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ActiveMQ example source code file (ReliableTransport.java)

This example ActiveMQ source code file (ReliableTransport.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - ActiveMQ tags/keywords

command, command, futureresponse, futureresponse, io, ioexception, ioexception, object, reliabletransport, replaybuffer, replayer, replaystrategy, replaystrategy, response, udptransport, util

The ActiveMQ ReliableTransport.java source code

/**
 * 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.activemq.transport.reliable;

import java.io.IOException;
import java.util.SortedSet;
import java.util.TreeSet;

import org.apache.activemq.command.Command;
import org.apache.activemq.command.ReplayCommand;
import org.apache.activemq.command.Response;
import org.apache.activemq.openwire.CommandIdComparator;
import org.apache.activemq.transport.FutureResponse;
import org.apache.activemq.transport.ResponseCorrelator;
import org.apache.activemq.transport.Transport;
import org.apache.activemq.transport.udp.UdpTransport;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * This interceptor deals with out of order commands together with being able to
 * handle dropped commands and the re-requesting dropped commands.
 * 
 * 
 */
public class ReliableTransport extends ResponseCorrelator {
    private static final Logger LOG = LoggerFactory.getLogger(ReliableTransport.class);

    private ReplayStrategy replayStrategy;
    private SortedSet<Command> commands = new TreeSet(new CommandIdComparator());
    private int expectedCounter = 1;
    private int replayBufferCommandCount = 50;
    private int requestTimeout = 2000;
    private ReplayBuffer replayBuffer;
    private Replayer replayer;
    private UdpTransport udpTransport;

    public ReliableTransport(Transport next, ReplayStrategy replayStrategy) {
        super(next);
        this.replayStrategy = replayStrategy;
    }

    public ReliableTransport(Transport next, UdpTransport udpTransport) throws IOException {
        super(next, udpTransport.getSequenceGenerator());
        this.udpTransport = udpTransport;
        this.replayer = udpTransport.createReplayer();
    }

    /**
     * Requests that a range of commands be replayed
     */
    public void requestReplay(int fromCommandId, int toCommandId) {
        ReplayCommand replay = new ReplayCommand();
        replay.setFirstNakNumber(fromCommandId);
        replay.setLastNakNumber(toCommandId);
        try {
            oneway(replay);
        } catch (IOException e) {
            getTransportListener().onException(e);
        }
    }

    public Object request(Object o) throws IOException {
        final Command command = (Command)o;
        FutureResponse response = asyncRequest(command, null);
        while (true) {
            Response result = response.getResult(requestTimeout);
            if (result != null) {
                return result;
            }
            onMissingResponse(command, response);
        }
    }

    public Object request(Object o, int timeout) throws IOException {
        final Command command = (Command)o;
        FutureResponse response = asyncRequest(command, null);
        while (timeout > 0) {
            int time = timeout;
            if (timeout > requestTimeout) {
                time = requestTimeout;
            }
            Response result = response.getResult(time);
            if (result != null) {
                return result;
            }
            onMissingResponse(command, response);
            timeout -= time;
        }
        return response.getResult(0);
    }

    public void onCommand(Object o) {
        Command command = (Command)o;
        // lets pass wireformat through
        if (command.isWireFormatInfo()) {
            super.onCommand(command);
            return;
        } else if (command.getDataStructureType() == ReplayCommand.DATA_STRUCTURE_TYPE) {
            replayCommands((ReplayCommand)command);
            return;
        }

        int actualCounter = command.getCommandId();
        boolean valid = expectedCounter == actualCounter;

        if (!valid) {
            synchronized (commands) {
                int nextCounter = actualCounter;
                boolean empty = commands.isEmpty();
                if (!empty) {
                    Command nextAvailable = commands.first();
                    nextCounter = nextAvailable.getCommandId();
                }

                try {
                    boolean keep = replayStrategy.onDroppedPackets(this, expectedCounter, actualCounter, nextCounter);

