 2 only, as | ||
| 7 | * published by the Free Software Foundation. Oracle designates this | ||
| 8 | * particular file as subject to the "Classpath" exception as provided | ||
| 9 | * by Oracle in the LICENSE file that accompanied this code. | ||
| 10 | * | ||
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT | ||
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | ||
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | ||
| 14 | * version 2 for more details (a copy is included in the LICENSE file that | ||
| 15 | * accompanied this code). | ||
| 16 | * | ||
| 17 | * You should have received a copy of the GNU General Public License version | ||
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, | ||
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | ||
| 20 | * | ||
| 21 | * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | ||
| 22 | * or visit www.oracle.com if you need additional information or have any | ||
| 23 | * questions. | ||
| 24 | */ | ||
| 25 | |||
| 26 | package sun.misc; | ||
| 27 | |||
| 28 | import java.io.BufferedReader; | ||
| 29 | import java.io.IOException; | ||
| 30 | import java.io.InputStream; | ||
| 31 | import java.io.InputStreamReader; | ||
| 32 | import java.net.URL; | ||
| 33 | import java.util.ArrayList; | ||
| 34 | import java.util.Enumeration; | ||
| 35 | import java.util.Iterator; | ||
| 36 | import java.util.List; | ||
| 37 | import java.util.NoSuchElementException; | ||
| 38 | import java.util.Set; | ||
| 39 | import java.util.TreeSet; | ||
| 40 | |||
| 41 | |||
| 42 | /** | ||
| 43 | * A simple service-provider lookup mechanism. A <i>service</i> is a | ||
| 44 | * well-known set of interfaces and (usually abstract) classes. A <i>service | ||
| 45 | * provider</i> is a specific implementation of a service. The classes in a | ||
| 46 | * provider typically implement the interfaces and subclass the classes defined | ||
| 47 | * in the service itself. Service providers may be installed in an | ||
| 48 | * implementation of the Java platform in the form of extensions, that is, jar | ||
| 49 | * files placed into any of the usual extension directories. Providers may | ||
| 50 | * also be made available by adding them to the applet or application class | ||
| 51 | * path or by some other platform-specific means. | ||
| 52 | * | ||
| 53 | * <p> In this lookup mechanism a service is represented by an interface or an | ||
| 54 | * abstract class. (A concrete class may be used, but this is not | ||
| 55 | * recommended.) A provider of a given service contains one or more concrete | ||
| 56 | * classes that extend this <i>service class</i> with data and code specific to | ||
| 57 | * the provider. This <i>provider class</i> will typically not be the entire | ||
| 58 | * provider itself but rather a proxy that contains enough information to | ||
| 59 | * decide whether the provider is able to satisfy a particular request together | ||
| 60 | * with code that can create the actual provider on demand. The details of | ||
| 61 | * provider classes tend to be highly service-specific; no single class or | ||
| 62 | * interface could possibly unify them, so no such class has been defined. The | ||
| 63 | * only requirement enforced here is that provider classes must have a | ||
| 64 | * zero-argument constructor so that they may be instantiated during lookup. | ||
| 65 | * | ||
| 66 | * <p> A service provider identifies itself by placing a provider-configuration | ||
| 67 | * file in the resource directory <tt>META-INF/services</tt>. The file's name | ||
| 68 | * should consist of the fully-qualified name of the abstract service class. | ||
| 69 | * The file should contain a list of fully-qualified concrete provider-class | ||
| 70 | * names, one per line. Space and tab characters surrounding each name, as | ||
