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package com.sun.xml.ws.policy.privateutil;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.lang.reflect.Array;
import java.net.URL;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.TreeSet;
/**
*
* A simple service-provider lookup mechanism. A <i>service</i> is a
* well-known set of interfaces and (usually abstract) classes. A <i>service
* provider</i> is a specific implementation of a service. The classes in a
* provider typically implement the interfaces and subclass the classes defined
* in the service itself. Service providers may be installed in an
* implementation of the Java platform in the form of extensions, that is, jar
* files placed into any of the usual extension directories. Providers may
* also be made available by adding them to the applet or application class
* path or by some other platform-specific means.
* <p/>
* <p> In this lookup mechanism a service is represented by an interface or an
* abstract class. (A concrete class may be used, but this is not
* recommended.) A provider of a given service contains one or more concrete
* classes that extend this <i>service class</i> with data and code specific to
* the provider. This <i>provider class</i> will typically not be the entire
* provider itself but rather a proxy that contains enough information to
* decide whether the provider is able to satisfy a particular request together
* with code that can create the actual provider on demand. The details of
* provider classes tend to be highly service-specific; no single class or
* interface could possibly unify them, so no such class has been defined. The
* only requirement enforced here is that provider classes must have a
* zero-argument constructor so that they may be instantiated during lookup.
* <p/>
* <p> A service provider identifies itself by placing a provider-configuration
* file in the resource directory <tt>META-INF/services</tt>. The file's name
* should consist of the fully-qualified name of the abstract service class.
* The file should contain a list of fully-qualified concrete provider-class
* names, one per line. Space and tab characters surrounding each name, as
* well as blank lines, are ignored. The comment character is <tt>'#'</tt>
* (<tt>0x23</tt>); on each line all characters following the first comment
* character are ignored. The file must be encoded in UTF-8.
* <p/>
* <p> If a particular concrete provider class is named in more than one
* configuration file, or is named in the same configuration file more than
* once, then the duplicates will be ignored. The configuration file naming a
* particular provider need not be in the same jar file or other distribution
* unit as the provider itself. The provider must be accessible from the same
* class loader that was initially queried to locate the configuration file;
* note that this is not necessarily the class loader that found the file.
* <p/>
* <p> <b>Example:</b> Suppose we have a service class named
* <tt>java.io.spi.CharCodec</tt>. It has two abstract methods:
* <p/>
* <pre>
* public abstract CharEncoder getEncoder(String encodingName);
* public abstract CharDecoder getDecoder(String encodingName);
* </pre>
* <p/>
* Each method returns an appropriate object or <tt>null</tt> if it cannot
* translate the given encoding. Typical <tt>CharCodec</tt> providers will
* support more than one encoding.
* <p/>
* <p> If <tt>sun.io.StandardCodec</tt> is a provider of the <tt>CharCodec</tt>
* service then its jar file would contain the file
* <tt>META-INF/services/java.io.spi.CharCodec</tt>. This file would contain
* the single line:
* <p/>
* <pre>
* sun.io.StandardCodec # Standard codecs for the platform
* </pre>
* <p/>
* To locate an encoder for a given encoding name, the internal I/O code would
* do something like this:
* <p/>
* <pre>
* CharEncoder getEncoder(String encodingName) {
* for( CharCodec cc : ServiceFinder.find(CharCodec.class) ) {
* CharEncoder ce = cc.getEncoder(encodingName);
* if (ce != null)
* return ce;
* }
* return null;
* }
* </pre>
* <p/>
* The provider-lookup mechanism always executes in the security context of the
* caller. Trusted system code should typically invoke the methods in this
* class from within a privileged security context.
*
* @author Mark Reinhold
* @version 1.11, 03/12/19
* @since 1.3
*/
final class ServiceFinder<T> implements Iterable<T> {
private static final PolicyLogger LOGGER = PolicyLogger.getLogger(ServiceFinder.class);
private static final String prefix = "META-INF/services/";
private final Class<T> serviceClass;
private final ClassLoader classLoader;
/**
* Locates and incrementally instantiates the available providers of a
* given service using the given class loader.
