Mercurial > jdk8-mips64-public > langtools / file revision

 /*

  * Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.  Oracle designates this

  * particular file as subject to the "Classpath" exception as provided

  * by Oracle in the LICENSE file that accompanied this code.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.com if you need additional information or have any

  * questions.

  */

 package com.sun.tools.javac.util;

 import java.io.BufferedReader;

 import java.io.IOException;

 import java.io.InputStream;

 import java.io.InputStreamReader;

 import java.net.URL;

 import java.net.URLConnection;

 import java.util.ArrayList;

 import java.util.Enumeration;

 import java.util.Iterator;

 import java.util.LinkedHashMap;

 import java.util.List;

 import java.util.Map;

 import java.util.NoSuchElementException;

 import java.util.Objects;

 import java.util.ServiceConfigurationError;

 /**

  * This is a temporary, modified copy of java.util.ServiceLoader, for use by

  * javac, to work around bug JDK-8004082.

  *

  * The bug describes problems in the interaction between ServiceLoader and

  * URLClassLoader, such that references to a jar file passed to URLClassLoader

  * may be retained after calling URLClassLoader.close(), preventing the jar

  * file from being deleted on Windows.

  *

  *  <p><b>This is NOT part of any supported API.

  *  If you write code that depends on this, you do so at your own risk.

  *  This code and its internal interfaces are subject to change or

  *  deletion without notice.</b>

  */

 public final class ServiceLoader<S>

     implements Iterable<S>

 {

     private static final String PREFIX = "META-INF/services/";

     // The class or interface representing the service being loaded

     private Class<S> service;

     // The class loader used to locate, load, and instantiate providers

     private ClassLoader loader;

     // Cached providers, in instantiation order

     private LinkedHashMap<String,S> providers = new LinkedHashMap<>();

     // The current lazy-lookup iterator

     private LazyIterator lookupIterator;

     /**

      * Clear this loader's provider cache so that all providers will be

      * reloaded.

      *

      * <p> After invoking this method, subsequent invocations of the {@link

      * #iterator() iterator} method will lazily look up and instantiate

      * providers from scratch, just as is done by a newly-created loader.

      *

      * <p> This method is intended for use in situations in which new providers

      * can be installed into a running Java virtual machine.

      */

     public void reload() {

         providers.clear();

         lookupIterator = new LazyIterator(service, loader);

     }

     private ServiceLoader(Class<S> svc, ClassLoader cl) {

         service = Objects.requireNonNull(svc, "Service interface cannot be null");

         loader = (cl == null) ? ClassLoader.getSystemClassLoader() : cl;

         reload();

     }

     private static void fail(Class<?> service, String msg, Throwable cause)

         throws ServiceConfigurationError

     {

         throw new ServiceConfigurationError(service.getName() + ": " + msg,

                                             cause);

     }

     private static void fail(Class<?> service, String msg)

         throws ServiceConfigurationError

     {

         throw new ServiceConfigurationError(service.getName() + ": " + msg);

     }

     private static void fail(Class<?> service, URL u, int line, String msg)

         throws ServiceConfigurationError

     {

         fail(service, u + ":" + line + ": " + msg);

     }

     // Parse a single line from the given configuration file, adding the name

     // on the line to the names list.

     //

     private int parseLine(Class<?> service, URL u, BufferedReader r, int lc,

                           List<String> names)

         throws IOException, ServiceConfigurationError

     {

         String ln = r.readLine();

         if (ln == null) {

             return -1;

         }

         int ci = ln.indexOf('#');

         if (ci >= 0) ln = ln.substring(0, ci);

         ln = ln.trim();

         int n = ln.length();

         if (n != 0) {

             if ((ln.indexOf(' ') >= 0) || (ln.indexOf('\t') >= 0))

                 fail(service, u, lc, "Illegal configuration-file syntax");

             int cp = ln.codePointAt(0);

             if (!Character.isJavaIdentifierStart(cp))

                 fail(service, u, lc, "Illegal provider-class name: " + ln);

             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, "Illegal provider-class name: " + ln);

             }

             if (!providers.containsKey(ln) && !names.contains(ln))

                 names.add(ln);

         }

         return lc + 1;

     }

     // Parse the content of the given URL as a provider-configuration file.

