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| 1 | /* | ||
| 2 | * Copyright (c) 2005, 2010, 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 java.util; | ||
| 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 | |||
| 39 | |||
| 40 | /** | ||
| 41 | * A simple service-provider loading facility. | ||
| 42 | * | ||
| 43 | * <p> A <i>service</i> is a well-known set of interfaces and (usually | ||
| 44 | * abstract) classes. A <i>service provider</i> is a specific implementation | ||
| 45 | * of a service. The classes in a provider typically implement the interfaces | ||
| 46 | * and subclass the classes defined in the service itself. Service providers | ||
| 47 | * can be installed in an implementation of the Java platform in the form of | ||
| 48 | * extensions, that is, jar files placed into any of the usual extension | ||
| 49 | * directories. Providers can also be made available by adding them to the | ||
| 50 | * application's class path or by some other platform-specific means. | ||
| 51 | * | ||
| 52 | * <p> For the purpose of loading, a service is represented by a single type, | ||
| 53 | * that is, a single interface or abstract class. (A concrete class can be | ||
| 54 | * used, but this is not recommended.) A provider of a given service contains | ||
| 55 | * one or more concrete classes that extend this <i>service type</i> with data | ||
| 56 | * and code specific to the provider. The <i>provider class</i> is typically | ||
| 57 | * not the entire provider itself but rather a proxy which contains enough | ||
| 58 | * information to decide whether the provider is able to satisfy a particular | ||
| 59 | * request together with code that can create the actual provider on demand. | ||
| 60 | * The details of provider classes tend to be highly service-specific; no | ||
| 61 | * single class or interface could possibly unify them, so no such type is | ||
| 62 | * defined here. The only requirement enforced by this facility is that | ||
| 63 | * provider classes must have a zero-argument constructor so that they can be | ||
| 64 | * instantiated during loading. | ||
| 65 | * | ||
| 66 | * <p><a name="format"> A service provider is identified by placing a | ||
| 67 | * <i>provider-configuration file</i> in the resource directory | ||
| 68 | * <tt>META-INF/services</tt>. The file's name is the fully-qualified <a | ||
| 69 | * href="../lang/ClassLoader.html#name">binary name</a> of the service's type. | ||
| 70 | * The file contains a list of fully-qualified binary names of concrete | ||
| 71 | * provider classes, one per line. Space and tab characters surrounding each | ||
| 72 | * name, as well as blank lines, are ignored. The comment character is | ||
| 73 | * <tt>'#'</tt> (<tt>'\u0023'</tt>, <font size="-1">NUMBER SIGN</font>); on | ||
| 74 | * each line all characters following the first comment character are ignored. | ||
| 75 | * The file must be encoded in UTF-8. | ||
| 76 | * | ||
| 77 | * <p> If a particular concrete provider class is named in more than one | ||
| 78 | * configuration file, or is named in the same configuration file more than | ||
| 79 | * once, then the duplicates are ignored. The configuration file naming a | ||
| 80 | * particular provider need not be in the same jar file or other distribution | ||
| 81 | * unit as the provider itself. The provider must be accessible from the same | ||
| 82 | * class loader that was initially queried to locate the configuration file; | ||
| 83 | * note that this is not necessarily the class loader from which the file was | ||
| 84 | * actually loaded. | ||
| 85 | * | ||
| 86 | * <p> Providers are located and instantiated lazily, that is, on demand. A | ||
| 87 | * service loader maintains a cache of the providers that have been loaded so | ||
| 88 | * far. Each invocation of the {@link #iterator iterator} method returns an | ||
| 89 | * iterator that first yields all of the elements of the cache, in | ||