                    if (keep) {
                        // lets add it to the list for later on
                        if (LOG.isDebugEnabled()) {
                            LOG.debug("Received out of order command which is being buffered for later: " + command);
                        }
                        commands.add(command);
                    }
                } catch (IOException e) {
                    onException(e);
                }

                if (!empty) {
                    // lets see if the first item in the set is the next
                    // expected
                    command = commands.first();
                    valid = expectedCounter == command.getCommandId();
                    if (valid) {
                        commands.remove(command);
                    }
                }
            }
        }

        while (valid) {
            // we've got a valid header so increment counter
            replayStrategy.onReceivedPacket(this, expectedCounter);
            expectedCounter++;
            super.onCommand(command);

            synchronized (commands) {
                // we could have more commands left
                valid = !commands.isEmpty();
                if (valid) {
                    // lets see if the first item in the set is the next
                    // expected
                    command = commands.first();
                    valid = expectedCounter == command.getCommandId();
                    if (valid) {
                        commands.remove(command);
                    }
                }
            }
        }
    }

    public int getBufferedCommandCount() {
        synchronized (commands) {
            return commands.size();
        }
    }

    public int getExpectedCounter() {
        return expectedCounter;
    }

    /**
     * This property should never really be set - but is mutable primarily for
     * test cases
     */
    public void setExpectedCounter(int expectedCounter) {
        this.expectedCounter = expectedCounter;
    }

    public int getRequestTimeout() {
        return requestTimeout;
    }

    /**
     * Sets the default timeout of requests before starting to request commands
     * are replayed
     */
    public void setRequestTimeout(int requestTimeout) {
        this.requestTimeout = requestTimeout;
    }

    public ReplayStrategy getReplayStrategy() {
        return replayStrategy;
    }

    public ReplayBuffer getReplayBuffer() {
        if (replayBuffer == null) {
            replayBuffer = createReplayBuffer();
        }
        return replayBuffer;
    }

    public void setReplayBuffer(ReplayBuffer replayBuffer) {
        this.replayBuffer = replayBuffer;
    }

    public int getReplayBufferCommandCount() {
        return replayBufferCommandCount;
    }

    /**
     * Sets the default number of commands which are buffered
     */
    public void setReplayBufferCommandCount(int replayBufferSize) {
        this.replayBufferCommandCount = replayBufferSize;
    }

    public void setReplayStrategy(ReplayStrategy replayStrategy) {
        this.replayStrategy = replayStrategy;
    }

    public Replayer getReplayer() {
        return replayer;
    }

    public void setReplayer(Replayer replayer) {
        this.replayer = replayer;
    }

    public String toString() {
        return next.toString();
    }

    public void start() throws Exception {
        if (udpTransport != null) {
            udpTransport.setReplayBuffer(getReplayBuffer());
        }
        if (replayStrategy == null) {
            throw new IllegalArgumentException("Property replayStrategy not specified");
        }
        super.start();
    }

    /**
     * Lets attempt to replay the request as a command may have disappeared
     */
    protected void onMissingResponse(Command command, FutureResponse response) {
        LOG.debug("Still waiting for response on: " + this + " to command: " + command + " sending replay message");

        int commandId = command.getCommandId();
        requestReplay(commandId, commandId);
    }

    protected ReplayBuffer createReplayBuffer() {
        return new DefaultReplayBuffer(getReplayBufferCommandCount());
    }

    protected void replayCommands(ReplayCommand command) {
        try {
            if (replayer == null) {
                onException(new IOException("Cannot replay commands. No replayer property configured"));
            }
            if (LOG.isDebugEnabled()) {
                LOG.debug("Processing replay command: " + command);
            }
            getReplayBuffer().replayMessages(command.getFirstNakNumber(), command.getLastNakNumber(), replayer);

            // TODO we could proactively remove ack'd stuff from the replay
            // buffer
            // if we only have a single client talking to us
        } catch (IOException e) {
            onException(e);
        }
    }

}

Other ActiveMQ examples (source code examples)

Here is a short list of links related to this ActiveMQ ReliableTransport.java source code file:

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