建立多个jdbc数据库连接

Question

Please take a look at the following code at the following link:

 Connection connMain = DriverManager.getConnection("jdbc:mysql://XX.XX.X.XXX:3306/test","myusername","mypassword");

Connection connRemote = DriverManager.getConnection("jdbc:mysql://" + CurrRemoteIPAddress + ":3306/test","myusername1","mypassword1"); 

http://ideone.com/28GaFh

Right now, as shown in the code, I am extracting some information from one database (located at IP address XX.XX.X.XXX) and inserting it at another database ( located at IP address defined by CurrRemoteIPAddress which is currently set to AA.YY.Z.PPP on line #30 in my code)

The above stuff is working perfectly fine.

Now, I have 6 more databases besides the one located at AA.YY.Z.PPP(let's call it as db1 for discussing purpose, db2,db3,...,db6) where I would like to insert the same extracted information from XX.XX.X.XXX.

I have to keep following points in my mind while doing this: a) If a connection to one database get's lost, I should move onto next one. In an ideal case, I should be able to insert the information into all the six databases(db1 to db6).

I am wondering, should I define new connection string for new each of the six databases?

Can I define it in same try catch?

Please advise

Answer 1

I would create a collection of connections (for db1 to db6) and then iterate over this, invoking the same insertion logic.

You could catch any exception which is the result of failing to connect to a database, log it and simply move onto the next one.

// step 1 create connection to database db1
// step 2 if successful, add to collection
// step 3 repeat steps 1 and 2 for databases db2 to db6
// step 4 retrieve data from source database
// step 5 for each connection in collection, insert into database
// step 6 close each connection in collection

Answer 2

Although there may be better solutions, I would work with an array of Connection objects. That way you could iterate on them until you get what you need:

Connection connMain = DriverManager.getConnection(
    "jdbc:mysql://XX.XX.X.XXX:3306/test","myusername","mypassword");
Connection[] connections = new Connection[10]; // Assuming you need ten connections
connections[0] = DriverManager.getConnection(
    "jdbc:mysql://" + CurrRemoteIPAddress + ":3306/db1","myusername1","mypassword1"); 
connections[1] = DriverManager.getConnection(
    "jdbc:mysql://" + CurrRemoteIPAddress + ":3306/db2","myusername1","mypassword1"); 
// Add as many as you need

About your comment: How to catch an exception in a connection?

At some point you will have to retrieve data from your databases. So that is the place where you catch the exception. A dummy example:

Statement stmt;
ResultSet rs;
boolean done = false;
int i = 0;
while(!done) {
    try {
        stmt = connections[i].createStatement();
        rs = stmt.executeQuery("select * from aTable");
        rs.beforeFirst();
        while(rs.next()) {
            // Do whatever you need with the result set
        }
        done = true;
    } catch(SQLException e) {
        // Catch the exception and try with the next connection
        i++;
    }
}

This is a general idea. You'll need to write your own solution, but this is a possible approach.

Answer 3

I am wondering, should I define new connection string for new each of the six databases?

Yes - you'll want to have all the connections open at the same time.

Can I define it in same try catch?

No. Each connection should be created in it's own try/catch so if one fails the other will still work.

Please advise

Okay, assuming you want this to run somewhat fast...

• Create a class just for holding the data you want to copy. This is your DTO.
• Create 6 queues, one for each destination DB
• Start 6 threads, each one should connect to the a different target DB. Have it read from it's queue and execute the insert statement.
• Have the main thread select from the source database, create and populate a DTO, and put it on each queue. Loop until you're done
• Wait until all the other threads are finished.