ImportStrategyHolder.java

/*******************************************************************************
 * Copyright (c) 2013, 2015 Pivotal, Inc.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 * 	Pivotal, Inc. - initial API and implementation
 *******************************************************************************/
package org.springframework.ide.eclipse.boot.wizard.importing;

import org.springframework.ide.eclipse.boot.wizard.BootWizardActivator;
import org.springframework.ide.eclipse.boot.wizard.content.BuildType;

/**
 * This is wrapper around a {@link ImportStrategyFactory}. It is repsonsible for creating
 * a single instance from the factory, and providing a fallback for when calling the
 * factory fails.
 *
 * @author Kris De Volder
 */
public class ImportStrategyHolder {

	private BuildType buildType;
	private ImportStrategyFactory factory;
	private String notInstalledMessage; //Message tailored to the particular tooling that is needed for an
	private String name; //Short name that can be used to identify strategy to the user (this is useful when more than one
						// strategy is available for a single build-type).

	private ImportStrategy instance = null;

	public ImportStrategyHolder(BuildType buildType, ImportStrategyFactory factory, String notInstalledMessage, String name) {
		this.buildType = buildType;
		this.factory = factory;
		this.notInstalledMessage = notInstalledMessage;
		this.name = name;
	}

	public ImportStrategy get() {
		if (instance == null) {
			try {
				this.instance = factory.create(buildType, name, notInstalledMessage);
			} catch (ClassNotFoundException e) {
				//ignore: happens when optional dependencies for strategy support are not installed
			} catch (Exception e) {
				//Somewhat unexpected, so log it.
				BootWizardActivator.log(e);
			}
			if (this.instance==null) {
				//Something prevented the creation of the import strategy.
				this.instance = new NullImportStrategy(buildType, name, notInstalledMessage);
			}
		}
		return instance;
	}

}