package org.codehaus.plexus.component.factory.java;
   
   /*
    * Copyright 2001-2006 Codehaus Foundation.
    *
    * 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.
   */
  
  import java.lang.reflect.Modifier;
  
  import org.codehaus.plexus.PlexusContainer;
  import org.codehaus.plexus.classworlds.realm.ClassRealm;
  import org.codehaus.plexus.component.factory.AbstractComponentFactory;
  import org.codehaus.plexus.component.factory.ComponentInstantiationException;
  import org.codehaus.plexus.component.repository.ComponentDescriptor;
  
  /**
   * Component Factory for components written in Java Language which have default no parameter constructor
   *
   * @author Jason van Zyl
   * @author <a href="mailto:mmaczka@interia.pl">Michal Maczka</a>
   */
  public class JavaComponentFactory extends AbstractComponentFactory {
      public String getId() {
          return "java";
      }
  
      public Object newInstance(ComponentDescriptor componentDescriptor, ClassRealm classRealm, PlexusContainer container)
              throws ComponentInstantiationException {
          Class implementationClass = null;
  
          try {
              String implementation = componentDescriptor.getImplementation();
  
              implementationClass = classRealm.loadClass(implementation);
  
              int modifiers = implementationClass.getModifiers();
  
              if (Modifier.isInterface(modifiers)) {
                  throw new ComponentInstantiationException(
                          "Cannot instantiate implementation '" + implementation + "' because the class is a interface.");
              }
  
              if (Modifier.isAbstract(modifiers)) {
                  throw new ComponentInstantiationException(
                          "Cannot instantiate implementation '" + implementation + "' because the class is abstract.");
              }
  
              Object instance = implementationClass.newInstance();
  
              return instance;
          } catch (InstantiationException e) {
              // PLXAPI: most probably cause of this is the implementation class not having
              //        a default constructor.
              throw makeException(classRealm, componentDescriptor, implementationClass, e);
          } catch (ClassNotFoundException e) {
              throw makeException(classRealm, componentDescriptor, implementationClass, e);
          } catch (IllegalAccessException e) {
              throw makeException(classRealm, componentDescriptor, implementationClass, e);
          } catch (LinkageError e) {
              throw makeException(classRealm, componentDescriptor, implementationClass, e);
          }
      }
  
      private ComponentInstantiationException makeException(
              ClassRealm componentClassRealm,
              ComponentDescriptor componentDescriptor,
              Class implementationClass,
              Throwable e) {
          // ----------------------------------------------------------------------
          // Display the realm when there is an error, We should probably return a string here so we
          // can incorporate this into the error message for easy debugging.
          // ----------------------------------------------------------------------
  
          String msg;
  
          if (componentClassRealm == null) {
              msg = "classRealm is null for " + componentDescriptor;
          } else {
              msg = "Could not instantiate component: " + componentDescriptor.getHumanReadableKey() + " realm: "
                      + componentClassRealm.getId();
          }
  
          return new ComponentInstantiationException(msg, e);
      }
  }