001 /**
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017 package org.apache.camel.util;
018
019 import java.io.File;
020 import java.io.FileInputStream;
021 import java.io.IOException;
022 import java.lang.annotation.Annotation;
023 import java.net.URL;
024 import java.net.URLDecoder;
025 import java.util.Enumeration;
026 import java.util.HashSet;
027 import java.util.Set;
028 import java.util.jar.JarEntry;
029 import java.util.jar.JarInputStream;
030
031 import org.apache.commons.logging.Log;
032 import org.apache.commons.logging.LogFactory;
033
034 /**
035 * <p>
036 * ResolverUtil is used to locate classes that are available in the/a class path
037 * and meet arbitrary conditions. The two most common conditions are that a
038 * class implements/extends another class, or that is it annotated with a
039 * specific annotation. However, through the use of the {@link Test} class it is
040 * possible to search using arbitrary conditions.
041 * </p>
042 *
043 * <p>
044 * A ClassLoader is used to locate all locations (directories and jar files) in
045 * the class path that contain classes within certain packages, and then to load
046 * those classes and check them. By default the ClassLoader returned by
047 * {@code Thread.currentThread().getContextClassLoader()} is used, but this can
048 * be overridden by calling {@link #setClassLoader(ClassLoader)} prior to
049 * invoking any of the {@code find()} methods.
050 * </p>
051 *
052 * <p>
053 * General searches are initiated by calling the
054 * {@link #find(ResolverUtil.Test, String)} ()} method and supplying a package
055 * name and a Test instance. This will cause the named package <b>and all
056 * sub-packages</b> to be scanned for classes that meet the test. There are
057 * also utility methods for the common use cases of scanning multiple packages
058 * for extensions of particular classes, or classes annotated with a specific
059 * annotation.
060 * </p>
061 *
062 * <p>
063 * The standard usage pattern for the ResolverUtil class is as follows:
064 * </p>
065 *
066 * <pre>
067 * esolverUtil<ActionBean> resolver = new ResolverUtil<ActionBean>();
068 * esolver.findImplementation(ActionBean.class, pkg1, pkg2);
069 * esolver.find(new CustomTest(), pkg1);
070 * esolver.find(new CustomTest(), pkg2);
071 * ollection<ActionBean> beans = resolver.getClasses();
072 * </pre>
073 *
074 * @author Tim Fennell
075 */
076 public class ResolverUtil<T> {
077 private static final transient Log LOG = LogFactory.getLog(ResolverUtil.class);
078
079 /**
080 * A simple interface that specifies how to test classes to determine if
081 * they are to be included in the results produced by the ResolverUtil.
082 */
083 public static interface Test {
084 /**
085 * Will be called repeatedly with candidate classes. Must return True if
086 * a class is to be included in the results, false otherwise.
087 */
088 boolean matches(Class type);
089 }
090
091 /**
092 * A Test that checks to see if each class is assignable to the provided
093 * class. Note that this test will match the parent type itself if it is
094 * presented for matching.
095 */
096 public static class IsA implements Test {
097 private Class parent;
098
099 /**
100 * Constructs an IsA test using the supplied Class as the parent
101 * class/interface.
102 */
103 public IsA(Class parentType) {
104 this.parent = parentType;
105 }
106
107 /**
108 * Returns true if type is assignable to the parent type supplied in the
109 * constructor.
110 */
111 public boolean matches(Class type) {
112 return type != null && parent.isAssignableFrom(type);
113 }
114
115 @Override
116 public String toString() {
117 return "is assignable to " + parent.getSimpleName();
118 }
119 }
120
121 /**
122 * A Test that checks to see if each class is annotated with a specific
123 * annotation. If it is, then the test returns true, otherwise false.
124 */
125 public static class AnnotatedWith implements Test {
126 private Class<? extends Annotation> annotation;
127
128 /** Construts an AnnotatedWith test for the specified annotation type. */
129 public AnnotatedWith(Class<? extends Annotation> annotation) {
130 this.annotation = annotation;
131 }
132
133 /**
134 * Returns true if the type is annotated with the class provided to the
135 * constructor.
