/*
* 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 java.nio.channels.spi;
import java.io.IOException;
import java.nio.SelectorProviderImpl;
import java.nio.channels.Channel;
import java.nio.channels.DatagramChannel;
import java.nio.channels.Pipe;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.ServiceLoader;
/**
* {@code SelectorProvider} is an abstract base class that declares methods for
* providing instances of {@link DatagramChannel}, {@link Pipe},
* {@link java.nio.channels.Selector} , {@link ServerSocketChannel}, and
* {@link SocketChannel}. All the methods of this class are thread-safe.
*
* <p>A provider instance can be retrieved through a system property or the
* configuration file in a jar file; if no provider is available that way then
* the system default provider is returned.
*/
public abstract class SelectorProvider {
private static SelectorProvider provider = null;
/**
* Constructs a new {@code SelectorProvider}.
*/
protected SelectorProvider() {
}
/**
* Gets a provider instance by executing the following steps when called for
* the first time:
* <ul>
* <li> if the system property "java.nio.channels.spi.SelectorProvider" is
* set, the value of this property is the class name of the provider
* returned; </li>
* <li>if there is a provider-configuration file named
* "java.nio.channels.spi.SelectorProvider" in META-INF/services of a jar
* file valid in the system class loader, the first class name is the
* provider's class name; </li>
* <li> otherwise, a system default provider will be returned.</li>
* </ul>
*
* @return the provider.
*/
synchronized public static SelectorProvider provider() {
if (provider == null) {
provider = ServiceLoader.loadFromSystemProperty(SelectorProvider.class);
if (provider == null) {
provider = loadProviderByJar();
}
if (provider == null) {
provider = new SelectorProviderImpl();
}
}
return provider;
}
private static SelectorProvider loadProviderByJar() {
for (SelectorProvider provider : ServiceLoader.load(SelectorProvider.class)) {
return provider;
}
return null;
}
/**
* Creates a new open {@code DatagramChannel}.
*
* @return the new channel.
* @throws IOException
* if an I/O error occurs.
*/
public abstract DatagramChannel openDatagramChannel() throws IOException;
/**
* Creates a new {@code Pipe}.
*
* @return the new pipe.
* @throws IOException
* if an I/O error occurs.
*/
public abstract Pipe openPipe() throws IOException;
/**
* Creates a new selector.
*
* @return the new selector.
* @throws IOException
* if an I/O error occurs.
*/
public abstract AbstractSelector openSelector() throws IOException;
/**
* Creates a new open {@code ServerSocketChannel}.
*
* @return the new channel.
* @throws IOException
* if an I/O error occurs.
*/
public abstract ServerSocketChannel openServerSocketChannel()
throws IOException;
/**
* Create a new open {@code SocketChannel}.
*
* @return the new channel.
* @throws IOException
* if an I/O error occurs.
*/
public abstract SocketChannel openSocketChannel() throws IOException;
/**
* Returns the channel inherited from the process that created this VM.
* On Android, this method always returns null because stdin and stdout are
* never connected to a socket.
*
* @return the channel.
* @throws IOException
* if an I/O error occurs.
*/
public Channel inheritedChannel() throws IOException {
// Android never has stdin/stdout connected to a socket.
return null;
}
}