| 71 | * well as blank lines, are ignored. The comment character is <tt>'#'</tt> | ||
| 72 | * (<tt>0x23</tt>); on each line all characters following the first comment | ||
| 73 | * character are ignored. The file must be encoded in UTF-8. | ||
| 74 | * | ||
| 75 | * <p> If a particular concrete provider class is named in more than one | ||
| 76 | * configuration file, or is named in the same configuration file more than | ||
| 77 | * once, then the duplicates will be ignored. The configuration file naming a | ||
| 78 | * particular provider need not be in the same jar file or other distribution | ||
| 79 | * unit as the provider itself. The provider must be accessible from the same | ||
| 80 | * class loader that was initially queried to locate the configuration file; | ||
| 81 | * note that this is not necessarily the class loader that found the file. | ||
| 82 | * | ||
| 83 | * <p> <b>Example:</b> Suppose we have a service class named | ||
| 84 | * <tt>java.io.spi.CharCodec</tt>. It has two abstract methods: | ||
| 85 | * | ||
| 86 | * <pre> | ||
| 87 | * public abstract CharEncoder getEncoder(String encodingName); | ||
| 88 | * public abstract CharDecoder getDecoder(String encodingName); | ||
| 89 | * </pre> | ||
| 90 | * | ||
| 91 | * Each method returns an appropriate object or <tt>null</tt> if it cannot | ||
| 92 | * translate the given encoding. Typical <tt>CharCodec</tt> providers will | ||
| 93 | * support more than one encoding. | ||
| 94 | * | ||
| 95 | * <p> If <tt>sun.io.StandardCodec</tt> is a provider of the <tt>CharCodec</tt> | ||
| 96 | * service then its jar file would contain the file | ||
| 97 | * <tt>META-INF/services/java.io.spi.CharCodec</tt>. This file would contain | ||
| 98 | * the single line: | ||
| 99 | * | ||
| 100 | * <pre> | ||
| 101 | * sun.io.StandardCodec # Standard codecs for the platform | ||
| 102 | * </pre> | ||
| 103 | * | ||
| 104 | * To locate an encoder for a given encoding name, the internal I/O code would | ||
| 105 | * do something like this: | ||
| 106 | * | ||
| 107 | * <pre> | ||
| 108 | * CharEncoder getEncoder(String encodingName) { | ||
| 109 | * Iterator ps = Service.providers(CharCodec.class); | ||
| 110 | * while (ps.hasNext()) { | ||
| 111 | * CharCodec cc = (CharCodec)ps.next(); | ||
| 112 | * CharEncoder ce = cc.getEncoder(encodingName); | ||
| 113 | * if (ce != null) | ||
| 114 | * return ce; | ||
| 115 | * } | ||
| 116 | * return null; | ||
| 117 | * } | ||
| 118 | * </pre> | ||
| 119 | * | ||
| 120 | * The provider-lookup mechanism always executes in the security context of the | ||
| 121 | * caller. Trusted system code should typically invoke the methods in this | ||
| 122 | * class from within a privileged security context. | ||
| 123 | * | ||
| 124 | * @author Mark Reinhold | ||
| 125 | * @since 1.3 | ||
| 126 | */ | ||
| 127 | |||
| 128 | public final class Service { | ||
| 129 | |||
| 130 | private static final String prefix = "META-INF/services/"; | ||
| 131 | |||
| 132 | private Service() { } | ||
| 133 | |||
| 134 | private static void fail(Class service, String msg, Throwable cause) | ||
| 135 | throws ServiceConfigurationError | ||
| 136 | { | ||
| 137 | ServiceConfigurationError sce | ||
| 138 | = new ServiceConfigurationError(service.getName() + ": " + msg); | ||
| 139 | sce.initCause(cause); | ||
| 140 | throw sce; | ||
| 141 | } | ||
| 142 | |||
| 143 | private static void fail(Class service, String msg) | ||
| 144 | throws ServiceConfigurationError | ||
| 145 | { | ||
| 146 | throw new ServiceConfigurationError(service.getName() + ": " + msg); | ||
| 147 | } | ||
| 148 | |||
| 149 | private static void fail(Class service, URL u, int line, String msg) | ||
| 150 | throws ServiceConfigurationError | ||
| 151 | { | ||
| 152 | fail(service, u + ":" + line + ": " + msg); | ||
| 153 | } | ||
| 154 | |||
| 155 | /** | ||
