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 }