| 90 | * instantiation order, and then lazily locates and instantiates any remaining | ||
| 91 | * providers, adding each one to the cache in turn. The cache can be cleared | ||
| 92 | * via the {@link #reload reload} method. | ||
| 93 | * | ||
| 94 | * <p> Service loaders always execute in the security context of the caller. | ||
| 95 | * Trusted system code should typically invoke the methods in this class, and | ||
| 96 | * the methods of the iterators which they return, from within a privileged | ||
| 97 | * security context. | ||
| 98 | * | ||
| 99 | * <p> Instances of this class are not safe for use by multiple concurrent | ||
| 100 | * threads. | ||
| 101 | * | ||
| 102 | * <p> Unless otherwise specified, passing a <tt>null</tt> argument to any | ||
| 103 | * method in this class will cause a {@link NullPointerException} to be thrown. | ||
| 104 | * | ||
| 105 | * | ||
| 106 | * <p><span style="font-weight: bold; padding-right: 1em">Example</span> | ||
| 107 | * Suppose we have a service type <tt>com.example.CodecSet</tt> which is | ||
| 108 | * intended to represent sets of encoder/decoder pairs for some protocol. In | ||
| 109 | * this case it is an abstract class with two abstract methods: | ||
| 110 | * | ||
| 111 | * <blockquote><pre> | ||
| 112 | * public abstract Encoder getEncoder(String encodingName); | ||
| 113 | * public abstract Decoder getDecoder(String encodingName);</pre></blockquote> | ||
| 114 | * | ||
| 115 | * Each method returns an appropriate object or <tt>null</tt> if the provider | ||
| 116 | * does not support the given encoding. Typical providers support more than | ||
| 117 | * one encoding. | ||
| 118 | * | ||
| 119 | * <p> If <tt>com.example.impl.StandardCodecs</tt> is an implementation of the | ||
| 120 | * <tt>CodecSet</tt> service then its jar file also contains a file named | ||
| 121 | * | ||
| 122 | * <blockquote><pre> | ||
| 123 | * META-INF/services/com.example.CodecSet</pre></blockquote> | ||
| 124 | * | ||
| 125 | * <p> This file contains the single line: | ||
| 126 | * | ||
| 127 | * <blockquote><pre> | ||
| 128 | * com.example.impl.StandardCodecs # Standard codecs</pre></blockquote> | ||
| 129 | * | ||
| 130 | * <p> The <tt>CodecSet</tt> class creates and saves a single service instance | ||
| 131 | * at initialization: | ||
| 132 | * | ||
| 133 | * <blockquote><pre> | ||
| 134 | * private static ServiceLoader<CodecSet> codecSetLoader | ||
| 135 | * = ServiceLoader.load(CodecSet.class);</pre></blockquote> | ||
| 136 | * | ||
| 137 | * <p> To locate an encoder for a given encoding name it defines a static | ||
| 138 | * factory method which iterates through the known and available providers, | ||
| 139 | * returning only when it has located a suitable encoder or has run out of | ||
| 140 | * providers. | ||
| 141 | * | ||
| 142 | * <blockquote><pre> | ||
| 143 | * public static Encoder getEncoder(String encodingName) { | ||
| 144 | * for (CodecSet cp : codecSetLoader) { | ||
| 145 | * Encoder enc = cp.getEncoder(encodingName); | ||
| 146 | * if (enc != null) | ||
| 147 | * return enc; | ||
| 148 | * } | ||
| 149 | * return null; | ||
| 150 | * }</pre></blockquote> | ||
| 151 | * | ||
| 152 | * <p> A <tt>getDecoder</tt> method is defined similarly. | ||
| 153 | * | ||
| 154 | * | ||
| 155 | * <p><span style="font-weight: bold; padding-right: 1em">Usage Note</span> If | ||
| 156 | * the class path of a class loader that is used for provider loading includes | ||
| 157 | * remote network URLs then those URLs will be dereferenced in the process of | ||
| 158 | * searching for provider-configuration files. | ||
| 159 | * | ||
| 160 | * <p> This activity is normal, although it may cause puzzling entries to be | ||
| 161 | * created in web-server logs. If a web server is not configured correctly, | ||
| 162 | * however, then this activity may cause the provider-loading algorithm to fail | ||
| 163 | * spuriously. | ||
| 164 | * | ||
