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.Arrays;
026 import java.util.Enumeration;
027 import java.util.HashSet;
028 import java.util.Set;
029 import java.util.jar.JarEntry;
030 import java.util.jar.JarInputStream;
031
032 import org.apache.commons.logging.Log;
033 import org.apache.commons.logging.LogFactory;
034
035 /**
036 * <p>
037 * ResolverUtil is used to locate classes that are available in the/a class path
038 * and meet arbitrary conditions. The two most common conditions are that a
039 * class implements/extends another class, or that is it annotated with a
040 * specific annotation. However, through the use of the {@link Test} class it is
041 * possible to search using arbitrary conditions.
042 * </p>
043 *
044 * <p>
045 * A ClassLoader is used to locate all locations (directories and jar files) in
046 * the class path that contain classes within certain packages, and then to load
047 * those classes and check them. By default the ClassLoader returned by
048 * {@code Thread.currentThread().getContextClassLoader()} is used, but this can
049 * be overridden by calling {@link #setClassLoaders(Set)} prior to
050 * invoking any of the {@code find()} methods.
051 * </p>
052 *
053 * <p>
054 * General searches are initiated by calling the
055 * {@link #find(ResolverUtil.Test, String)} ()} method and supplying a package
056 * name and a Test instance. This will cause the named package <b>and all
057 * sub-packages</b> to be scanned for classes that meet the test. There are
058 * also utility methods for the common use cases of scanning multiple packages
059 * for extensions of particular classes, or classes annotated with a specific
060 * annotation.
061 * </p>
062 *
063 * <p>
064 * The standard usage pattern for the ResolverUtil class is as follows:
065 * </p>
066 *
067 * <pre>
068 * esolverUtil<ActionBean> resolver = new ResolverUtil<ActionBean>();
069 * esolver.findImplementation(ActionBean.class, pkg1, pkg2);
070 * esolver.find(new CustomTest(), pkg1);
071 * esolver.find(new CustomTest(), pkg2);
072 * ollection<ActionBean> beans = resolver.getClasses();
073 * </pre>
074 *
075 * @author Tim Fennell
076 */
077 public class ResolverUtil<T> {
078 private static final transient Log LOG = LogFactory.getLog(ResolverUtil.class);
079
080 /**
081 * A simple interface that specifies how to test classes to determine if
082 * they are to be included in the results produced by the ResolverUtil.
083 */
084 public static interface Test {
085 /**
086 * Will be called repeatedly with candidate classes. Must return True if
087 * a class is to be included in the results, false otherwise.
088 */
089 boolean matches(Class type);
090 }
091
092 /**
093 * A Test that checks to see if each class is assignable to the provided
094 * class. Note that this test will match the parent type itself if it is
095 * presented for matching.
096 */
097 public static class IsA implements Test {
098 private Class parent;
099
100 /**
101 * Constructs an IsA test using the supplied Class as the parent
102 * class/interface.
103 */
104 public IsA(Class parentType) {
105 this.parent = parentType;
106 }
107
108 /**
109 * Returns true if type is assignable to the parent type supplied in the
110 * constructor.
111 */
112 public boolean matches(Class type) {
113 return type != null && parent.isAssignableFrom(type);
114 }
115
116 @Override
117 public String toString() {
118 return "is assignable to " + parent.getSimpleName();
119 }
120 }
121
122 /**
123 * A Test that checks to see if each class is annotated with a specific
124 * annotation. If it is, then the test returns true, otherwise false.
125 */
126 public static class AnnotatedWith implements Test {
127 private Class<? extends Annotation> annotation;
128
129 /** Construts an AnnotatedWith test for the specified annotation type. */
130 public AnnotatedWith(Class<? extends Annotation> annotation) {
131 this.annotation = annotation;
132 }
133
134 /**
135 * Returns true if the type is annotated with the class provided to the
136 * constructor.
137 */
138 public boolean matches(Class type) {
139 return type != null && type.isAnnotationPresent(annotation);
140 }
141
142 @Override
143 public String toString() {
144 return "annotated with @" + annotation.getSimpleName();
145 }
146 }
147
148 /** The set of matches being accumulated. */
149 private Set<Class<? extends T>> matches = new HashSet<Class<? extends T>>();
150
151 /**
152 * The ClassLoader to use when looking for classes. If null then the
153 * ClassLoader returned by Thread.currentThread().getContextClassLoader()
154 * will be used.