     //

     // @param  service

     //         The service type for which providers are being sought;

     //         used to construct error detail strings

     //

     // @param  u

     //         The URL naming the configuration file to be parsed

     //

     // @return A (possibly empty) iterator 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

     //

     private Iterator<String> parse(Class<?> service, URL u)

         throws ServiceConfigurationError

     {

         InputStream in = null;

         BufferedReader r = null;

         ArrayList<String> names = new ArrayList<>();

         try {

             // The problem is that by default, streams opened with

             // u.openInputStream use a cached reference to a JarFile, which

             // is separate from the reference used by URLClassLoader, and

             // which is not closed by URLClassLoader.close().

             // The workaround is to disable caching for this specific jar file,

             // so that the reference to the jar file can be closed when the

             // file has been read.

             // Original code:

             // in = u.openStream();

             // Workaround ...

             URLConnection uc = u.openConnection();

             uc.setUseCaches(false);

             in = uc.getInputStream();

             // ... end of workaround.

             r = new BufferedReader(new InputStreamReader(in, "utf-8"));

             int lc = 1;

             while ((lc = parseLine(service, u, r, lc, names)) >= 0);

         } catch (IOException x) {

             fail(service, "Error reading configuration file", x);

         } finally {

             try {

                 if (r != null) r.close();

                 if (in != null) in.close();

             } catch (IOException y) {

                 fail(service, "Error closing configuration file", y);

             }

         }

         return names.iterator();

     }

     // Private inner class implementing fully-lazy provider lookup

     //

     private class LazyIterator

         implements Iterator<S>

     {

         Class<S> service;

         ClassLoader loader;

         Enumeration<URL> configs = null;

         Iterator<String> pending = null;

         String nextName = null;

         private LazyIterator(Class<S> service, ClassLoader loader) {

             this.service = service;

             this.loader = loader;

         }

         public boolean hasNext() {

             if (nextName != null) {

                 return true;

             }

             if (configs == null) {

                 try {

                     String fullName = PREFIX + service.getName();

                     if (loader == null)

                         configs = ClassLoader.getSystemResources(fullName);

                     else

                         configs = loader.getResources(fullName);

                 } catch (IOException x) {

                     fail(service, "Error locating configuration files", x);

                 }

             }

             while ((pending == null) || !pending.hasNext()) {

                 if (!configs.hasMoreElements()) {

                     return false;

                 }

                 pending = parse(service, configs.nextElement());

             }

             nextName = pending.next();

             return true;

         }

         public S next() {

             if (!hasNext()) {

                 throw new NoSuchElementException();

             }

             String cn = nextName;

             nextName = null;

             Class<?> c = null;

             try {

                 c = Class.forName(cn, false, loader);

             } catch (ClassNotFoundException x) {

                 fail(service,

                      "Provider " + cn + " not found");

             }

             if (!service.isAssignableFrom(c)) {

                 fail(service,

                      "Provider " + cn  + " not a subtype");

             }

             try {

                 S p = service.cast(c.newInstance());

                 providers.put(cn, p);

                 return p;

             } catch (Throwable x) {

                 fail(service,

                      "Provider " + cn + " could not be instantiated: " + x,

                      x);

             }

             throw new Error();          // This cannot happen

         }

         public void remove() {

             throw new UnsupportedOperationException();

         }

     }

     /**

      * Lazily loads the available providers of this loader's service.

      *

      * <p> The iterator returned by this method first yields all of the

      * elements of the provider cache, in instantiation order.  It then lazily

      * loads and instantiates any remaining providers, adding each one to the

      * cache in turn.

      *

      * <p> To achieve laziness the actual work of parsing the available

      * provider-configuration files and instantiating providers must be done by

      * the iterator itself.  Its {@link java.util.Iterator#hasNext hasNext} and

      * {@link java.util.Iterator#next next} methods can therefore throw a

      * {@link ServiceConfigurationError} if a provider-configuration file

      * violates the specified format, or if it names a provider class that

      * cannot be found and instantiated, or if the result of instantiating the

      * class is not assignable to the service type, or if any other kind of

      * exception or error is thrown as the next provider is located and

      * instantiated.  To write robust code it is only necessary to catch {@link

      * ServiceConfigurationError} when using a service iterator.

