org.jbasics.discover.ServiceClassDiscovery Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of jbasics Show documentation
jBasics is a collection of useful utility classes for Java. This includes helper for XML, mathematic functions, restful web services helper, pattern oriented programming interfaces and more. Currently Java7 and up is supported. Version 1.0 will required at leaset Java8.
There is a newer version: 2.0.0p3
Show newest version
/*
 * Copyright (c) 2009-2015
 * 	IT-Consulting Stephan Schloepke (http://www.schloepke.de/)
 * 	klemm software consulting Mirko Klemm (http://www.klemm-scs.com/)
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package org.jbasics.discover;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.LineNumberReader;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.net.URL;
import java.util.Enumeration;
import java.util.LinkedHashSet;
import java.util.Map;
import java.util.Set;

import org.jbasics.checker.ContractCheck;
import org.jbasics.configuration.properties.SystemProperty;
import org.jbasics.exception.DelegatedException;
import org.jbasics.types.builders.MapBuilder;
import org.jbasics.types.sequences.Sequence;

/**
 * Helper to discover an concrete class for an abstract one base on the java services concept.
 *
 * @author Stephan Schloepke
 * @since 1.0
 */
public class ServiceClassDiscovery {
	public final static String RESOURCE_BASE = "META-INF/services/"; //$NON-NLS-1$
	public static final String SERVICE_FILE_ENCODING = "UTF-8"; //$NON-NLS-1$
	public static final char COMMENT_CHARACTER = '#';

	public static  Class discoverImplementation(final Class abstractClass) {
		return ServiceClassDiscovery.discoverImplementation(abstractClass, null, ServiceClassDiscovery.getClassLoader(abstractClass));
	}

	public static  Class discoverImplementation(final Class abstractClass, final Class defaultImplementation,
																final ClassLoader loader) {
		Class temp = SystemProperty.classProperty(ContractCheck.mustNotBeNull(abstractClass, "abstractClass").getName(), null).value(); //$NON-NLS-1$
		if (temp == null) {
			final String resourceName = ServiceClassDiscovery.RESOURCE_BASE + abstractClass.getName();
			final URL resource = ContractCheck.mustNotBeNull(loader, "loader").getResource(resourceName); //$NON-NLS-1$
			if (resource != null) {
				try {
					final Set found = ServiceClassDiscovery.parseURL(resource, new LinkedHashSet());
					if (found.size() > 0) {
						final String clazzName = found.iterator().next();
						temp = Class.forName(clazzName, true, loader);
					}
				} catch (final IOException e) {
					throw new RuntimeException(e);
				} catch (final ClassNotFoundException e) {
					throw new RuntimeException(e);
				}
			}
		}
		return temp == null ? defaultImplementation : temp.asSubclass(abstractClass);
	}

	private static ClassLoader getClassLoader(final Class abstractClass) {
		ClassLoader loader = null;
		try {
			loader = Thread.currentThread().getContextClassLoader();
		} catch (final Throwable e) {
			if (abstractClass != null) {
				loader = abstractClass.getClassLoader();
			} else {
				loader = ServiceClassDiscovery.class.getClassLoader();
			}
		}
		if (loader == null) {
			loader = ClassLoader.getSystemClassLoader();
		}
		if (loader == null) {
			throw new RuntimeException("Giving up since no class loader can be found for " + abstractClass);
		}
		return loader;
	}

	private static Set parseURL(final URL url, final Set found) throws IOException {
		assert found != null;
		final InputStream in = url.openStream();
		InputStreamReader inputReader = null;
		LineNumberReader reader = null;
		try {
			inputReader = new InputStreamReader(in, ServiceClassDiscovery.SERVICE_FILE_ENCODING);
			reader = new LineNumberReader(inputReader);
			String line = null;
			while ((line = reader.readLine()) != null) {
				line = ServiceClassDiscovery.stripComment(line);
				if (!line.trim().isEmpty()) {
					if (!Character.isJavaIdentifierStart(line.charAt(0))) {
						throw new RuntimeException("Illegal class name found (" + line + ") at line " + reader.getLineNumber() + " in service file " //$NON-NLS-1$//$NON-NLS-2$//$NON-NLS-3$
								+ url);
					}
					for (int i = 1; i < line.length(); i++) {
						final char c = line.charAt(i);
						if (c != '.' && !Character.isJavaIdentifierPart(c)) {
							throw new RuntimeException("Illegal class name found (" + line + ") at line " + reader.getLineNumber() + " in service file " //$NON-NLS-1$//$NON-NLS-2$//$NON-NLS-3$
									+ url);
						}
					}
					found.add(line);
				}
			}
		} finally {
			try {
				if (reader != null) {
					reader.close();
				} else if (inputReader != null) {
					inputReader.close();
				} else {
					in.close();
				}
			} catch (final IOException e) {
				// Ignore any close exception
			}
		}
		return found;
	}