* <p/>
* <p> This method transforms the name of the given service class into a
* provider-configuration filename as described above and then uses the
* <tt>getResources</tt> method of the given class loader to find all
* available files with that name. These files are then read and parsed to
* produce a list of provider-class names. The iterator that is returned
* uses the given class loader to lookup and then instantiate each element
* of the list.
* <p/>
* <p> Because it is possible for extensions to be installed into a running
* Java virtual machine, this method may return different results each time
* it is invoked. <p>
*
* @param service The service's abstract service class
* @param loader The class loader to be used to load provider-configuration files
* and instantiate provider classes, or <tt>null</tt> if the system
* class loader (or, failing that the bootstrap class loader) is to
* be used
* @throws ServiceConfigurationError If a provider-configuration file violates the specified format
* or names a provider class that cannot be found and instantiated
* @see #find(Class)
*/
static <T> ServiceFinder<T> find(final Class<T> service, final ClassLoader loader) {
if (null==service) {
throw LOGGER.logSevereException(new NullPointerException(LocalizationMessages.WSP_0032_SERVICE_CAN_NOT_BE_NULL()));
}
return new ServiceFinder<T>(service,loader);
}
/**
* Locates and incrementally instantiates the available providers of a
* given service using the context class loader. This convenience method
* is equivalent to
* <p/>
* <pre>
* ClassLoader cl = Thread.currentThread().getContextClassLoader();
* return Service.providers(service, cl);
* </pre>
*
* @param service The service's abstract service class
*
* @throws ServiceConfigurationError If a provider-configuration file violates the specified format
* or names a provider class that cannot be found and instantiated
* @see #find(Class, ClassLoader)
*/
public static <T> ServiceFinder<T> find(final Class<T> service) {
return find(service,Thread.currentThread().getContextClassLoader());
}
private ServiceFinder(Class<T> service, ClassLoader loader) {
this.serviceClass = service;
this.classLoader = loader;
}
/**
* Returns discovered objects incrementally.
*
* @return An <tt>Iterator</tt> that yields provider objects for the given
* service, in some arbitrary order. The iterator will throw a
* <tt>ServiceConfigurationError</tt> if a provider-configuration
* file violates the specified format or if a provider class cannot
* be found and instantiated.
*/
public Iterator<T> iterator() {
return new LazyIterator<T>(serviceClass,classLoader);
}
/**
* Returns discovered objects all at once.
*
* @return
* can be empty but never null.
*
* @throws ServiceConfigurationError
*/
@SuppressWarnings({"unchecked"})
public T[] toArray() {
List<T> result = new ArrayList<T>();
for (T t : this) {
result.add(t);
}
return result.toArray((T[])Array.newInstance(serviceClass,result.size()));
}
private static void fail(final Class service, final String msg, final Throwable cause)
throws ServiceConfigurationError {
final ServiceConfigurationError sce
= new ServiceConfigurationError(LocalizationMessages.WSP_0025_SPI_FAIL_SERVICE_MSG(service.getName(), msg));
if (null != cause) {
sce.initCause(cause);
}
throw LOGGER.logSevereException(sce);
}
/* private static void fail(Class service, String msg)
throws ServiceConfigurationError {
throw new ServiceConfigurationError(LocalizationMessages.WSP_0025_SPI_FAIL_SERVICE_MSG(service.getName(), msg));
}*/
private static void fail(final Class service, final URL u, final int line, final String msg, final Throwable cause)
throws ServiceConfigurationError {
fail(service, LocalizationMessages.WSP_0024_SPI_FAIL_SERVICE_URL_LINE_MSG(u , line, msg), cause);
}
/**
* Parse a single line from the given configuration file, adding the name
* on the line to both the names list and the returned set iff the name is
* not already a member of the returned set.
