Java tutorial
/* Copyright 2005-2006 Tim Fennell * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.jeeframework.util.resource; import java.io.File; import java.io.FileInputStream; import java.io.IOException; import java.lang.annotation.Annotation; import java.net.URL; import java.net.URLDecoder; import java.util.Enumeration; import java.util.HashSet; import java.util.Set; import java.util.jar.JarEntry; import java.util.jar.JarInputStream; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; /** * <p>ResolverUtil is used to locate classes that are available in the/a class path and meet * arbitrary conditions. The two most common conditions are that a class implements/extends * another class, or that is it annotated with a specific annotation. However, through the use * of the {@link Test} class it is possible to search using arbitrary conditions.</p> * * <p>A ClassLoader is used to locate all locations (directories and jar files) in the class * path that contain classes within certain packages, and then to load those classes and * check them. By default the ClassLoader returned by * {@code Thread.currentThread().getContextClassLoader()} is used, but this can be overridden * by calling {@link #setClassLoader(ClassLoader)} prior to invoking any of the {@code find()} * methods.</p> * * <p>General searches are initiated by calling the * {@link #find(com.opensymphony.xwork2.util.ResolverUtil.Test, String...)} ()} method and supplying * a package name and a Test instance. This will cause the named package <b>and all sub-packages</b> * to be scanned for classes that meet the test. There are also utility methods for the common * use cases of scanning multiple packages for extensions of particular classes, or classes * annotated with a specific annotation.</p> * * <p>The standard usage pattern for the ResolverUtil class is as follows:</p> * *<pre> *ResolverUtil<ActionBean> resolver = new ResolverUtil<ActionBean>(); *resolver.findImplementation(ActionBean.class, pkg1, pkg2); *resolver.find(new CustomTest(), pkg1); *resolver.find(new CustomTest(), pkg2); *Collection<ActionBean> beans = resolver.getClasses(); *</pre> * * <p>This class was copied from Stripes - http://stripes.mc4j.org/confluence/display/stripes/Home * </p> * * @author Tim Fennell */ public class ResolverUtil<T> { /** An instance of Log to use for logging in this class. */ private static final Log log = LogFactory.getLog(ResolverUtil.class); /** * A simple interface that specifies how to test classes to determine if they * are to be included in the results produced by the ResolverUtil. */ public static interface Test { /** * Will be called repeatedly with candidate classes. Must return True if a class * is to be included in the results, false otherwise. */ boolean matches(Class type); } /** * A Test that checks to see if each class is assignable to the provided class. Note * that this test will match the parent type itself if it is presented for matching. */ public static class IsA implements Test { private Class parent; /** Constructs an IsA test using the supplied Class as the parent class/interface. */ public IsA(Class parentType) { this.parent = parentType; } /** Returns true if type is assignable to the parent type supplied in the constructor. */ public boolean matches(Class type) { return type != null && parent.isAssignableFrom(type); } @Override public String toString() { return "is assignable to " + parent.getSimpleName(); } } /** * A Test that checks to see if each class name ends with the provided suffix. */ public static class NameEndsWith implements Test { private String suffix; /** Constructs a NameEndsWith test using the supplied suffix. */ public NameEndsWith(String suffix) { this.suffix = suffix; } /** Returns true if type name ends with the suffix supplied in the constructor. */ public boolean matches(Class type) { return type != null && type.getName().endsWith(suffix); } @Override public String toString() { return "ends with the suffix " + suffix; } } /** * A Test that checks to see if each class is annotated with a specific annotation. If it * is, then the test returns true, otherwise false. */ public static class AnnotatedWith implements Test { private Class<? extends Annotation> annotation; /** Construts an AnnotatedWith test for the specified annotation type. */ public AnnotatedWith(Class<? extends Annotation> annotation) { this.annotation = annotation; } /** Returns true if the type is annotated with the class provided to the constructor. */ public boolean matches(Class type) { return type != null && type.isAnnotationPresent(annotation); } @Override public String toString() { return "annotated with @" + annotation.getSimpleName(); } } /** The set of matches being accumulated. */ private Set<Class<? extends T>> matches = new HashSet<Class<? extends T>>(); /** * The ClassLoader to use when looking for classes. If null then the ClassLoader returned * by Thread.currentThread().getContextClassLoader() will be used. */ private ClassLoader classloader; /** * Provides access to the classes discovered so far. If no calls have been made to * any of the {@code find()} methods, this set will be empty. * * @return the set of classes that have been discovered. */ public Set<Class<? extends T>> getClasses() { return matches; } /** * Returns the classloader that will be used for scanning for classes. If no explicit * ClassLoader has been set by the calling, the context class loader will be used. * * @return the ClassLoader that will be used to scan for classes */ public ClassLoader getClassLoader() { return classloader == null ? Thread.currentThread().getContextClassLoader() : classloader; } /** * Sets an explicit ClassLoader that should be used when scanning for classes. If none * is set then the context classloader will be used. * * @param classloader a ClassLoader to use when scanning for classes */ public void setClassLoader(ClassLoader classloader) { this.classloader = classloader; } /** * Attempts to discover classes that are assignable to the type provided. In the case * that an interface is provided this method will collect implementations. In the case * of a non-interface class, subclasses will be collected. Accumulated classes can be * accessed by calling {@link #getClasses()}. * * @param parent the class of interface to find subclasses or implementations