| 165 | * <p> A web server should return an HTTP 404 (Not Found) response when a | ||
| 166 | * requested resource does not exist. Sometimes, however, web servers are | ||
| 167 | * erroneously configured to return an HTTP 200 (OK) response along with a | ||
| 168 | * helpful HTML error page in such cases. This will cause a {@link | ||
| 169 | * ServiceConfigurationError} to be thrown when this class attempts to parse | ||
| 170 | * the HTML page as a provider-configuration file. The best solution to this | ||
| 171 | * problem is to fix the misconfigured web server to return the correct | ||
| 172 | * response code (HTTP 404) along with the HTML error page. | ||
| 173 | * | ||
| 174 | * @param <S> | ||
| 175 | * The type of the service to be loaded by this loader | ||
| 176 | * | ||
| 177 | * @author Mark Reinhold | ||
| 178 | * @since 1.6 | ||
| 179 | */ | ||
| 180 | |||
| 181 | public final class ServiceLoader<S> | ||
| 182 | implements Iterable<S> | ||
| 183 | { | ||
| 184 | |||
| 185 | private static final String PREFIX = "META-INF/services/"; | ||
| 186 | |||
| 187 | // The class or interface representing the service being loaded | ||
| 188 | private Class<S> service; | ||
| 189 | |||
| 190 | // The class loader used to locate, load, and instantiate providers | ||
| 191 | private ClassLoader loader; | ||
| 192 | |||
| 193 | // Cached providers, in instantiation order | ||
| 194 | private LinkedHashMap<String,S> providers = new LinkedHashMap<>(); | ||
| 195 | |||
| 196 | // The current lazy-lookup iterator | ||
| 197 | private LazyIterator lookupIterator; | ||
| 198 | |||
| 199 | /** | ||
| 200 | * Clear this loader's provider cache so that all providers will be | ||
| 201 | * reloaded. | ||
| 202 | * | ||
| 203 | * <p> After invoking this method, subsequent invocations of the {@link | ||
| 204 | * #iterator() iterator} method will lazily look up and instantiate | ||
| 205 | * providers from scratch, just as is done by a newly-created loader. | ||
| 206 | * | ||
| 207 | * <p> This method is intended for use in situations in which new providers | ||
| 208 | * can be installed into a running Java virtual machine. | ||
| 209 | */ | ||
| 210 | public void reload() { | ||
| 211 | providers.clear(); | ||
| 212 | lookupIterator = new LazyIterator(service, loader); | ||
| 213 | } | ||
| 214 | |||
| 215 | private ServiceLoader(Class<S> svc, ClassLoader cl) { | ||
| 216 | service = svc; | ||
| 217 | loader = cl; | ||
| 218 | reload(); | ||
| 219 | } | ||
| 220 | |||
| 221 | private static void fail(Class service, String msg, Throwable cause) | ||
| 222 | throws ServiceConfigurationError | ||
| 223 | { | ||
| 224 | throw new ServiceConfigurationError(service.getName() + ": " + msg, | ||
| 225 | cause); | ||
| 226 | } | ||
| 227 | |||
| 228 | private static void fail(Class service, String msg) | ||
| 229 | throws ServiceConfigurationError | ||
| 230 | { | ||
| 231 | throw new ServiceConfigurationError(service.getName() + ": " + msg); | ||
| 232 | } | ||
| 233 | |||
| 234 | private static void fail(Class service, URL u, int line, String msg) | ||
| 235 | throws ServiceConfigurationError | ||
| 236 | { | ||
| 237 | fail(service, u + ":" + line + ": " + msg); | ||
| 238 | } | ||
| 239 | |||
| 240 | // Parse a single line from the given configuration file, adding the name | ||
| 241 | // on the line to the names list. | ||
| 242 | // | ||
| 243 | private int parseLine(Class service, URL u, BufferedReader r, int lc, | ||
| 244 | List<String> names) | ||
| 245 | throws IOException, ServiceConfigurationError | ||
| 246 | { | ||
| 247 | String ln = r.readLine(); | ||
| 248 | if (ln == null) { | ||
| 249 | return -1; | ||
| 250 | } | ||
| 251 | int ci = ln.indexOf('#'); | ||
| 252 | if (ci >= 0) ln = ln.substring(0, ci); | ||
| 253 | ln = ln.trim(); | ||
| 254 | int n = ln.length(); | ||
| 255 | if (n != 0) { | ||
| 256 | if ((ln.indexOf(' ') >= 0) || (ln.indexOf('\t') >= 0)) | ||
