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<ActionBean> resolver = new ResolverUtil<ActionBean>(); 059 *resolver.findImplementation(ActionBean.class, pkg1, pkg2); 060 *resolver.find(new CustomTest(), pkg1); 061 *resolver.find(new CustomTest(), pkg2); 062 *Collection<ActionBean> 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 }