*/
private static int parseLine(final Class service, final URL u, final BufferedReader r, final int lc,
final List<String> names, final Set<String> returned)
throws IOException, ServiceConfigurationError {
String ln = r.readLine();
if (ln == null) {
return -1;
}
final int ci = ln.indexOf('#');
if (ci >= 0) ln = ln.substring(0, ci);
ln = ln.trim();
final int n = ln.length();
if (n != 0) {
if ((ln.indexOf(' ') >= 0) || (ln.indexOf('\t') >= 0))
fail(service, u, lc, LocalizationMessages.WSP_0067_ILLEGAL_CFG_FILE_SYNTAX(), null);
int cp = ln.codePointAt(0);
if (!Character.isJavaIdentifierStart(cp))
fail(service, u, lc, LocalizationMessages.WSP_0066_ILLEGAL_PROVIDER_CLASSNAME(ln), null);
for (int i = Character.charCount(cp); i < n; i += Character.charCount(cp)) {
cp = ln.codePointAt(i);
if (!Character.isJavaIdentifierPart(cp) && (cp != '.'))
fail(service, u, lc, LocalizationMessages.WSP_0066_ILLEGAL_PROVIDER_CLASSNAME(ln), null);
}
if (!returned.contains(ln)) {
names.add(ln);
returned.add(ln);
}
}
return lc + 1;
}
/**
* Parse the content of the given URL as a provider-configuration file.
*
* @param service The service class for which providers are being sought;
* used to construct error detail strings
* @param u The URL naming the configuration file to be parsed
* @param returned A Set containing the names of provider classes that have already
* been returned. This set will be updated to contain the names
* that will be yielded from the returned <tt>Iterator</tt>.
* @return A (possibly empty) <tt>Iterator</tt> that will yield the
* provider-class names in the given configuration file that are
* not yet members of the returned set
* @throws ServiceConfigurationError If an I/O error occurs while reading from the given URL, or
* if a configuration-file format error is detected
*/
@SuppressWarnings({"StatementWithEmptyBody"})
private static Iterator<String> parse(Class service, URL u, Set<String> returned)
throws ServiceConfigurationError {
InputStream in = null;
BufferedReader r = null;
ArrayList<String> names = new ArrayList<String>();
try {
in = u.openStream();
r = new BufferedReader(new InputStreamReader(in, "utf-8"));
int lc = 1;
while ((lc = parseLine(service, u, r, lc, names, returned)) >= 0) ;
} catch (IOException x) {
fail(service, ": " + x, x);
} finally {
try {
if (r != null) r.close();
if (in != null) in.close();
} catch (IOException y) {
fail(service, ": " + y, y);
}
}
return names.iterator();
}
/**
* Private inner class implementing fully-lazy provider lookup
*/
private static class LazyIterator<T> implements Iterator<T> {
Class<T> service;
ClassLoader loader;
Enumeration<URL> configs = null;
Iterator<String> pending = null;
Set<String> returned = new TreeSet<String>();
String nextName = null;
private LazyIterator(Class<T> service, ClassLoader loader) {
this.service = service;
this.loader = loader;
}
public boolean hasNext() throws ServiceConfigurationError {
if (nextName != null) {
return true;
}
if (configs == null) {
try {
final String fullName = prefix + service.getName();
if (loader == null)
configs = ClassLoader.getSystemResources(fullName);
else
configs = loader.getResources(fullName);
} catch (IOException x) {
fail(service, ": " + x, x);
}
}
while ((pending == null) || !pending.hasNext()) {
if (!configs.hasMoreElements()) {
return false;
}
pending = parse(service, configs.nextElement(), returned);
}
nextName = pending.next();
return true;
}
public T next() throws ServiceConfigurationError {
if (!hasNext()) {
throw new NoSuchElementException();
}
final String cn = nextName;
nextName = null;
try {
return service.cast(Class.forName(cn, true, loader).newInstance());
} catch (ClassNotFoundException x) {
fail(service, LocalizationMessages.WSP_0027_SERVICE_PROVIDER_NOT_FOUND(cn), x);
} catch (Exception x) {
fail(service, LocalizationMessages.WSP_0028_SERVICE_PROVIDER_COULD_NOT_BE_INSTANTIATED(cn), x);
}
return null; /* This cannot happen */
}
public void remove() {
throw new UnsupportedOperationException();
}
}
}
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