| 156 | * Parse a single line from the given configuration file, adding the name | ||
| 157 | * on the line to both the names list and the returned set iff the name is | ||
| 158 | * not already a member of the returned set. | ||
| 159 | */ | ||
| 160 | private static int parseLine(Class service, URL u, BufferedReader r, int lc, | ||
| 161 | List names, Set returned) | ||
| 162 | throws IOException, ServiceConfigurationError | ||
| 163 | { | ||
| 164 | String ln = r.readLine(); | ||
| 165 | if (ln == null) { | ||
| 166 | return -1; | ||
| 167 | } | ||
| 168 | int ci = ln.indexOf('#'); | ||
| 169 | if (ci >= 0) ln = ln.substring(0, ci); | ||
| 170 | ln = ln.trim(); | ||
| 171 | int n = ln.length(); | ||
| 172 | if (n != 0) { | ||
| 173 | if ((ln.indexOf(' ') >= 0) || (ln.indexOf('\t') >= 0)) | ||
| 174 | fail(service, u, lc, "Illegal configuration-file syntax"); | ||
| 175 | int cp = ln.codePointAt(0); | ||
| 176 | if (!Character.isJavaIdentifierStart(cp)) | ||
| 177 | fail(service, u, lc, "Illegal provider-class name: " + ln); | ||
| 178 | for (int i = Character.charCount(cp); i < n; i += Character.charCount(cp)) { | ||
| 179 | cp = ln.codePointAt(i); | ||
| 180 | if (!Character.isJavaIdentifierPart(cp) && (cp != '.')) | ||
| 181 | fail(service, u, lc, "Illegal provider-class name: " + ln); | ||
| 182 | } | ||
| 183 | if (!returned.contains(ln)) { | ||
| 184 | names.add(ln); | ||
| 185 | returned.add(ln); | ||
| 186 | } | ||
| 187 | } | ||
| 188 | return lc + 1; | ||
| 189 | } | ||
| 190 | |||
| 191 | /** | ||
| 192 | * Parse the content of the given URL as a provider-configuration file. | ||
| 193 | * | ||
| 194 | * @param service | ||
| 195 | * The service class for which providers are being sought; | ||
| 196 | * used to construct error detail strings | ||
| 197 | * | ||
| 198 | * @param url | ||
| 199 | * The URL naming the configuration file to be parsed | ||
| 200 | * | ||
| 201 | * @param returned | ||
| 202 | * A Set containing the names of provider classes that have already | ||
| 203 | * been returned. This set will be updated to contain the names | ||
| 204 | * that will be yielded from the returned <tt>Iterator</tt>. | ||
| 205 | * | ||
| 206 | * @return A (possibly empty) <tt>Iterator</tt> that will yield the | ||
| 207 | * provider-class names in the given configuration file that are | ||
| 208 | * not yet members of the returned set | ||
| 209 | * | ||
| 210 | * @throws ServiceConfigurationError | ||
| 211 | * If an I/O error occurs while reading from the given URL, or | ||
| 212 | * if a configuration-file format error is detected | ||
| 213 | */ | ||
| 214 | private static Iterator parse(Class service, URL u, Set returned) | ||
| 215 | throws ServiceConfigurationError | ||
| 216 | { | ||
| 217 | InputStream in = null; | ||
| 218 | BufferedReader r = null; | ||
| 219 | ArrayList names = new ArrayList(); | ||
| 220 | try { | ||
| 221 | in = u.openStream(); | ||
| 222 | r = new BufferedReader(new InputStreamReader(in, "utf-8")); | ||
| 223 | int lc = 1; | ||
| 224 | while ((lc = parseLine(service, u, r, lc, names, returned)) >= 0); | ||
| 225 | } catch (IOException x) { | ||
| 226 | fail(service, ": " + x); | ||
| 227 | } finally { | ||
| 228 | try { | ||
| 229 | if (r != null) r.close(); | ||
| 230 | if (in != null) in.close(); | ||
| 231 | } catch (IOException y) { | ||
| 232 | fail(service, ": " + y); | ||
| 233 | } | ||
| 234 | } | ||
| 235 | return names.iterator(); | ||
| 236 | } | ||
| 237 | |||
| 238 | |||
| 239 | /** | ||
| 240 | * Private inner class implementing fully-lazy provider lookup | ||
| 241 | */ | ||
| 242 | private static class LazyIterator implements Iterator { | ||
| 243 | |||
| 244 | Class service; | ||
| 245 | ClassLoader loader; | ||
| 246 | Enumeration configs = null; | ||
| 247 | Iterator pending = null; | ||