136 */
137 public boolean matches(Class type) {
138 return type != null && type.isAnnotationPresent(annotation);
139 }
140
141 @Override
142 public String toString() {
143 return "annotated with @" + annotation.getSimpleName();
144 }
145 }
146
147 /** The set of matches being accumulated. */
148 private Set<Class<? extends T>> matches = new HashSet<Class<? extends T>>();
149
150 /**
151 * The ClassLoader to use when looking for classes. If null then the
152 * ClassLoader returned by Thread.currentThread().getContextClassLoader()
153 * will be used.
154 */
155 private ClassLoader classloader;
156
157 /**
158 * Provides access to the classes discovered so far. If no calls have been
159 * made to any of the {@code find()} methods, this set will be empty.
160 *
161 * @return the set of classes that have been discovered.
162 */
163 public Set<Class<? extends T>> getClasses() {
164 return matches;
165 }
166
167 /**
168 * Returns the classloader that will be used for scanning for classes. If no
169 * explicit ClassLoader has been set by the calling, the context class
170 * loader will be used.
171 *
172 * @return the ClassLoader that will be used to scan for classes
173 */
174 public ClassLoader getClassLoader() {
175 return classloader == null ? Thread.currentThread().getContextClassLoader() : classloader;
176 }
177
178 /**
179 * Sets an explicit ClassLoader that should be used when scanning for
180 * classes. If none is set then the context classloader will be used.
181 *
182 * @param classloader a ClassLoader to use when scanning for classes
183 */
184 public void setClassLoader(ClassLoader classloader) {
185 this.classloader = classloader;
186 }
187
188 /**
189 * Attempts to discover classes that are assignable to the type provided. In
190 * the case that an interface is provided this method will collect
191 * implementations. In the case of a non-interface class, subclasses will be
192 * collected. Accumulated classes can be accessed by calling
193 * {@link #getClasses()}.
194 *
195 * @param parent the class of interface to find subclasses or
196 * implementations of
197 * @param packageNames one or more package names to scan (including
198 * subpackages) for classes
199 */
200 public void findImplementations(Class parent, String... packageNames) {
201 if (packageNames == null) {
202 return;
203 }
204
205 Test test = new IsA(parent);
206 for (String pkg : packageNames) {
207 find(test, pkg);
208 }
209 }
210
211 /**
212 * Attempts to discover classes that are annotated with to the annotation.
213 * Accumulated classes can be accessed by calling {@link #getClasses()}.
214 *
215 * @param annotation the annotation that should be present on matching
216 * classes
217 * @param packageNames one or more package names to scan (including
218 * subpackages) for classes
219 */
220 public void findAnnotated(Class<? extends Annotation> annotation, String... packageNames) {
221 if (packageNames == null) {
222 return;
223 }
224
225 Test test = new AnnotatedWith(annotation);
226 for (String pkg : packageNames) {
227 find(test, pkg);
228 }
229 }
230
231 /**
232 * Scans for classes starting at the package provided and descending into
233 * subpackages. Each class is offered up to the Test as it is discovered,
234 * and if the Test returns true the class is retained. Accumulated classes
235 * can be fetched by calling {@link #getClasses()}.
