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Base functionality for leanIX dropwizard-based services

There is a newer version: 2.0.10

package net.leanix.dropkit.amqp;

import com.google.inject.Inject;
import com.google.inject.Singleton;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
import com.rabbitmq.client.ShutdownSignalException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;

/**
 * Holds and manages a connection to an AMQP server. When the connection drops,
 * a new one may be created and put here.
 */
@Singleton
public class ConnectionHolder {

    private final Logger log = LoggerFactory.getLogger(ConnectionHolder.class);

    private final ConnectionFactory connectionFactory;
    private volatile Connection connection;

    @Inject
    public ConnectionHolder(ConnectionFactory connectionFactory) {
        this.connectionFactory = connectionFactory;
    }

    public Connection getConnection() throws IOException {
        if (connection == null) {
            synchronized (this) {
                if (connection == null) {
                    log.info("creating a connection to AMQP server");
                    connection = connectionFactory.newConnection();
                }
            }
        }
        return connection;
    }

    public void closeConnection() {
        if (connection == null) {
            // no connection to close
            return;
        }

        Connection oldConnection = connection;
        connection = null;
        log.info("closing connection");
        try {
            oldConnection.close();
        } catch (IOException | ShutdownSignalException e) {
            log.error("could not close connection, ignore", e);
        }
    }

    public Channel createNewChannel() throws IOException {
        if (connection == null) {
            getConnection();
        }

        try {
            log.debug("..createChannel");
            return connection.createChannel();
        } catch (IOException | ShutdownSignalException e) {
            log.error("could not create channel from connection -- closing connection", e);
            closeConnection();
            throw e;
        }
    }
}