Java tutorial
/* * 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.nifi.distributed.cache.client; import java.io.DataInputStream; import java.io.IOException; import java.util.ArrayList; import java.util.List; import java.util.concurrent.BlockingQueue; import java.util.concurrent.LinkedBlockingQueue; import java.util.concurrent.TimeUnit; import org.apache.commons.io.IOUtils; import org.apache.nifi.annotation.documentation.CapabilityDescription; import org.apache.nifi.annotation.documentation.SeeAlso; import org.apache.nifi.annotation.documentation.Tags; import org.apache.nifi.annotation.lifecycle.OnEnabled; import org.apache.nifi.components.PropertyDescriptor; import org.apache.nifi.controller.AbstractControllerService; import org.apache.nifi.controller.ConfigurationContext; import org.apache.nifi.distributed.cache.protocol.ProtocolHandshake; import org.apache.nifi.distributed.cache.protocol.exception.HandshakeException; import org.apache.nifi.processor.util.StandardValidators; import org.apache.nifi.remote.StandardVersionNegotiator; import org.apache.nifi.remote.VersionNegotiator; import org.apache.nifi.ssl.SSLContextService; import org.apache.nifi.ssl.SSLContextService.ClientAuth; import org.apache.nifi.stream.io.ByteArrayOutputStream; import org.apache.nifi.stream.io.DataOutputStream; import org.slf4j.Logger; import org.slf4j.LoggerFactory; @Tags({ "distributed", "cache", "state", "set", "cluster" }) @SeeAlso(classNames = { "org.apache.nifi.distributed.cache.server.DistributedSetCacheServer", "org.apache.nifi.ssl.StandardSSLContextService" }) @CapabilityDescription("Provides the ability to communicate with a DistributedSetCacheServer. This can be used in order to share a Set " + "between nodes in a NiFi cluster") public class DistributedSetCacheClientService extends AbstractControllerService implements DistributedSetCacheClient { private static final Logger logger = LoggerFactory.getLogger(DistributedMapCacheClientService.class); public static final PropertyDescriptor HOSTNAME = new PropertyDescriptor.Builder().name("Server Hostname") .description("The name of the server that is running the DistributedSetCacheServer service") .required(true).addValidator(StandardValidators.NON_EMPTY_VALIDATOR).build(); public static final PropertyDescriptor PORT = new PropertyDescriptor.Builder().name("Server Port").description( "The port on the remote server that is to be used when communicating with the DistributedSetCacheServer service") .required(true).addValidator(StandardValidators.PORT_VALIDATOR).defaultValue("4557").build(); public static final PropertyDescriptor SSL_CONTEXT_SERVICE = new PropertyDescriptor.Builder() .name("SSL Context Service") .description("If specified, indicates the SSL Context Service that is used to communicate with the " + "remote server. If not specified, communications will not be encrypted") .required(false).identifiesControllerService(SSLContextService.class).build(); public static final PropertyDescriptor COMMUNICATIONS_TIMEOUT = new PropertyDescriptor.Builder() .name("Communications Timeout") .description("Specifices how long to wait when communicating with the remote server before determining " + "that there is a communications failure if data cannot be sent or received") .required(true).addValidator(StandardValidators.TIME_PERIOD_VALIDATOR).defaultValue("30 secs").build(); private final BlockingQueue<CommsSession> queue = new LinkedBlockingQueue<>(); private volatile ConfigurationContext configContext; private volatile boolean closed = false; @Override protected List<PropertyDescriptor> getSupportedPropertyDescriptors() { final List<PropertyDescriptor> descriptors = new ArrayList<>(); descriptors.add(HOSTNAME); descriptors.add(PORT); descriptors.add(SSL_CONTEXT_SERVICE); descriptors.add(COMMUNICATIONS_TIMEOUT); return descriptors; } @OnEnabled public void onConfigured(final ConfigurationContext context) { this.configContext = context; } public CommsSession createCommsSession(final ConfigurationContext context) throws IOException { final String hostname = context.getProperty(HOSTNAME).getValue(); final int port = context.getProperty(PORT).asInteger(); final long timeoutMillis = context.getProperty(COMMUNICATIONS_TIMEOUT).asTimePeriod(TimeUnit.MILLISECONDS); final SSLContextService sslContextService = context.getProperty(SSL_CONTEXT_SERVICE) .asControllerService(SSLContextService.class); final CommsSession commsSession; if (sslContextService == null) { commsSession = new StandardCommsSession(hostname, port); } else { commsSession = new SSLCommsSession(sslContextService.createSSLContext(ClientAuth.REQUIRED), hostname, port); } commsSession.setTimeout(timeoutMillis, TimeUnit.MILLISECONDS); return commsSession; } private CommsSession leaseCommsSession() throws IOException { CommsSession session = queue.poll(); if (session != null && !session.isClosed()) { return session; } session = createCommsSession(configContext); final VersionNegotiator versionNegotiator = new StandardVersionNegotiator(1); try { ProtocolHandshake.initiateHandshake(session.getInputStream(), session.getOutputStream(), versionNegotiator); session.setProtocolVersion(versionNegotiator.getVersion()); } catch (final HandshakeException e) { IOUtils.closeQuietly(session); throw new IOException(e); } return session; } @Override public <T> boolean addIfAbsent(final T value, final Serializer<T> serializer) throws IOException { return invokeRemoteBoolean("addIfAbsent", value, serializer); } @Override public <T> boolean contains(final T value, final Serializer<T> serializer) throws IOException { return invokeRemoteBoolean("contains", value, serializer); } @Override public <T> boolean remove(final T value, final Serializer<T> serializer) throws IOException { return invokeRemoteBoolean("remove", value, serializer); } @Override public void close() throws IOException { this.closed = true; CommsSession commsSession; while ((commsSession = queue.poll()) != null) { try (final DataOutputStream dos = new DataOutputStream(commsSession.getOutputStream())) { dos.writeUTF("close"); dos.flush(); } catch (final IOException e) { } IOUtils.closeQuietly(commsSession); } if (logger.isDebugEnabled() && getIdentifier() != null) { logger.debug("Closed {}", new Object[] { getIdentifier() }); } } @Override protected void finalize() throws Throwable { if (!closed) { close(); } logger.debug("Finalize called"); } private <T> boolean invokeRemoteBoolean(final String methodName, final T value, final Serializer<T> serializer) throws IOException { if (closed) { throw new IllegalStateException("Client is closed"); } final CommsSession session = leaseCommsSession(); boolean tryToRequeue = true; try { final DataOutputStream dos = new DataOutputStream(session.getOutputStream()); dos.writeUTF(methodName); final ByteArrayOutputStream baos = new ByteArrayOutputStream(); serializer.serialize(value, baos); dos.writeInt(baos.size()); baos.writeTo(dos); dos.flush(); final DataInputStream dis = new DataInputStream(session.getInputStream()); return dis.readBoolean(); } catch (final IOException ioe) { tryToRequeue = false; throw ioe; } finally { if (tryToRequeue == true && this.closed == false) { queue.offer(session); } else { IOUtils.closeQuietly(session); } } } }