| 257 | fail(service, u, lc, "Illegal configuration-file syntax"); | ||
| 258 | int cp = ln.codePointAt(0); | ||
| 259 | if (!Character.isJavaIdentifierStart(cp)) | ||
| 260 | fail(service, u, lc, "Illegal provider-class name: " + ln); | ||
| 261 | for (int i = Character.charCount(cp); i < n; i += Character.charCount(cp)) { | ||
| 262 | cp = ln.codePointAt(i); | ||
| 263 | if (!Character.isJavaIdentifierPart(cp) && (cp != '.')) | ||
| 264 | fail(service, u, lc, "Illegal provider-class name: " + ln); | ||
| 265 | } | ||
| 266 | if (!providers.containsKey(ln) && !names.contains(ln)) | ||
| 267 | names.add(ln); | ||
| 268 | } | ||
| 269 | return lc + 1; | ||
| 270 | } | ||
| 271 | |||
| 272 | // Parse the content of the given URL as a provider-configuration file. | ||
| 273 | // | ||
| 274 | // @param service | ||
| 275 | // The service type for which providers are being sought; | ||
| 276 | // used to construct error detail strings | ||
| 277 | // | ||
| 278 | // @param u | ||
| 279 | // The URL naming the configuration file to be parsed | ||
| 280 | // | ||
| 281 | // @return A (possibly empty) iterator that will yield the provider-class | ||
| 282 | // names in the given configuration file that are not yet members | ||
| 283 | // of the returned set | ||
| 284 | // | ||
| 285 | // @throws ServiceConfigurationError | ||
| 286 | // If an I/O error occurs while reading from the given URL, or | ||
| 287 | // if a configuration-file format error is detected | ||
| 288 | // | ||
| 289 | private Iterator<String> parse(Class service, URL u) | ||
| 290 | throws ServiceConfigurationError | ||
| 291 | { | ||
| 292 | InputStream in = null; | ||
| 293 | BufferedReader r = null; | ||
| 294 | ArrayList<String> names = new ArrayList<>(); | ||
| 295 | try { | ||
| 296 | in = u.openStream(); | ||
| 297 | r = new BufferedReader(new InputStreamReader(in, "utf-8")); | ||
| 298 | int lc = 1; | ||
| 299 | while ((lc = parseLine(service, u, r, lc, names)) >= 0); | ||
| 300 | } catch (IOException x) { | ||
| 301 | fail(service, "Error reading configuration file", x); | ||
| 302 | } finally { | ||
| 303 | try { | ||
| 304 | if (r != null) r.close(); | ||
| 305 | if (in != null) in.close(); | ||
| 306 | } catch (IOException y) { | ||
| 307 | fail(service, "Error closing configuration file", y); | ||
| 308 | } | ||
| 309 | } | ||
| 310 | return names.iterator(); | ||
| 311 | } | ||
| 312 | |||
| 313 | // Private inner class implementing fully-lazy provider lookup | ||
| 314 | // | ||
| 315 | private class LazyIterator | ||
| 316 | implements Iterator<S> | ||
| 317 | { | ||
| 318 | |||
| 319 | Class<S> service; | ||
| 320 | ClassLoader loader; | ||
| 321 | Enumeration<URL> configs = null; | ||
| 322 | Iterator<String> pending = null; | ||
| 323 | String nextName = null; | ||
| 324 | |||
| 325 | private LazyIterator(Class<S> service, ClassLoader loader) { | ||
| 326 | this.service = service; | ||
| 327 | this.loader = loader; | ||
| 328 | } | ||
| 329 | |||
| 330 | public boolean hasNext() { | ||
| 331 | if (nextName != null) { | ||
| 332 | return true; | ||
| 333 | } | ||
| 334 | if (configs == null) { | ||
| 335 | try { | ||
| 336 | String fullName = PREFIX + service.getName(); | ||
| 337 | if (loader == null) | ||
| 338 | configs = ClassLoader.getSystemResources(fullName); | ||
| 339 | else | ||
| 340 | configs = loader.getResources(fullName); | ||
| 341 | } catch (IOException x) { | ||
| 342 | fail(service, "Error locating configuration files", x); | ||
| 343 | } | ||
| 344 | } | ||
| 345 | while ((pending == null) || !pending.hasNext()) { | ||
| 346 | if (!configs.hasMoreElements()) { | ||
| 347 | return false; | ||
| 348 | } | ||
| 349 | pending = parse(service, configs.nextElement()); | ||
| 350 | } | ||
| 351 | nextName = pending.next(); | ||
| 352 | return true; | ||
| 353 | } | ||
| 354 | |||
| 355 | public S next() { | ||
| 356 | if (!hasNext()) { | ||
| 357 | throw new NoSuchElementException(); | ||