of * @param packageNames one or more package names to scan (including subpackages) for classes */ public void findImplementations(Class parent, String... packageNames) { if (packageNames == null) return; Test test = new IsA(parent); for (String pkg : packageNames) { findInPackage(test, pkg); } } /** * Attempts to discover classes who's name ends with the provided suffix. Accumulated classes can be * accessed by calling {@link #getClasses()}. * * @param suffix The class name suffix to match * @param packageNames one or more package names to scan (including subpackages) for classes */ public void findSuffix(String suffix, String... packageNames) { if (packageNames == null) return; Test test = new NameEndsWith(suffix); for (String pkg : packageNames) { findInPackage(test, pkg); } } /** * Attempts to discover classes that are annotated with to the annotation. Accumulated * classes can be accessed by calling {@link #getClasses()}. * * @param annotation the annotation that should be present on matching classes * @param packageNames one or more package names to scan (including subpackages) for classes */ public void findAnnotated(Class<? extends Annotation> annotation, String... packageNames) { if (packageNames == null) return; Test test = new AnnotatedWith(annotation); for (String pkg : packageNames) { findInPackage(test, pkg); } } /** * Attempts to discover classes that pass the test. Accumulated * classes can be accessed by calling {@link #getClasses()}. * * @param test the test to determine matching classes * @param packageNames one or more package names to scan (including subpackages) for classes */ public void find(Test test, String... packageNames) { if (packageNames == null) return; for (String pkg : packageNames) { findInPackage(test, pkg); } } /** * Scans for classes starting at the package provided and descending into subpackages. * Each class is offered up to the Test as it is discovered, and if the Test returns * true the class is retained. Accumulated classes can be fetched by calling * {@link #getClasses()}. * * @param test an instance of {@link Test} that will be used to filter classes * @param packageName the name of the package from which to start scanning for * classes, e.g. {@code net.sourceforge.stripes} */ public void findInPackage(Test test, String packageName) { packageName = packageName.replace('.', '/'); ClassLoader loader = getClassLoader(); Enumeration<URL> urls; try { urls = loader.getResources(packageName); } catch (IOException ioe) { log.warn("Could not read package: " + packageName, ioe); return; } while (urls.hasMoreElements()) { try { String urlPath = urls.nextElement().getFile(); urlPath = URLDecoder.decode(urlPath, "UTF-8"); // If it's a file in a directory, trim the stupid file: spec if (urlPath.startsWith("file:")) { urlPath = urlPath.substring(5); } // Else it's in a JAR, grab the path to the jar if (urlPath.indexOf('!') > 0) { urlPath = urlPath.substring(0, urlPath.indexOf('!')); } log.info("Scanning for classes in [" + urlPath + "] matching criteria: " + test); File file = new File(urlPath); if (file.isDirectory()) { loadImplementationsInDirectory(test, packageName, file); } else { loadImplementationsInJar(test, packageName, file); } } catch (IOException ioe) { log.warn("could not read entries", ioe); } } } /** * Finds matches in a physical directory on a filesystem. Examines all * files within a directory - if the File object is not a directory, and ends with <i>.class</i> * the file is loaded and tested to see if it is acceptable according to the Test. Operates * recursively to find classes within a folder structure matching the package structure. * * @param test a Test used to filter the classes that are discovered * @param parent the package name up to this directory in the package hierarchy. E.g. if * /classes is in the classpath and we wish to examine files in /classes/org/apache then * the values of <i>parent</i> would be <i>org/apache</i> * @param location a File object representing a directory */ private void loadImplementationsInDirectory(Test test, String parent, File location) { File[] files = location.listFiles(); StringBuilder builder = null; for (File file : files) { builder = new StringBuilder(100); builder.append(parent).append("/").append(file.getName()); String packageOrClass = (parent == null ? file.getName() : builder.toString()); if (file.isDirectory()) { loadImplementationsInDirectory(test, packageOrClass, file); } else if (file.getName().endsWith(".class")) { addIfMatching(test, packageOrClass); } } } /** * Finds matching classes within a jar files that contains a folder structure * matching the package structure. If the File is not a JarFile or does not exist a warning * will be logged, but no error will be raised. * * @param test a Test used to filter the classes that are discovered * @param parent the parent package under which classes must be in order to be considered * @param jarfile the jar file to be examined for classes */ private void loadImplementationsInJar(Test test, String parent, File jarfile) { try { JarEntry entry; JarInputStream jarStream = new JarInputStream(new FileInputStream(jarfile)); while ((entry = jarStream.getNextJarEntry()) != null) { String name = entry.getName(); if (!entry.isDirectory() && name.startsWith(parent) && name.endsWith(".class")) { addIfMatching(test, name); } } } catch (IOException ioe) { log.error("Could not search jar file '" + jarfile + "' for classes matching criteria: " + test + " due to an IOException", ioe); } } /** * Add the class designated by the fully qualified class name provided to the set of * resolved classes if and only if it is approved by the Test supplied. * * @param test the test used to determine if the class matches * @param fqn the fully qualified name of a class */ protected void addIfMatching(Test test, String fqn) { try { String externalName = fqn.substring(0, fqn.indexOf('.')).replace('/', '.'); ClassLoader loader = getClassLoader(); if (log.isDebugEnabled()) { log.debug("Checking to see if class " + externalName + " matches criteria [" + test + "]"); } Class type = loader.loadClass(externalName); if (test.matches(type)) { matches.add((Class<T>) type); } } catch (Throwable t) { log.warn("Could not examine class '" + fqn + "' due to a " + t.getClass().getName() + " with message: " + t.getMessage()); } } }