      *

      * <p> If such an error is thrown then subsequent invocations of the

      * iterator will make a best effort to locate and instantiate the next

      * available provider, but in general such recovery cannot be guaranteed.

      *

      * <blockquote style="font-size: smaller; line-height: 1.2"><span

      * style="padding-right: 1em; font-weight: bold">Design Note</span>

      * Throwing an error in these cases may seem extreme.  The rationale for

      * this behavior is that a malformed provider-configuration file, like a

      * malformed class file, indicates a serious problem with the way the Java

      * virtual machine is configured or is being used.  As such it is

      * preferable to throw an error rather than try to recover or, even worse,

      * fail silently.</blockquote>

      *

      * <p> The iterator returned by this method does not support removal.

      * Invoking its {@link java.util.Iterator#remove() remove} method will

      * cause an {@link UnsupportedOperationException} to be thrown.

      *

      * @return  An iterator that lazily loads providers for this loader's

      *          service

      */

     public Iterator<S> iterator() {

         return new Iterator<S>() {

             Iterator<Map.Entry<String,S>> knownProviders

                 = providers.entrySet().iterator();

             public boolean hasNext() {

                 if (knownProviders.hasNext())

                     return true;

                 return lookupIterator.hasNext();

             }

             public S next() {

                 if (knownProviders.hasNext())

                     return knownProviders.next().getValue();

                 return lookupIterator.next();

             }

             public void remove() {

                 throw new UnsupportedOperationException();

             }

         };

     }

     /**

      * Creates a new service loader for the given service type and class

      * loader.

      *

      * @param  service

      *         The interface or abstract class representing the service

      *

      * @param  loader

      *         The class loader to be used to load provider-configuration files

      *         and provider classes, or <tt>null</tt> if the system class

      *         loader (or, failing that, the bootstrap class loader) is to be

      *         used

      *

      * @return A new service loader

      */

     public static <S> ServiceLoader<S> load(Class<S> service,

                                             ClassLoader loader)

     {

         return new ServiceLoader<>(service, loader);

     }

     /**

      * Creates a new service loader for the given service type, using the

      * current thread's {@linkplain java.lang.Thread#getContextClassLoader

      * context class loader}.

      *

      * <p> An invocation of this convenience method of the form

      *

      * <blockquote><pre>

      * ServiceLoader.load(<i>service</i>)</pre></blockquote>

      *

      * is equivalent to

      *

      * <blockquote><pre>

      * ServiceLoader.load(<i>service</i>,

      *                    Thread.currentThread().getContextClassLoader())</pre></blockquote>

      *

      * @param  service

      *         The interface or abstract class representing the service

      *

      * @return A new service loader

      */

     public static <S> ServiceLoader<S> load(Class<S> service) {

         ClassLoader cl = Thread.currentThread().getContextClassLoader();

         return ServiceLoader.load(service, cl);

     }

     /**

      * Creates a new service loader for the given service type, using the

      * extension class loader.

      *

      * <p> This convenience method simply locates the extension class loader,

      * call it <tt><i>extClassLoader</i></tt>, and then returns

      *

      * <blockquote><pre>

      * ServiceLoader.load(<i>service</i>, <i>extClassLoader</i>)</pre></blockquote>

      *

      * <p> If the extension class loader cannot be found then the system class

      * loader is used; if there is no system class loader then the bootstrap

      * class loader is used.

      *

      * <p> This method is intended for use when only installed providers are

      * desired.  The resulting service will only find and load providers that

      * have been installed into the current Java virtual machine; providers on

      * the application's class path will be ignored.

      *

      * @param  service

      *         The interface or abstract class representing the service

      *

      * @return A new service loader

      */

     public static <S> ServiceLoader<S> loadInstalled(Class<S> service) {

         ClassLoader cl = ClassLoader.getSystemClassLoader();

         ClassLoader prev = null;

         while (cl != null) {

             prev = cl;

             cl = cl.getParent();

         }

         return ServiceLoader.load(service, prev);

     }

     /**

      * Returns a string describing this service.

      *

      * @return  A descriptive string

      */

     public String toString() {

         return "java.util.ServiceLoader[" + service.getName() + "]";

     }

 }