package org.apache.lucene.util;
/*
* 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.
*/
import java.io.IOException;
import java.io.InputStream;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URL;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.Locale;
import java.util.NoSuchElementException;
import java.util.ServiceConfigurationError;
/**
* Helper class for loading SPI classes from classpath (META-INF files).
* This is a light impl of {@link java.util.ServiceLoader} but is guaranteed to
* be bug-free regarding classpath order and does not instantiate or initialize
* the classes found.
*
* @lucene.internal
*/
public final class SPIClassIterator<S> implements Iterator<Class<? extends S>> {
private static final String META_INF_SERVICES = "META-INF/services/";
private final Class<S> clazz;
private final ClassLoader loader;
private final Enumeration<URL> profilesEnum;
private Iterator<String> linesIterator;
public static <S> SPIClassIterator<S> get(Class<S> clazz) {
return new SPIClassIterator<S>(clazz, Thread.currentThread().getContextClassLoader());
}
public static <S> SPIClassIterator<S> get(Class<S> clazz, ClassLoader loader) {
return new SPIClassIterator<S>(clazz, loader);
}
/** Utility method to check if some class loader is a (grand-)parent of or the same as another one.
* This means the child will be able to load all classes from the parent, too. */
public static boolean isParentClassLoader(final ClassLoader parent, ClassLoader child) {
while (child != null) {
if (child == parent) {
return true;
}
child = child.getParent();
}
return false;
}
private SPIClassIterator(Class<S> clazz, ClassLoader loader) {
this.clazz = clazz;
try {
final String fullName = META_INF_SERVICES + clazz.getName();
this.profilesEnum = (loader == null) ? ClassLoader.getSystemResources(fullName) : loader.getResources(fullName);
} catch (IOException ioe) {
throw new ServiceConfigurationError("Error loading SPI profiles for type " + clazz.getName() + " from classpath", ioe);
}
this.loader = (loader == null) ? ClassLoader.getSystemClassLoader() : loader;
this.linesIterator = Collections.<String>emptySet().iterator();
}
private boolean loadNextProfile() {
ArrayList<String> lines = null;
while (profilesEnum.hasMoreElements()) {
if (lines != null) {
lines.clear();
} else {
lines = new ArrayList<String>();
}
final URL url = profilesEnum.nextElement();
try {
final InputStream in = url.openStream();
IOException priorE = null;
try {
final BufferedReader reader = new BufferedReader(new InputStreamReader(in, IOUtils.CHARSET_UTF_8));
String line;
while ((line = reader.readLine()) != null) {
final int pos = line.indexOf('#');
if (pos >= 0) {
line = line.substring(0, pos);
}
line = line.trim();
if (line.length() > 0) {
lines.add(line);
}
}
} catch (IOException ioe) {
priorE = ioe;
} finally {
IOUtils.closeWhileHandlingException(priorE, in);
}
} catch (IOException ioe) {
throw new ServiceConfigurationError("Error loading SPI class list from URL: " + url, ioe);
}
if (!lines.isEmpty()) {
this.linesIterator = lines.iterator();
return true;
}
}
return false;
}
@Override
public boolean hasNext() {
return linesIterator.hasNext() || loadNextProfile();
}
@Override
public Class<? extends S> next() {
// hasNext() implicitely loads the next profile, so it is essential to call this here!
if (!hasNext()) {
throw new NoSuchElementException();
}
assert linesIterator.hasNext();
final String c = linesIterator.next();
try {
// don't initialize the class (pass false as 2nd parameter):
return Class.forName(c, false, loader).asSubclass(clazz);
} catch (ClassNotFoundException cnfe) {
throw new ServiceConfigurationError(String.format(Locale.ROOT, "A SPI class of type %s with classname %s does not exist, "+
"please fix the file '%s%1$s' in your classpath.", clazz.getName(), c, META_INF_SERVICES));
}
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
}