Java tutorial
/** * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Copyright (C) 2007 Matthias Braeuer (braeuer.matthias@web.de). * * All rights reserved. * * * * This work was done as a project at the Chair for Software Technology, * * Dresden University Of Technology, Germany (http://st.inf.tu-dresden.de). * * It is understood that any modification not identified as such is not * * covered by the preceding statement. * * * * This work is free software; you can redistribute it and/or modify it * * under the terms of the GNU Library General Public License as published * * by the Free Software Foundation; either version 2 of the License, or * * (at your option) any later version. * * * * This work 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 Library General Public * * License for more details. * * * * You should have received a copy of the GNU Library General Public License * * along with this library; if not, you can view it online at * * http://www.fsf.org/licensing/licenses/gpl.html. * * * * To submit a bug report, send a comment, or get the latest news on this * * project, please visit the website: http://dresden-ocl.sourceforge.net. * * For more information on OCL and related projects visit the OCL Portal: * * http://st.inf.tu-dresden.de/ocl * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * $Id$ */ package org.dresdenocl.modelbus.descriptor; import java.net.URL; import javax.management.Descriptor; import org.apache.commons.lang.IllegalClassException; import org.apache.commons.lang.StringUtils; import org.apache.commons.lang.builder.ToStringBuilder; import org.apache.commons.lang.builder.ToStringStyle; import org.apache.log4j.Logger; import org.eclipse.core.runtime.CoreException; import org.eclipse.core.runtime.IConfigurationElement; import org.eclipse.core.runtime.IExtension; import org.eclipse.core.runtime.Platform; import org.osgi.framework.Bundle; import org.dresdenocl.modelbus.ModelBusPlugin; /** * <p> * This is a simple base class for classes realizing a descriptor for an * extension point. It provides methods to load strings and icon resources as * well as instantiate executable extensions specified in an * {@link IConfigurationElement}. This is a generally reusable class that could * also be located outside of this plug-in. * </p> * * @author Matthias Braeuer */ public abstract class AbstractDescriptor implements IDescriptor { /** a {@link Logger} for this class. */ private static final Logger LOGGER = ModelBusPlugin.getLogger(AbstractDescriptor.class); /** The id of the extension. */ private String id; /** The configuration element that is the source of this descriptor. */ private IConfigurationElement configElement; /** * <p> * Creates a new {@link Descriptor} and is supposed to be called by * subclasses. * </p> * * @param configElement * The {@link IllegalClassException} this {@link AbstractDescriptor} * shall be created for. * @throws IllegalArgumentException * Throw if <code>configElement</code> is <code>null</code>. */ protected AbstractDescriptor(IConfigurationElement configElement) { if (configElement == null) { throw new IllegalArgumentException("The configuration element was null."); //$NON-NLS-1$ } // no else. this.configElement = configElement; id = getAttribute(ATT_ID, false); } /* * (non-Javadoc) * @see org.dresdenocl.modelbus.internal.descriptor.IDescriptor#getId() */ public String getId() { return this.id; } /** * <p> * This implementation simply delegates to {@link #getId()}. * </p> * * @see org.eclipse.ui.IPluginContribution#getLocalId() */ public String getLocalId() { return this.getId(); } /* * (non-Javadoc) * @see org.eclipse.ui.IPluginContribution#getPluginId() */ public String getPluginId() { return this.configElement.getContributor().getName(); } /* * (non-Javadoc) * @seeorg.dresdenocl.modelbus.internal.descriptor.IDescriptor# * getDeclaringExtension() */ public IExtension getDeclaringExtension() { return this.configElement.getDeclaringExtension(); } /* * (non-Javadoc) * @see java.lang.Object#toString() */ @Override public String toString() { return new ToStringBuilder(this, ToStringStyle.SHORT_PREFIX_STYLE).append("id", id).toString(); //$NON-NLS-1$ } /** * <p> * Helper method for sub-classes to check whether an attribute has been * assigned a value. This is useful for validating attributes that contain a * java class name, for instance. * </p> * * @param attributeName * The name of the attribute. * * @throws InvalidDescriptorException * If the value is empty. */ protected void checkAttribute(String attributeName) { if (LOGGER.isDebugEnabled()) { LOGGER.debug("checkAttribute(attributeName=" + attributeName + ") - enter"); //$NON-NLS-1$ //$NON-NLS-2$ } // no else. // simple use the checks implemented in #getAttribute() getAttribute(attributeName, true); if (LOGGER.isDebugEnabled()) { LOGGER.debug("checkAttribute() - exit"); //$NON-NLS-1$ } // no else. } /** * <p> * Creates an instance for the specified attribute. This must be an attribute * of type 'java' that defines a class. * </p> * * @param attributeName * The name of the attribute. * @param type * The expected type of the executable extension. * * @return The instantiated object. * * @throws InvalidDescriptorException * If the extension cannot be instantiated. */ protected <T> T createInstance(String attributeName, Class<T> type) { if (LOGGER.isDebugEnabled()) { LOGGER.debug("createInstance(attributeName=" + attributeName + //$NON-NLS-1$ ", type=" + type + ") - enter"); //$NON-NLS-1$ //$NON-NLS-2$ } // no else. Object instance = null; try { instance = configElement.createExecutableExtension(attributeName); } catch (CoreException e) { throwInvalidDescriptorException(attributeName, "Failed to instantiate an executable extension.", e); //$NON-NLS-1$ } // check if the created instance has the correct type if (!type.isInstance(instance)) { throwInvalidDescriptorException(attributeName, "Specified class does not derive from " //$NON-NLS-1$ + type.getCanonicalName() + ".", null); //$NON-NLS-1$ } // no else. T returnT = type.cast(instance); if (LOGGER.isDebugEnabled()) { LOGGER.debug("createInstance() - exit - return value=" + returnT); //$NON-NLS-1$ } return returnT; } /** * <p> * Helper method that returns the value of an attribute. Throws an * {@link InvalidDescriptorException} if the attribute is empty and required. * </p> * * @param attributeName * The name of the extension point attribute. * @param required * Whether the attribute should have a non-empty value. * * @throws InvalidDescriptorException * If the value of the attribute is invalid. */ protected String getAttribute(String attributeName, boolean required) { if (LOGGER.isDebugEnabled()) { LOGGER.debug("getAttribute(attributeName=" + attributeName + ", required=" + required //$NON-NLS-1$ //$NON-NLS-2$ + ") - enter"); //$NON-NLS-1$ } // no else. String value = configElement.getAttribute(attributeName); if (required && StringUtils.isEmpty(value)) { throwInvalidDescriptorException(attributeName, "Value of attribute was empty.", null); //$NON-NLS-1$ } // no else. if (LOGGER.isDebugEnabled()) { LOGGER.debug("getAttribute() - exit - return value=" + value); //$NON-NLS-1$ } // no else. return value; } /** * <p> * Helper method for subclasses that returns an icon's {@link URL} for the * given attribute name. If no {@link URL} can be found, <code>null</code> is * returned. * </p> */ protected URL getIconURL(String attributeName) { if (LOGGER.isDebugEnabled()) { LOGGER.debug("getIconURL(attributeName=" + attributeName + ") - enter"); //$NON-NLS-1$ //$NON-NLS-2$ } // no else. URL result; result = null; String iconName; /* Get the value of the icon attribute. */ iconName = configElement.getAttribute(attributeName); /* Try to get the URL. */ if (iconName != null) { Bundle metaModelBundle; metaModelBundle = Platform.getBundle(this.getDeclaringExtension().getContributor().getName()); result = metaModelBundle.getResource(iconName); } /* If no icon was found use the error icon. */ if (result == null) { LOGGER.warn("No icon resource found for attribute " + attributeName + " in extension " + id); //$NON-NLS-1$ //$NON-NLS-2$ } // no else. if (LOGGER.isDebugEnabled()) { LOGGER.debug("getIconURL() - exit - return value=" + result); //$NON-NLS-1$ } // no else. return result; } /** * <p> * Helper method that throws an exception with some additional information. * </p> * * @param propertyName * The name of the property causing the error. * @param message * An optional message. * @param cause * An optional cause. */ protected void throwInvalidDescriptorException(String propertyName, String message, Exception cause) { StringBuilder errorMsg = new StringBuilder(); errorMsg.append("The value of attribute '").append(propertyName).append( //$NON-NLS-1$ "' defined in element '").append(id).append("' of extension point '").append( //$NON-NLS-2$ //$NON-NLS-2$ getDeclaringExtension().getExtensionPointUniqueIdentifier()) .append("' in plugin '") //$NON-NLS-1$ .append(getDeclaringExtension().getContributor().getName()).append("' is invalid."); //$NON-NLS-1$ if (message != null) { errorMsg.append(" ").append(message); //$NON-NLS-1$ } throw new InvalidDescriptorException(errorMsg.toString(), cause); } }