7. 环境变量 : vi /etc/profile : export PATH=/usr/local/mongodb/bin:$PATH

14. 

1. public static void main(String[] args)  {  
2.         try {   
3.             List<ServerAddress> addresses = new ArrayList<ServerAddress>();    
4.             ServerAddress address1 = new ServerAddress("127.0.0.1" , 1111);   
5.             ServerAddress address2 = new ServerAddress("127.0.0.1" , 2222);   
6.             ServerAddress address3 = new ServerAddress("127.0.0.1" , 3333);   
7.             addresses.add(address1);    
8.             addresses.add(address2);   
9.             addresses.add(address3);   
10.             MongoClient client = new MongoClient(addresses);   
11.             DB db = client.getDB( "test");   
12.             DBCollection coll = db.getCollection( "test");   
13.               
14.             BasicDBObject object = new BasicDBObject();    
15.             object.append( "key1", "value1" );   
16.             ReadPreference preference = ReadPreference.secondary();    // 设置从备份节点读取 实现读写分离
17.             DBObject dbObject = coll.findOne(object, null , preference);    
18.             System. out .println(dbObject);    
19.         } catch (Exception e) {   
20.             e.printStackTrace();    
21.         }   
22.     }