| 248 | Set returned = new TreeSet(); | ||
| 249 | String nextName = null; | ||
| 250 | |||
| 251 | private LazyIterator(Class service, ClassLoader loader) { | ||
| 252 | this.service = service; | ||
| 253 | this.loader = loader; | ||
| 254 | } | ||
| 255 | |||
| 256 | public boolean hasNext() throws ServiceConfigurationError { | ||
| 257 | if (nextName != null) { | ||
| 258 | return true; | ||
| 259 | } | ||
| 260 | if (configs == null) { | ||
| 261 | try { | ||
| 262 | String fullName = prefix + service.getName(); | ||
| 263 | if (loader == null) | ||
| 264 | configs = ClassLoader.getSystemResources(fullName); | ||
| 265 | else | ||
| 266 | configs = loader.getResources(fullName); | ||
| 267 | } catch (IOException x) { | ||
| 268 | fail(service, ": " + x); | ||
| 269 | } | ||
| 270 | } | ||
| 271 | while ((pending == null) || !pending.hasNext()) { | ||
| 272 | if (!configs.hasMoreElements()) { | ||
| 273 | return false; | ||
| 274 | } | ||
| 275 | pending = parse(service, (URL)configs.nextElement(), returned); | ||
| 276 | } | ||
| 277 | nextName = (String)pending.next(); | ||
| 278 | return true; | ||
| 279 | } | ||
| 280 | |||
| 281 | public Object next() throws ServiceConfigurationError { | ||
| 282 | if (!hasNext()) { | ||
| 283 | throw new NoSuchElementException(); | ||
| 284 | } | ||
| 285 | String cn = nextName; | ||
| 286 | nextName = null; | ||
| 287 | try { | ||
| 288 | return Class.forName(cn, true, loader).newInstance(); | ||
| 289 | } catch (ClassNotFoundException x) { | ||
| 290 | fail(service, | ||
| 291 | "Provider " + cn + " not found"); | ||
| 292 | } catch (Exception x) { | ||
| 293 | fail(service, | ||
| 294 | "Provider " + cn + " could not be instantiated: " + x, | ||
| 295 | x); | ||
| 296 | } | ||
| 297 | return null; /* This cannot happen */ | ||
| 298 | } | ||
| 299 | |||
| 300 | public void remove() { | ||
| 301 | throw new UnsupportedOperationException(); | ||
| 302 | } | ||
| 303 | |||
| 304 | } | ||
| 305 | |||
| 306 | |||
| 307 | /** | ||
| 308 | * Locates and incrementally instantiates the available providers of a | ||
| 309 | * given service using the given class loader. | ||
| 310 | * | ||
| 311 | * <p> This method transforms the name of the given service class into a | ||
| 312 | * provider-configuration filename as described above and then uses the | ||
| 313 | * <tt>getResources</tt> method of the given class loader to find all | ||
| 314 | * available files with that name. These files are then read and parsed to | ||
| 315 | * produce a list of provider-class names. The iterator that is returned | ||
| 316 | * uses the given class loader to lookup and then instantiate each element | ||
| 317 | * of the list. | ||
| 318 | * | ||
| 319 | * <p> Because it is possible for extensions to be installed into a running | ||
| 320 | * Java virtual machine, this method may return different results each time | ||
| 321 | * it is invoked. <p> | ||
| 322 | * | ||
| 323 | * @param service | ||
| 324 | * The service's abstract service class | ||
| 325 | * | ||
| 326 | * @param loader | ||
| 327 | * The class loader to be used to load provider-configuration files | ||
| 328 | * and instantiate provider classes, or <tt>null</tt> if the system | ||
| 329 | * class loader (or, failing that the bootstrap class loader) is to | ||
| 330 | * be used | ||
| 331 | * | ||
| 332 | * @return An <tt>Iterator</tt> that yields provider objects for the given | ||
| 333 | * service, in some arbitrary order. The iterator will throw a | ||
| 334 | * <tt>ServiceConfigurationError</tt> if a provider-configuration | ||
| 335 | * file violates the specified format or if a provider class cannot | ||
| 336 | * be found and instantiated. | ||
| 337 | * | ||
| 338 | * @throws ServiceConfigurationError | ||
| 339 | * If a provider-configuration file violates the specified format | ||
