MongoDB的对象的创建

package com.voice.db;

import com.mongodb.DB;
import com.mongodb.DBCollection;
import com.mongodb.Mongo;
import com.mongodb.MongoClient;
import com.mongodb.MongoClientOptions;
import com.mongodb.ReadPreference;
import com.mongodb.ServerAddress;
import com.mongodb.WriteConcern;


public class MongoDB {

    private Mongo wMongodb;
    
    private static MongoDB instance = null;
    
    private static synchronized MongoDB GetInstance()
    {
        if(!isInstanceAlive())
        {
            instance = new MongoDB();
        }
        return instance;
    }

    /**
     * 判断数据库是否处于连接状态中
     * @return true:连接中<br/>
     *        false:已断开
     */
    private static boolean isInstanceAlive() {
        boolean retBool = false;
        try {
            // 尝试访问一次数据库
            DBCollection col = instance.wMongodb.getDB("database_name").getCollection("table_name");
            col.count();
            retBool = true;
        } catch (Exception e) {
            try {
                instance.wMongodb.close();
            } catch (Exception ex) {}
        }
        return retBool;
    }
    
    private MongoDB()
    {
        try {
            MongoClientOptions.Builder voicedbBuilder = MongoClientOptions.builder();
            voicedbBuilder.connectTimeout(3000);
            voicedbBuilder.socketTimeout(6000);
            voicedbBuilder.autoConnectRetry(true);
            voicedbBuilder.connectionsPerHost(5);
            voicedbBuilder.readPreference(ReadPreference.secondaryPreferred());
            voicedbBuilder.socketKeepAlive(true);
            MongoClientOptions voicedbOptions = voicedbBuilder.build();

//          wMongodb = new MongoClient(new ServerAddress("172.16.10.15", 27020),voicedbOptions);
            wMongodb = new MongoClient(new ServerAddress("localhost", 27020),voicedbOptions);
            
            DB db = wMongodb.getDB("db_name");
//            DB db = wMongodb.getDB("olacloud_internal");
            db.authenticate("id", "id".toCharArray());
            db.setWriteConcern(WriteConcern.SAFE);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
    }

    /**
     * 获取数据库连接
     * @return 已经连接的数据库
     */
    public static DB getDB() {
        DB db = MongoDB.GetInstance().wMongodb.getDB("db_name");
//        DB db = MongoDB.GetInstance().wMongodb.getDB("olacloud_internal");
        return db;
    }

    /**
     * 获取table的连接
     * @param tableName table名
     * @return table连接
     */
    public static DBCollection getDBCollection(String tableName) {
        DB db = MongoDB.getDB();
        DBCollection col = db.getCollection(tableName);
        return col;
    }
    
    /**
     * 关闭当前的Mongodb连接
     */
    public static void close() {
        if (instance != null) {
            instance.wMongodb.close();
        }
    }

}