org.waveprotocol.wave.examples.fedone.persistence.mongodb.MongoDbProvider.java Source code

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Here is the source code for org.waveprotocol.wave.examples.fedone.persistence.mongodb.MongoDbProvider.java

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/**
 * Copyright 2010 Google Inc.
 *
 * Licensed 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.waveprotocol.wave.examples.fedone.persistence.mongodb;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Preconditions;

import com.mongodb.DB;
import com.mongodb.Mongo;
import com.mongodb.MongoException;

import org.waveprotocol.wave.examples.fedone.persistence.PersistenceStartException;

import java.io.IOException;
import java.net.UnknownHostException;
import java.util.Properties;
import java.util.logging.Logger;

/**
 * Class to lazily setup and manage the MongoDb connection.
 *
 * @author ljvderijk@google.com (Lennard de Rijk)
 *
 */
public class MongoDbProvider {
    private static final Logger LOG = Logger.getLogger(MongoDbProvider.class.getName());

    /** Location of the MongoDB properties file in the classpath. */
    private static final String PROPERTIES_LOC = "org/waveprotocol/wave/examples/fedone/persistence/mongodb/mongodb.properties";

    /** Name of the property that stores the host. */
    private static final String HOST_PROPERTY = "mongoDbHost";

    /** Name of the property that stores the port. */
    private static final String PORT_PROPERTY = "mongoDbPort";

    /** Name of the property that stores the name of the database. */
    private static final String DATABASE_NAME_PROPERTY = "mongoDbDatabase";

    /**
     * Our {@link Mongo} instance, should be accessed by getMongo unless during
     * start().
     */
    private Mongo mongo;

    /**
     * Our lazily loaded {@link Properties} instance.
     */
    private Properties properties;

    /**
     * Lazily instantiated {@link MongoDbStore}.
     */
    private MongoDbStore mongoDbStore;

    /** Stores whether we have successfully setup a live {@link Mongo} instance. */
    private boolean isRunning;

    /**
     * Constructs a new empty {@link MongoDbProvider}.
     */
    public MongoDbProvider() {
    }

    /**
     * Starts the {@link Mongo} instance and explicitly checks whether it is
     * actually alive.
     *
     * @throws PersistenceStartException if we can't make a connection to MongoDb.
     */
    private void start() {
        Preconditions.checkState(!isRunning(), "Can't start after a connection has been established");

        ensurePropertiesLoaded();

        String host = properties.getProperty(HOST_PROPERTY);
        int port = Integer.parseInt(properties.getProperty(PORT_PROPERTY));
        try {
            mongo = new Mongo(host, port);
        } catch (UnknownHostException e) {
            throw new PersistenceStartException("Unable to resolve the MongoDb hostname", e);
        }

        try {
            // Check to see if we are alive
            mongo.getDB(getDatabaseName()).command("ping");
        } catch (MongoException e) {
            throw new PersistenceStartException("Can't ping MongoDb", e);
        }

        isRunning = true;
        LOG.info("Started MongoDb persistence");
    }

    /**
     * Ensures that the properties for MongoDb are loaded.
     *
     * @throws PersistenceStartException if the properties can not be loaded.
     */
    private void ensurePropertiesLoaded() {
        if (properties != null) {
            // Already loaded
            return;
        }
        Properties properties = new Properties();
        try {
            properties.load(ClassLoader.getSystemResourceAsStream(PROPERTIES_LOC));
        } catch (IOException e) {
            throw new PersistenceStartException("Unable to load Properties for MongoDb", e);
        }
        this.properties = properties;
    }

    /**
     * Returns the {@link DB} with the name that is specified in the properties
     * file.
     */
    private DB getDatabase() {
        return getDatabaseForName(getDatabaseName());
    }

    /**
     * Returns the name of the database as specified in the properties file.
     */
    private String getDatabaseName() {
        ensurePropertiesLoaded();
        return properties.getProperty(DATABASE_NAME_PROPERTY);
    }

    /**
     * Returns a {@link DB} instance for the database with the given name
     *
     * @param name the name of the database
     */
    @VisibleForTesting
    DB getDatabaseForName(String name) {
        return getMongo().getDB(name);
    }

    /**
     * Return the {@link Mongo} instance that we are managing.
     */
    private Mongo getMongo() {
        if (!isRunning) {
            start();
        }
        return mongo;
    }

    /**
     * Returns true iff the {@link MongoDbProvider} is running.
     */
    public boolean isRunning() {
        return isRunning;
    }

    /**
     * Returns a {@link MongoDbStore} instance created from the settings in this
     * provider.
     */
    public MongoDbStore provideMongoDbStore() {
        if (mongoDbStore == null) {
            mongoDbStore = new MongoDbStore(getDatabase());
        }
        return mongoDbStore;
    }
}