/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.apache.openjpa.lib.util;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
import java.net.URLConnection;
import java.security.AccessController;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.StringTokenizer;
import java.util.TreeSet;
/**
* Utility classes to locate services, as defined in the <a
* href="http://java.sun.com/j2se/1.3/docs/guide/jar/jar.html
* #Service%20Provider">Jar File Specification</a>. Most of the methods in this
* class can also be found in the <em>sun.misc.Service</em> class, but since
* it is undocumented, we cannot rely on its API.
* Service location for a specified interface is done by searching for the
* resource <em>/META-INF/services/</em><i>service.class.name</i>, and
* loading the resource.
* Methods in this class that do not declare exceptions will never throw
* Runtime exceptions: exceptions are silently swallowed and empty array values
* are returned.
*
* @author Marc Prud'hommeaux
* @nojavadoc
*/
public class Services {
private static final String PREFIX = "META-INF/services/";
/**
* Return an array of Strings of class names of all known service
* implementors of the specified interface or class.
*/
public static String[] getImplementors(Class serviceClass) {
return getImplementors(serviceClass, null);
}
/**
* Return an array of Strings of class names of all known service
* implementors of the specified interface or class.
*/
public static String[] getImplementors(Class serviceClass,
ClassLoader loader) {
return getImplementors(serviceClass.getName(), loader);
}
/**
* Return an array of Strings of class names of all known service
* implementors of the specified class name(as resolved by the current
* thread's context class loader).
*/
public static String[] getImplementors(String serviceName) {
return getImplementors(serviceName, null);
}
/**
* Return an array of Strings of class names of all known service
* implementors of the specified class name, as resolved by the specified
* {@link ClassLoader}.
*/
public static String[] getImplementors(String serviceName,
ClassLoader loader) {
if (loader == null)
loader = (ClassLoader) AccessController.doPrivileged(
J2DoPrivHelper.getContextClassLoaderAction());
try {
Set resourceList = new TreeSet();
Enumeration resources = (Enumeration) AccessController.doPrivileged(
J2DoPrivHelper.getResourcesAction(loader, PREFIX + serviceName));
while (resources.hasMoreElements())
addResources((URL) resources.nextElement(), resourceList);
return (String[]) resourceList.toArray(new String[resourceList
.size()]);
} catch (Exception e) {
// silently swallow all exceptions.
return new String[0];
}
}
/**
* Parse the URL resource and add the listed class names to the specified
* Set. Class names are separated by lines. Lines starting with '#' are
* ignored.
*/
private static void addResources(URL url, Set set) throws IOException {
InputStream in = null;
BufferedReader reader = null;
URLConnection urlCon = null;
try {
urlCon = url.openConnection();
urlCon.setUseCaches(false);
in = urlCon.getInputStream();
reader = new BufferedReader(new InputStreamReader(in));
String line;
while ((line = reader.readLine()) != null) {
if (line.trim().startsWith("#")
|| line.trim().length() == 0)
continue;
StringTokenizer tok = new StringTokenizer(line, "# \t");
if (tok.hasMoreTokens()) {
String next = tok.nextToken();
if (next != null) {
next = next.trim();
if (next.length() > 0 && !next.startsWith("#"))
set.add(next);
}
}
}
} finally {
try {
reader.close();
} catch (IOException ioe) {
// silently consume exception
}
try {
in.close();
} catch (IOException ioe) {
// silently consume exception
}
}
}
public static Class[] getImplementorClasses(Class serviceClass) {
return getImplementorClasses(serviceClass.getName(), null);
}
public static Class[] getImplementorClasses(Class serviceClass,
ClassLoader loader) {
Set invalid = new HashSet();
Class[] classes = getImplementorClasses(serviceClass.getName(), loader);
// filter out any classes that have any classloader issues wrt.
// the specified service class.
for (int i = 0; i < classes.length; i++)
if (!serviceClass.isAssignableFrom(classes[i]))
invalid.add(classes[i]);
if (invalid.size() != 0) {
List list = new ArrayList(Arrays.asList(classes));
list.removeAll(invalid);
return (Class[]) list.toArray(new Class[list.size()]);
} else {
return classes;
}
}
/**
* Return an array of Class objects of all known service implementors of the
* specified class name(as resolved by the current thread's context class
* loader).
*/
public static Class[] getImplementorClasses(String serviceName) {
return getImplementorClasses(serviceName, null);
}
public static Class[] getImplementorClasses(String serviceName,
ClassLoader loader) {
try {
return getImplementorClasses(serviceName, loader, true);
} catch (Exception cnfe) {
// this will never happen with skipmissing
return new Class[0];
}
}
/**
* Return an array of Class objects of all known service implementors of the
* specified class name, as resolved by the specified {@link ClassLoader}.
*
* @param skipMissing if true, then ignore classes that cannot be loaded by
* the classloader; otherwise, resolution failures will throw a
* {@link ClassNotFoundException}.
*/
public static Class[] getImplementorClasses(String serviceName,
ClassLoader loader, boolean skipMissing) throws ClassNotFoundException {
if (loader == null)
loader = (ClassLoader) AccessController.doPrivileged(
J2DoPrivHelper.getContextClassLoaderAction());
String[] names = getImplementors(serviceName, loader);
if (names == null)
return new Class[0];
List classes = new ArrayList(names.length);
for (int i = 0; i < names.length; i++) {
try {
classes.add(Class.forName(names[i], false, loader));
} catch (ClassNotFoundException e) {
if (!skipMissing)
throw e;
} catch (UnsupportedClassVersionError ecve) {
if (!skipMissing)
throw ecve;
} catch (LinkageError le) {
if (!skipMissing)
throw le;
}
}
return (Class[]) classes.toArray(new Class[classes.size()]);
}
}