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  /*
   * JBoss, Home of Professional Open Source
   * Copyright 2010, Red Hat, Inc., and individual contributors
   * by the @authors tag. See the copyright.txt in the distribution for a
   * full listing of individual contributors.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
  * http://www.apache.org/licenses/LICENSE-2.0
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
 package org.jboss.weld.util;
 
 import static java.util.logging.Level.WARNING;
 
 import java.net.URL;
 import java.util.List;
 import java.util.Set;
 
 
 import  edu.umd.cs.findbugs.annotations.SuppressWarnings;

This class handles looking up service providers on the class path. It implements the Service Provider section of the JAR File Specification.

The Service Provider programmatic lookup was not specified prior to Java 6 so this interface allows use of the specification prior to Java 6.

The API is copied from java.util.ServiceLoader and enhanced to support the Metadata contract.

Author(s):
Pete Muir
Avalon Development Team
Nicklas Karlsson
 
 public class ServiceLoader<S> implements Iterable<Metadata<S>> {
 
     private static final String ERROR_INSTANTIATING = "Error instantiating ";
 
     private static final String SERVICES = "META-INF/services";
 
     private static final Logger log = Logger.getLogger("ServiceLoader");

    
Creates a new service loader for the given service type, using the current thread's context class loader.

An invocation of this convenience method of the form

ServiceLoader.load(service)</code>

is equivalent to

ServiceLoader.load(service, Thread.currentThread().getContextClassLoader())

Parameters:
service The interface or abstract class representing the service
Returns:
A new service loader
 
     public static <S> ServiceLoader<S> load(Class<S> service) {
         return load(service, Thread.currentThread().getContextClassLoader());
     }

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

Parameters:
service The interface or abstract class representing the service
loader The class loader to be used to load provider-configuration files and provider classes, or null if the system class loader (or, failing that, the bootstrap class loader) is to be used
Returns:
A new service loader
 
     public static <S> ServiceLoader<S> load(Class<S> serviceClassLoader loader) {
         if (loader == null) {
             loader = service.getClassLoader();
        }
        return new ServiceLoader<S>(servicenew ClassLoaderResourceLoader(loader));
    }
    public static <S> ServiceLoader<S> load(Class<S> serviceResourceLoader loader) {
        if (loader == null) {
            return load(serviceservice.getClassLoader());
        }
        return new ServiceLoader<S>(serviceloader);
    }

    
Creates a new service loader for the given service type, using the extension class loader.

This convenience method simply locates the extension class loader, call it extClassLoader, and then returns

ServiceLoader.load(service, extClassLoader)

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.

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.

Parameters:
service The interface or abstract class representing the service
Returns:
A new service loader
    public static <S> ServiceLoader<S> loadInstalled(Class<S> service) {
        throw new UnsupportedOperationException("Not implemented");
    }
    private final String serviceFile;
    private Class<S> expectedType;
    private final ResourceLoader loader;
    private Set<Metadata<S>> providers;
    private ServiceLoader(Class<S> serviceResourceLoader loader) {
        this. = loader;
        this. =  + "/" + service.getName();
        this. = service;
    }

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

After invoking this method, subsequent invocations of the iterator method will lazily look up and instantiate providers from scratch, just as is done by a newly-created loader.

This method is intended for use in situations in which new providers can be installed into a running Java virtual machine.

    public void reload() {
         = new HashSet<Metadata<S>>();
        for (URL serviceFile : loadServiceFiles()) {
            loadServiceFile(serviceFile);
        }
    }
    private List<URLloadServiceFiles() {
        return new ArrayList<URL>(.getResources());
    }
    @SuppressWarnings(value = "OS_OPEN_STREAM", justification = "False positive")
    private void loadServiceFile(URL serviceFile) {
        InputStream is = null;
        try {
            is = serviceFile.openStream();
            BufferedReader reader = new BufferedReader(new InputStreamReader(is"UTF-8"));
            String serviceClassName = null;
            int i = 0;
            while ((serviceClassName = reader.readLine()) != null) {
                i++;
                serviceClassName = trim(serviceClassName);
                if (serviceClassName.length() > 0) {
                    loadService(serviceClassNameserviceFilei);
                }
            }
        } catch (IOException e) {
            // FIXME: correct exception
            throw new RuntimeException("Could not read services file " + serviceFile);
        } finally {
            if (is != null) {
                try {
                    is.close();
                } catch (IOException e) {
                    // FIXME: correct exception
                    throw new RuntimeException("Could not close services file " + serviceFilee);
                }
            }
        }
    }
    private String trim(String line) {
        final int comment = line.indexOf('#');
        if (comment > -1) {
            line = line.substring(0, comment);
        }
        return line.trim();
    }
    private void loadService(String serviceClassNameURL fileint lineNumber) {
        Class<? extends S> serviceClass = loadClass(serviceClassName);
        if (serviceClass == null) {
            return;
        }
        S serviceInstance = prepareInstance(serviceClass);
        if (serviceInstance == null) {
            return;
        }
        .add(new FileMetadata<S>(serviceInstancefilelineNumber));
    }
    private Class<? extends S> loadClass(String serviceClassName) {
        Class<?> clazz = null;
        Class<? extends S> serviceClass = null;
        try {
            clazz = .classForName(serviceClassName);
            serviceClass = clazz.asSubclass();
        } catch (ResourceLoadingException e) {
            .warning("Could not load service class " + serviceClassName);
        } catch (ClassCastException e) {
            throw new RuntimeException("Service class " + serviceClassName + " didn't implement the required interface");
        }
        return serviceClass;
    }
    private S prepareInstance(Class<? extends S> serviceClass) {
        try {
            // TODO Support the SM
            Constructor<? extends S> constructor = serviceClass.getDeclaredConstructor();
            constructor.setAccessible(true);
            return constructor.newInstance();
        } catch (LinkageError e) {
            .log("Could not instantiate service class " + serviceClass.getName(), e);
            return null;
        } catch (InvocationTargetException e) {
            throw new RuntimeException( + serviceClasse.getCause());
        } catch (IllegalArgumentException e) {
            throw new RuntimeException( + serviceClasse);
        } catch (InstantiationException e) {
            throw new RuntimeException( + serviceClasse);
        } catch (IllegalAccessException e) {
            throw new RuntimeException( + serviceClasse);
        } catch (SecurityException e) {
            throw new RuntimeException( + serviceClasse);
        } catch (NoSuchMethodException e) {
            throw new RuntimeException( + serviceClasse);
        }
    }

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

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.

To achieve laziness the actual work of parsing the available provider-configuration files and instantiating providers must be done by the iterator itself. Its hasNext and next methods can therefore throw a 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 ServiceConfigurationError when using a service iterator.

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.

Design Note 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.

The iterator returned by this method does not support removal. Invoking its remove method will cause an UnsupportedOperationException to be thrown.

Returns:
An iterator that lazily loads providers for this loader's service
    public Iterator<Metadata<S>> iterator() {
        if ( == null) {
            reload();
        }
        return .iterator();
    }

    
Returns a string describing this service.

Returns:
A descriptive string
    @Override
    public String toString() {
        return "Services for " + ;
    }
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