| 358 | } | ||
| 359 | String cn = nextName; | ||
| 360 | nextName = null; | ||
| 361 | try { | ||
| 362 | S p = service.cast(Class.forName(cn, true, loader) | ||
| 363 | .newInstance()); | ||
| 364 | providers.put(cn, p); | ||
| 365 | return p; | ||
| 366 | } catch (ClassNotFoundException x) { | ||
| 367 | fail(service, | ||
| 368 | "Provider " + cn + " not found"); | ||
| 369 | } catch (Throwable x) { | ||
| 370 | fail(service, | ||
| 371 | "Provider " + cn + " could not be instantiated: " + x, | ||
| 372 | x); | ||
| 373 | } | ||
| 374 | throw new Error(); // This cannot happen | ||
| 375 | } | ||
| 376 | |||
| 377 | public void remove() { | ||
| 378 | throw new UnsupportedOperationException(); | ||
| 379 | } | ||
| 380 | |||
| 381 | } | ||
| 382 | |||
| 383 | /** | ||
| 384 | * Lazily loads the available providers of this loader's service. | ||
| 385 | * | ||
| 386 | * <p> The iterator returned by this method first yields all of the | ||
| 387 | * elements of the provider cache, in instantiation order. It then lazily | ||
| 388 | * loads and instantiates any remaining providers, adding each one to the | ||
| 389 | * cache in turn. | ||
| 390 | * | ||
| 391 | * <p> To achieve laziness the actual work of parsing the available | ||
| 392 | * provider-configuration files and instantiating providers must be done by | ||
| 393 | * the iterator itself. Its {@link java.util.Iterator#hasNext hasNext} and | ||
| 394 | * {@link java.util.Iterator#next next} methods can therefore throw a | ||
| 395 | * {@link ServiceConfigurationError} if a provider-configuration file | ||
| 396 | * violates the specified format, or if it names a provider class that | ||
| 397 | * cannot be found and instantiated, or if the result of instantiating the | ||
| 398 | * class is not assignable to the service type, or if any other kind of | ||
| 399 | * exception or error is thrown as the next provider is located and | ||
| 400 | * instantiated. To write robust code it is only necessary to catch {@link | ||
| 401 | * ServiceConfigurationError} when using a service iterator. | ||
| 402 | * | ||
| 403 | * <p> If such an error is thrown then subsequent invocations of the | ||
| 404 | * iterator will make a best effort to locate and instantiate the next | ||
| 405 | * available provider, but in general such recovery cannot be guaranteed. | ||
| 406 | * | ||
| 407 | * <blockquote style="font-size: smaller; line-height: 1.2"><span | ||
| 408 | * style="padding-right: 1em; font-weight: bold">Design Note</span> | ||
| 409 | * Throwing an error in these cases may seem extreme. The rationale for | ||
| 410 | * this behavior is that a malformed provider-configuration file, like a | ||
| 411 | * malformed class file, indicates a serious problem with the way the Java | ||
| 412 | * virtual machine is configured or is being used. As such it is | ||
| 413 | * preferable to throw an error rather than try to recover or, even worse, | ||
| 414 | * fail silently.</blockquote> | ||
| 415 | * | ||
| 416 | * <p> The iterator returned by this method does not support removal. | ||
| 417 | * Invoking its {@link java.util.Iterator#remove() remove} method will | ||
| 418 | * cause an {@link UnsupportedOperationException} to be thrown. | ||
| 419 | * | ||
| 420 | * @return An iterator that lazily loads providers for this loader's | ||
| 421 | * service | ||
| 422 | */ | ||
| 423 | public Iterator<S> iterator() { | ||
| 424 | return new Iterator<S>() { | ||
| 425 | |||
| 426 | Iterator<Map.Entry<String,S>> knownProviders | ||
| 427 | = providers.entrySet().iterator(); | ||
| 428 | |||
| 429 | public boolean hasNext() { | ||
| 430 | if (knownProviders.hasNext()) | ||
| 431 | return true; | ||
| 432 | return lookupIterator.hasNext(); | ||
| 433 | } | ||
| 434 | |||
| 435 | public S next() { | ||
| 436 | if (knownProviders.hasNext()) | ||
| 437 | return knownProviders.next().getValue(); | ||
| 438 | return lookupIterator.next(); | ||
