Calling Method of another class from Recursion Method: Java

Question

I have two class as A and B-

Class A:- This class has getData method, which is used to get data from DB.

class A {
    public synchronized getData() {
       // get some data from database, in finally block close connection
    }
}

Class B:- Which has recursion method m(), inside this method I am calling the getData() of class A.

class B {
   m() {
      //some condition to terminate the recursion
      A a = new A();
      a.getData();
      m();
   }
}

Error I am getting:-

java.lang.NullPointerException: null at com.mchange.v2.c3p0.impl.NewProxyConnection.getAutoCommit(NewProxyConnection.java:1226) ~[c3p0-0.9.5.1.jar:0.9.5.1]

For the first call of getData() method, I am able to get data from DB, but after second recursion onward I am getting the connection as closed. Any help would be highly appreciated.

Update:

I have DB Util method which is opening the connection each time when getData() method is calling. It's working fine if I am calling this without recursion method(many times) but if I am using recursion I'm getting error. Is any special case I have to handle for recursion method?

I believe here you can get your answer https://stackoverflow.com/questions/21884701/hibernate-c3p0-throws-nullpointerexception-at-newproxyconnection-commit — Sasikumar Murugesan, Dec 06 '17 at 06:55
@SasikumarMurugesan thanks! I have gone through the link which you have shared but it's didn't help me. In my case I have recursion method from where I am calling getData of another class. — deen, Dec 06 '17 at 07:05

score 2 · Accepted Answer · answered Dec 06 '17 at 07:14

2

The error specifies that connection is closed. Also, in your comment // get some data from database, in finally block close connection, you have mentioned that you have closed the connection after use but, you didn't mentioned that if you are opening the connection in he getData() method or not.

I would suggest following:

Check if you are opening the connection in getData() method. If not then either open the connection in this method only(remove the code for opening connection from some other method) or don't close the connection after use in this method instead use a different method to close the connection as per need.

Check if connection resource is reusable.

answered Dec 06 '17 at 07:14

cse

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I don't think this is the case. I have DB Util method which is opening the connection each time when getData() method is calling. It's working fine if I am calling this without recursion method(many times) but if I am using recursion I'm getting error. – deen Dec 06 '17 at 07:21
@rish Because in recursion the `getData()` method called very first time, it uses the connection and close it, so the connection is not available for further calls of `getData()` method. If you will call `getData()` method without recursion then this situation doesn't occurs. Try once as suggested then please comment your observation. – cse Dec 06 '17 at 07:45
After looking into the code, have noticed my DBUtil class was giving the existing connection(which already closed). I come from Angular2 background, need to learn more about Java :) . Thanks! – deen Dec 06 '17 at 10:56

Calling Method of another class from Recursion Method: Java

1 Answers1