com.alipay.sofa.jraft.util.JRaftServiceLoader Maven / Gradle / Ivy
/*
* 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 com.alipay.sofa.jraft.util;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.ServiceConfigurationError;
/**
* A simple service-provider loading facility (SPI).
*
* @author jiachun.fjc
*/
public final class JRaftServiceLoader implements Iterable {
private static final String PREFIX = "META-INF/services/";
// the class or interface representing the service being loaded
private final Class service;
// the class loader used to locate, load, and instantiate providers
private final ClassLoader loader;
// cached providers, in instantiation order
private LinkedHashMap providers = new LinkedHashMap<>();
// the current lazy-lookup iterator
private LazyIterator lookupIterator;
public static JRaftServiceLoader load(final Class service) {
return JRaftServiceLoader.load(service, Thread.currentThread().getContextClassLoader());
}
public static JRaftServiceLoader load(final Class service, final ClassLoader loader) {
return new JRaftServiceLoader<>(service, loader);
}
public List sort() {
final Iterator it = iterator();
final List sortList = new ArrayList<>();
while (it.hasNext()) {
sortList.add(it.next());
}
if (sortList.size() <= 1) {
return sortList;
}
sortList.sort((o1, o2) -> {
final SPI o1_spi = o1.getClass().getAnnotation(SPI.class);
final SPI o2_spi = o2.getClass().getAnnotation(SPI.class);
final int o1_priority = o1_spi == null ? 0 : o1_spi.priority();
final int o2_priority = o2_spi == null ? 0 : o2_spi.priority();
return -(o1_priority - o2_priority);
});
return sortList;
}
public S first() {
final List sortList = sort();
if (sortList.isEmpty()) {
throw fail(this.service, "could not find any implementation for class");
}
return sortList.get(0);
}
public S find(final String implName) {
for (final S s : this.providers.values()) {
final SPI spi = s.getClass().getAnnotation(SPI.class);
if (spi != null && spi.name().equalsIgnoreCase(implName)) {
return s;
}
}
while (this.lookupIterator.hasNext()) {
final Class cls = this.lookupIterator.next();
final SPI spi = cls.getAnnotation(SPI.class);
if (spi != null && spi.name().equalsIgnoreCase(implName)) {
try {
final S provider = this.service.cast(cls.newInstance());
this.providers.put(cls.getName(), provider);
return provider;
} catch (Throwable x) {
throw fail(this.service, "provider " + cls.getName() + " could not be instantiated", x);
}
}
}
throw fail(this.service, "provider " + implName + " not found");
}
public void reload() {
this.providers.clear();
this.lookupIterator = new LazyIterator(this.service, this.loader);
}
private JRaftServiceLoader(final Class service, final ClassLoader loader) {
this.service = Requires.requireNonNull(service, "service interface cannot be null");
this.loader = (loader == null) ? ClassLoader.getSystemClassLoader() : loader;
reload();
}
private static ServiceConfigurationError fail(final Class service, final String msg, final Throwable cause) {
return new ServiceConfigurationError(service.getName() + ": " + msg, cause);
}
private static ServiceConfigurationError fail(final Class service, final String msg) {
return new ServiceConfigurationError(service.getName() + ": " + msg);
}
private static ServiceConfigurationError fail(final Class service, final URL url, final int line,
final String msg) {
return fail(service, url + ":" + line + ": " + msg);
}
// parse a single line from the given configuration file, adding the name
// on the line to the names list.
private int parseLine(final Class service, final URL u, final BufferedReader r, final int lc,
final List names) throws IOException, ServiceConfigurationError {
String ln = r.readLine();
if (ln == null) {
return -1;
}
final int ci = ln.indexOf('#');
if (ci >= 0) {
ln = ln.substring(0, ci);
}
ln = ln.trim();
final int n = ln.length();
if (n != 0) {
if ((ln.indexOf(' ') >= 0) || (ln.indexOf('\t') >= 0)) {
throw fail(service, u, lc, "illegal configuration-file syntax");
}
int cp = ln.codePointAt(0);
if (!Character.isJavaIdentifierStart(cp)) {
throw fail(service, u, lc, "illegal provider-class name: " + ln);
}
for (int i = Character.charCount(cp); i < n; i += Character.charCount(cp)) {
cp = ln.codePointAt(i);
if (!Character.isJavaIdentifierPart(cp) && (cp != '.')) {
throw fail(service, u, lc, "Illegal provider-class name: " + ln);
}
}
if (!this.providers.containsKey(ln) && !names.contains(ln)) {
names.add(ln);
}
}
return lc + 1;
}
private Iterator parse(final Class service, final URL url) {
final ArrayList names = new ArrayList<>();
try (final InputStream in = url.openStream();
final BufferedReader r = new BufferedReader(new InputStreamReader(in, StandardCharsets.UTF_8))) {
int lc = 1;
// noinspection StatementWithEmptyBody
while ((lc = parseLine(service, url, r, lc, names)) >= 0)
;
} catch (final IOException x) {
throw fail(service, "error reading configuration file", x);
}
return names.iterator();
}
@Override
public Iterator iterator() {
return new Iterator() {
final Iterator> knownProviders = JRaftServiceLoader.this.providers.entrySet()
.iterator();
@Override
public boolean hasNext() {
return this.knownProviders.hasNext() || JRaftServiceLoader.this.lookupIterator.hasNext();
}
@Override
public S next() {
if (this.knownProviders.hasNext()) {
return this.knownProviders.next().getValue();
}
final Class cls = JRaftServiceLoader.this.lookupIterator.next();
try {
final S provider = JRaftServiceLoader.this.service.cast(cls.newInstance());
JRaftServiceLoader.this.providers.put(cls.getName(), provider);
return provider;
} catch (final Throwable x) {
throw fail(JRaftServiceLoader.this.service, "provider " + cls.getName()
+ " could not be instantiated", x);
}
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
};
}
private class LazyIterator implements Iterator> {
Class service;
ClassLoader loader;
Enumeration configs = null;
Iterator pending = null;
String nextName = null;
private LazyIterator(Class service, ClassLoader loader) {
this.service = service;
this.loader = loader;
}
@Override
public boolean hasNext() {
if (this.nextName != null) {
return true;
}
if (this.configs == null) {
try {
final String fullName = PREFIX + this.service.getName();
if (this.loader == null) {
this.configs = ClassLoader.getSystemResources(fullName);
} else {
this.configs = this.loader.getResources(fullName);
}
} catch (final IOException x) {
throw fail(this.service, "error locating configuration files", x);
}
}
while ((this.pending == null) || !this.pending.hasNext()) {
if (!this.configs.hasMoreElements()) {
return false;
}
this.pending = parse(this.service, this.configs.nextElement());
}
this.nextName = this.pending.next();
return true;
}
@SuppressWarnings("unchecked")
@Override
public Class next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
final String name = this.nextName;
this.nextName = null;
final Class cls;
try {
cls = Class.forName(name, false, this.loader);
} catch (final ClassNotFoundException x) {
throw fail(this.service, "provider " + name + " not found");
}
if (!this.service.isAssignableFrom(cls)) {
throw fail(this.service, "provider " + name + " not a subtype");
}
return (Class) cls;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
}
/**
* Returns a string describing this service.
*/
@Override
public String toString() {
return "com.alipay.sofa.jraft.util.JRaftServiceLoader[" + this.service.getName() + "]";
}
}
© 2015 - 2025 Weber Informatics LLC | Privacy Policy