236 *
237 * @param test an instance of {@link Test} that will be used to filter
238 * classes
239 * @param packageName the name of the package from which to start scanning
240 * for classes, e.g. {@code net.sourceforge.stripes}
241 */
242 public void find(Test test, String packageName) {
243 packageName = packageName.replace('.', '/');
244 ClassLoader loader = getClassLoader();
245 Enumeration<URL> urls;
246
247 try {
248 urls = loader.getResources(packageName);
249 } catch (IOException ioe) {
250 LOG.warn("Could not read package: " + packageName, ioe);
251 return;
252 }
253
254 while (urls.hasMoreElements()) {
255 try {
256 String urlPath = urls.nextElement().getFile();
257 urlPath = URLDecoder.decode(urlPath, "UTF-8");
258
259 // If it's a file in a directory, trim the stupid file: spec
260 if (urlPath.startsWith("file:")) {
261 urlPath = urlPath.substring(5);
262 }
263
264 // Else it's in a JAR, grab the path to the jar
265 if (urlPath.indexOf('!') > 0) {
266 urlPath = urlPath.substring(0, urlPath.indexOf('!'));
267 }
268
269 LOG.debug("Scanning for classes in [" + urlPath + "] matching criteria: " + test);
270 File file = new File(urlPath);
271 if (file.isDirectory()) {
272 loadImplementationsInDirectory(test, packageName, file);
273 } else {
274 loadImplementationsInJar(test, packageName, file);
275 }
276 } catch (IOException ioe) {
277 LOG.warn("could not read entries", ioe);
278 }
279 }
280 }
281
282 /**
283 * Finds matches in a physical directory on a filesystem. Examines all files
284 * within a directory - if the File object is not a directory, and ends with
285 * <i>.class</i> the file is loaded and tested to see if it is acceptable
286 * according to the Test. Operates recursively to find classes within a
287 * folder structure matching the package structure.
288 *
289 * @param test a Test used to filter the classes that are discovered
290 * @param parent the package name up to this directory in the package
291 * hierarchy. E.g. if /classes is in the classpath and we
292 * wish to examine files in /classes/org/apache then the
293 * values of <i>parent</i> would be <i>org/apache</i>
294 * @param location a File object representing a directory
295 */
296 private void loadImplementationsInDirectory(Test test, String parent, File location) {
297 File[] files = location.listFiles();
298 StringBuilder builder = null;
299
300 for (File file : files) {
301 builder = new StringBuilder(100);
302 builder.append(parent).append("/").append(file.getName());
303 String packageOrClass = parent == null ? file.getName() : builder.toString();
304
305 if (file.isDirectory()) {
306 loadImplementationsInDirectory(test, packageOrClass, file);
307 } else if (file.getName().endsWith(".class")) {
308 addIfMatching(test, packageOrClass);
309 }
310 }
311 }
312
313 /**
314 * Finds matching classes within a jar files that contains a folder
315 * structure matching the package structure. If the File is not a JarFile or
316 * does not exist a warning will be logged, but no error will be raised.
317 *
318 * @param test a Test used to filter the classes that are discovered
319 * @param parent the parent package under which classes must be in order to
320 * be considered
321 * @param jarfile the jar file to be examined for classes
322 */
323 private void loadImplementationsInJar(Test test, String parent, File jarfile) {
324
325 try {
326 JarEntry entry;
327 JarInputStream jarStream = new JarInputStream(new FileInputStream(jarfile));
328
329 while ((entry = jarStream.getNextJarEntry()) != null) {
330 String name = entry.getName();
331 if (!entry.isDirectory() && name.startsWith(parent) && name.endsWith(".class")) {
332 addIfMatching(test, name);
333 }
334 }
335 } catch (IOException ioe) {
336 LOG.error("Could not search jar file '" + jarfile + "' for classes matching criteria: " + test
337 + "due to an IOException: " + ioe.getMessage());
338 }
339 }
340
341 /**
342 * Add the class designated by the fully qualified class name provided to
343 * the set of resolved classes if and only if it is approved by the Test
344 * supplied.
345 *
346 * @param test the test used to determine if the class matches
347 * @param fqn the fully qualified name of a class
348 */
349 protected void addIfMatching(Test test, String fqn) {
350 try {
351 String externalName = fqn.substring(0, fqn.indexOf('.')).replace('/', '.');
352 ClassLoader loader = getClassLoader();
353 LOG.trace("Checking to see if class " + externalName + " matches criteria [" + test + "]");
354
355 Class type = loader.loadClass(externalName);
356 if (test.matches(type)) {
357 matches.add((Class<T>)type);
358 }
359 } catch (Throwable t) {
360 LOG.warn("Could not examine class '" + fqn + "' due to a " + t.getClass().getName()
361 + " with message: " + t.getMessage());
362 }
363 }
364 }