155 */
156 private Set<ClassLoader> classLoaders;
157
158 /**
159 * Provides access to the classes discovered so far. If no calls have been
160 * made to any of the {@code find()} methods, this set will be empty.
161 *
162 * @return the set of classes that have been discovered.
163 */
164 public Set<Class<? extends T>> getClasses() {
165 return matches;
166 }
167
168
169 /**
170 * Returns the classloaders that will be used for scanning for classes. If no
171 * explicit ClassLoader has been set by the calling, the context class
172 * loader will be used.
173 *
174 * @return the ClassLoader instances that will be used to scan for classes
175 */
176 public Set<ClassLoader> getClassLoaders() {
177 if (classLoaders == null) {
178 classLoaders = new HashSet<ClassLoader>();
179 classLoaders.add(Thread.currentThread().getContextClassLoader());
180 }
181 return classLoaders;
182 }
183
184 /**
185 * Sets the ClassLoader instances that should be used when scanning for
186 * classes. If none is set then the context classloader will be used.
187 *
188 * @param classLoaders a ClassLoader to use when scanning for classes
189 */
190 public void setClassLoaders(Set<ClassLoader> classLoaders) {
191 this.classLoaders = classLoaders;
192 }
193
194 /**
195 * Attempts to discover classes that are assignable to the type provided. In
196 * the case that an interface is provided this method will collect
197 * implementations. In the case of a non-interface class, subclasses will be
198 * collected. Accumulated classes can be accessed by calling
199 * {@link #getClasses()}.
200 *
201 * @param parent the class of interface to find subclasses or
202 * implementations of
203 * @param packageNames one or more package names to scan (including
204 * subpackages) for classes
205 */
206 public void findImplementations(Class parent, String... packageNames) {
207 if (packageNames == null) {
208 return;
209 }
210
211 LOG.debug("Searching for implementations of " + parent.getName() + " in packages: " + Arrays.asList(packageNames));
212
213 Test test = new IsA(parent);
214 for (String pkg : packageNames) {
215 find(test, pkg);
216 }
217
218 LOG.debug("Found: " + getClasses());
219 }
220
221 /**
222 * Attempts to discover classes that are annotated with to the annotation.
223 * Accumulated classes can be accessed by calling {@link #getClasses()}.
224 *
225 * @param annotation the annotation that should be present on matching
226 * classes
227 * @param packageNames one or more package names to scan (including
228 * subpackages) for classes
229 */
230 public void findAnnotated(Class<? extends Annotation> annotation, String... packageNames) {
231 if (packageNames == null) {
232 return;
233 }
234
235 Test test = new AnnotatedWith(annotation);
236 for (String pkg : packageNames) {
237 find(test, pkg);
238 }
239 }
240
241 /**
242 * Scans for classes starting at the package provided and descending into
243 * subpackages. Each class is offered up to the Test as it is discovered,
244 * and if the Test returns true the class is retained. Accumulated classes
245 * can be fetched by calling {@link #getClasses()}.
246 *
247 * @param test an instance of {@link Test} that will be used to filter
248 * classes
249 * @param packageName the name of the package from which to start scanning
250 * for classes, e.g. {@code net.sourceforge.stripes}
251 */
252 public void find(Test test, String packageName) {
253 packageName = packageName.replace('.', '/');
254
255 Set<ClassLoader> set = getClassLoaders();
256 for (ClassLoader classLoader : set) {
257 LOG.trace("Searching: " + classLoader);
258
259 find(test, packageName, classLoader);
260 }
261 }
262
263 protected void find(Test test, String packageName, ClassLoader loader) {
264 Enumeration<URL> urls;
265
266 try {
267 urls = loader.getResources(packageName);
268 } catch (IOException ioe) {
269 LOG.warn("Could not read package: " + packageName, ioe);
270 return;
271 }
272
273 while (urls.hasMoreElements()) {
274 try {
275 URL url = urls.nextElement();
276
277 String urlPath = url.getFile();
278 urlPath = URLDecoder.decode(urlPath, "UTF-8");
279
280 // If it's a file in a directory, trim the stupid file: spec
281 if (urlPath.startsWith("file:")) {
282 urlPath = urlPath.substring(5);
283 }
284
285 // Else it's in a JAR, grab the path to the jar
286 if (urlPath.indexOf('!') > 0) {
287 urlPath = urlPath.substring(0, urlPath.indexOf('!'));
288 }
289
290 LOG.debug("Scanning for classes in [" + urlPath + "] matching criteria: " + test);
291 File file = new File(urlPath);
292 if (file.isDirectory()) {
293 loadImplementationsInDirectory(test, packageName, file);
294 } else {
295 loadImplementationsInJar(test, packageName, file);
296 }
297 } catch (IOException ioe) {
298 LOG.warn("could not read entries", ioe);
299 }
300 }
301 }
302
303 /**
304 * Finds matches in a physical directory on a filesystem. Examines all files
305 * within a directory - if the File object is not a directory, and ends with
306 * <i>.class</i> the file is loaded and tested to see if it is acceptable
307 * according to the Test. Operates recursively to find classes within a
308 * folder structure matching the package structure.