| 439 | } | ||
| 440 | |||
| 441 | public void remove() { | ||
| 442 | throw new UnsupportedOperationException(); | ||
| 443 | } | ||
| 444 | |||
| 445 | }; | ||
| 446 | } | ||
| 447 | |||
| 448 | /** | ||
| 449 | * Creates a new service loader for the given service type and class | ||
| 450 | * loader. | ||
| 451 | * | ||
| 452 | * @param service | ||
| 453 | * The interface or abstract class representing the service | ||
| 454 | * | ||
| 455 | * @param loader | ||
| 456 | * The class loader to be used to load provider-configuration files | ||
| 457 | * and provider classes, or <tt>null</tt> if the system class | ||
| 458 | * loader (or, failing that, the bootstrap class loader) is to be | ||
| 459 | * used | ||
| 460 | * | ||
| 461 | * @return A new service loader | ||
| 462 | */ | ||
| 463 | public static <S> ServiceLoader<S> load(Class<S> service, | ||
| 464 | ClassLoader loader) | ||
| 465 | { | ||
| 466 | return new ServiceLoader<>(service, loader); | ||
| 467 | } | ||
| 468 | |||
| 469 | /** | ||
| 470 | * Creates a new service loader for the given service type, using the | ||
| 471 | * current thread's {@linkplain java.lang.Thread#getContextClassLoader | ||
| 472 | * context class loader}. | ||
| 473 | * | ||
| 474 | * <p> An invocation of this convenience method of the form | ||
| 475 | * | ||
| 476 | * <blockquote><pre> | ||
| 477 | * ServiceLoader.load(<i>service</i>)</pre></blockquote> | ||
| 478 | * | ||
| 479 | * is equivalent to | ||
| 480 | * | ||
| 481 | * <blockquote><pre> | ||
| 482 | * ServiceLoader.load(<i>service</i>, | ||
| 483 | * Thread.currentThread().getContextClassLoader())</pre></blockquote> | ||
| 484 | * | ||
| 485 | * @param service | ||
| 486 | * The interface or abstract class representing the service | ||
| 487 | * | ||
| 488 | * @return A new service loader | ||
| 489 | */ | ||
| 490 | public static <S> ServiceLoader<S> load(Class<S> service) { | ||
| 491 | ClassLoader cl = Thread.currentThread().getContextClassLoader(); | ||
| 492 | return ServiceLoader.load(service, cl); | ||
| 493 | } | ||
| 494 | |||
| 495 | /** | ||
| 496 | * Creates a new service loader for the given service type, using the | ||
| 497 | * extension class loader. | ||
| 498 | * | ||
| 499 | * <p> This convenience method simply locates the extension class loader, | ||
| 500 | * call it <tt><i>extClassLoader</i></tt>, and then returns | ||
| 501 | * | ||
| 502 | * <blockquote><pre> | ||
| 503 | * ServiceLoader.load(<i>service</i>, <i>extClassLoader</i>)</pre></blockquote> | ||
| 504 | * | ||
| 505 | * <p> If the extension class loader cannot be found then the system class | ||
| 506 | * loader is used; if there is no system class loader then the bootstrap | ||
| 507 | * class loader is used. | ||
| 508 | * | ||
| 509 | * <p> This method is intended for use when only installed providers are | ||
| 510 | * desired. The resulting service will only find and load providers that | ||
| 511 | * have been installed into the current Java virtual machine; providers on | ||
| 512 | * the application's class path will be ignored. | ||
| 513 | * | ||
| 514 | * @param service | ||
| 515 | * The interface or abstract class representing the service | ||
| 516 | * | ||
| 517 | * @return A new service loader | ||
| 518 | */ | ||
| 519 | public static <S> ServiceLoader<S> loadInstalled(Class<S> service) { | ||
| 520 | ClassLoader cl = ClassLoader.getSystemClassLoader(); | ||
| 521 | ClassLoader prev = null; | ||
| 522 | while (cl != null) { | ||
| 523 | prev = cl; | ||
| 524 | cl = cl.getParent(); | ||
| 525 | } | ||
| 526 | return ServiceLoader.load(service, prev); | ||
| 527 | } | ||
| 528 | |||
| 529 | /** | ||
| 530 | * Returns a string describing this service. | ||
| 531 | * | ||
| 532 | * @return A descriptive string | ||
| 533 | */ | ||
| 534 | public String toString() { | ||
| 535 | return "java.util.ServiceLoader[" + service.getName() + "]"; | ||
| 536 | } | ||
| 537 | |||
| 538 | } | ||