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ActiveMQ example source code file (DefaultDatabaseLocker.java)

This example ActiveMQ source code file (DefaultDatabaseLocker.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

caught, default_lock_acquire_sleep_interval, defaultdatabaselocker, defaultdatabaselocker, exception, exception, failed, failed, handler, io, ioexception, jdbc, master, preparedstatement, sql, sqlexception, sqlexception

The ActiveMQ DefaultDatabaseLocker.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.store.jdbc;

import java.io.IOException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;

import javax.sql.DataSource;

import org.apache.activemq.util.Handler;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Represents an exclusive lock on a database to avoid multiple brokers running
 * against the same logical database.
 * 
 * @org.apache.xbean.XBean element="database-locker"
 * 
 */
public class DefaultDatabaseLocker implements DatabaseLocker {
    public static final long DEFAULT_LOCK_ACQUIRE_SLEEP_INTERVAL = 1000;
    private static final Logger LOG = LoggerFactory.getLogger(DefaultDatabaseLocker.class);
    protected DataSource dataSource;
    protected Statements statements;
    protected long lockAcquireSleepInterval = DEFAULT_LOCK_ACQUIRE_SLEEP_INTERVAL;

    protected Connection connection;
    protected boolean stopping;
    protected Handler<Exception> exceptionHandler;
    
    public DefaultDatabaseLocker() {
    }
    
    public DefaultDatabaseLocker(JDBCPersistenceAdapter persistenceAdapter) throws IOException {
        setPersistenceAdapter(persistenceAdapter);
    }

    public void setPersistenceAdapter(JDBCPersistenceAdapter adapter) throws IOException {
        this.dataSource = adapter.getLockDataSource();
        this.statements = adapter.getStatements();
    }
    
    public void start() throws Exception {
        stopping = false;

        LOG.info("Attempting to acquire the exclusive lock to become the Master broker");
        String sql = statements.getLockCreateStatement();
        LOG.debug("Locking Query is "+sql);
        
        PreparedStatement statement = null;
        while (true) {
            try {
                connection = dataSource.getConnection();
                connection.setAutoCommit(false);
                statement = connection.prepareStatement(sql);
                statement.execute();
                break;
            } catch (Exception e) {
                try {
                    if (stopping) {
                        throw new Exception(
                                "Cannot start broker as being asked to shut down. " 
                                        + "Interrupted attempt to acquire lock: "
                                        + e, e);
                    }
                    if (exceptionHandler != null) {
                        try {
                            exceptionHandler.handle(e);
                        } catch (Throwable handlerException) {
                            LOG.error( "The exception handler "
                                    + exceptionHandler.getClass().getCanonicalName()
                                    + " threw this exception: "
                                    + handlerException
                                    + " while trying to handle this exception: "
                                    + e, handlerException);
                        }

                    } else {
                        LOG.debug("Lock failure: "+ e, e);
                    }
                } finally {
                    // Let's make sure the database connection is properly
                    // closed when an error occurs so that we're not leaking
                    // connections 
                    if (null != connection) {
                        try {
                            connection.close();
                        } catch (SQLException e1) {
                            LOG.error("Caught exception while closing connection: " + e1, e1);
                        }
                        
                        connection = null;
                    }
                }
            } finally {
                if (null != statement) {
                    try {
                        statement.close();
                    } catch (SQLException e1) {
                        LOG.debug("Caught while closing statement: " + e1, e1);
                    }
                    statement = null;
                }
            }

            LOG.info("Failed to acquire lock.  Sleeping for " + lockAcquireSleepInterval + " milli(s) before trying again...");
            try {
                Thread.sleep(lockAcquireSleepInterval);
            } catch (InterruptedException ie) {
                LOG.warn("Master lock retry sleep interrupted", ie);
            }
        }

        LOG.info("Becoming the master on dataSource: " + dataSource);
    }

    public void stop() throws Exception {
        stopping = true;
        try {
            if (connection != null && !connection.isClosed()) {
                try {
                    connection.rollback();
                } catch (SQLException sqle) {
                    LOG.warn("Exception while rollbacking the connection on shutdown", sqle);
                } finally {
                    try {
                        connection.close();
                    } catch (SQLException ignored) {
                        LOG.debug("Exception while closing connection on shutdown", ignored);
                    }
                }
            }
        } catch (SQLException sqle) {
            LOG.warn("Exception while checking close status of connection on shutdown", sqle);
        }
    }

    public boolean keepAlive() {
        PreparedStatement statement = null;
        boolean result = false;
        try {
            statement = connection.prepareStatement(statements.getLockUpdateStatement());
            statement.setLong(1, System.currentTimeMillis());
            int rows = statement.executeUpdate();
            if (rows == 1) {
                result=true;
            }
        } catch (Exception e) {
            LOG.error("Failed to update database lock: " + e, e);
        } finally {
            if (statement != null) {
                try {
                    statement.close();
                } catch (SQLException e) {
                    LOG.error("Failed to close statement",e);
                }
            }
        }
        return result;
    }
 
    public long getLockAcquireSleepInterval() {
        return lockAcquireSleepInterval;
    }

    public void setLockAcquireSleepInterval(long lockAcquireSleepInterval) {
        this.lockAcquireSleepInterval = lockAcquireSleepInterval;
    }
    
    public Handler getExceptionHandler() {
        return exceptionHandler;
    }

    public void setExceptionHandler(Handler exceptionHandler) {
        this.exceptionHandler = exceptionHandler;
    }

}

Other ActiveMQ examples (source code examples)

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

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