同时打开到两个mysql数据库的连接

Question

I have a java JDBC program,which opens connection to mysql database and do some operations.

I want to connect to two databases, one in local machine and another in remote machine.

I am able to connect one at a time, but I want to open both the connections at the same time, at one shot.

This is my java program:

public class DatabaseOperations {

    Connection con = null;
    String driver = "com.mysql.jdbc.Driver";
    String user = "root";
    String password = "root";
    //tring url = "jdbc:mysql://192.168.2.26:3306/time_entries_test";
    String dbName = "time_entries_test";
    String connect1 = "jdbc:mysql://192.168.2.26:3306/" + dbName + "?user=" + user + "&password=" + password + "&useUnicode=true&characterEncoding=UTF-8&autoReconnect=true&failOverReadOnly=false&maxReconnects=10";
    String connect2 = "jdbc:mysql://localhost:3306/" + dbName + "?user=" + user + "&password=" + password + "&useUnicode=true&characterEncoding=UTF-8&autoReconnect=true&failOverReadOnly=false&maxReconnects=10";

    public Connection createConnection() {
        try {
            Class.forName(driver);
            //con = DriverManager.getConnection(connect2);
            con = DriverManager.getConnection(connect2);
        } catch (ClassNotFoundException cnfe) {
            cnfe.printStackTrace();
        } catch (SQLException sqle) {
            sqle.printStackTrace();
        }
        return con;
    }
}

Here connect1 and connect2 are two url strings to which I want to open connections.

Answer 1

You can't have single con reference to two database connections.
You definitely need to maintain two different references.

Connection con1 = DriverManger.getConnection( connect1 );  
Connection con2 = DriverManger.getConnection( connect2 );  

No alternative.

---

Update 1 :

how do i return both con1 and con2,so that i can use both there in my method to do operations??

Solution 1 : Create multiple methods that returns local and remote connections.

public Connection getLocalConnection() {
  ...
  Connection localCon = DriverManger.getConnection( connect1 );  
  ...
  return localCon;
}

public Connection getRemoteConnection() {
  ...
  Connection remoteCon = DriverManger.getConnection( connect2 );  
  ...
  return remoteCon;
}

Solution 2 : If you want to generate both connection on every call and return them, you better use a list object to return..

public List<Connection> createConnection() {
  ...
  Connection localCon = DriverManger.getConnection( connect1 );  
  Connection remoteCon = DriverManger.getConnection( connect2 );  
  ...
  List<Connection> connectionsList = new ArrayList<Connection>( 2 );
  connectionsList.add( localCon );
  connectionsList.add( remoteCon );
  ...
  return connectionsList;
}

I prefer to use Solution 1 , because I am not sure every time you will be requiring both connections. At times you may be checking some data in only one database.