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  /*
   * JBoss, Home of Professional Open Source.
   * Copyright 2006, Red Hat Middleware LLC, and individual contributors
   * as indicated by the @author tags. See the copyright.txt file in the
   * distribution for a full listing of individual contributors.
   *
   * This is free software; you can redistribute it and/or modify it
   * under the terms of the GNU Lesser General Public License as
   * published by the Free Software Foundation; either version 2.1 of
  * the License, or (at your option) any later version.
  *
  * This software 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
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with this software; if not, write to the Free
  * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
  * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
  */
 package org.jboss.bpm.console.server.util;
 
 import java.io.*;
Load a service class using a ordered lookup procedure

Author(s):
Thomas.Diesler@jboss.com
Heiko.Braun@jboss.com
Since:
14-Dec-2006
 
 public abstract class ServiceLoader
 {
   
This method uses the algorithm below using the JAXWS Provider as an example. 1. If a resource with the name of META-INF/services/javax.xml.ws.spi.Provider exists, then its first line, if present, is used as the UTF-8 encoded name of the implementation class. 2. If the ${java.home}/lib/service-loader.properties file exists and it is readable by the java.util.Properties.load(InputStream) method and it contains an entry whose key is javax.xml.ws.spi.Provider, then the value of that entry is used as the name of the implementation class. 3. If a system property with the name javax.xml.ws.spi.Provider is defined, then its value is used as the name of the implementation class. 4. Finally, a default implementation class name is used.
 
    public static Object loadService(String propertyNameString defaultFactory)
    {
       Object factory = loadFromServices(propertyNamenull);
       if (factory == null)
       {
          factory = loadFromPropertiesFile(propertyNamenull);
       }
       if (factory == null)
       {
          factory = loadFromSystemProperty(propertyNamedefaultFactory);
       }
       return factory;
    }

   
Use the Services API (as detailed in the JAR specification), if available, to determine the classname.
 
    public static Object loadFromServices(String propertyNameString defaultFactory)
    {
       Object factory = null;
       String factoryName = null;
       ClassLoader loader = Thread.currentThread().getContextClassLoader();
 
       // Use the Services API (as detailed in the JAR specification), if available, to determine the classname.
       String filename = "META-INF/services/" + propertyName;
       InputStream inStream = loader.getResourceAsStream(filename);
       if (inStream != null)
       {
          try
          {
             BufferedReader br = new BufferedReader(new InputStreamReader(inStream"UTF-8"));
             factoryName = br.readLine();
             br.close();
             if (factoryName != null)
             {
                Class factoryClass = loader.loadClass(factoryName);
                factory = factoryClass.newInstance();
             }
          }
          catch (Throwable t)
          {
             throw new IllegalStateException("Failed to load " + propertyName + ": " + factoryNamet);
          }
       }
 
       // Use the default factory implementation class.
       if (factory == null && defaultFactory != null)
      {
         factory = loadDefault(defaultFactory);
      }
      return factory;
   }

   
Use the system property
   public static Object loadFromSystemProperty(String propertyNameString defaultFactory)
   {
      Object factory = null;
      ClassLoader loader = Thread.currentThread().getContextClassLoader();
      PrivilegedAction action = new PropertyAccessAction(propertyName);
      String factoryName = (String)AccessController.doPrivileged(action);
      if (factoryName != null)
      {
         try
         {
            //if(log.isDebugEnabled()) log.debug("Load from system property: " + factoryName);
            Class factoryClass = loader.loadClass(factoryName);
            factory = factoryClass.newInstance();
         }
         catch (Throwable t)
         {
            throw new IllegalStateException("Failed to load " + propertyName + ": " + factoryNamet);
         }
      }
      // Use the default factory implementation class.
      if (factory == null && defaultFactory != null)
      {
         factory = loadDefault(defaultFactory);
      }
      return factory;
   }

   
Use the properties file "${java.home}/lib/service-loader.properties" in the JRE directory. This configuration file is in standard java.util.Properties format and contains the fully qualified name of the implementation class with the key being the system property defined above.
   public static Object loadFromPropertiesFile(String propertyNameString defaultFactory)
   {
      Object factory = null;
      String factoryName = null;
      ClassLoader loader = Thread.currentThread().getContextClassLoader();
      // Use the properties file "lib/jaxm.properties" in the JRE directory.
      // This configuration file is in standard java.util.Properties format and contains the fully qualified name of the implementation class with the key being the system property defined above.
      PrivilegedAction action = new PropertyAccessAction("java.home");
      String javaHome = (String)AccessController.doPrivileged(action);
      File jaxmFile = new File(javaHome + "/lib/service-loader.properties");
      if (jaxmFile.exists())
      {
         try
         {
            action = new PropertyFileAccessAction(jaxmFile.getCanonicalPath());
            Properties jaxmProperties = (Properties)AccessController.doPrivileged(action);
            factoryName = jaxmProperties.getProperty(propertyName);
            if (factoryName != null)
            {
               //if(log.isDebugEnabled()) log.debug("Load from " + jaxmFile + ": " + factoryName);
               Class factoryClass = loader.loadClass(factoryName);
               factory = factoryClass.newInstance();
            }
         }
         catch (Throwable t)
         {
            throw new IllegalStateException("Failed to load " + propertyName + ": " + factoryNamet);
         }
      }
      // Use the default factory implementation class.
      if (factory == null && defaultFactory != null)
      {
         factory = loadDefault(defaultFactory);
      }
      return factory;
   }
   private static Object loadDefault(String defaultFactory)
   {
      Object factory = null;
      ClassLoader loader = Thread.currentThread().getContextClassLoader();
      // Use the default factory implementation class.
      if (defaultFactory != null)
      {
         try
         {
            //if(log.isDebugEnabled()) log.debug("Load from default: " + factoryName);
            Class factoryClass = loader.loadClass(defaultFactory);
            factory = factoryClass.newInstance();
         }
         catch (Throwable t)
         {
            throw new IllegalStateException("Failed to load: " + defaultFactoryt);
         }
      }
      return factory;
   }
   private static class PropertyAccessAction implements PrivilegedAction
   {
      private String name;
      PropertyAccessAction(String name)
      {
         this. = name;
      }
      public Object run()
      {
         return System.getProperty();
      }
   }
   private static class PropertyFileAccessAction implements PrivilegedAction
   {
      private String filename;
      PropertyFileAccessAction(String filename)
      {
         this. = filename;
      }
      public Object run()
      {
         try
         {
            InputStream inStream = new FileInputStream();
            Properties props = new Properties();
            props.load(inStream);
            return props;
         }
         catch (IOException ex)
         {
            throw new SecurityException("Cannot load properties: " + ex);
         }
      }
   }
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