59 * in the service itself. Service providers may be installed in an
60 * implementation of the Java platform in the form of extensions, that is, jar
61 * files placed into any of the usual extension directories. Providers may
62 * also be made available by adding them to the applet or application class
63 * path or by some other platform-specific means.
64 * <p/>
65 * <p> In this lookup mechanism a service is represented by an interface or an
66 * abstract class. (A concrete class may be used, but this is not
67 * recommended.) A provider of a given service contains one or more concrete
68 * classes that extend this <i>service class</i> with data and code specific to
69 * the provider. This <i>provider class</i> will typically not be the entire
70 * provider itself but rather a proxy that contains enough information to
71 * decide whether the provider is able to satisfy a particular request together
72 * with code that can create the actual provider on demand. The details of
73 * provider classes tend to be highly service-specific; no single class or
74 * interface could possibly unify them, so no such class has been defined. The
75 * only requirement enforced here is that provider classes must have a
76 * zero-argument constructor so that they may be instantiated during lookup.
77 * <p/>
78 * <p> A service provider identifies itself by placing a provider-configuration
79 * file in the resource directory <tt>META-INF/services</tt>. The file's name
80 * should consist of the fully-qualified name of the abstract service class.
81 * The file should contain a list of fully-qualified concrete provider-class
82 * names, one per line. Space and tab characters surrounding each name, as
83 * well as blank lines, are ignored. The comment character is <tt>'#'</tt>
84 * (<tt>0x23</tt>); on each line all characters following the first comment
85 * character are ignored. The file must be encoded in UTF-8.
86 * <p/>
87 * <p> If a particular concrete provider class is named in more than one
88 * configuration file, or is named in the same configuration file more than
89 * once, then the duplicates will be ignored. The configuration file naming a
90 * particular provider need not be in the same jar file or other distribution
91 * unit as the provider itself. The provider must be accessible from the same
92 * class loader that was initially queried to locate the configuration file;
93 * note that this is not necessarily the class loader that found the file.
94 * <p/>
95 * <p> <b>Example:</b> Suppose we have a service class named
96 * <tt>java.io.spi.CharCodec</tt>. It has two abstract methods:
97 * <p/>
98 * <pre>
99 * public abstract CharEncoder getEncoder(String encodingName);
100 * public abstract CharDecoder getDecoder(String encodingName);
101 * </pre>
102 * <p/>
103 * Each method returns an appropriate object or <tt>null</tt> if it cannot
104 * translate the given encoding. Typical <tt>CharCodec</tt> providers will
105 * support more than one encoding.
106 * <p/>
107 * <p> If <tt>sun.io.StandardCodec</tt> is a provider of the <tt>CharCodec</tt>
108 * service then its jar file would contain the file
109 * <tt>META-INF/services/java.io.spi.CharCodec</tt>. This file would contain
110 * the single line:
111 * <p/>
112 * <pre>
113 * sun.io.StandardCodec # Standard codecs for the platform
114 * </pre>
115 * <p/>
116 * To locate an codec for a given encoding name, the internal I/O code would
117 * do something like this:
118 * <p/>
119 * <pre>
120 * CharEncoder getEncoder(String encodingName) {
121 * for( CharCodec cc : ServiceFinder.find(CharCodec.class) ) {
122 * CharEncoder ce = cc.getEncoder(encodingName);
123 * if (ce != null)
124 * return ce;
125 * }
126 * return null;
127 * }
128 * </pre>
129 * <p/>
152 public ServiceName(String className, URL config) {
153 this.className = className;
154 this.config = config;
155 }
156 }
157
158 public static <T> ServiceFinder<T> find(@NotNull Class<T> service, @Nullable ClassLoader loader, Component component) {
159 return new ServiceFinder<T>(service, loader, component);
160 }
161
162 public static <T> ServiceFinder<T> find(@NotNull Class<T> service, Component component) {
163 return find(service,Thread.currentThread().getContextClassLoader(),component);
164 }
165
166 /**
167 * Locates and incrementally instantiates the available providers of a
168 * given service using the given class loader.
169 * <p/>
170 * <p> This method transforms the name of the given service class into a
171 * provider-configuration filename as described above and then uses the
172 * <tt>getResources</tt> method of the given class loader to find all
173 * available files with that name. These files are then read and parsed to
174 * produce a list of provider-class names. The iterator that is returned
175 * uses the given class loader to lookup and then instantiate each element
176 * of the list.
