pl.bristleback.server.bristle.utils.ResolverUtil Maven / Gradle / Ivy
// Bristleback plugin - Copyright (c) 2010 bristleback.googlecode.com
// ---------------------------------------------------------------------------
// This program is free software; you can redistribute it and/or modify it
// under the terms of the GNU Lesser General Public License as published by the
// Free Software Foundation; either version 3 of the License, or (at your
// option) any later version.
// This library is distributed in the hope that it will be useful,
// but without any warranty; without even the implied warranty of merchantability
// or fitness for a particular purpose.
// You should have received a copy of the GNU Lesser General Public License along
// with this program; if not, see .
// ---------------------------------------------------------------------------
package pl.bristleback.server.bristle.utils;
import org.apache.log4j.Logger;
import pl.bristleback.server.bristle.exceptions.ImplementationResolvingException;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.URL;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.Set;
import java.util.jar.JarEntry;
import java.util.jar.JarInputStream;
/**
* This class is a part of Stripes Framework, version 1.5, www.stripesframework.org.
* Class is modified by Wojciech Niemiec.
* 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(pl.bristleback.server.bristle.utils.ResolverUtil.Test, String)} ()} method 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
*/
public final class ResolverUtil {
private static Logger log = Logger.getLogger(ResolverUtil.class.getName());
private static final int INITIAL_BUFFER_CAPACITY = 100;
/**
* 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() {
if (classLoader == null) {
return Thread.currentThread().getContextClassLoader();
} else {
return 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 found implementations
*/
public ResolverUtil findImplementations(Class parent, String... packageNames) {
if (packageNames == null) {
return this;
}
Test test = new IsAasignatedFrom(parent);
for (String pkg : packageNames) {
find(test, pkg);
}
return this;
}
public Class getImplementation(Class interfaceClass, String className) {
try {
Test test = new IsAasignatedFrom(interfaceClass);
Class type = getClassLoader().loadClass(className);
if (test.matches(type)) {
return type;
} else {
throw new ImplementationResolvingException(className, interfaceClass);
}
} catch (Exception e) {
throw new ImplementationResolvingException(className, interfaceClass);
}
}
/**
* 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 this object
*/
public ResolverUtil find(Test test, String packageName) {
packageName = packageName.replace('.', '/');
ClassLoader loader = getClassLoader();
Enumeration urls;
try {
urls = loader.getResources(packageName);
} catch (IOException ioe) {
log.warn("Could not read package: " + packageName, ioe);
return this;
}
while (urls.hasMoreElements()) {
String urlPath = urls.nextElement().getFile();
urlPath = StringUtil.urlDecode(urlPath);
// 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.toString());
File file = new File(urlPath);
if (file.isDirectory()) {
loadImplementationsInDirectory(test, packageName, file);
} else {
loadImplementationsInJar(test, packageName, file);
}
}
return this;
}
/**
* 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 .class
* 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 parent would be org/apache
* @param location a File object representing a directory
*/
private void loadImplementationsInDirectory(Test test, String parent, File location) {
File[] files = location.listFiles();
StringBuilder builder;
// File.listFiles() can return null when an IO error occurs!
if (files == null) {
log.warn("Could not list directory " + location.getAbsolutePath()
+ " when looking for classes matching: " + test);
return;
}
for (File file : files) {
builder = new StringBuilder(INITIAL_BUFFER_CAPACITY);
builder.append(parent).append("/").append(file.getName());
String packageOrClass;
if (parent == null) {
packageOrClass = file.getName();
} else {
packageOrClass = 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.getMessage());
}
}
/**
* 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();
log.trace("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());
}
}
/**
* 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.
*
* @param type class type
* @return true if class meets conditions
*/
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 IsAasignatedFrom implements Test {
private Class parent;
/**
* Constructs an IsA test using the supplied Class as the parent class/interface.
*
* @param parentType parent type
*/
public IsAasignatedFrom(Class parentType) {
this.parent = parentType;
}
/**
* Returns true if type is assignable to the parent type supplied in the constructor.
*/
@SuppressWarnings("unchecked")
public boolean matches(Class type) {
return type != null && parent.isAssignableFrom(type);
}
@Override
public String toString() {
return "is assignable to " + parent.getSimpleName();
}
}
}
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