Question

Recently I attended interview in java, the interviewer asked a question like below:

I have a request which go throgh A,B,C modules and response go back throgh A , in module A I need to talk to database and again in module C I need to talk to database, so in this situation how many connections you will open and where do you close those connections?

My Answer: I said that in module A I will open a connection and I will close it then and there, then control go to module B then module C, in module C again I will open one more connection and i will close it again. then he asked me again another question I want to open one connection per one request processing, how can i do this?

Answer 1

Sharing the connection in the modules.

EDIT
You can share the connection by passing it to the different modules:

class ModuleA {
    void process(){
        Connection c = getConnection();
        doA();
        new ModuleB( c ).doBs();
        new ModuleC( c ).doCs();
        doSomeMoreA();
        c.close();
    }
}

You can also have the connection in a external class and search for it when needed ( perhaps using a sessionid )

I’m not sure if this counts as “Connection pooling”

Here’s it anyway.

class Db {
    private static Map<Integer, Connection> map;

    public static Connection getConnection( int sessionId ){

        if( !map.containsKey( sessionId ) ) {
            map.put( sessionId, createConnection());
        }
        return map.get( sessionId );
    }
}
class Main {
    void processs() {
        int sessionId = createSesionId();
        ModuleA a = new ModuleA( sessionId );
        a.doAsStuff();
        ModuleB b = new ModuleB( sessionId );
        b.doBsStuff();
        ModuleC c = new ModuleC( sessionId );
        b.doCsStuff();
        a.closeTransaction();

    }
}
class ModuleA{

    public doAsStuff() {
        Connection c = Db.getConnection(sessionId);
        doSomethingWith( c );
    }
    public closeTransaction() {
        Connection c = Db.getConnection(sessionId);
        c.close();
    }
}
class ModuleB{

    public doBsStuff() {
        Connection c = Db.getConnection(sessionId);
        doSomethingWith( c );
    }
}
class ModuleC{

    public doCsStuff() {
        Connection c = Db.getConnection(sessionId);
        doSomethingWith( c );
    }
}