177 * <p/>
178 * <p> Because it is possible for extensions to be installed into a running
179 * Java virtual machine, this method may return different results each time
180 * it is invoked. <p>
181 *
182 * @param service The service's abstract service class
183 * @param loader The class loader to be used to load provider-configuration files
184 * and instantiate provider classes, or <tt>null</tt> if the system
185 * class loader (or, failing that the bootstrap class loader) is to
186 * be used
187 * @throws ServiceConfigurationError If a provider-configuration file violates the specified format
188 * or names a provider class that cannot be found and instantiated
189 * @see #find(Class)
190 */
191 public static <T> ServiceFinder<T> find(@NotNull Class<T> service, @Nullable ClassLoader loader) {
192 return find(service, loader, ContainerResolver.getInstance().getContainer());
193 }
194
195 /**
196 * Locates and incrementally instantiates the available providers of a
197 * given service using the context class loader. This convenience method
198 * is equivalent to
199 * <p/>
200 * <pre>
201 * ClassLoader cl = Thread.currentThread().getContextClassLoader();
202 * return Service.providers(service, cl);
203 * </pre>
204 *
210 */
211 public static <T> ServiceFinder<T> find(Class<T> service) {
212 return find(service,Thread.currentThread().getContextClassLoader());
213 }
214
215 private ServiceFinder(Class<T> service, ClassLoader loader, Component component) {
216 this.serviceClass = service;
217 this.classLoader = loader;
218 this.component = getComponentEx(component);
219 }
220
221 private static ServiceName[] serviceClassNames(Class serviceClass, ClassLoader classLoader) {
222 ArrayList<ServiceName> l = new ArrayList<ServiceName>();
223 for (Iterator<ServiceName> it = new ServiceNameIterator(serviceClass,classLoader);it.hasNext();) l.add(it.next());
224 return l.toArray(new ServiceName[l.size()]);
225 }
226
227 /**
228 * Returns discovered objects incrementally.
229 *
230 * @return An <tt>Iterator</tt> that yields provider objects for the given
231 * service, in some arbitrary order. The iterator will throw a
232 * <tt>ServiceConfigurationError</tt> if a provider-configuration
233 * file violates the specified format or if a provider class cannot
234 * be found and instantiated.
235 */
236 @SuppressWarnings("unchecked")
237 public Iterator<T> iterator() {
238 Iterator<T> it = new LazyIterator<T>(serviceClass,classLoader);
239 return component != null ?
240 new CompositeIterator<T>(
241 component.getIterableSPI(serviceClass).iterator(),it) :
242 it;
243 }
244
245 /**
246 * Returns discovered objects all at once.
247 *
248 * @return
249 * can be empty but never null.
250 *
251 * @throws ServiceConfigurationError
252 */
302 cp = ln.codePointAt(i);
303 if (!Character.isJavaIdentifierPart(cp) && (cp != '.'))
304 fail(service, u, lc, "Illegal provider-class name: " + ln);
305 }
306 if (!returned.contains(ln)) {
307 names.add(ln);
308 returned.add(ln);
309 }
310 }
311 return lc + 1;
312 }
313
314 /**
315 * Parse the content of the given URL as a provider-configuration file.
316 *
317 * @param service The service class for which providers are being sought;
318 * used to construct error detail strings
319 * @param u The URL naming the configuration file to be parsed
320 * @param returned A Set containing the names of provider classes that have already
321 * been returned. This set will be updated to contain the names
322 * that will be yielded from the returned <tt>Iterator</tt>.
323 * @return A (possibly empty) <tt>Iterator</tt> that will yield the
324 * provider-class names in the given configuration file that are
325 * not yet members of the returned set
326 * @throws ServiceConfigurationError If an I/O error occurs while reading from the given URL, or
327 * if a configuration-file format error is detected
328 */
329 @SuppressWarnings({"StatementWithEmptyBody"})
330 private static Iterator<String> parse(Class service, URL u, Set<String> returned)
331 throws ServiceConfigurationError {
332 InputStream in = null;
333 BufferedReader r = null;
334 ArrayList<String> names = new ArrayList<String>();
335 try {
336 in = u.openStream();
337 r = new BufferedReader(new InputStreamReader(in, "utf-8"));
338 int lc = 1;
339 while ((lc = parseLine(service, u, r, lc, names, returned)) >= 0) ;
340 } catch (IOException x) {
341 fail(service, ": " + x);
342 } finally {
343 try {
|
59 * in the service itself. Service providers may be installed in an
60 * implementation of the Java platform in the form of extensions, that is, jar
61 * files placed into any of the usual extension directories. Providers may
62 * also be made available by adding them to the applet or application class
63 * path or by some other platform-specific means.