	private static String stripComment(String line) {
		line = line.trim();
		if (line.length() == 0) {
			return ""; //$NON-NLS-1$
		}
		final int commentStart = line.indexOf(ServiceClassDiscovery.COMMENT_CHARACTER);
		if (commentStart == 0) {
			return ""; //$NON-NLS-1$
		} else if (commentStart > 0) {
			line = line.substring(0, commentStart);
		}
		return line;
	}

	public static  Class discoverImplementation(final Class abstractClass, final Class defaultImplementation) {
		return ServiceClassDiscovery
				.discoverImplementation(abstractClass, defaultImplementation, ServiceClassDiscovery.getClassLoader(abstractClass));
	}

	public static  Map>, V> discoverGenericsMappedImplementations(final Class abstractType,
																									final Class... genericTypes) {
		try {
			final Set> temp = ServiceClassDiscovery.discoverClasses(abstractType);
			return ServiceClassDiscovery.transformClasses(abstractType, temp, genericTypes);
		} catch (final Exception e) {
			throw DelegatedException.delegate(e);
		}
	}

	public static  Set> discoverClasses(final Class abstractClass) throws IOException, ClassNotFoundException {
		return ServiceClassDiscovery.discoverClasses(abstractClass, ServiceClassDiscovery.getClassLoader(abstractClass));
	}

	@SuppressWarnings({"unchecked"})
	public static  Map>, V> transformClasses(final Class abstractType, final Set> temp,
																			   final Class... genericTypes) {
		try {
			final MapBuilder>, V> builder = new MapBuilder>, V>().immutable();
			for (final Class possibleStrategyType : temp) {
interfaceFor:
				for (final Type t : possibleStrategyType.getGenericInterfaces()) {
					if (t instanceof ParameterizedType) {
						final ParameterizedType pt = (ParameterizedType) t;
						if (pt.getRawType() == abstractType && pt.getActualTypeArguments().length == genericTypes.length) {
							Sequence> key = Sequence.emptySequence();
							for (int i = 0; i < genericTypes.length; i++) {
								final Class requestedType = genericTypes[i];
								final Type genericType = pt.getActualTypeArguments()[i];
								if (genericType instanceof Class) {
									if (requestedType == null) {
										key = key.cons((Class) genericType);
									} else if (!requestedType.isAssignableFrom((Class) genericType)) {
										break interfaceFor;
									}
								} else if (genericType instanceof ParameterizedType) {
									Class argumentClass = (Class) ((ParameterizedType) genericType).getRawType();
									if (requestedType == null) {
										key = key.cons(argumentClass);
									} else if (!requestedType.isAssignableFrom(argumentClass)) {
										break interfaceFor;
									}
								} else {
									break interfaceFor;
								}
							}
							final V instance = ((Class) possibleStrategyType).newInstance();
							if (!key.isEmpty()) {
								builder.put(key.reverse(), instance);
							}
						}
					}
				}
			}
			return builder.build();
		} catch (final Exception e) {
			throw DelegatedException.delegate(e);
		}
	}

	public static  Set> discoverClasses(final Class abstractClass, final ClassLoader loader) throws IOException,
			ClassNotFoundException {
		final Set classNames = ServiceClassDiscovery.discoverClassNames(abstractClass, loader);
		final Set> classes = new LinkedHashSet>();
		for (final String className : classNames) {
			classes.add(Class.forName(className, true, loader).asSubclass(abstractClass));
		}
		return classes;
	}

	public static Set discoverClassNames(final Class abstractClass, final ClassLoader loader) throws IOException {
		final String resourceName = ServiceClassDiscovery.RESOURCE_BASE + ContractCheck.mustNotBeNull(abstractClass, "abstractClass").getName(); //$NON-NLS-1$
		final Enumeration resources = ContractCheck.mustNotBeNull(loader, "loader").getResources(resourceName); //$NON-NLS-1$
		final Set classNames = new LinkedHashSet();
		while (resources.hasMoreElements()) {
			ServiceClassDiscovery.parseURL(resources.nextElement(), classNames);
		}
		return classNames;
	}

	public static Set discoverClassNames(final Class abstractClass) throws IOException {
		return ServiceClassDiscovery.discoverClassNames(abstractClass, ServiceClassDiscovery.getClassLoader(abstractClass));
	}
}