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