64 * <p/>
65 * <p> In this lookup mechanism a service is represented by an interface or an
66 * abstract class. (A concrete class may be used, but this is not
67 * recommended.) A provider of a given service contains one or more concrete
68 * classes that extend this <i>service class</i> with data and code specific to
69 * the provider. This <i>provider class</i> will typically not be the entire
70 * provider itself but rather a proxy that contains enough information to
71 * decide whether the provider is able to satisfy a particular request together
72 * with code that can create the actual provider on demand. The details of
73 * provider classes tend to be highly service-specific; no single class or
74 * interface could possibly unify them, so no such class has been defined. The
75 * only requirement enforced here is that provider classes must have a
76 * zero-argument constructor so that they may be instantiated during lookup.
77 * <p/>
78 * <p> A service provider identifies itself by placing a provider-configuration
79 * file in the resource directory {@code META-INF/services}. The file's name
80 * should consist of the fully-qualified name of the abstract service class.
81 * The file should contain a list of fully-qualified concrete provider-class
82 * names, one per line. Space and tab characters surrounding each name, as
83 * well as blank lines, are ignored. The comment character is {@code '#'}
84 * ({@code 0x23}); on each line all characters following the first comment
85 * character are ignored. The file must be encoded in UTF-8.
86 * <p/>
87 * <p> If a particular concrete provider class is named in more than one
88 * configuration file, or is named in the same configuration file more than
89 * once, then the duplicates will be ignored. The configuration file naming a
90 * particular provider need not be in the same jar file or other distribution
91 * unit as the provider itself. The provider must be accessible from the same
92 * class loader that was initially queried to locate the configuration file;
93 * note that this is not necessarily the class loader that found the file.
94 * <p/>
95 * <p> <b>Example:</b> Suppose we have a service class named
96 * {@code java.io.spi.CharCodec}. It has two abstract methods:
97 * <p/>
98 * <pre>
99 * public abstract CharEncoder getEncoder(String encodingName);
100 * public abstract CharDecoder getDecoder(String encodingName);
101 * </pre>
102 * <p/>
103 * Each method returns an appropriate object or {@code null} if it cannot
104 * translate the given encoding. Typical {@code CharCodec} providers will
105 * support more than one encoding.
106 * <p/>
107 * <p> If {@code sun.io.StandardCodec} is a provider of the {@code CharCodec}
108 * service then its jar file would contain the file
109 * {@code META-INF/services/java.io.spi.CharCodec}. This file would contain
110 * the single line:
111 * <p/>
112 * <pre>
113 * sun.io.StandardCodec # Standard codecs for the platform
114 * </pre>
115 * <p/>
116 * To locate an codec for a given encoding name, the internal I/O code would
117 * do something like this:
118 * <p/>
119 * <pre>
120 * CharEncoder getEncoder(String encodingName) {
121 * for( CharCodec cc : ServiceFinder.find(CharCodec.class) ) {
122 * CharEncoder ce = cc.getEncoder(encodingName);
123 * if (ce != null)
124 * return ce;
125 * }
126 * return null;
127 * }
128 * </pre>
129 * <p/>
152 public ServiceName(String className, URL config) {
153 this.className = className;
154 this.config = config;
155 }
156 }
157
158 public static <T> ServiceFinder<T> find(@NotNull Class<T> service, @Nullable ClassLoader loader, Component component) {
159 return new ServiceFinder<T>(service, loader, component);
160 }
161
162 public static <T> ServiceFinder<T> find(@NotNull Class<T> service, Component component) {
163 return find(service,Thread.currentThread().getContextClassLoader(),component);
164 }
165
166 /**
167 * Locates and incrementally instantiates the available providers of a
168 * given service using the given class loader.
169 * <p/>
170 * <p> This method transforms the name of the given service class into a
171 * provider-configuration filename as described above and then uses the
172 * {@code getResources} method of the given class loader to find all
173 * available files with that name. These files are then read and parsed to
174 * produce a list of provider-class names. The iterator that is returned
175 * uses the given class loader to lookup and then instantiate each element
176 * of the list.