309 *
310 * @param test a Test used to filter the classes that are discovered
311 * @param parent the package name up to this directory in the package
312 * hierarchy. E.g. if /classes is in the classpath and we
313 * wish to examine files in /classes/org/apache then the
314 * values of <i>parent</i> would be <i>org/apache</i>
315 * @param location a File object representing a directory
316 */
317 private void loadImplementationsInDirectory(Test test, String parent, File location) {
318 File[] files = location.listFiles();
319 StringBuilder builder = null;
320
321 for (File file : files) {
322 builder = new StringBuilder(100);
323 String name = file.getName();
324 if (name != null) {
325 name = name.trim();
326 }
327 builder.append(parent).append("/").append(name);
328 String packageOrClass = parent == null ? name : builder.toString();
329
330 if (file.isDirectory()) {
331 loadImplementationsInDirectory(test, packageOrClass, file);
332 } else if (name.endsWith(".class")) {
333 addIfMatching(test, packageOrClass);
334 }
335 }
336 }
337
338 /**
339 * Finds matching classes within a jar files that contains a folder
340 * structure matching the package structure. If the File is not a JarFile or
341 * does not exist a warning will be logged, but no error will be raised.
342 *
343 * @param test a Test used to filter the classes that are discovered
344 * @param parent the parent package under which classes must be in order to
345 * be considered
346 * @param jarfile the jar file to be examined for classes
347 */
348 private void loadImplementationsInJar(Test test, String parent, File jarfile) {
349
350 try {
351 JarEntry entry;
352 JarInputStream jarStream = new JarInputStream(new FileInputStream(jarfile));
353
354 while ((entry = jarStream.getNextJarEntry()) != null) {
355 String name = entry.getName();
356 if (name != null) {
357 name = name.trim();
358 }
359 if (!entry.isDirectory() && name.startsWith(parent) && name.endsWith(".class")) {
360 addIfMatching(test, name);
361 }
362 }
363 } catch (IOException ioe) {
364 LOG.error("Could not search jar file '" + jarfile + "' for classes matching criteria: " + test
365 + "due to an IOException: " + ioe.getMessage());
366 }
367 }
368
369 /**
370 * Add the class designated by the fully qualified class name provided to
371 * the set of resolved classes if and only if it is approved by the Test
372 * supplied.
373 *
374 * @param test the test used to determine if the class matches
375 * @param fqn the fully qualified name of a class
376 */
377 protected void addIfMatching(Test test, String fqn) {
378 try {
379 String externalName = fqn.substring(0, fqn.indexOf('.')).replace('/', '.');
380 Set<ClassLoader> set = getClassLoaders();
381 boolean found = false;
382 for (ClassLoader classLoader : set) {
383 LOG.trace("Checking to see if class " + externalName + " matches criteria [" + test + "]");
384
385 try {
386 Class type = classLoader.loadClass(externalName);
387 if (test.matches(type)) {
388 matches.add((Class<T>)type);
389 }
390 found = true;
391 break;
392 } catch (ClassNotFoundException e) {
393 LOG.debug("Could not find class '" + fqn + "' in class loader: " + classLoader
394 + ". Reason: " + e, e);
395 }
396 }
397 if (!found) {
398 LOG.warn("Could not find class '" + fqn + "' in any class loaders: " + set);
399 }
400 } catch (Throwable t) {
401 LOG.warn("Could not examine class '" + fqn + "' due to a " + t.getClass().getName()
402 + " with message: " + t.getMessage());
403 }
404 }
405 }