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/*
 *    Copyright 2009-2023 the original author or authors.
 *
 *    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
 *
 *       https://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 org.apache.ibatis.io;

import java.io.IOException;
import java.lang.annotation.Annotation;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

import org.apache.ibatis.logging.Log;
import org.apache.ibatis.logging.LogFactory;

/**
 * 

* 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. *

* 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. *

* General searches are initiated by calling the {@link #find(Test, String)} and supplying a package name and a Test * instance. This will cause the named package and all sub-packages 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. *

* The standard usage pattern for the ResolverUtil class is as follows: * *

 * 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();
 * 
* * @author Tim Fennell * * @param * the generic type */ public class ResolverUtil { /** * 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 interface Test { /** * Will be called repeatedly with candidate classes. Must return True if a class is to be included in the results, * false otherwise. * * @param type * the type * * @return true, if successful */ 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 { /** The parent. */ private final Class parent; /** * Constructs an IsA test using the supplied Class as the parent class/interface. * * @param parentType * the parent type */ public IsA(Class parentType) { this.parent = parentType; } /** Returns true if type is assignable to the parent type supplied in the constructor. */ @Override 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 is annotated with a specific annotation. If it is, then the test returns * true, otherwise false. */ public static class AnnotatedWith implements Test { /** The annotation. */ private final Class annotation; /** * Constructs an AnnotatedWith test for the specified annotation type. * * @param annotation * the annotation */ public AnnotatedWith(Class annotation) { this.annotation = annotation; } /** Returns true if the type is annotated with the class provided to the constructor. */ @Override 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> matches = new HashSet<>(); /** * 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> 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 * * @return the resolver util */ public ResolverUtil findImplementations(Class parent, String... packageNames) { if (packageNames == null) { return this; } Test test = new IsA(parent); for (String pkg : packageNames) { find(test, pkg); } return this; } /** * Attempts to discover classes that are annotated with 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 * * @return the resolver util */ public ResolverUtil findAnnotated(Class annotation, String... packageNames) { if (packageNames == null) { return this; } Test test = new AnnotatedWith(annotation); for (String pkg : packageNames) { find(test, pkg); } return this; } /** * 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} * * @return the resolver util */ public ResolverUtil find(Test test, String packageName) { String path = getPackagePath(packageName); try { List children = VFS.getInstance().list(path); for (String child : children) { if (child.endsWith(".class")) { addIfMatching(test, child); } } } catch (IOException ioe) { log.error("Could not read package: " + packageName, ioe); } return this; } /** * Converts a Java package name to a path that can be looked up with a call to * {@link ClassLoader#getResources(String)}. * * @param packageName * The Java package name to convert to a path * * @return the package path */ protected String getPackagePath(String packageName) { return packageName == null ? null : packageName.replace('.', '/'); } /** * 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 */ @SuppressWarnings("unchecked") 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) type); } } catch (Throwable t) { log.warn("Could not examine class '" + fqn + "'" + " due to a " + t.getClass().getName() + " with message: " + t.getMessage()); } } }




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