177 * <p/>
178 * <p> Because it is possible for extensions to be installed into a running
179 * Java virtual machine, this method may return different results each time
180 * it is invoked. <p>
181 *
182 * @param service The service's abstract service class
183 * @param loader The class loader to be used to load provider-configuration files
184 * and instantiate provider classes, or {@code null} if the system
185 * class loader (or, failing that the bootstrap class loader) is to
186 * be used
187 * @throws ServiceConfigurationError If a provider-configuration file violates the specified format
188 * or names a provider class that cannot be found and instantiated
189 * @see #find(Class)
190 */
191 public static <T> ServiceFinder<T> find(@NotNull Class<T> service, @Nullable ClassLoader loader) {
192 return find(service, loader, ContainerResolver.getInstance().getContainer());
193 }
194
195 /**
196 * Locates and incrementally instantiates the available providers of a
197 * given service using the context class loader. This convenience method
198 * is equivalent to
199 * <p/>
200 * <pre>
201 * ClassLoader cl = Thread.currentThread().getContextClassLoader();
202 * return Service.providers(service, cl);
203 * </pre>
204 *
210 */
211 public static <T> ServiceFinder<T> find(Class<T> service) {
212 return find(service,Thread.currentThread().getContextClassLoader());
213 }
214
215 private ServiceFinder(Class<T> service, ClassLoader loader, Component component) {
216 this.serviceClass = service;
217 this.classLoader = loader;
218 this.component = getComponentEx(component);
219 }
220
221 private static ServiceName[] serviceClassNames(Class serviceClass, ClassLoader classLoader) {
222 ArrayList<ServiceName> l = new ArrayList<ServiceName>();
223 for (Iterator<ServiceName> it = new ServiceNameIterator(serviceClass,classLoader);it.hasNext();) l.add(it.next());
224 return l.toArray(new ServiceName[l.size()]);
225 }
226
227 /**
228 * Returns discovered objects incrementally.
229 *
230 * @return An {@code Iterator} that yields provider objects for the given
231 * service, in some arbitrary order. The iterator will throw a
232 * {@code ServiceConfigurationError} if a provider-configuration
233 * file violates the specified format or if a provider class cannot
234 * be found and instantiated.
235 */
236 @SuppressWarnings("unchecked")
237 public Iterator<T> iterator() {
238 Iterator<T> it = new LazyIterator<T>(serviceClass,classLoader);
239 return component != null ?
240 new CompositeIterator<T>(
241 component.getIterableSPI(serviceClass).iterator(),it) :
242 it;
243 }
244
245 /**
246 * Returns discovered objects all at once.
247 *
248 * @return
249 * can be empty but never null.
250 *
251 * @throws ServiceConfigurationError
252 */
302 cp = ln.codePointAt(i);
303 if (!Character.isJavaIdentifierPart(cp) && (cp != '.'))
304 fail(service, u, lc, "Illegal provider-class name: " + ln);
305 }
306 if (!returned.contains(ln)) {
307 names.add(ln);
308 returned.add(ln);
309 }
310 }
311 return lc + 1;
312 }
313
314 /**
315 * Parse the content of the given URL as a provider-configuration file.
316 *
317 * @param service The service class for which providers are being sought;
318 * used to construct error detail strings
319 * @param u The URL naming the configuration file to be parsed
320 * @param returned A Set containing the names of provider classes that have already
321 * been returned. This set will be updated to contain the names
322 * that will be yielded from the returned {@code Iterator}.
323 * @return A (possibly empty) {@code Iterator} that will yield the
324 * provider-class names in the given configuration file that are
325 * not yet members of the returned set
326 * @throws ServiceConfigurationError If an I/O error occurs while reading from the given URL, or
327 * if a configuration-file format error is detected
328 */
329 @SuppressWarnings({"StatementWithEmptyBody"})
330 private static Iterator<String> parse(Class service, URL u, Set<String> returned)
331 throws ServiceConfigurationError {
332 InputStream in = null;
333 BufferedReader r = null;
334 ArrayList<String> names = new ArrayList<String>();
335 try {
336 in = u.openStream();
337 r = new BufferedReader(new InputStreamReader(in, "utf-8"));
338 int lc = 1;
339 while ((lc = parseLine(service, u, r, lc, names, returned)) >= 0) ;
340 } catch (IOException x) {
341 fail(service, ": " + x);
342 } finally {
343 try {
|