| 340 | * or names a provider class that cannot be found and instantiated | ||
| 341 | * | ||
| 342 | * @see #providers(java.lang.Class) | ||
| 343 | * @see #installedProviders(java.lang.Class) | ||
| 344 | */ | ||
| 345 | public static Iterator providers(Class service, ClassLoader loader) | ||
| 346 | throws ServiceConfigurationError | ||
| 347 | { | ||
| 348 | return new LazyIterator(service, loader); | ||
| 349 | } | ||
| 350 | |||
| 351 | |||
| 352 | /** | ||
| 353 | * Locates and incrementally instantiates the available providers of a | ||
| 354 | * given service using the context class loader. This convenience method | ||
| 355 | * is equivalent to | ||
| 356 | * | ||
| 357 | * <pre> | ||
| 358 | * ClassLoader cl = Thread.currentThread().getContextClassLoader(); | ||
| 359 | * return Service.providers(service, cl); | ||
| 360 | * </pre> | ||
| 361 | * | ||
| 362 | * @param service | ||
| 363 | * The service's abstract service class | ||
| 364 | * | ||
| 365 | * @return An <tt>Iterator</tt> that yields provider objects for the given | ||
| 366 | * service, in some arbitrary order. The iterator will throw a | ||
| 367 | * <tt>ServiceConfigurationError</tt> if a provider-configuration | ||
| 368 | * file violates the specified format or if a provider class cannot | ||
| 369 | * be found and instantiated. | ||
| 370 | * | ||
| 371 | * @throws ServiceConfigurationError | ||
| 372 | * If a provider-configuration file violates the specified format | ||
| 373 | * or names a provider class that cannot be found and instantiated | ||
| 374 | * | ||
| 375 | * @see #providers(java.lang.Class, java.lang.ClassLoader) | ||
| 376 | */ | ||
| 377 | public static Iterator providers(Class service) | ||
| 378 | throws ServiceConfigurationError | ||
| 379 | { | ||
| 380 | ClassLoader cl = Thread.currentThread().getContextClassLoader(); | ||
| 381 | return Service.providers(service, cl); | ||
| 382 | } | ||
| 383 | |||
| 384 | |||
| 385 | /** | ||
| 386 | * Locates and incrementally instantiates the available providers of a | ||
| 387 | * given service using the extension class loader. This convenience method | ||
| 388 | * simply locates the extension class loader, call it | ||
| 389 | * <tt>extClassLoader</tt>, and then does | ||
| 390 | * | ||
| 391 | * <pre> | ||
| 392 | * return Service.providers(service, extClassLoader); | ||
| 393 | * </pre> | ||
| 394 | * | ||
| 395 | * If the extension class loader cannot be found then the system class | ||
| 396 | * loader is used; if there is no system class loader then the bootstrap | ||
| 397 | * class loader is used. | ||
| 398 | * | ||
| 399 | * @param service | ||
| 400 | * The service's abstract service class | ||
| 401 | * | ||
| 402 | * @return An <tt>Iterator</tt> that yields provider objects for the given | ||
| 403 | * service, in some arbitrary order. The iterator will throw a | ||
| 404 | * <tt>ServiceConfigurationError</tt> if a provider-configuration | ||
| 405 | * file violates the specified format or if a provider class cannot | ||
| 406 | * be found and instantiated. | ||
| 407 | * | ||
| 408 | * @throws ServiceConfigurationError | ||
| 409 | * If a provider-configuration file violates the specified format | ||
| 410 | * or names a provider class that cannot be found and instantiated | ||
| 411 | * | ||
| 412 | * @see #providers(java.lang.Class, java.lang.ClassLoader) | ||
| 413 | */ | ||
| 414 | public static Iterator installedProviders(Class service) | ||
| 415 | throws ServiceConfigurationError | ||
| 416 | { | ||
| 417 | ClassLoader cl = ClassLoader.getSystemClassLoader(); | ||
| 418 | ClassLoader prev = null; | ||
| 419 | while (cl != null) { | ||
| 420 | prev = cl; | ||
| 421 | cl = cl.getParent(); | ||
| 422 | } | ||
| 423 | return Service.providers(service, prev); | ||
| 424 | } | ||
| 425 | |||
| 426 | } | ||