jpa4azure.util.ResolverUtil Maven / Gradle / Ivy
/* 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 jpa4azure.util;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
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;
/**
*
* 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(Test1.sourceforge.stripes.util.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:
*
*
*
* esolverUtil<ActionBean> resolver = new ResolverUtil<ActionBean>();
* esolver.findImplementation(ActionBean.class, pkg1, pkg2);
* esolver.find(new CustomTest(), pkg1);
* esolver.find(new CustomTest(), pkg2);
* ollection<ActionBean> beans = resolver.getClasses();
*
*
* @author Tim Fennell
*/
public class ResolverUtil {
/** An instance of Log to use for logging in this 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.
*/
@SuppressWarnings("unchecked")
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 {
private Class annotation;
/** Constructs an AnnotatedWith test for the specified annotation type. */
public AnnotatedWith(Class annotation) {
this.annotation = annotation;
}
/**
* Returns true if the type is annotated with the class provided to the
* constructor.
*/
@SuppressWarnings("unchecked")
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
*/
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
*/
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}
*/
public ResolverUtil find(Test test, String packageName) {
packageName = packageName.replace('.', '/');
ClassLoader loader = getClassLoader();
Enumeration urls;
try {
urls = loader.getResources(packageName);
} catch (IOException ioe) {
return this;
}
while (urls.hasMoreElements()) {
String urlPath = urls.nextElement().getFile();
try {
urlPath = URLDecoder.decode(urlPath, "UTF-8");
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
// 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('!'));
}
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 = null;
// File.listFiles() can return null when an IO error occurs!
if (files == null) {
return;
}
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) {
ioe.printStackTrace();
}
}
/**
* 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();
Class type = loader.loadClass(externalName);
if (test.matches(type)) {
matches.add((Class) type);
}
} catch (Throwable t) {
t.printStackTrace();
}
}
}
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